Choosing an IFR Alternate Airport
Flying under instrument meteorological conditions keeps even a good pilot on their toes. As a student pilot you were always taught “see and avoid”, keep your eyes outside, etc. But now, while flying in low visibility and overcast cloud layers, you have to rely on your instrumentation more than ever before and keep your eyes inside the airplane. Flight planning becomes more advanced than before, flying SIDs and STARs, and instrument approaches. But a crucial part of this flight planning is planning for the worst case scenario: What if you can’t land at your original destination?
When MUST I Plan for an Alternate?
- 91.169 IFR flight plan: Information required. (b)(2)
(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.
The FAA requires under Part 91, that within the TAF (Terminal Aerodrome Forecast) period between 1 hour before and after, the weather at the airport of intended landing must show ceilings of at least 2,000ft AGL and 3 statute miles of visibility, to preclude the filing of an alternate. If the airport does not have a TAF, you should use the Graphical Area Forecasts located at AviationWeather.gov to see if your airport is cleared.
Ideally, you should plan for an alternate when the weather is above those minima if you believe the weather is unstable and may deteriorate. Forecasts are predictions and are not always accurate.
How Do I Choose an Alternate Airport?
Choose an airport that has the services you will require and that is not too close to your original destination. Remember that weather conditions vary the further away you get. It may not be safe to plan for an alternate that is 10 miles away. Ideally, you should choose one that is at least 50 nautical miles away, with a long runway, abundant FBO/ maintenance services, and a precision approach. Additionally, it may be a good idea to stretch the window further than 1hr. before/after if you expect you could be delayed due to airspace, passenger arrival, fueling, etc.
(91.169 continued)
- 91.169 IFR flight plan: Information required. (c)(1)(2)
(i) For aircraft other than helicopters: The alternate airport minima specified in that procedure, or if none are specified the following standard approach minima:
(A) For a precision approach procedure. Ceiling 600 feet and visibility 2 statute miles.
(B) For a non-precision approach procedure. Ceiling 800 feet and visibility 2 statute miles.
(2) If no instrument approach procedure has been published in part 97 of this chapter and no special instrument approach procedure has been issued by the Administrator to the operator, for the alternate airport, the ceiling and visibility minima are those allowing descent from the MEA, approach, and landing under basic VFR.
These are the FAA’s required minima for an alternate airport, 1 hour before and 1 hour after the estimated time of arrival.
1 hr. Before/After ETA
600/2: Precision Approach Available
800/2: Non-Precision Approach Available
VFR Descent: No Approach Available
Make Sure You Carry Enough Fuel
Ensure that your aircraft has enough fuel onboard to legally comply with regulatory requirements. Also add in a safety buffer of at least another hour just in case your alternate airport is also unusable, even if that means you must add a fuel stop on your flight plan.
- 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.
Takeaways
Always plan for an alternate, even if you do not think it is required. As part of pre-flight planning and action, you should always look for diversionary airports in case of an emergency. When flying in IFR conditions, this amplifies problems if they occur. Stay ahead of the airplane and be safe!
by Gustin Robinson, FAA CFI-I ASEL
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