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I have been wondering if endurance time actually includes the fuel reserve time?

For example:

  • Total usable FOB = 84 litres
  • Fuel burn rate = 16 litres/hour
  • Aircraft's reserve fuel = 30 minutes

Therefore is the endurance time 5h 15mins, or 4h 45mins?

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  • $\begingroup$ Are you referencing the POH to get endurance time or a company document or flight plan? Surely the POH would not list endurance with a fuel reserve. Flight plans and company documents may adjust the POH numbers to provide such reserves. $\endgroup$
    – wbeard52
    Oct 10, 2021 at 13:32

2 Answers 2

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Endurance is the length of time the aircraft will fly for a given set of conditions. There is no reserve fuel built into aircraft or their designs, because there's no constant definition of reserve.

The reserve is defined by the pilot/captain/law depending on the circumstances, and is simply defined as the extra fuel/endurance required in addition to the expected mission requirement.

The answer to your question is that, based on your fuel burn you have 5hr 15minutes endurance. If you need 30 minutes reserve, then the longest you can plan to fly is 4hr 45 minutes

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Endurance time probably does include reserve time, though this is not made a specific stipulation as per ICAO Annex 2, Annex 6 nor in Doc 9976 (Flight Planning and Fuel Management).

Based on the nature of your question, where you give an example, I presume you are concerned about flight planning.

A flight plan shall comprise information regarding such of the following items as are considered relevant by the appropriate ATS authority: ... ... - Fuel Endurance

ICAO Annex 2 Rules of the Air - 3.3.2 Contents of a flight plan

Sections 4.16-4.26 of ICAO Doc 9976 outline pre flight planning for fuel but does not define fuel endurance. Neither does Annex 2 and 6.

None the less, the best interpretation of all of this is that it would make sense that endurance does include reserves, it lets ATS know when the aircraft will continue to fly with its engines running. Also 'complete' fuel endurance (including reserves) is good for emergency dead reckoning crash site location estimations.

So let the ATS know via flight plan or booking out that your endurance fuel is 5hr 15 mins

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