IFR FUEL RESERVES

5 Answers

1. 
   

   
   

   Mark Kolber on May 05, 2020

   The concept of “normal cruising speed” isn’t brain surgery. We’re talking your normal cruise speed for the flight based on the flight planning you did with respect to altitude selection, winds, and weather. Are you planning to fly at 65% power or 75% power. .

   “when calculating the amount of fuel required to meet the 45-minute reserve requirement under § 91.167, pilots must take into account weather reports and forecasts, but may also consider fuel consumption based on factors such as its normal cruise-speed fuel consumption.” That’s from a 2009 Chief Counsel letter echoing the sentiments in one from 30 years earlier.

   Does it have to match up with your filed TAS? A requirement, no. But remember that the fuel reserve issue is both a planning and an in-flight issue. As the Chief Counsel said later in the same letter (also repeating an older one):

   “a pilot whose aircraft suffers fuel exhaustion prior to reaching either the destination or alternate airport, or who must declare an emergency for an expedited landing (due to low fuel), can be found to have failed to exercise’ good judgment,’ which could result in a violation of section 91.13, for the careless or reckless operation of the aircraft.”

   I’m not sure I’d want to provide evidence to the FAA of my bad judgment by filing a flight plan based on a TAS at 55% power while actually flying at 80% power.

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   JOHN STILES on May 07, 2020

   MK, thank you for your helpful reply.

   The original question was not suggesting that you can ‘stretch’ or ‘jimmy’ the fuel on board shown on the flight plan by flying at a TAS different that the one filed, but just asking at what power setting the mandatory 45 min. reserve is to be calculated.

   You said that the power setting used for the 45 min. reserve does not need to relate to the TAS filed in the flight plan. But the question remains what is a normal cruise speed? OK, not brain surgery, but if a regulation uses a number as the basis for rule then it should correspond to that number.

   For example and using the POH, an aircraft flies 1000nm at FL330 and high speed cruise settings burning 420# of fuel /hr., misses the approach and proceeds to a 100nm alternate. His cruise altitude to the alternate is 8,000 ft. and he flies at long range cruise power settings burning 535#/hr. of fuel. He lands and says that he has 45 minutes of fuel remaining. But how much fuel is that? Is it based on 420#/hr., on 535#/hr., or some other number?

   The POH states the amount of fuel required to satisfy the 45 min. requirement is calculated using the “cruise altitude and holding power settings” or approximately 300# (400#/hr.). This seems to me to be failing to comply with the “normal cruise speed” requirement.

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3. 
   

   
   

   Mark Kolber on May 07, 2020

   >>But the question remains what is a normal cruise speed?
   >>but if a regulation uses a number as the basis for rule then it should correspond to that number.

   There are a number of rules which do this.

   Consider for example the rule in 91.175 about leaving the MDA

   “The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers…”

   What is a normal rate of descent? What are normal maneuvers?

   And I am definitely not suggestsing that one should make up some number for planned TAS which bears no relation to reality. Quite the contrary. In my very next sentence I point out the suggestsing downside of doing exactly that. You cause a low reserve problem and your flight plan says you listed a TAS based on a significantly lower fuel burn that you are actually using for the flight. It’s evidence against you.

   Just suggesting that it is not set in stone.

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   Warren Webb Jr on May 10, 2020

   The POH is approved by the FAA so it is unlikely that the calculations for reserve fuel don’t comply with FAA standards. The reg doesn’t say the reserve fuel has to be calculated at the power setting used for the enroute portion of the flight. The term ‘normal cruise speed’ at least eliminates extreme power settings either high or low and gives a logical range of power with which to work. For a C172R the recommended enroute cruising power range is 60-80% so it seems if the reserve calculation is made anywhere in that range, and you use that power setting in the event of holding to ensure 45 minutes endurance, then you’ve complied completely. Does the calculation you noted (400#/hr) fit within the recommended cruising power limits in your POH?

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5. 
   

   
   

   NAT_HLA on Aug 16, 2020

   >>For example and using the POH, an aircraft flies 1000nm at FL330 and high speed cruise settings burning 420# of fuel /hr., misses the approach and proceeds to a 100nm alternate. His cruise altitude to the alternate is 8,000 ft. and he flies at long range cruise power settings burning 535#/hr. of fuel. He lands and says that he has 45 minutes of fuel remaining. But how much fuel is that? Is it based on 420#/hr., on 535#/hr., or some other number?

   Short answer: It should be based on the 535 pounds/hour in your example.

   Long answer: It’s ambiguously worded, but you have to assume the worst-case REALISTIC scenario. If that pilot flies to the destination, flies the approach, does the missed approach, and cruises to the alternate at 8000 feet…. what if they overfly the alternate and just keep going until fuel exhaustion? Is it plausible that they’re going to climb back up to FL330? (no) Did they plan for that as a clearance? (no) Did they calculate fuel-to-climb up to FL330? (no) Their planning is for diversion to alternate at 8000 feet, so in case of lost comm they will be expected to fly 8000 feet. There is no plausible scenario for them to climb to and fly at any other altitude than the diversion-planned altitude, so there is no plausible scenario to use any other fuel burn than the diversion-planned fuel burn. Upon landing they need to have 45 minutes of “doing what they were doing”, which for the alternate is the lower altitude with the higher fuel burn.

   A pilot of a turbine aircraft using a good-quality planning service (e.g. ARINC Direct) will have this automagically planned for. Depending on how you specify the reserve fuel in ARINC Direct, putting “0+45” in the relevant reserve planning field will give you VASTLY different results for fuel requirements depending on distance and altitude to the alternate.

   >>The POH states the amount of fuel required to satisfy the 45 min. requirement is calculated using the “cruise altitude and holding power settings” or approximately 300# (400#/hr.). This seems to me to be failing to comply with the “normal cruise speed” requirement.

   Ah, see, the POH is being compliant with ICAO regulations so it is applicable for any country. The POH is not written only to comply with the US regulations. The US regulations for reserve (destination + alternate + 45 min normal cruise) is poorly worded, more ambiguous, and less safe than the actual ICAO regulations in Annex 6 that *every other country on the planet* conforms to. For ICAO IFR fuel requirements, you need:
   • Taxi fuel at the departure point
   • Trip fuel to the destination including an approach and landing
   • 5% of the Trip fuel for unforeseen circumstances
   • if an alternate is required, fuel to conduct the missed approach, and fly to the alternate at an appropriate altitude at normal cruise for that altitude
   • Final Reserve fuel of 45 minutes at holding speed at 1500 feet AGL above the destination (or alternate, if required).

   The POH in your example is providing the Final Reserve number, the rest all vary depending on the individual flight.

   >>But the question remains what is a normal cruise speed?
   How long is a piece of string? 😉

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