Emergency RT phraseology for DGCA RTR(A)

Airport is closed

Use this procedure when ATC tells a flight already airborne that its planned destination is unavailable and gives no reopening estimate. After asking the crew to state its intentions, ATC may clear the aircraft to a suitable diversion aerodrome. When the present sector and that aerodrome are served by the same control unit, the diversion clearance can be issued without an immediate handoff, although later handoffs may still be needed. The crew should assess fuel, weather, runway condition, traffic, and operator policy before selecting the alternate.

Pilot

[station] [callsign], [response or report]

ATC

[callsign], [instruction or information]

ATC

Air India 447, Hyderabad Control.

Pilot

Hyderabad Control, Air India 447, go ahead.

ATC

Air India 447, Bengaluru airport is closed to all traffic following an aircraft accident, time of reopening not known, advise intentions.

Pilot

Air India 447, request diversion to Hyderabad.

ATC

Air India 447, cleared to Hyderabad, proceed direct, maintain flight level three one zero, report position.

Pilot

Cleared to Hyderabad, direct, maintain flight level three one zero, Air India 447. Position Warangal at zero eight three zero, flight level three one zero, estimating Hyderabad zero nine zero zero, Air India 447.

The controller opens this exchange, which reverses the usual sequence in which a flight crew makes the first call. The pilot's GO AHEAD tells the controller the crew is listening and ready for the closure message.
The lack of a reopening estimate means the crew cannot base its plan on remaining at the filed destination. Holding might still be reasonable if fuel, weather, and operator policy permit it, but it cannot depend on a known reopening time.
Here, ADVISE INTENTIONS asks the crew to state its proposed action; it does not assign the alternate. The commander should assess remaining endurance, destination weather, runway availability, traffic, and the operator's diversion policy before replying.
Because the aircraft is already airborne, a full departure clearance would be unnecessary. The new destination and any essential route, level, frequency, or heading instructions can be handled in a concise ATC clearance. A later sector handoff may still be required even when the current controller approves the diversion.
REPORT POSITION gives the controller an updated surveillance fix following the diversion. It confirms progress toward the new aerodrome and provides a reference for subsequent traffic coordination.
A position report normally presents the aircraft's location and observation time first, followed by level and any details requested by ATC. Here the pilot adds the revised estimate for Hyderabad.
Routine handling of a closed destination does not call for a passenger count or an automatic repetition of remaining endurance. Those figures become relevant when the pilot reports an aircraft emergency or when ATC specifically requests fuel information for a decision.
If the crew cannot safely reach the proposed alternate because of fuel, it should use the appropriate urgency signal. PAN PAN indicates an urgent situation that could become dangerous, while MAYDAY indicates a dangerous situation requiring immediate assistance. This exchange contains no such declaration.
A closed destination is an external operational problem, not automatically an emergency aboard the diverting aircraft. Unless the closure also produces a fuel, weather, medical, or mechanical problem for the crew, the flight is managed through routine diversion procedures.

Reference: ICAO Doc 9432

Airprox - No risk of collision

Use this report when another aircraft came close enough that you want the encounter formally recorded, but you judge that there was never a real chance of the two aircraft hitting each other. Your own assessment goes into the call as NO RISK OF COLLISION, which matches ICAO risk category C. The encounter is still worth reporting because repeated near encounters in the same place can point to an airspace or procedure problem.

Pilot

[station], [callsign], AIRPROX, NO RISK OF COLLISION. LOCATION [position], OBSERVATION TIME [time], [weather], [level], TRUE AIR SPEED [speed]. INCIDENT TIME [time], OTHER TRAFFIC [type], MOVEMENT [movement], SEPARATION [separation], RELATIVE LEVEL [level offset], HEADING [heading], AVOIDING ACTION [action].

ATC

[callsign] [station], ROGER YOUR AIRPROX.

Pilot

Chennai Control, Air India 447, AIRPROX, NO RISK OF COLLISION. Position two five miles north of Chennai at one one three zero, flight level two one zero, VMC, true air speed four two zero knots. Incident time one one two seven. An Airbus crossed from left to right about two miles ahead and one thousand feet below, heading zero zero zero. TCAS traffic advisory received, no avoiding action taken.

ATC

Air India 447, Chennai Control, ROGER YOUR AIRPROX

Stating AIRPROX, NO RISK OF COLLISION at the start of the pilot's message records the crew's assessment; it does not request immediate action from the controller. The investigation authority, rather than ATC or the reporting flight crew, assigns the final category after reviewing all available evidence.
Category C commonly follows a close visual or electronic observation, including a TCAS TRAFFIC ADVISORY without a RESOLUTION ADVISORY. The crew may initially have expected less proximity; nevertheless, the observed distance, track geometry and time available indicated that safeguards remained adequate and no collision threat developed.
ICAO uses four risk categories: A, risk of collision; B, safety not assured; C, no risk of collision; D, risk not determined. In a category C event a traffic advisory or a close sighting may be alarming, yet the distance and time available show that a collision was never credible.
Pilots may submit a Category C report when an encounter seemed sufficiently concerning at the time, even if later evidence shows ample separation. Such data support trend analysis. Repeated "felt close" events may identify a routing, airspace or procedure that repeatedly produces encounters perceived as uncomfortably close.
Provide the basic information expected for any occurrence report: position, event time, flight level, weather and a clear account of nearby traffic. State how the other aircraft was detected, give its estimated distance, movement and relative level, and say whether any avoidance was immediate, precautionary or unnecessary. This allows investigators to reconstruct the encounter accurately.
ATC generally acknowledges the report with ROGER and does not validate or change the pilot's stated category. A request for traffic information, separation or other help belongs in a separate exchange so that the Airprox report remains clear and complete.

Reference: ICAO Doc 9432

Airprox - Risk not determined

Use this category when a pilot files an AIRPROX report under Category D because the evidence does not permit a reliable finding on collision risk. A short TCAS indication, an incomplete visual sighting, or information supplied by another person may leave the crew unable to establish separation, relative movement, or closure. In that situation, the event is reported as risk not determined rather than being placed in Category A, B, or C.

Pilot

[station], [callsign], AIRPROX RISK NOT DETERMINED. POSITION [position] AT [time], [level], TRUE AIR SPEED [speed], [weather]. TIME OF INCIDENT [time]. [details of the other aircraft and any unresolved information].

ATC

[callsign] [station] ROGER AIRPROX

Pilot

Hyderabad Control, Air India 447, AIRPROX RISK NOT DETERMINED. Position three zero miles southeast of Hyderabad at zero two three zero, flight level two seven zero, true air speed four four zero knots, visibility six kilometres. Time of incident zero two two five. A TCAS traffic indication appeared briefly, but no visual contact was made. Aircraft type, separation, altitude difference, and heading could not be confirmed.

ATC

Air India 447, Hyderabad Control, ROGER AIRPROX.

Stating AIRPROX RISK NOT DETERMINED immediately after the callsign tells the controller that the crew is documenting a close encounter for safety purposes but does not assert a definite level of risk. It separates Category D from Categories A, B, and C, for which a pilot can give a preliminary risk judgement.
Limited evidence commonly leads to this classification. Cases include a TCAS indication that disappears before useful parameters can be verified, a fleeting visual observation that does not establish relative height or distance, or a warning from another party that the reporting crew cannot independently confirm.
Details of the other aircraft should clearly identify what remains unknown. Wording such as BELIEVED TO BE, TYPE UNKNOWN, or SEPARATION NOT ESTABLISHED may be used. Category D requires uncertainty to be stated openly rather than replaced with conjecture.
Even if the other aircraft cannot be fully described, the pilot should supply every confirmed detail about position, incident time, speed, level, and weather. Investigators can compare these data with surveillance recordings and records from the other aircraft, where available, to fill gaps in the crew's direct observations.
Later analysis may reveal information that was unavailable when the report was made. Radar, flight-data, and cockpit records may allow the authority to reassign an initial Category D report as A, B, or C. The category records what the pilot could establish during the original report; it does not predetermine the authority's final finding.
Controllers use the same short reply, ROGER AIRPROX, for every airprox category. They need not debate or explain the risk classification during the transmission.

Reference: ICAO Doc 9432

Airprox - Risk of collision

Use this when a pilot gives an immediate Risk of Collision assessment for an Airprox encounter, Category A, the highest class. Another aircraft was so near, with relative motion, speed and inadequate protection that a collision was a real possibility without avoidance, or despite the action attempted. Report it promptly once the encounter no longer requires urgent control. ATC can then retain radar data, identify the other aircraft and contact those involved. If collision danger is still developing, use PAN PAN or MAYDAY instead of waiting for an after-event report.

Pilot

[station], [callsign], AIRPROX, risk of collision. POSITION [position] at [time], TRUE AIR SPEED [speed], [level], [weather], TIME OF INCIDENT [time], [details of other traffic including type, movement, closest separation, any resolution advisory and response, and direction]

ATC

[callsign] [station] ROGER AIRPROX

Pilot

Bengaluru Control, IndiGo 5231, AIRPROX, risk of collision. Position one five miles east of Bengaluru at zero six three six, flight level two nine zero, in cloud, true air speed four three zero knots, time of incident zero six three two. One twin-engine jet crossed beneath our path from right to left. Closest separation was about one hundred feet vertically and under half a nautical mile laterally. We received a TCAS resolution advisory to CLIMB and complied. Its heading was about three six zero.

ATC

IndiGo 5231, Bengaluru Control, ROGER AIRPROX

The opening category is the pilot's provisional judgement and tells the controller why immediate safeguarding and preservation are important. It does not finally establish the official outcome. The competent investigation authority reviews the encounter geometry and all available evidence before deciding whether it meets Category A, Risk of Collision.
A TCAS resolution advisory can be useful evidence because it is issued when the system predicts a collision risk from the two aircraft's trajectories. State whether the crew got CLIMB or DESCEND, whether the instruction was obeyed and what action followed. Do not imply that TCAS alone proves the encounter met Category A; actual separation, relative paths and crew observations still matter.
For Category B, safety was not assured. Category A indicates a more acute possibility of impact. It can involve less than one nautical mile laterally, only a few hundred feet vertically, or both, depending on encounter geometry. A converging course makes the report more significant, especially if the paths would have met without avoidance.
Describe what the other pilot did, not merely the fact that an aircraft was nearby. Useful details include whether it descended through the occupied level, crossed directly under or over the flight path, or turned toward the reporting aircraft. Add the estimated minimum separation, its direction and the order of avoidance actions. These facts help investigators reconstruct convergence instead of treating the occurrence as an unrelated altitude excursion.
The report is normally sent after the event, once separation has been restored and any avoiding manoeuvre is complete. It must not delay PAN PAN or MAYDAY while danger is still active. A crew facing imminent collision should declare MAYDAY first; PAN PAN is appropriate for an urgent situation that has not reached that point. Give the Airprox facts later when it is safe to do so.
A controller usually acknowledges the notification with ROGER AIRPROX and provides no avoidance instruction merely because of the report. The formal inquiry is handled off the control frequency by the designated authority. Evidence may include radar or surveillance recordings, ATC transcripts, aircraft data and accounts from both crews. That review determines the official category and identifies any wider safety issue.

Reference: ICAO Doc 9432

Airprox - Safety not assured

Use this message when a crew has just experienced an aircraft encounter and judges that safety was not assured. Treat the wording as the pilot's immediate assessment, not as a final Category B determination. Supply the controller with both times, the aircraft's position, true airspeed, level, weather, and observed details of the other traffic. Make the report promptly so surveillance recordings and flight records can be preserved and referred for formal investigation. A separate written report must be completed after landing.

Pilot

[station], [callsign], AIRPROX [category]. POSITION [position] AT [time], TRUE AIR SPEED [speed], [level], IN [weather conditions]. INCIDENT TIME [time], [other aircraft type and movement], ESTIMATED HORIZONTAL DISTANCE [distance], BEARING [bearing].

ATC

[callsign] [station], ROGER AIRPROX.

Pilot

Hyderabad Control, IndiGo 5231, AIRPROX, SAFETY NOT ASSURED. Position Hyderabad VOR at zero five one zero, flight level three five zero, in IMC, true air speed four six zero knots. Incident time zero five zero five. An Airbus A320 descended through our level, estimated horizontal distance two miles, bearing zero six zero.

ATC

IndiGo 5231, Hyderabad Control, ROGER AIRPROX.

Begin the substantive message with AIRPROX and SAFETY NOT ASSURED so the controller immediately understands the crew's concern. The assessment records what the pilot believed at that moment. It neither assigns blame nor fixes the eventual Airprox category, which must be determined from the full investigation by the competent authority.
Position, UTC, true airspeed and flight level form a snapshot of the reporting aircraft. The location and time let a controller match that snapshot to surveillance data, while speed and altitude support reconstruction of the encounter. If several minutes have passed before transmission, state both the current reporting point and the earlier event time.
IMC means Instrument Meteorological Conditions. In such conditions, visual discovery and avoidance are more difficult, so this detail is important when risk is assessed. However, IMC alone neither creates nor removes a conflict. The final assessment must also consider actual separation, relative vertical movement, visibility, and what either crew did.
Do not assume that the position-report time and the occurrence time are identical. A transmission made after the event may describe the aircraft's present position, while the conflict happened earlier. State both timestamps in UTC, using Zulu on the frequency, so investigators replay the correct interval and match the correct surveillance tracks.
The description of the other aircraft should identify its type and observed vertical movement. Also provide the estimated horizontal separation and the bearing from your aircraft at the relevant moment. The bearing indicates where the traffic was observed, not necessarily the direction in which it was travelling. Treat the distance as the crew's estimate unless surveillance data confirms it.
ROGER AIRPROX confirms that the controller received the report. It does not mean that the controller accepts the pilot's risk estimate or has completed an investigation. Questions about blame, separation, or final classification should not be debated during this initial frequency exchange. Operational priorities must still be met if the situation changes.
The transmission starts the notification record but does not remove the need for the formal written report. After landing, the pilot submits the prescribed Airprox form and supporting information to the appropriate authority. That later submission allows a fuller account of the encounter to be assessed without delaying the urgent radio alert.
An Airprox report concerns a safety event affecting the reporting aircraft. It should not be used merely to announce another person's distress. MAYDAY means that immediate danger requires assistance; PAN PAN identifies an urgent safety situation that does not yet require immediate assistance. If either emergency condition continues, transmit the appropriate emergency call rather than AIRPROX alone.

Reference: ICAO Doc 9432

Altimeter System Unreliable

Use this report when an RVSM-approved aircraft can no longer meet the monitoring or altimetry requirements within the band from flight level two nine zero through flight level four one zero. Give its position and present level, identify the Mode C or altimeter defect, declare RVSM non-compliant, and request clearance for a descent below the band. The controller normally requires the aircraft to leave its ATS route and descend to flight level two seven zero, with normal navigation resuming after passing flight level two nine zero. The action is unchanged for either defect. A PAN PAN declaration is not normally needed because the crew can maintain control and coordinate the exit.

Pilot

[station], [callsign], [position], FLIGHT LEVEL [level], ALTIMETER SYSTEM UNRELIABLE, RVSM NON-COMPLIANT, REQUEST LOWER LEVEL

ATC

[callsign], [station], LEAVE ATS ROUTE, DESCEND TO FLIGHT LEVEL [cleared level], PASSING FLIGHT LEVEL [boundary level] RESUME NORMAL NAVIGATION

Pilot

Hyderabad Control, IndiGo 5231, position three two miles southeast of Hyderabad, flight level three seven zero, altimeter system unreliable, RVSM non-compliant, request lower level.

ATC

IndiGo 5231, Hyderabad Control, leave ATS route, descend to flight level two seven zero, passing flight level two nine zero resume normal navigation.

Pilot

Leave ATS route, descend to flight level two seven zero, passing flight level two nine zero resume normal navigation, IndiGo 5231.

RVSM stands for Reduced Vertical Separation Minima. The Indian RVSM band covers flight level two nine zero through flight level four one zero, where approved aircraft are separated vertically by at least one thousand feet. Operations in this band require reliable pressure altimetry and a functioning Mode C transmission. If either capability is lost, the crew must promptly report RVSM non-compliance and coordinate an exit from the band with ATC.
Include the current flight level in the first call. It gives the controller an immediate indication of the aircraft's height and the distance required to reach the lower edge of the RVSM band.
Flight level two seven zero gives a buffer of two thousand feet below the RVSM band. It puts the aircraft clearly below the lower boundary of the band, where the RVSM approval no longer matters.
Mode C automatically transmits encoded pressure altitude to the ground surveillance system. Without that reply, the controller cannot independently confirm the aircraft's reported level, and suitable separation under the RVSM standard cannot be assured.
RVSM approval depends on two accurate and independent altimeters. A fault in either unit prevents dependable cross-checking, so the aircraft can no longer claim compliance with the reduced separation standard.
Mode C failure and altimeter malfunction have different technical causes, yet both lead to the same ATC action. In either case, the crew states that RVSM compliance is lost and coordinates an exit from the band. The defect is also entered in the technical records.
The instruction LEAVE ATS ROUTE directs a temporary departure from the published airway or route. The controller may supply a heading or lateral offset as necessary to avoid converging with traffic on nearby levels during the descent.
Flight level two nine zero marks the bottom of the RVSM band. The normal routing instruction takes effect when the aircraft passes that level downward, although it must continue to observe the assigned altitude until ATC issues another clearance.
An urgent communication is not automatically a PAN PAN. If the crew can manage the aircraft and coordinate the descent without an immediate threat to safety, report the system defect and request descent in normal wording. Use PAN PAN for urgent conditions and MAYDAY for grave and immediate danger.
When ATC specifies a turn for the route deviation, repeat that direction without alteration. If no direction was assigned, do not invent one. The controller bases the turn on airway geometry, nearby traffic and operational restrictions.

Reference: ICAO Doc 9432

Bad Weather at Destination

Use this call when the crew already has reliable information about hazardous weather at the intended landing aerodrome, obtained from dispatch, an ATIS, onboard radar, or another source outside the ATC frequency. The pilot has selected an alternate and now needs any clearance required to begin the revised routing. This is a pilot-initiated diversion, not a response to ATC asking for the aircraft's intentions. One transmission can state present position, explain the destination problem, name the alternate and its expected arrival time, and request descent clearance.

Pilot

[station], [callsign], INFORMED OF [condition] AT [destination]. [position] AT [time], [level]. WILL DIVERT TO [alternate], ESTIMATING ARRIVAL AT [time]. REQUEST [instruction].

ATC

[callsign], [station], CLEARED TO [alternate]. DESCEND TO [level]. REPORT PASSING [level].

Pilot

Bengaluru Control, IndiGo 5231, informed of thunderstorms at Hyderabad. Overhead Bengaluru at zero six one zero, flight level two seven zero. Will divert to Chennai, estimating Chennai at zero six four zero. Request descent to flight level one six zero.

ATC

IndiGo 5231, Bengaluru Control, cleared to Chennai. Descend to flight level one six zero. Report passing flight level one eight zero.

Pilot

Cleared to Chennai, descend to flight level one six zero, report passing flight level one eight zero, request Chennai weather, IndiGo 5231.

Stating the weather problem early gives the controller the reason for a route change and may prompt the addition of useful weather reports available at that unit. Diversion remains a flight crew decision, not something ATC must approve. Controllers supply the clearances needed for the revised route and vertical profile.
Giving the aircraft's position and present flight level allows the controller to understand where the aircraft is before authorizing descent. The time of the report remains important because the arrival sequence is no longer the one originally planned.
Stating both the selected alternate and its estimated arrival time prepares arrival management for a revised destination. The controller can then consider traffic demand, runway capacity, and any operating restrictions affecting the new arrival.
Requesting descent in the same call saves a separate exchange and allows the aircraft to start descending towards the alternate. Early descent can avoid an unnecessarily high rate of descent or prolonged holding near the destination.
The clearance gives a diversion destination, an assigned level, and a mandatory progress report. The pilot reads back Chennai, flight level one six zero, and the requirement to report passing flight level one eight zero, then requests current weather there.
Current weather for Chennai is needed because the crew must now plan the approach and landing at the alternate. This is especially important when hazardous weather at Hyderabad, rather than a simple runway or notice limitation, prompted the diversion. Conditions may affect runway choice, approach type, and landing performance.
If the information is not immediately available, the controller may respond with STANDBY and check the latest METAR or ATIS. The follow-up should state the conditions and observation time while the crew remains on frequency.
A diversion may be raised by ATC or by the flight crew. If the controller holds warning information that the crew has not received, ATC may ask for the pilot's intentions. In a crew-initiated case, the opening call combines the known hazard, chosen alternate, and clearance needed.

Reference: ICAO Doc 9432

Brakes Hot Indication

Use this urgency call when brake overheating is suspected after a heavy landing, extended taxi braking, heavy deceleration or a take-off abort, especially if smoke, unusual noise, tyre damage or reduced braking is present. The situation needs prompt emergency assistance and ground handling support. Unless there is an immediate threat to life, such as a serious fire or wheel failure, PAN PAN is appropriate rather than MAYDAY.

Pilot

PAN PAN, PAN PAN, PAN PAN [station], [callsign], [aircraft type], BRAKES OVERHEATED, [position and observed effects], REQUEST [assistance required]

ATC

[callsign] [station], ROGER PAN PAN, [position acknowledged], [hold or stop instruction], [services dispatched], [towing status]

Pilot

PAN PAN, PAN PAN, PAN PAN, Hyderabad Ground, Alliance 912, ATR 72, brakes overheating, aircraft stopped on taxiway Golf, one hundred metres before holding point Charlie. Strong burning smell noted, request fire service attendance.

ATC

Alliance 912, Hyderabad Ground, ROGER PAN PAN. Fire service dispatched to taxiway Golf, one hundred metres before holding point Charlie. Towing unit on standby.

If brake overheating is suspected, stop at the first safe place and avoid unnecessary brake pressure. Retain only enough braking for steering and ATC compliance, and tell the ground controller what action is being taken.
State the exact position in a form that a fire appliance can find easily, for example the taxiway, stand, nearest intersection and side of the movement area. A precise reference prevents responders from searching along the taxiway.
Include POB in the urgency report or a follow-up transmission, because a developing brake fire may require immediate evacuation support. If the initial call is busy, prioritise position, assistance and flight deck actions, then pass POB as soon as practicable.
Brake cooling time varies with aircraft type, recent braking and ambient conditions, so the aircraft may not be safe to taxi under its own power. Towing can be necessary, and a stopped aircraft on a live taxiway may also need rapid clearance for other traffic. Follow operator guidance before any return to service.
Hot brakes alone do not automatically require engine shutdown or evacuation. The commander must reassess smoke, flames, tyre separation and brake control, coordinate with responders, and choose the safest action. An open door or ramp evacuation may expose people to heat, smoke or moving vehicles, so do not initiate it without a clear operational reason.
Use MAYDAY when the problem becomes grave and imminent, such as rapidly spreading fire, flames endangering fuel, wheel or tyre failure threatening directional control, or another immediate threat to life. A hot-brake report with no immediate life-threatening danger remains a PAN PAN matter.
After the aircraft is secure and fire services report that temperatures are reducing with no fire, advise ATC that the urgency condition has ended. A suitable cancellation is: [station], [callsign], CANCEL PAN PAN, BRAKES COOLING, NO FIRE OBSERVED. Coordinate any return to service with the operator and ATC.

Reference: ICAO Doc 9432

Cancel Distress

Once the condition that caused the MAYDAY has been resolved, you cancel the distress so ATC can stand the emergency services down and give the frequency back to everyone else. Say it in plain, unmistakable words.

Pilot

[Station], [Callsign], CANCEL DISTRESS, [reason], REQUEST [intentions]

ATC

[Callsign], ROGER, DISTRESS CANCELLED, [further instructions]

Pilot

Mumbai Approach, VT-AIR, cancel distress, engine serviceable, runway in sight, request landing

ATC

VT-AIR, roger, distress cancelled, cleared to land runway 27

Pilot

Cleared to land runway 27, distress cancelled, VT-AIR

Use the words CANCEL DISTRESS. Saying the problem has gone away is not a cancellation, and the controller cannot release the fire service on a hint.
Say why it is cancelled. The controller has to be able to justify standing the response down.
Cancel only when the condition is genuinely resolved. An engine that has been restarted and an engine that is running normally are not the same thing.
The same form is used to cancel an urgency. CANCEL PAN, or in full, CANCEL PAN PAN.

Reference: ICAO Doc 9432

Co-pilot fainted

Use this format when the co-pilot has collapsed and remains unconscious, creating an urgent medical need and requiring an expedited landing. MAYDAY is justified when the event represents grave and imminent danger to the aircraft or anyone aboard, especially where the remaining pilot cannot continue safely. If safe flight is assured and no grave danger exists, PAN PAN is generally more suitable. Declare the condition early, state what aid is needed, and arrange assistance before arrival.

Pilot

MAYDAY MAYDAY MAYDAY [station] [callsign], [aircraft model]. [nature of emergency]. POSITION [position], [level]. [intentions]. ETA [destination] [time]. PERSONS ON BOARD [number]. ENDURANCE [time]. ASSISTANCE REQUIRED [assistance]

ATC

[callsign], [station], ROGER MAYDAY, SQUAWK [code], DESCEND [level], QNH [pressure], EXPECT [approach] RUNWAY [runway], CONTACT [unit] [frequency]

Pilot

MAYDAY, MAYDAY, MAYDAY, Ahmedabad Control, SpiceJet 318, Boeing 737, co-pilot unconscious and not responding, position two five DME on the Ahmedabad zero five five radial, flight level two eight zero, heading two three five, continuing to Ahmedabad for immediate landing, estimating one one four five, persons on board one six four, endurance two hours three zero minutes, request ambulance on arrival.

ATC

SpiceJet 318, Ahmedabad Control, roger MAYDAY, squawk seven seven zero zero, descend flight level one two zero, QNH one zero one two, expect ILS approach runway two three, contact Ahmedabad Approach one one nine decimal seven.

Pilot

Squawk seven seven zero zero, descend flight level one two zero, QNH one zero one two, expect ILS runway two three, Ahmedabad Approach one one nine decimal seven, SpiceJet 318.

A MAYDAY announcement should contain five core items: aircraft identity, the nature of distress, position, intended action, and persons on board. This call gives SpiceJet 318, the unresponsive co-pilot, the DME and radial position, the planned Ahmedabad landing, and one hundred sixty-four occupants. Aircraft model, heading, endurance, destination time, and requested medical support are useful additions.
Select transponder code seven seven zero zero at once, without waiting for ATC to repeat it. The emergency code makes the aircraft's distress status immediately apparent to surveillance and controller systems.
A collapsed co-pilot who stays unresponsive is a serious medical event and can quickly tax the remaining pilot's capacity. Report only what has been observed, without offering a diagnosis. MAYDAY is used when grave and imminent danger is present, while an urgent situation without that degree of danger may fit PAN PAN.
A distance and radial pair, such as two five DME on the zero five five radial from Ahmedabad, gives both range and direction in one phrase. The controller can plot it at once. Use only what the aircraft's own navigation shows; never guess a fix.
EXPECT ILS APPROACH RUNWAY two three is planning information, not an approach clearance. The crew may brief and set up for it, but the approach clearance itself will come later from Approach.
A MAYDAY aircraft may still be moved to another frequency when that unit is better placed to help. The controller hands over the emergency details in advance, so the crew does not have to repeat the whole distress message on the new frequency.
Repeat the transponder code, level, QNH, runway and frequency. In this lesson, finish the readback with the aircraft callsign. Any difference from the ATC instruction must be corrected before the crew acts on it.
Controllers can begin airport emergency coordination while the aircraft is still airborne. The medical declaration and the total of one hundred sixty-four occupants allow early arrangement of an ambulance, stretcher access, fire cover, and suitable ground handling. These preparations normally proceed without a separate pilot request.
Two hours and thirty minutes of endurance is ample for the stated flight to Ahmedabad, yet it remains useful emergency information. Controllers may consider remaining endurance when selecting alternates, arranging rescue support, or setting landing priorities. If endurance cannot be verified, leave it out rather than guess.

Reference: ICAO Doc 9432

Diversion

Use this exchange when the planned destination cannot be reached or used safely or legally. Causes include weather below landing minima, an unavailable runway, insufficient fuel, a technical defect or an urgent medical need. Give the intended alternate, explain why it is needed, and ask for the desired route or flight level. ATC provides any revised clearances needed and continues the applicable priority handling when a MAYDAY or PAN PAN remains in effect.

Pilot

[station], [callsign], [reason], REQUEST DIVERSION TO [alternate], [routing], [level]

ATC

[callsign], CLEARED [routing] [alternate], [level instruction], [squawk], CONTACT [unit] [frequency]

Pilot

Hyderabad Control, SpiceJet 318, Bengaluru runway closed, request diversion to Chennai, direct, flight level two nine zero

ATC

SpiceJet 318, Hyderabad Control, cleared direct Chennai, descend flight level two nine zero, squawk six seven two four, contact Chennai Control one three two decimal five five, advise endurance and persons on board

Pilot

Cleared direct Chennai, descend flight level two nine zero, squawk six seven two four, Chennai Control one three two decimal five five, endurance one hour one five minutes, persons on board one seven nine, SpiceJet 318

Pilot

Chennai Control, SpiceJet 318, information Delta, flight level two nine zero, direct Chennai, diverting from Bengaluru

ATC

SpiceJet 318, Chennai Control, descend flight level one five zero, expect ILS approach runway two five, QNH one zero zero nine

Pilot

Descend flight level one five zero, expect ILS runway two five, QNH one zero zero nine, SpiceJet 318

Give the cause in the first diversion call. The controller distinguishes weather, fuel, technical and medical cases because each may need different coordination. A serious defect may prompt a check of rescue and firefighting readiness, while routine weather avoidance does not automatically require an emergency response. Update the controller if the situation changes.
If a MAYDAY or PAN PAN was declared before the diversion, a change of destination does not cancel it. ATC continues the applicable priority handling until the pilot formally cancels the emergency or normal handling resumes. Report the alternate and any new failure, such as an engine fire, while retaining the earlier declaration.
For the first transmission to the ATS unit serving the alternate aerodrome, give the ATIS letter immediately after the callsign. The controller then knows that you have checked the runway in use, QNH, weather and temporary restrictions. In a spoken test, give the designator before position, flight level or diversion details when asked how to begin the call.
Recalculate fuel for the revised route and ETA once diversion is confirmed. Compare forecast landing fuel at the alternate with the applicable final reserve and any company or regulatory requirement. If the required reserve would not remain at landing, or fuel endurance becomes critical, declare MAYDAY MAYDAY MAYDAY FUEL at once. A diversion report alone does not tell ATC that a fuel emergency exists.
Notify the operator's operations centre in parallel through ACARS, SATCOM or the company frequency. Staff can then arrange ground handling, passenger assistance, customs clearance and any technical or fuel support required at the alternate before arrival.

Reference: Doc 9432 §11.8 / DGCA CAR Section 8 Series O Part II

Emergency Descent

Use this procedure when sudden cabin pressure loss, smoke, fire, or another urgent condition requires altitude to be reduced at once. Transmit MAYDAY, select the emergency transponder code seven seven zero zero, and begin the descent under the approved aircraft procedure. For a pressure-loss event, fit the oxygen mask at the same time. The vertical rate can exceed six thousand feet per minute, and a track offset may be needed for separation from traffic. If cabin altitude continues to rise, speech and radio reception may become unreliable.

Pilot

MAYDAY MAYDAY MAYDAY, [station], [callsign], [aircraft type], EMERGENCY DESCENT, [reason], [position], DESCENDING FROM [level] TO [level], [offset], [intentions], PERSONS ON BOARD [number]

ATC

[callsign], [station], ROGER MAYDAY, DESCEND [level], [traffic information], [routing]

Pilot

MAYDAY MAYDAY MAYDAY, Nagpur Control, Vistara 815, Airbus A320, emergency descent due rapid decompression, five five miles west of Nagpur, descending from flight level three five zero to flight level one hundred, turning right off track, diverting to Nagpur, persons on board one seven two

ATC

Vistara 815, Nagpur Control, roger MAYDAY, descend flight level one hundred, traffic opposite direction flight level two nine zero, one five miles east of you, cleared direct Nagpur, report level

Pilot

Descend flight level one hundred, cleared direct Nagpur, wilco, Vistara 815

Pilot

Nagpur Control, Vistara 815, emergency descent complete, maintaining flight level one hundred, five zero miles west of Nagpur, persons on board one seven two, endurance one hour two zero minutes

ATC

Vistara 815, roger, expect ILS approach runway three two, Nagpur QNH one zero zero eight

Emergency descent coordination forms part of Indian ATC procedures. Set the transponder to seven seven zero zero and make a verbal MAYDAY report. The code assists identification but does not clear traffic or replace controller separation. Radar contact and aircraft reports enable the controller to prioritise the flight and coordinate a separation plan.
If you leave the airway to descend, turn off track as your operator's procedure and the regional rules require, and say which side you are turning. The controller can then move other traffic around you.
After depressurisation, the crew of a transport aircraft normally targets flight level one hundred when the approved procedure, terrain, and traffic permit. A higher minimum safe altitude, weather, or an aircraft-specific instruction may require another level. Higher cruising levels make continued pressurisation and oxygen provision more critical, so state the intended level in the initial MAYDAY report.
After reaching the assigned level, tell ATC that the emergency descent is complete and state the flight level. The controller can then revise separation for nearby traffic and return the aircraft to routine handling. Make this report to ATC rather than broadcasting it as a routine message to other aircraft.
When smoke or fire is the cause, plan to land at the nearest suitable aerodrome; simply reaching a lower cruising level does not resolve the emergency. Follow the approved smoke, fire, or emergency procedure, maintain aircraft control, and report fuel, persons on board, hazards, and the intended destination as soon as practicable.

Reference: Doc 9432 §11.6 / Airbus/Boeing AFM emergency-descent procedures

Engine Failure (Enroute Drift Down)

Use PAN PAN when a twin aircraft suffers an engine failure in cruise but can still sustain flight at a lower altitude and reach the nearest suitable diversion airport. State the engine number, position, present altitude, planned drift-down level and intended destination in the initial alert. Upgrade to MAYDAY if the operating engine is affected or terrain, weather or performance prevents a safe descent and diversion.

Pilot

PAN PAN, PAN PAN, PAN PAN, [station], [callsign], [aircraft type], ENGINE FAILURE NUMBER [n], ENGINE SHUT DOWN, [position], [level], DRIFTING DOWN TO [level], DIVERTING TO [alternate], REQUEST [clearance]

ATC

[callsign], [station], ROGER PAN PAN, DESCEND [level], CLEARED DIRECT [alternate], [emergency services information]

Pilot

PAN PAN, PAN PAN, PAN PAN, Ahmedabad Control, Vistara 815, Airbus A320, engine failure number two, engine shut down, six zero miles northeast of Ahmedabad, flight level three five zero, drifting down to flight level two three zero, diverting to Ahmedabad, request descent and direct Ahmedabad

ATC

Vistara 815, Ahmedabad Control, roger PAN PAN, descend flight level two three zero, cleared direct Ahmedabad, report reaching, advise persons on board, endurance and dangerous goods

Pilot

Descend flight level two three zero, cleared direct Ahmedabad, wilco, persons on board one six two, endurance two hours one zero minutes, no dangerous goods, Vistara 815

ATC

Vistara 815, fire services and ambulance will stand by at Ahmedabad, contact Ahmedabad Approach one two six decimal seven at three zero DME

Pilot

Ahmedabad Approach one two six decimal seven at three zero DME, Vistara 815

The drift-down level is the highest level the aircraft can hold on the remaining engine at its present weight and in the present conditions. The flight management computer usually works it out. Give it in the first call so the controller can clear you straight to it and keep other traffic clear.
After confirming the affected engine is secured, report ENGINE FAILURE, NUMBER [n], ENGINE SHUT DOWN. This wording identifies both the engine and its current status. The shutdown report does not establish whether a relight is planned, so state that intention separately.
During a stable PAN PAN, the controller may put the airport rescue and fire fighting service and an ambulance on standby at the diversion airport. This precaution is often justified when the descent takes the aircraft below RVSM, the one-engine performance margin is small or rescue support at the alternate is limited.
Issue MAYDAY immediately if the operating engine loses power, develops excessive vibration or indicates a fire. Unsafe descent caused by terrain, weather or performance also requires MAYDAY, as does a fire involving the secured engine. Do not remain on PAN PAN while any of these conditions exists.

Reference: ICAO Annex 6 / Doc 9432 §11.5

Fire / Smoke On Board

Smoke or flame that creates a grave and imminent danger warrants a declared MAYDAY, even if the crew believes the source is under control. State what is burning or smoking, its exact location, the aircraft's position and level, the intended airport and routing, total persons aboard, and remaining endurance. ATC then clears a direct route and suitable altitude, places rescue and fire fighting services at the intended touchdown runway, and coordinates the response.

Pilot

MAYDAY MAYDAY MAYDAY, [station], [callsign], [aircraft type], [fire or smoke and where], [intentions], [position], [level], PERSONS ON BOARD [number], ENDURANCE [hours and minutes]

ATC

[callsign], [station], ROGER MAYDAY, [routing], [level], [expected approach], [fire services information], CONTACT [unit] [frequency]

Pilot

MAYDAY MAYDAY MAYDAY, Ahmedabad Control, SpiceJet 318, Boeing 737, fire in the aft galley, extinguisher used, smoke still in the cabin, request immediate landing Ahmedabad runway two three, four zero miles east of Ahmedabad, flight level two four zero, persons on board one eight six, endurance one hour two five minutes

ATC

SpiceJet 318, Ahmedabad Control, roger MAYDAY, cleared direct Ahmedabad, descend eight thousand feet, QNH one zero zero four, expect ILS approach runway two three, fire services standing by, contact Ahmedabad Approach one two one decimal three

Pilot

Direct Ahmedabad, descend eight thousand feet, QNH one zero zero four, expect ILS runway two three, Ahmedabad Approach one two one decimal three, SpiceJet 318

Pilot

Ahmedabad Approach, SpiceJet 318, MAYDAY, galley fire, smoke in the cabin, two five miles east of the field, leaving flight level one six zero for eight thousand feet, request straight in ILS runway two three

ATC

SpiceJet 318, Ahmedabad Approach, roger MAYDAY, fly heading two four zero, cleared ILS approach runway two three, fire services will be on one two one decimal nine

Pilot

Heading two four zero, cleared ILS approach runway two three, fire services one two one decimal nine, SpiceJet 318

Report the total number of people on board and the fuel endurance in hours and minutes. Fuel weight must not replace endurance. Providing both figures in the first call avoids a separate request from the controller while time is critical.
Identify both the source and the compartment, for example flight deck, cabin, galley, lavatory, cargo hold, engine, or wheel well. This detail selects the appropriate emergency checklist and helps RFFS anticipate the hazard during rescue.
Apply the nearest suitable aerodrome principle by choosing the closest field with a usable runway, acceptable weather, and adequate rescue support, even when it differs from the scheduled destination. During smoke or fire events, rapid landing takes priority, although performance, terrain, obstacles, and navigation aids must remain satisfactory.
The emergency transponder setting is SQUAWK seven seven zero zero. It promptly alerts ATC, allowing airport operations, medical support, and rescue crews to prepare before the aircraft arrives.
After landing the aircraft may have to stop on the runway for an evacuation. Use the discrete fire services frequency ATC gives you, often one two one decimal nine, to talk directly to the fire and rescue commander.

Reference: ICAO Annex 6 Part I §4.5 / Doc 9432 §11.5

Flaps stuck, Overweight landing

Apply this procedure after departure if the flap system cannot provide a usable landing configuration and the aircraft remains above its permitted landing mass. A partial or retracted flap setting usually raises approach speed and may extend the landing distance. Extra mass adds further stopping distance and gear loading, so an immediate return may be unsuitable. PAN PAN is appropriate when the aircraft is still flyable but needs an achievable level and protected airspace for fuel burn. Use MAYDAY only if an immediate danger to life or the aircraft develops.

Pilot

PAN PAN, PAN PAN, PAN PAN, [station], [callsign], [aircraft type], [malfunction], [position and level], OVERWEIGHT FOR LANDING, REQUEST [level] AND HOLDING AT [fix] TO BURN FUEL

ATC

[callsign], [station], ROGER PAN PAN, SQUAWK [code], CLIMB [level], [routing to the fix], HOLD AT [fix], EXPECT [minutes] HOLDING, RUNWAY [runway], QNH [pressure]

Pilot

PAN PAN, PAN PAN, PAN PAN, Hyderabad Approach, Air India 447, Boeing 787, flaps jammed at five, passing flight level nine zero climbing, overweight for landing, request flight level one three zero and holding at DUKIR to burn fuel, then return to Hyderabad.

ATC

Air India 447, Hyderabad Approach, roger PAN PAN, squawk seven one four three, climb flight level one three zero, maintain runway heading until DUKIR, hold at DUKIR, runway two seven left, QNH one zero one three.

Pilot

Squawk seven one four three, climb flight level one three zero, runway heading until DUKIR, hold at DUKIR, runway two seven left, QNH one zero one three, Air India 447.

ATC

Air India 447, expect three five minutes holding.

Pilot

Hyderabad Approach, Air India 447, flaps now operating normally after the checklist, cancel PAN PAN, request to continue to Jaipur and climb flight level three three zero.

ATC

Air India 447, Hyderabad Approach, roger, climb flight level one five zero in the holding area, then direct Jaipur, expect higher from Hyderabad Control.

Two separate limitations are present: an unsuitable flap setting and mass above the permitted landing limit. With less flap, the aircraft normally flies faster on approach and needs more runway. Added mass also raises stopping distance and gear loading, so an immediate return may not offer the required performance margin.
The crew needs a level it can safely reach and a protected area suitable for continuous turns. The racetrack is used to reduce fuel quantity, not to cure a defective flap system. The applicable flight manual and company procedure determine when landing mass is acceptable.
By assigning a fix, heading and altitude, ATC gives the aircraft a clear operating area while protecting it from conflicting traffic. Terrain and nearby airway structure also matter, so a fuel-burn manoeuvre must remain within the cleared airspace.
The readback covers the squawk, the cleared level, the routing to the fix, the holding instruction, the runway and QNH. Query anything unclear before entering the hold.
Runway and QNH information allows the crew to recheck landing performance and the aircraft configuration. The controller's holding estimate is advisory because it depends on expected routing and traffic rather than direct knowledge of the remaining fuel.
Fuel burned per holding cycle can vary with aircraft type, wind, turbulence and power setting. The crew should monitor the trend and request additional time or a different arrangement if the aircraft will remain above landing mass at the end of the planned hold.
Cancel PAN PAN only once the checklist confirms the flaps really work and no other urgent problem is left. If the flaps later fail again, or anything else goes wrong, declare again without hesitation.
With the flaps working the crew may choose to continue to the planned destination instead of returning, which also removes the overweight landing problem because fuel will be burned en route. ATC still has to check traffic before approving the new routing and level.
PAN PAN is suitable here because the aircraft is still controllable and the problem is urgent but not immediately catastrophic. MAYDAY becomes appropriate only if the malfunction or associated performance condition develops into a serious and immediate threat.

Reference: ICAO Doc 9432

Hydraulic Failure (Single System)

Declare PAN PAN when one hydraulic system on a multi-system aircraft fails and the others keep working. Say which system has gone and what it takes with it, for example nosewheel steering, autobrake, slow flaps or gravity gear extension, depending on the type. Also say what runway you need and whether you will need a tow, so ATC can pick a suitable runway, space the traffic behind you and have a tug ready.

Pilot

PAN PAN, PAN PAN, PAN PAN, [station], [callsign], [aircraft type], [system] HYDRAULIC SYSTEM FAILURE, [effects], REQUEST [runway, vectors, tow]

ATC

[callsign], [station], ROGER PAN PAN, [runway and landing distance available], [vectors], [squawk and QNH], REPORT PERSONS ON BOARD AND ENDURANCE

Pilot

PAN PAN, PAN PAN, PAN PAN, Chennai Approach, Vistara 815, Airbus A320, yellow hydraulic system failure, nosewheel steering lost, flaps slow, flight level one two zero, heading two eight zero, request longest runway, vectors for a long final and a tow after landing.

ATC

Vistara 815, Chennai Approach, roger PAN PAN, expect runway zero seven, landing distance available three thousand six hundred metres, vectors for a one five mile final, squawk four three one seven, QNH one zero zero nine, report persons on board and endurance.

Pilot

Runway zero seven, squawk four three one seven, QNH one zero zero nine, persons on board one seven seven, endurance one hour two five minutes, Vistara 815.

ATC

Vistara 815, tug will meet you on the runway, turn left heading zero nine zero, descend to two thousand five hundred feet, cleared ILS approach runway zero seven, reduce speed one six zero knots.

Pilot

Left heading zero nine zero, descend two thousand five hundred feet, cleared ILS approach runway zero seven, speed one six zero knots, Vistara 815.

Identify the circuit with terminology appropriate to the type. An A320 uses green, blue and yellow systems; a B737 uses system A, system B and standby; a B777 uses left, centre and right systems. Include the applicable label, since an exam answer mentioning only hydraulic loss may be judged incomplete.
An opening PAN should identify the failed circuit, explain the operational limitations and state the runway or distance requirement. With all three points present, ATC can select a suitable runway and issue arrival instructions without another exchange.
On an A320, losing the yellow system takes away nosewheel steering and makes the flaps slow, while the normal brakes on the green system still work. Losing the green system instead means gravity gear extension and no autobrake. Take the exact list of losses from the checklist, not from memory, and take the landing distance from the performance data.
Request a tow because, without nosewheel steering, the aircraft may be unable to clear the runway under its own power. Explain why a tug is needed so ATC can position it and hold following arrivals until sufficient separation is available.

Reference: Doc 9432 §11.5 / Airbus/Boeing AFM hydraulic-failure procedures

Impose Silence During a Distress

While a distress is being worked, only the aircraft in distress, the station controlling it and any station it authorises may transmit. If someone else blocks the frequency, either the controlling station or the aircraft in distress can silence them.

Pilot

ALL STATIONS, [Callsign], STOP TRANSMITTING, MAYDAY

ATC

ALL STATIONS, [Station], STOP TRANSMITTING, MAYDAY

ATC

All stations, Mumbai Approach, stop transmitting, MAYDAY

Pilot

VT-ABC, stop transmitting, MAYDAY, VT-AIR

ATC

All stations, Mumbai Approach, distress traffic ended

The phrase is STOP TRANSMITTING, MAYDAY. The word MAYDAY at the end is what makes it an imposition of silence rather than an ordinary request.
It can be addressed to all stations or to the single station that is causing the interference, by that station's callsign.
Silence is lifted by the controlling station with DISTRESS TRAFFIC ENDED. Do not resume normal calls until you hear it.
If you are not involved in the distress, the correct action is simply to listen. Do not offer help on the frequency unless you are asked.

Reference: ICAO Doc 9432

Inter-Aircraft Relay

VT-KRA may be beyond reliable VHF coverage of Kolkata Control because of distance or terrain. Kolkata Control may use Alliance 912 as an intermediate link only after confirming that the relay pilot can contact both aircraft. Alliance 912 then carries VT-KRA's position report and request, receives the instruction, and passes the controller's reply with the granting authority clearly stated. Direct contact should resume as soon as it becomes possible.

Pilot

[station], [relay callsign], RELAYING FOR [callsign], POSITION [fix] AT [time], [level], ESTIMATING [boundary] AT [time], [destination] AT [time], TRUE AIRSPEED [speed] KNOTS, REQUEST [clearance]

ATC

[relay callsign], [station], ROGER, RELAY TO [callsign], CLEARED TO CROSS [boundary], MAINTAIN [level]

Pilot

Kolkata Control, Alliance 912, relaying for VT-KRA, position Bhubaneswar at zero four four zero, flight level two four zero, estimating the Chennai Kolkata boundary at zero five one five, Kolkata at zero six one zero, true airspeed two seven zero knots, request crossing clearance.

ATC

Alliance 912, Kolkata Control, roger, relay to VT-KRA, cleared to cross the Chennai Kolkata boundary, maintain flight level two four zero.

Pilot

Relaying to VT-KRA, cleared to cross the Chennai Kolkata boundary, maintain flight level two four zero, Alliance 912.

Pilot

VT-KRA, Alliance 912, Kolkata Control clears you to cross the Chennai Kolkata boundary, maintain flight level two four zero.

Pilot

Alliance 912, VT-KRA, cleared to cross the Chennai Kolkata boundary, maintain flight level two four zero.

By saying "relaying for VT-KRA", Alliance 912 identifies whose information it is carrying. The controller therefore knows that the report, request and any later reply belong to VT-KRA, not to the aircraft providing the radio link.
Every value supplied by VT-KRA should pass unchanged: position, UTC, level, boundary estimate, destination time, true airspeed and the request. No item should be silently omitted or guessed; check any missing detail with VT-KRA first.
"Position Bhubaneswar at zero four four zero, flight level two four zero" links a stated place with UTC and the aircraft's level. Here, read the time and flight level two four zero digit by digit. Under AAI MATS Part 1, Edition 7 (May 2025), paragraph 12.5.1, you use HUNDRED for whole-hundred flight levels, for example flight level three hundred. Do not say "three zero zero" for flight level three hundred: it is marked wrong.
The Chennai-Kolkata boundary estimate shows when VT-KRA expects to enter Kolkata's sector. It helps the controller assess traffic and respond before the aircraft reaches the boundary, but it is only a planning statement and grants no permission to enter.
Kolkata Control places VT-KRA's callsign directly with the clearance and specifies both the boundary and the level. Alliance 912 must retain those exact details while repeating and relaying the instruction; any change must be clarified with the controller.
After a clearance involving a level, Alliance 912 repeats the boundary and flight level to Kolkata Control. The word "wilco" alone cannot replace a complete readback of those safety items because the relay pilot is confirming an instruction, not merely acknowledging its receipt.
The wording "Kolkata Control clears you" makes the granting authority explicit. Alliance 912 is only the communication link and must not imply that it issued the clearance. This attribution prevents VT-KRA from treating the relay pilot as the clearing authority.
VT-KRA's reply repeats the assigned level and boundary, then closes with its own callsign. The relay is not fully verified until Alliance 912 has passed that readback to Kolkata Control in a separate call; until then, clearance confirmation remains incomplete.

Reference: ICAO Doc 9432

Inter-Unit Coordination Failure

Use this procedure when an aircraft is near an ATS sector boundary and the outgoing unit has not informed the receiving unit of the flight. Attempts to complete the handover remain unanswered. The pilot therefore contacts the receiving approach or control sector directly on the current coordination frequency, supplies position, heading, level, next fix and estimated time, and remains on that frequency until responsibility and further instructions are confirmed.

Pilot

[station], [callsign], NEGATIVE CONTACT WITH [unit], [distance] [direction] OF [boundary], HEADING [heading], [level], ESTIMATING [fix] AT [time]

ATC

[callsign], [station], ROGER, MAINTAIN [level], REPORT [fix], REMAIN THIS FREQUENCY

Pilot

Chennai Approach, Air India 447, negative contact with Kolkata Control, two zero miles east of the Chennai approach boundary, heading two seven zero, flight level two three zero, estimating ADKAL at zero six four five

ATC

Air India 447, Chennai Approach, roger, maintain flight level two three zero, report ADKAL, remain this frequency

Pilot

Maintain flight level two three zero, wilco, Air India 447

NEGATIVE CONTACT indicates that repeated attempts to reach Kolkata Control produced no usable two-way exchange. It does not describe a communication link that was operating earlier and then stopped without warning.
The distance from the sector boundary, direction of flight and present flight level give Chennai an immediate traffic picture. The fix estimate connects the aircraft's current position with its expected progress.
ADKAL is the reporting point in this example. The zero six four five estimate helps the controller plan the arrival even though no handover message arrived.
REMAIN THIS FREQUENCY keeps the aircraft on the channel it has just used to make contact. Avoiding another change during the confusion reduces the chance of a tuning error.
Chennai confirms the level to hold and asks for a report at a definite fix, which gives a clean position check while responsibility for the flight is sorted out.
The pilot reads back the level, which is the safety item, and answers the report request with WILCO. The report itself comes later, when the aircraft actually reaches the fix.
A crew should promptly contact the receiving sector if the outgoing frequency produces no usable handover. A direct call gives the next controller an accurate traffic picture and establishes contact while responsibility for the aircraft is clarified.

Reference: ICAO Doc 9432

Lost contact during climb

Use this procedure during a departure climb when the aircraft cannot obtain a reply from the expected ground or local control unit and must contact the next appropriate ATS facility. The pilot identifies the previous controller, reports position, heading, present level and the last clearance received, then stays on the new frequency. The receiving controller confirms identity, issues any required hold instruction, passes essential traffic information, and permits further climb only after separation has been assessed.

Pilot

[station], [callsign], NEGATIVE CONTACT WITH [unit], POSITION [position], HEADING [heading], [aircraft type], [present level], CLEARED [cleared level]

ATC

[callsign], [station], REMAIN THIS FREQUENCY, MAINTAIN [level], [traffic information]

Pilot

Delhi Control, Vistara 815, negative contact with Jaipur Tower, position one two DME northwest of Jaipur, heading three three zero, Airbus A320, flight level one four zero, cleared flight level three seven zero.

ATC

Vistara 815, Delhi Control, remain this frequency, maintain flight level one four zero, reciprocal traffic Air India 447, Boeing 787, descending to flight level one six zero, crossing one eight DME northwest of Jaipur at one three three zero.

Pilot

Remain this frequency, maintain flight level one four zero, traffic Air India 447, Vistara 815.

Pilot

Delhi Control, Vistara 815, one nine DME northwest of Jaipur, Air India 447 reported passing one one DME northwest of Jaipur, request climb flight level three seven zero.

The opening call tells the new controller that contact with Jaipur Tower was lost. Position, heading, present level and the last clearance received allow Vistara 815 to be identified and assessed without another exchange.
Flight level one four zero states the aeroplane's present level, while flight level three seven zero is the upper level already cleared. The new controller must check whether that earlier clearance can safely remain in effect.
REMAIN THIS FREQUENCY keeps the flight on the channel that works instead of sending it back to one that gave no reply. Delhi Control can keep watching and instructing while the communication problem is sorted out.
MAINTAIN FLIGHT LEVEL ONE FOUR ZERO replaces the earlier climb clearance for now. It keeps Vistara 815 below the descending traffic until the controller can safely allow further climb.
Air India 447 is described by callsign, type, vertical movement and where and when it will cross: a Boeing 787 descending to flight level one six zero, crossing one eight DME northwest of Jaipur at one three three zero. Opposite tracks and converging levels are exactly what the controller is protecting against.
The frequency and level instructions are read back because they are clearances. Traffic information only needs acknowledging, though naming the other callsign shows it was heard.
By the final call, Vistara 815 at one nine DME and Air India 447 at one one DME have passed each other, since each has flown beyond the one eight DME crossing point in its own direction. The pilot passes this as a report, not as a claim that separation exists.
Knowing that the other aircraft has passed does not bring back the old climb clearance. Delhi Control must check separation and say CLIMB FLIGHT LEVEL THREE SEVEN ZERO before Vistara 815 leaves flight level one four zero.
Putting a position update and a request into one transmission limits radio congestion and keeps the message efficient. It still does not create authority to climb; the hold remains effective until a new clearance is issued and read back.

Reference: ICAO Doc 9432

MAYDAY (Distress Call)

Use MAYDAY when the aircraft faces immediate and serious danger and prompt assistance is essential, for example fire, loss of all engines, major control or structural failure, or fuel so low that no safe landing option remains. It has priority over every other communication on the frequency. Say MAYDAY three times so the emergency is unmistakable even if part of the call is lost, then give the station, callsign, aircraft type, what is wrong, what you intend to do, your position and level, persons on board and endurance.

Pilot

MAYDAY MAYDAY MAYDAY, [station], [callsign], [aircraft type], [nature of emergency], [intentions], [position], [level], PERSONS ON BOARD [number], ENDURANCE [hours and minutes]

ATC

[callsign], [station], ROGER MAYDAY, [clearance or vectors], [emergency services information]

Pilot

MAYDAY MAYDAY MAYDAY, Hyderabad Approach, Alliance 912, ATR 72, left engine fire, request immediate vectors for landing runway zero nine right, one five DME southeast of Hyderabad, passing six thousand feet descending, persons on board seven four, endurance one hour three zero minutes

ATC

Alliance 912, Hyderabad Approach, roger MAYDAY, descend four thousand feet, fly heading zero three zero, vectors for ILS approach runway zero nine right, fire services alerted

Pilot

Descend four thousand feet, heading zero three zero, vectors ILS runway zero nine right, Alliance 912

ATC

Alliance 912, advise dangerous goods and any passengers needing assistance

Pilot

No dangerous goods, one passenger in a wheelchair, Alliance 912

Select SQUAWK seven seven zero zero on the transponder, if it is fitted and serviceable, while transmitting the MAYDAY. This emergency code enables surveillance controllers to identify the aircraft quickly, but it does not replace the spoken distress message or explain the cause of the emergency.
Annex 10 lists the content of a distress message as: the station addressed, your callsign, the nature of the emergency, your intentions, then present position, level and heading. Aircraft type, persons on board and endurance are commonly added. Getting the call out quickly matters more than perfect order; if a detail is not known yet, skip it and pass it later.
Controllers may ask for dangerous goods, wheelchair access, infant handling, the number of occupants, and endurance. Complete the main distress message before answering such questions. Before using the microphone, verify the occupant count, fuel endurance, cargo status, and assistance needs so that missing details can be supplied without delay.
If the danger has ended and immediate assistance is no longer required, send [station], Alliance 912, CANCEL DISTRESS, [reason]. The controller replies, Alliance 912, DISTRESS CANCELLED, [time] UTC. Use PAN PAN if urgent help remains necessary but the circumstances no longer meet the distress criteria.
Normally remain on the frequency used for the emergency until ATC directs otherwise or confirms a transfer. Maintain continuous watch so instructions are not missed and rescue coordination remains intact. Any move to approach, tower, ground, or an emergency frequency should be coordinated with ATC. After landing, agree the handover so airport rescue and fire fighting services receive the latest position and person count.

Reference: ICAO Annex 10 Vol II §5.3 / Doc 9432 §11

MAYDAY versus PAN PAN

MAYDAY for distress requiring immediate assistance. PAN PAN for urgency concerning safety when immediate assistance is not required.

Pilot

MAYDAY MAYDAY MAYDAY, [unit], [callsign], [problem], [intentions], [position level heading]. PAN PAN, PAN PAN, PAN PAN follows the same order for urgency.

ATC

[callsign], MAYDAY received, [assistance and instructions].

Pilot

MAYDAY MAYDAY MAYDAY, Mumbai Control, Skyline 345, engine failure, diverting to Mumbai, two zero miles north, flight level one eight zero, heading one eight zero.

ATC

Skyline 345, Mumbai Control, MAYDAY received, runway two seven available, descend and maintain one two thousand feet, report heading.

Say the signal three times at the start of the first distress or urgency transmission.
Give the unit addressed if possible, then aircraft identification, nature of the problem, intentions, position, level and heading.
Declare early. You may cancel the state later if the situation improves.
Distress traffic has absolute priority. Urgency traffic has priority over all communications except distress traffic.

Reference: ICAO Doc 9432, 9.2 to 9.3

Medical Priority (HOSP / MEDEVAC / PAN PAN)

Use this phraseology when a person aboard needs urgent treatment or a time-sensitive organ-transport flight requires close ground coordination. STS/HOSP and STS/MEDEVAC identify the flight-plan status, but the urgency stated on frequency reflects the current situation. For a seriously ill passenger, declare urgency with PAN PAN, and reserve MAYDAY for circumstances in which delay would immediately endanger life.

Pilot

PAN PAN, PAN PAN, PAN PAN, [station], [callsign], [medical situation], [position], [level], REQUEST [action required]

ATC

[callsign], [station], ROGER PAN PAN, [clearance and priority information], ADVISE PERSONS ON BOARD AND ENDURANCE

Pilot

PAN PAN, PAN PAN, PAN PAN, Hyderabad Control, Vistara 815, one passenger unresponsive, cabin crew giving CPR, three zero miles northwest of Hyderabad on the three zero zero radial, flight level three five zero, request descent flight level one two zero and priority landing at Hyderabad

ATC

Vistara 815, Hyderabad Control, roger PAN PAN, descend flight level one two zero, expect vectors for ILS approach runway two seven left, QNH one zero one two, ambulance and doctor will meet the aircraft, advise persons on board and endurance

Pilot

Descend flight level one two zero, expect ILS runway two seven left, QNH one zero one two, persons on board one seven four, endurance two hours, Vistara 815

Flight-plan field eighteen uses STS/HUM, STS/HOSP and STS/MEDEVAC for humanitarian, hospital and medical-evacuation flights. These designators state the mission type; they do not create an automatic priority ranking or guarantee handling ahead of other traffic.
On flights designated STS/MEDEVAC, pilots say MEDEVAC before the aircraft call sign, for example, MEDEVAC Vistara 815. A flight designated STS/HOSP uses HOSPITAL before its call sign. Apply the relevant prefix on every pilot transmission for that flight, but do not add it merely because a normal flight has a medical emergency.
PAN PAN MEDICAL is not the call for a sick passenger. Under ICAO Annex 10 it identifies an aircraft engaged in protected medical transport under the Geneva Conventions. A passenger medical emergency on a normal flight uses the plain urgency signal, PAN PAN said three times.
After the prefix, give the station, call sign, medical situation, position, level and requested action, in that order. Position information should come before any request, allowing the controller to consider traffic, terrain and diversion options before issuing clearance.
Use concise, factual observations, such as one passenger unresponsive and cabin crew performing CPR. Do not say 'unable to revive'; it is not standard ICAO phraseology. State the number of affected passengers, their condition and any treatment already started.
Use MAYDAY MAYDAY MAYDAY only when the danger is grave and imminent and immediate ATC assistance is indispensable. The threat may concern a person aboard even if the aircraft has no fault. If PAN PAN can obtain the necessary response, use that lower level of urgency instead.
Before making the call, check how many persons are aboard and the remaining fuel endurance. Controllers use these figures to assess diversion options and arrange suitable assistance at the destination. Provide both details promptly when requested.

Reference: ICAO Doc 4444 §16.4 / Doc 9432 §11 / Annex 2

Minimum Fuel & MAYDAY FUEL

MINIMUM FUEL advises ATC that the aircraft is committed to a particular destination and that delay, a route change, or an amended clearance could leave less than final reserve on landing. It is not, by itself, an emergency declaration. Use MAYDAY FUEL when the aircraft can still reach the nearest suitable aerodrome, but the expected landing fuel there would be less than the applicable final reserve. Final reserve is often expressed as thirty minutes of flight at one thousand five hundred feet above the alternate under normal conditions, subject to operator policy and local terrain.

Pilot

[station], [callsign], MINIMUM FUEL; or for an emergency: MAYDAY MAYDAY MAYDAY FUEL, [station], [callsign], [endurance], [persons on board], [intentions]

ATC

[callsign], [station], ROGER MINIMUM FUEL, NO DELAY EXPECTED (or EXPECT [delay information]); for an emergency: ROGER MAYDAY, [priority instructions]

Pilot

Chennai Control, IndiGo 5231, minimum fuel

ATC

IndiGo 5231, Chennai Control, roger minimum fuel, no delay expected, descend flight level one two zero, contact Chennai Approach one two four decimal five

Pilot

Descend flight level one two zero, Chennai Approach one two four decimal five, IndiGo 5231

Pilot

MAYDAY MAYDAY MAYDAY FUEL, Chennai Approach, IndiGo 5231, endurance one five minutes, persons on board one one two, request immediate vectors for ILS approach runway zero seven

ATC

IndiGo 5231, Chennai Approach, roger MAYDAY, turn left heading zero seven zero, descend two thousand feet, QNH one zero zero eight, cleared ILS approach runway zero seven, number one

Pilot

Left heading zero seven zero, descend two thousand feet, QNH one zero zero eight, cleared ILS approach runway zero seven, IndiGo 5231

MINIMUM FUEL tells ATC that further delay or rerouting could leave too little final reserve. Controllers seek to prevent avoidable holding and unnecessary track extension, and handling remains aimed at the selected airport. The advisory does not itself create an emergency, reserve a dedicated frequency, or order airport rescue and firefighting services to stand by.
Once MAYDAY FUEL is declared, emergency handling applies. The call opens with MAYDAY MAYDAY MAYDAY FUEL, then the station and callsign, then endurance, persons on board and intentions. ATC gives priority vectors and an approach clearance with as little delay as possible.
On R/T, give fuel as time, not weight. Report hours and minutes as required, for example, fuel remaining two five minutes. Do not substitute a kilogram or tonne figure for the fuel remaining report.
Do not use the planned alternate fuel figure as a trigger. It is a planning allowance linked to the selected alternate, not the protected final reserve. Use expected landing fuel and the operator's policy when choosing between MINIMUM FUEL and MAYDAY FUEL.
After landing, keep the fuel records and flight data, and report the occurrence through your operator's safety reporting system as the regulator requires.

Reference: ICAO Annex 6 Part I §4.3.7.2 / Doc 9432 §9.6 / DGCA CAR Section 8 Series O Part II

Negative Contact During Descend

Use this procedure when an aircraft descending toward an aerodrome cannot raise the next ATC unit, usually Approach, after a frequency handover. The failure may result from an incorrect setting, poor reception, or an unanswered call. The crew should return to the last controller with reliable two-way contact and report that the intended transfer did not work. It should not assume that an unavailable station is monitoring the aircraft or providing clearances. Once responsibility is clear and any necessary coordination is complete, the earlier unit may retain the aircraft and issue descent or approach instructions on the working frequency.

Pilot

[station], [callsign], NEGATIVE CONTACT [unit] ON [frequency], PASSING [level] FOR [level]

ATC

[callsign], [station], ROGER, REMAIN THIS FREQUENCY, [descent and approach clearance], [report instruction]

Pilot

Hyderabad Tower, IndiGo 5231, negative contact Hyderabad Approach on one one nine decimal seven, passing flight level eight zero for flight level six zero.

ATC

IndiGo 5231, Hyderabad Tower, roger, remain this frequency, descend four thousand feet, QNH one zero one one, cleared ILS approach runway zero nine right, report established on the localiser.

A failure to reach Approach is not, by itself, a lost communications event. The crew still has two-way contact with Tower, so it should keep the assigned transponder code rather than select seven six zero zero.
State both the flight level being crossed and the level already authorised for the descent. The words PASSING and FOR allow Tower to determine the aircraft's vertical position immediately while the new controller is contacted.
REMAIN THIS FREQUENCY means Tower has accepted responsibility instead of leaving the aircraft with an unreachable Approach sector. Here, Approach could not be raised on one one nine decimal seven, while the crew had returned to Tower on one one eight decimal one. Follow any revised handoff instruction before tuning again.
Tower must not issue an approach clearance merely because Approach is silent. Before retaining the aircraft, the controller should establish responsibility and coordinate with the approach function. At some aerodromes these duties are combined, while at others explicit delegation is required. The worked example assumes such coordination has already been completed.
The descent level, approach clearance and runway must be read back. The report point gives the controller a definite checkpoint for sequencing and separation, and an absent call allows the controller to investigate or provide alternative instructions.
If Approach becomes reachable later, resume only the handoff authorised by the controllers and confirm the assigned frequency and transponder code. Otherwise, remain on Tower's channel while Tower explicitly retains control, and request clarification whenever responsibility is uncertain.

Reference: ICAO Doc 9432

Negative Contact with Tower After Departure

Use this procedure after becoming airborne when the departure tower or another responsible VHF unit cannot be reached. Contact Kolkata Radio on its HF service, state the attempted VHF frequency, identify the facility that failed to answer, provide position and time, and report the level being passed. The relay may confirm an existing climb instruction and request a report at a specified level. Read back the instruction and the requested level accurately. It provides a relay path when a direct VHF link with a controlling unit is unavailable.

Pilot

[relay station], [callsign], NEGATIVE CONTACT WITH [unit] ON [frequency], [distance] MILES [direction] OF [reference] AT [time], PASSING [level], CONTINUING CLIMB AS CLEARED

ATC

[callsign], [station], REPORT PASSING [level], CONTINUE CLIMB AS CLEARED

Pilot

Kolkata Radio, Air India 447, negative contact with Guwahati Tower on one two zero decimal two five, three six miles southeast of Guwahati at zero seven one five, passing flight level one hundred, continuing climb as cleared.

ATC

Air India 447, Kolkata Radio, report passing flight level one six zero, continue climb as cleared.

Pilot

Wilco, continuing climb as cleared, Air India 447.

"Kolkata Radio" operates an HF service for aeronautical messages and is not itself an air traffic control unit. It relays information between aircraft and ground controllers when the normal VHF link is unavailable because of terrain, range or equipment limitations. If the relevant facility cannot be raised, use this service after the contact attempts prescribed by local procedure.
"Negative contact with Guwahati Tower" identifies the facility that did not answer. Giving the attempted frequency, one two zero decimal two five, also lets the relay contact the responsible controller and verify the aircraft's departure status.
No navigation fix is named in the report. The pilot therefore gives direction and distance from the departure aerodrome, which provides a usable position reference. Terrain around Guwahati can make low-level VHF reception unreliable, while the location details help the controller identify the aircraft's route.
"Zero seven one five UTC" is the observation time attached to the position report. Combining the clock time with direction and distance tells the controller where the aircraft was at that moment, which supports coordination and traffic awareness.
"Passing flight level one hundred" gives the relay the latest height attained. The added statement that the aircraft is continuing the assigned climb confirms compliance with the existing clearance despite the missing direct tower link.
The relay confirms that the earlier climb instruction remains valid. Kolkata Radio passes the responsible controller's decision and is not the clearance authority itself. Any change to the assigned climb must be received as an amended clearance.
"Report passing flight level one six zero" establishes a definite point for the next height report. Kolkata Radio can pass that progress information onward and keep the relevant ATC unit informed as the aircraft enters the next controlled airspace segment.
The report request is answered with WILCO and the climb confirmation, closed with the callsign. The frequency, position and time came from the pilot's own report and are not read back.

Reference: ICAO Doc 9432

Response to a Low Altitude or Terrain Alert

The controller's terrain warning system triggers when your level is below the minimum safe altitude for the area. The alert is passed as an urgent instruction to check your altitude, and the answer is a climb, not a discussion.

Pilot

CLIMBING TO [altitude], QNH [value], [Callsign]

ATC

[Callsign], LOW ALTITUDE ALERT, CHECK YOUR ALTITUDE IMMEDIATELY, THE QNH IS [value], THE MINIMUM SAFE ALTITUDE IN YOUR AREA IS [altitude]

ATC

VT-AIR, low altitude alert, check your altitude immediately, the QNH is 1013, the minimum safe altitude in your area is 4500 feet

Pilot

Climbing to 4500 feet, QNH 1013, VT-AIR

ATC

VT-AIR, roger

Climb first, then check the setting. If there is any doubt at all about your terrain clearance, height is the only thing that buys time.
Read back the altitude and the QNH. A wrong subscale is the most likely reason you were low in the first place.
This alert is one of the very few instructions where the expected response is immediate action before analysis. Treat it the way you would treat a TCAS resolution advisory.

Reference: ICAO Doc 9432

Series of Red Flares

Use this when you see a distress signal from someone else, here red flares fired from a boat at sea, and need ATC to pass it to the maritime rescue services. Your own aircraft is fine; you are simply the only witness able to raise the alarm. The report goes out as PAN PAN because it is urgent and needs action at once, even though the danger is not yours.

Pilot

PAN PAN, PAN PAN, PAN PAN, [station], [callsign], POSITION [own position], [what was seen], BEARING [bearing], [distance] MILES

ATC

[callsign], [station], ROGER PAN PAN, TAKING ACTION

Pilot

PAN PAN, PAN PAN, PAN PAN, Chennai Control, SpiceJet 318, position overhead Puducherry, red flares seen fired from a vessel at sea, bearing zero nine five, about four zero miles from us.

ATC

SpiceJet 318, Chennai Control, roger PAN PAN, taking action.

Red flares are an internationally recognised distress signal at sea. A pilot who sees them must report them, because the flares may be the only sign of the emergency that reaches anyone able to help.
You probably cannot tell the boat's exact position, so give your own position and the bearing and distance of the flares from you. The rescue centre can turn that into a fix.
There is no statement of intentions about your own flight, because nothing is wrong with it. You carry on as planned unless ATC asks for help, such as staying in the area to keep watch.
TAKING ACTION is deliberately short. ATC does not need to tell you who it will alert; it just confirms that the report is in hand.
ATC may come back with questions: when you saw the flares, how many, what the vessel looked like, or whether you can stay nearby. Otherwise the exchange is complete.
Seeing and reporting signals like this is part of search and rescue awareness that every pilot is expected to have, whatever the flight is doing.
This differs from relaying another aircraft's routine message. Here you are reporting something you saw happen outside aviation altogether.

Reference: ICAO Doc 9432

Sinking Ship in Sight

Use a PAN PAN urgency call when the crew observes a vessel in danger and must alert ATC promptly. The urgency concerns the ship, not the aircraft, which remains able to operate normally. Provide the observed position, bearing from a known reference, range, sea state, likely vessel type and visible condition. ATC can then notify the relevant maritime rescue authority.

Pilot

PAN PAN, PAN PAN, PAN PAN, [station] [station] [station], [callsign] [callsign] [callsign], [what is seen], [position], [sea state], [vessel type], [condition], [request]

ATC

[callsign] [station] ROGER PAN PAN

Pilot

PAN PAN, PAN PAN, PAN PAN, Kochi Control Kochi Control Kochi Control, Vistara 815 Vistara 815 Vistara 815, ship in sight and sinking, position two two five degrees, three two miles from Kochi, sea state moderate, vessel appears to be a cargo ship, listing to starboard and partly submerged, request immediate assistance for the vessel.

ATC

Vistara 815, Kochi Control, ROGER PAN PAN.

"PAN PAN" signals an urgent situation requiring prompt attention, whereas "MAYDAY" is used for grave and imminent danger. In this report, the aircraft is not the craft in danger. Controllers are being asked to respond to a serious incident involving a vessel.
"PAN PAN, PAN PAN, PAN PAN" is the urgency signal spoken three times. The station and callsign are also each repeated three times. This clear identification improves the chance that the correct controller receives every part of the report.
Repeat the controller's name at the start as prescribed for an urgency broadcast. This repetition improves clarity on a congested frequency; it is not meant to summon several air stations simultaneously.
Place a short description of the observed emergency immediately after the identities. Here, "ship in sight and sinking" gives the controller an early indication that assistance may involve ships, aircraft and helicopters.
For an offshore casualty, state the location relative to a named landmark and then add a magnetic bearing and range. Speak each bearing digit separately. This gives rescue coordinators a location that can be relayed without confusion.
Report sea conditions because a rough swell may limit the speed and safe handling of surface rescue craft or make a helicopter approach more difficult. A qualitative report is useful when exact wave measurements are unavailable.
Use "appears to be" when the type of vessel cannot be confirmed. Seen from an aircraft, cloud, darkness or distance may prevent certain identification, so an accurate impression is better than an unsupported claim.
"Listing to starboard" means that the vessel is heeled towards its right side. Maritime personnel understand this nautical description more readily than an informal reference to the ship leaning right.
"ROGER PAN PAN" provides an acknowledgement of the report and should not be delayed. The controller then communicates the casualty details to the appropriate rescue coordination centre. A verbal readback of the complete position is not required.

Reference: ICAO Doc 9432

TCAS Resolution Advisory (RA)

Use this the moment TCAS gives a Resolution Advisory, such as CLIMB, CLIMB or DESCEND, DESCEND. The pilot flying follows the RA at once, even when it takes the aircraft away from the ATC clearance; ICAO procedures allow, and require, that deviation. The pilot monitoring then tells ATC with the words TCAS RA, so the controller stops giving instructions that could clash. When TCAS says CLEAR OF CONFLICT, a second call tells ATC you are returning to the cleared level.

Pilot

[station], [callsign], TCAS RA; then, once clear: [station], [callsign], CLEAR OF CONFLICT, RETURNING TO [cleared level]

ATC

[callsign], ROGER (no instructions while the RA lasts); then after the clear of conflict report: [callsign], ROGER, [confirm or amend clearance]

Pilot

Kolkata Control, IndiGo 5231, TCAS RA

ATC

IndiGo 5231, Kolkata Control, roger

Pilot

Kolkata Control, IndiGo 5231, clear of conflict, returning to flight level three three zero

ATC

IndiGo 5231, roger, maintain flight level three three zero, report level

Pilot

Maintain flight level three three zero, wilco, IndiGo 5231

Follow the RA straight away. ICAO rules permit the departure from your clearance and require you to comply with the RA. Answering "I would check with ATC first" is marked wrong.
Two calls, in this order: TCAS RA when you deviate, and CLEAR OF CONFLICT, RETURNING TO the level when it is over. Do not improvise with phrases like "avoiding traffic"; the words examiners look for are TCAS RA.
After you report TCAS RA, the controller should not give you new instructions until you report clear of conflict. It is one of the few times you fly a profile other than the cleared one without asking first.
If the RA strengthens, for example INCREASE CLIMB, just fly it. The first TCAS RA call already covers the manoeuvre; the next call is only due at clear of conflict.
Unless your aircraft flies RAs through the autopilot, disconnect it and fly the manoeuvre by hand, as your type's procedure requires. It is quicker and stops the autopilot pulling you back towards the old level.
Never manoeuvre against an RA because you can see the other aircraft. The two TCAS units coordinate their advisories, and going the other way can turn a solved conflict into a collision.

Reference: ICAO Doc 4444 §15.7.4 / Annex 2 §3.6.2.3 / Doc 9432 §11.6

Transmitting Blind

When you believe your receiver has failed but your transmitter may still work, you keep talking on the assumption that someone can hear you. You say everything twice and you tell them when you will next transmit, so the ground can plan around your silence.

Pilot

TRANSMITTING BLIND DUE TO RECEIVER FAILURE, [Station], [Callsign], [message], [message repeated], NEXT TRANSMISSION AT [time]

ATC

[no reply expected. ATC continues to pass instructions blind in case your receiver is working]

Pilot

Transmitting blind due to receiver failure, Mumbai Approach, VT-AIR, FL150, position GULAB, continuing to Mumbai, estimating 1130, will land runway 27. Transmitting blind due to receiver failure, Mumbai Approach, VT-AIR, FL150, position GULAB, continuing to Mumbai, estimating 1130, will land runway 27. Next transmission at 1115

ATC

VT-AIR, Mumbai Approach, transmitting blind, if you read Mumbai Approach, squawk ident

Say the whole message twice. You have no way of knowing whether the first one was blocked.
Squawk 7600 so the failure appears on the radar label. That single action tells every controller who can see you what has happened.
State your intentions in the message, because nobody can ask you. Give position, level, route, estimate and the runway you intend to use.
Give the time of your next transmission. It lets ATC hold the frequency and the airspace open for you.
Keep flying the last clearance you received, then the published lost communication procedure. Transmitting blind does not change the route you are expected to fly.

Reference: ICAO Doc 9432

Transponder Codes (7500 / 7600 / 7700)

Three transponder codes are set aside to show particular emergencies on a radar screen even when nobody speaks. Knowing all three, and the rules for selecting them, comes up in almost every DGCA RTR viva.

Pilot

[set the code; no call is needed, but talk to ATC as soon as you safely can]

ATC

[ATC alerts the emergency services and gives the flight priority; 7500 also starts the security response]

ATC

Examiner: What does squawk seven five zero zero mean?

Pilot

Candidate: Seven five zero zero is unlawful interference, which means the aircraft is being hijacked or seized.

ATC

Examiner: And seven six zero zero?

Pilot

Candidate: Seven six zero zero is radio failure, the crew has lost two-way communication.

ATC

Examiner: And seven seven zero zero?

Pilot

Candidate: Seven seven zero zero is a general emergency, set with a MAYDAY or PAN PAN call unless ATC has told you to keep your assigned code.

Seven seven zero zero is the general emergency code. It makes the aircraft stand out on every radar display that can see it and sets off an alert for the controller.
Never select seven five zero zero casually or as a test. On the ground it starts a full security response, and once seen it cannot be quietly undone.
A common memory aid: seven five, "man with a knife"; seven six, "radio nix"; seven seven, "going to heaven". Examiners accept it, but want the proper meaning first.
When changing code, avoid passing through the emergency codes on the way, for example by turning the digits in an order that never shows seven five, seven six or seven seven in the first two positions. Many transponders guard against this.
A Mode S transponder also sends the aircraft identification. Check on first contact that it matches your callsign, because ATC will query a mismatch.

Reference: ICAO Annex 10 Vol IV §2.1.4 / Doc 9432 §11.4

Transponder Mode C Unserviceable

Use this when a failed Mode C (altitude reporting) makes an aircraft unfit for RVSM airspace. The same call works for an unreliable altimeter system; only the reason changes. Give your position and level, say what has failed, say you are RVSM non-compliant, and ask to descend below the RVSM band. ATC normally takes you off the route, down to flight level two seven zero, and back to normal navigation once below flight level two nine zero. No PAN PAN is needed, because the aircraft is under control and the crew can manage the situation.

Pilot

[station], [callsign], [position], [level], TRANSPONDER MODE C UNSERVICEABLE, RVSM NON-COMPLIANT, REQUEST DESCENT [level]

ATC

[callsign], [station], LEAVE ATS ROUTE, DESCEND [level], PASSING [level] RESUME NORMAL NAVIGATION

Pilot

Nagpur Control, SpiceJet 318, five zero miles north of Nagpur, flight level three seven zero, transponder Mode C unserviceable, RVSM non-compliant, request descent flight level two seven zero.

ATC

SpiceJet 318, Nagpur Control, leave ATS route, descend flight level two seven zero, passing flight level two nine zero resume normal navigation.

Pilot

Leaving ATS route, turning right, descend flight level two seven zero, passing flight level two nine zero resume normal navigation, SpiceJet 318.

RVSM airspace runs from flight level two nine zero to flight level four one zero, with one thousand feet between levels. An aircraft needs accurate altimeters and working altitude reporting to fly there; losing either makes it non-compliant and it must leave the band.
Giving your present level in the first call shows ATC at once how far you are above the bottom of the band.
Flight level two seven zero sits two thousand feet under flight level two nine zero, so the aircraft ends up clearly below the RVSM band rather than just at its edge.
Mode C sends the aircraft's pressure altitude to radar automatically. Without it the controller has no independent check of your level, so the reduced separation cannot be guaranteed.
For the altimeter version of this call, the point is the same: RVSM relies on two independent altimeters agreeing, and if one becomes unreliable you cannot prove accurate height keeping.
Whichever system has failed, ATC gives the same instruction and you give the same readback. The difference only matters for the technical log.
LEAVE ATS ROUTE takes you sideways off the airway before or during the descent, so you do not descend through traffic on the same route at the levels below.
Flight level two nine zero is the bottom of the RVSM band. Once through it you are clear of the band and may rejoin normal navigation.
No PAN PAN is needed while the crew is in control and simply needs to leave the band. Declare one only if the problem grows, for example if you lose confidence in your height altogether.
Saying which way you are turning off the route in the readback tells ATC where to expect you. The side depends on the route and traffic at the time, so follow any direction ATC gives.

Reference: ICAO Doc 9432

Unlawful Interference (Hijack)

Use this when the aircraft is under unlawful interference, such as a hijack, and open talk on the radio may not be safe. Select squawk seven five zero zero; if speech is impossible, the code alone does the job. If you can speak, a short standard call confirms it. Once ATC sees seven five zero zero, the aircraft is handled as a security event, and after landing it is normally sent to an isolated parking position that security forces can surround before anyone approaches.

Pilot

[squawk 7500]; if you can speak: [station], [callsign], TRANSPONDER SEVEN FIVE ZERO ZERO (or your operator's briefed covert phrase)

ATC

[callsign], [station], ROGER, [minimum instructions only; routine requests stop]

Pilot

Kolkata Control, Air India 447, transponder seven five zero zero

ATC

Air India 447, Kolkata Control, roger, continue present route, advise intentions when you can

Pilot

Present route, will advise, Air India 447

Pilot

Kolkata Control, Air India 447, request diversion to Kolkata, request priority and a direct routing

ATC

Air India 447, Kolkata Control, cleared direct Kolkata, descend flight level one two zero, expect ILS approach runway one nine left

The code on its own is enough. Every controller whose radar sees the aircraft is alerted, and the security services on the ground are informed. Never speak if doing so would put the aircraft in more danger.
If ATC asks you to confirm the code, do not change it away and back again. Answer in the way your operator's procedure says, for example with AFFIRM, and avoid repeating the code aloud if that is unsafe.
Operators may brief crews on a covert phrase that sounds routine to someone listening in the flight deck but tells ATC what is really happening. Learn and use the one your company gives you.
After landing, ATC will normally direct the aircraft to the isolated parking position, a stand kept well away from terminals and fuel storage where the response teams can work.
Once seven five zero zero is seen, ATC keeps transmissions to the aircraft to essentials. Expect no routine requests such as level reports or checks, only what is needed for safety.

Reference: ICAO Annex 17 / Doc 9432 §11.4 / AIP India ENR 1.13

Wake Turbulence Caution

ATC will caution you when you are following a heavier aircraft. The caution is information, so the useful reply says what you are going to do about it rather than simply that you heard it.

Pilot

ROGER, EXTENDING DOWNWIND, [Callsign]

ATC

[Callsign], CAUTION WAKE TURBULENCE, [aircraft type] AHEAD

ATC

VT-AIR, caution wake turbulence, Boeing 777 ahead

Pilot

Roger, extending downwind, VT-AIR

Say what you intend to do. Extending, holding or asking for more spacing all tell the controller how to sequence the traffic behind you.
The prescribed separation is a minimum, not a target. You may ask for more, and on a light aircraft behind a heavy you should.
Wake sinks and drifts downwind. Staying at or above the heavy aircraft's path, and touching down beyond its touchdown point, is what keeps you out of it.
If you need more spacing than the controller has given you, say UNABLE and ask. Accepting a caution is not the same as accepting the spacing.

Reference: ICAO Doc 9432

Wind Shear Report

Report wind shear as soon as you are stable enough to talk. What you experienced is passed straight to the aircraft behind you, and on a hot afternoon at an Indian aerodrome that report can be the only warning they get.

Pilot

[Station], [Callsign], WIND SHEAR ENCOUNTERED [height] ON [FINAL or DEPARTURE] RUNWAY [number]

ATC

[Callsign], ROGER, WIND SHEAR ADVISORY ISSUED, ALL STATIONS ADVISED

Pilot

Mumbai Tower, VT-AIR, wind shear encountered 200 feet on final runway 27

ATC

VT-AIR, roger, wind shear advisory issued, all stations advised

Give the height, the runway and the phase of flight. Shear at 200 feet on final and shear at 1000 feet on departure are different warnings.
Add the airspeed change if you have it, for example a loss of 20 knots. That number tells the next crew how much performance to hold in reserve.
Report it even if the encounter was mild and even if you landed normally. The aircraft behind you may be heavier, slower or less lucky.
If the shear forces a go-around, that is a PAN PAN or a MAYDAY depending on how close it came. Report the encounter afterwards as a separate call.

Reference: ICAO Doc 9432

Emergency RT phraseology

Emergency, phrase by phrase

Airport is closed

Airprox - No risk of collision

Airprox - Risk not determined

Airprox - Risk of collision

Airprox - Safety not assured

Altimeter System Unreliable

Bad Weather at Destination

Brakes Hot Indication

Cancel Distress

Co-pilot fainted

Diversion

Emergency Descent

Engine Failure (Enroute Drift Down)

Fire / Smoke On Board

Flaps stuck, Overweight landing

Hydraulic Failure (Single System)

Impose Silence During a Distress

Inter-Aircraft Relay

Inter-Unit Coordination Failure

Lost contact during climb

MAYDAY (Distress Call)

MAYDAY versus PAN PAN

Medical Priority (HOSP / MEDEVAC / PAN PAN)

Minimum Fuel & MAYDAY FUEL

Negative Contact During Descend

Negative Contact with Tower After Departure

Response to a Low Altitude or Terrain Alert

Series of Red Flares

Sinking Ship in Sight

TCAS Resolution Advisory (RA)

Transmitting Blind

Transponder Codes (7500 / 7600 / 7700)

Transponder Mode C Unserviceable

Unlawful Interference (Hijack)

Wake Turbulence Caution

Wind Shear Report

Say it out loud