Originally Posted by
rickair7777
There's been debate over the years due to the language (slightly vague IMO) in this section. Also debate or "IFR" vs. "IMC".
But I think it's safe to say that you're good with your dispatch planning up until you become aware that you're going to come up short on reserves, and then you should divert somewhere else or stop and get more gas before continuing.
In many cases, by the time you realistically know you're short on gas, the destination or alternate are going to be the nearest/quickest diversion points anyway.
Interestingly enough, the FAA defines IFR and IMC but not specifically IFR conditions, which is what they use in the regulation I quoted (91.167). IFR conditions must be deduced from the combination of the definitions.
FAA definitions:
Instrument flight rules (IFR) means rules governing the procedures for conducting flight under
instrument meteorological conditions (IMC)
instrument flight.
Instrument meteorological conditions (IMC) means weather conditions below the minimums prescribed for flight under
Visual Flight Rules (VFR).
At any rate, the intent of the regulation is that we plan to have at least 45 minutes of fuel in the tanks when we land at the Alternate. When do we plan this? Sure during preflight, but also during the flight, usually while flying the hold. We must leave the hold when the fuel equals the amount to fly from the Hold to the Destination and then on to the farthest filed Alternate. Then be able to fly 45 minutes after that at normal cruising speed.