FAR 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.

Most instrument rated pilots are (or should), be very familiar with the FAA mandated minimum fuel requirements for
IFR flight.  But is this good enough to keep one safe in the real world?  Remember, there is another FAR pilots should
be aware of and apply during preflight planning:
91.103   Preflight action.
Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that
flight. This information must include—
(a)        For a flight under IFR or a flight not in the vicinity of an airport, weather reports and forecasts, fuel
requirements, alternatives available if the planned flight cannot be completed, and any known traffic delays of which
the pilot in command has been advised by ATC;

Let’s examine a hypothetical instrument flight and see how strictly applying FAR 91.167 can get one into trouble.  Our
flight originates somewhere East of El Paso, Texas.  Our destination is Dona Ana Airport, 5T6 (see chart).  

We will assume for the purpose of this exercise that the weather at 5T6 is less than 2000’ ceiling, and/or 3 miles
visibility during our arrival time, requiring an alternate.  To keep this simple we will assume El Paso International
(KELP), just to the East of 5T6 meets the alternate requirements and we decide to use it as our alternate, planning
on the ILS 22 (see next page).  We will use a Cessna 172 SP in this exercise, and again for the sake of simplicity we
will assume 120 knots TAS and 9 gallons/hour and calm winds.  Most pilots would slow down for the approach to 90
knots, and climb speed during a missed approach would be less, but I’m trying to make things simple.

When I have given this scenario or similar ones to instrument pilots during an IPC I am almost always told by them
during preflight planning that they need enough fuel to arrive at 5T6, fly directly to KELP and land.  No consideration
is made of the approach into 5T6, the missed approach, nor the approach at KELP.  Let’s examine what this does to
our fuel requirement.
When Legal is Not Good
IFR Fuel Minimums