IFR Alternate Airport Requirements

When you file an IFR flight plan, you should probably also file an alternate airport; it’s good judgment. Often, it is required. Here is what IFR pilots need to know about filing alternate airports per FAR 91.169, the AIM, and AC 91-92.

When Must You File An Alternate?

Every IFR flight plan must include a suitable alternate airport unless:

(1) The first airport of intended landing has an FAA-published Standard Instrument Approach Procedure (“IAP”); and

(2) 1-2-3 Rule is satisfied: Appropriate weather reports or weather forecasts, or a combination thereof, indicate a forecast ceiling is at least 2,000’ AGL and visibility is at least 3 SM for a period of 1 hour before to 1 hour after ETA.

What is a Suitable Alternate?

Appropriate weather reports and forecasts must indicate that the ceiling (“CIG”) and visibility (“VIZ”) at the alternate ETA, will be at or above:

1. If the alternate has a published IAP:

     a. The alternate weather minima specified in an IAP for the alternate; or

     b.  If no alternate weather minima or specified, then

                        i. 600’ CIG and 2 SM VIZ for a precision approach; or

                        ii. 800’ CIG and 2 SM VIZ for a nonprecision approach.

2. If no IAP is published for the alternate, then the forecast CIG and VIZ must allow descent from MEA, approach, and landing under basic VFR.

3. If the airport has published alternate minima (dTPP), then the weather must satisfy those criteria for the approach to be relied upon.

*If planning an alternate based on a GPS approach with a WAAS navigator, then the “nonprecision” weather minima must be satisfied (800’ CIG and 2 SM VIZ at ETA). AIM 1-1-18.c.9(a).

**When using a non-WAAS navigator, then the flight plan may rely on a GPS approach at either the destination or the alternate—but not both. Further, the navigator must have Fault Detection Exclusion capability and a preflight RAIM prediction must be conducted for the airport where the GPS-based approach is planned. The forecast weather must be 800’ and 2 SM at the alternate ETA if the GPS approach relied upon is at the alternate. AIM 1-1-17.b.5(c).

What is an “appropriate weather report or forecast?”

For Part 91 operations, use National Weather Service Aviation Weather Service-sourced forecast information (METARs, TAFs, Surface Observations, Prog Charts, etc.).

 Note: The above applies to Part 91 operations. For Part 91K, 121, and 135 operations, refer to the relevant FAR Part and Ops Specs.