The Pilot / Controller Glossary in the AIM defines minimum fuel as an indication that an aircraft’s fuel supply has reached a state where, upon reaching the destination, it can accept little or no delay. It is important to keep in mind that a minimum fuel advisory is not an emergency; it is only an advisory that an emergency situation is possible should any undue delay occur. But when should you declare minimum fuel?
According to the Jeppesen Instrument / Commercial textbook, a pilot should advise ATC of minimum fuel when fuel demands that little or no delay can be accepted. Unfortunately, this definition leaves a lot of ambiguity to the pilot: your concept of minimum fuel may be very different from mine.
The Federal Aviation Regulations (14-CFR) shed little light on the matter. 14 CFR 91.151 outlines fuel requirements for beginning a flight under VFR conditions. Pilots are required to have enough fuel to fly to their destination at normal cruising speed, then fly for an additional 30 minutes by day, or 45 minutes by night in an airplane.
§ 91.151 Fuel requirements for flight in VFR conditions.
(a) No person may begin a flight in an airplane under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed—
(1) During the day, to fly after that for at least 30 minutes; or
(2) At night, to fly after that for at least 45 minutes.
(b) No person may begin a flight in a rotorcraft under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed, to fly after that for at least 20 minutes.
For IFR flights, 14 CFR 91.167 requires that pilots take off with enough fuel to fly to the destination, continue to the alternate airport (when an alternate is required), then fly for an additional 45 minutes in an airplane, all at normal cruising speed.
§ 91.167 Fuel requirements for flight in IFR conditions.
(a) No person may operate a civil aircraft in IFR conditions unless it carries enough fuel (considering weather reports and forecasts and weather conditions) to—
(1) 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.
(b) Paragraph (a)(2) of this section does not apply if:
(1) Part 97 of this chapter prescribes a standard instrument approach procedure to, or a special instrument approach procedure has been issued by the Administrator to the operator for, the first airport of intended landing; and
(2) Appropriate weather reports or weather forecasts, or a combination of them, indicate the following:
(i) For aircraft other than helicopters. For at least 1 hour before and for 1 hour after the estimated time of arrival, the ceiling will be at least 2,000 feet above the airport elevation and the visibility will be at least 3 statute miles.
(ii) For helicopters. At the estimated time of arrival and for 1 hour after the estimated time of arrival, the ceiling will 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 will be at least 2 statute miles.
This is all good and well, but we are no closer to quantifying precisely when to declare minimum fuel. Enter the airlines: those aviation leaders who improve safety by documenting each eventuality of a flight within their FAA approved manuals. You have not flown “by the book” until you have flown for an airline.
Indeed, a quick look at my company’s manuals reveals an exact time and procedure for declaring minimum fuel. It states that a minimum fuel condition exists only after two conditions are met:
- The expected fuel on arrival based on the flight’s expected route will only allow for 30 minutes of flight after arrival until fuel exhaustion.
- All available options to reduce fuel required have been used, such as slowing down or changing altitude to reduce fuel burn, or flying a more direct route to the airport.
Keep in mind that these two conditions are an airline’s policy for IFR flights, but I feel that they are a useful and conservative target for any IFR traffic approaching a fuel situation. VFR pilots may be able to skimp a bit more, say 20 minutes fuel reserve, since they have no need to shoot time consuming instrument approaches.
Ideally pilots will travel with a plentiful reserve of fuel, precluding the need to declare minimum fuel, but weight limitations and operational needs will occasionally force us to operate closer to the margin. Always maintain awareness of your fuel situation and do not hesitate to declare minimum fuel should the need arise.