Pilot Cousel: Running on empty (2)

IFR fuel requirements

December 1, 2013

John S. YodiceLast month I reviewed the minimum fuel requirements for flight in VFR conditions (“Pilot Counsel: Running on Empty,” November 2013 AOPA Pilot). This month I am on to the IFR requirements, with some of its more important nuances and interpretations.

The wording of FAR 91.167(a) provides that, “No person may operate a civil aircraft in IFR conditions unless it carries enough fuel (considering weather reports and forecasts and weather conditions) to: complete the flight to the first airport of intended landing; (2) Except as provided in paragraph (b) of this section, fly from that airport to the alternate airport; and (3) Fly after that for 45 minutes at normal cruising speed or, for helicopters, fly after that for 30 minutes at normal cruising speed.”

The paragraph (b) exception allows a pilot to eliminate from his or her computation the fuel necessary to fly from the first airport to the alternate if the first airport is expecting good weather and if it has an instrument approach. The first airport must have a standard instrument approach procedure (or a special instrument procedure issued to the aircraft operator). And, for at least one hour before and one hour after the estimated time of arrival, the relevant weather reports/forecasts must indicate that the ceiling will be at least 2,000 feet above the airport elevation and visibility will be at least three statute miles. For helicopters, at the estimated time of arrival and for one hour after that, the ceiling must be expected to be at least 1,000 feet above the airport elevation, or at least 400 feet above the lowest applicable approach minima—whichever is higher—and the visibility must be expected to be at least two statute miles.

These IFR fuel requirements apply only to flight in IFR conditions. An IFR flight that will be conducted completely in VFR conditions need only meet the VFR fuel requirements of FAR 91.151, discussed last month.

And as discussed last month, here is nuance that merits special mention. In calculating the fuel requirement a pilot must assume “normal cruising speed,” taking into account weather reports and forecasts and weather conditions. Clearly, although the rule may read to mean normal cruising airspeed, the expected groundspeed must be computed as well. The winds that are forecast and reported, and the computed headwind components, must be taken into account in computing the fuel needed at “normal cruising speed.”

A more difficult question is the word “normal” in that phrase. We know that there is a whole range of fuel consumption figures for various cruise configurations of an aircraft. Would it be legal to select the most fuel-efficient cruise configuration in figuring the required reserve? After all, you could always go to that configuration in flight if fuel becomes a problem. An old FAA interpretation suggests that the FAA would not consider it “normal” to use a different cruising speed for computing the fuel reserve than that used for the flight itself.

What about landing without all of the required reserve in the tanks? In a past FAA enforcement case, the NTSB had no problem with it: “Inasmuch as the [FAA] did not establish that the [pilot’s] planned flight time was invalid or unreasonable, it is of no consequence, for purposes of determining whether the [pilot] began the flight with the fuel reserves required by FAR section 91.167, that the flight took longer than was anticipated and, as a result, the aircraft landed with less fuel than had been estimated.” In a similar vein, the FAA chief counsel interpreted the rule to allow a pilot to “legally” use some of the 45-minute fuel reserve in flight without declaring an emergency.

Another question answered by an FAA chief counsel interpretation is, if an alternate airport is required, must there be sufficient fuel carried onboard to make approaches at both the destination airport and the flight’s final landing at the alternate? The chief counsel answers “yes.” Nowhere in paragraph (a) of the rule do the words “instrument approach” appear. But the words that do appear, “complete the flight to the first airport” and “fly…to the alternate airport,” certainly imply the possibility of an instrument approach or two. According to the interpretation: “To promote aviation safety, the FAA’s rule assumes the pilot will attempt to land at the destination airport and then fly to the alternate for the ultimate conclusion of the safe flight. This reasonable scenario includes an approach at both the destination airport and the flight’s final landing at the alternate. The FAA believes marginal weather conditions change rapidly. A pilot may start an approach to the destination airport with adequate minimum weather, but the weather may change and force a missed approach. Accordingly, the FAA rules require fuel for approaches at both the destination and alternate airports.”

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