Free tool

Fuel and endurance calculator

Enter the fuel, the flow, the reserve and the leg, and this calculator gives you the endurance, the range, the point of no return and the critical point.

Safe endurance

4 h 27 min

On 800 usable, which is the fuel on board less the reserve. This is how long you may fly, and it is what the point of no return is computed from.

Still air range

1,166.67

Nautical miles in nil wind on ALL the fuel, reserve included. It is a performance figure, not a distance you may plan to fly.

Point of no return

459.65

Nautical miles out, reached at 2 h 26 min. Past this point the fuel will not bring you back to where you started.

Critical point

507.81

Nautical miles out, reached at 2 h 42 min. From here it takes the same time to go on as to turn back.

the two questions this answers

On this fuel you cannot reach the destination: the trip needs 883.8 and you have 800 usable.

Being able to arrive and being able to come back are different questions, and this is why both are on the page. The point of no return is at 459.65 nm and the destination is at 925 nm, so there is a stretch of this leg you can fly on to the destination from but not return from.

Exam trap. The critical point does not depend on how much fuel you carry at all, only on the distance and the two groundspeeds. The point of no return depends on the fuel and not on the distance. A question that changes the fuel and asks what happened to the CP is asking whether you know that.

The working

  1. Groundspeed out = 188.4 kt and groundspeed home = 229.3 kt, both solved as wind triangles on track 153 and its reciprocal, at 210 kt true in a 30 kt wind from 200.
  2. Usable fuel = 1000 - 200 = 800. Safe endurance = 800 / 180 = 4.4 hours, which is 4 h 27 min.
  3. Still air range = total endurance x TAS = 5.6 x 210 = 1166.67 nm. This uses ALL the fuel including the reserve, so it is a performance figure and not a distance you may plan to fly.
  4. PNR = endurance x O x H / (O + H) = 4.4 x 188.4 x 229.3 / 417.7 = 459.65 nm, reached at 2 h 26 min.
  5. CP = D x H / (O + H) = 925 x 229.3 / 417.7 = 507.81 nm, reached at 2 h 42 min. The CP does not depend on how much fuel you carry, only on the two groundspeeds and the distance.
  6. Fuel to the destination = 180 x 925 / 188.4 = 883.8, against 800 usable.

The units are yours. Kilograms, pounds or gallons all work, as long as the flow is in the same unit per hour, which is why no unit is printed beside the fuel figures above.

Free tool

Groundspeed and wind

Track, TAS and wind solved as a triangle, with the triangle drawn to scale.

Free tool

Holding entry

The arrival against the inbound course, and which of the three entries it gives.

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