1, 2, 3 Rule for Alternate Airports

Updated: Dec 30, 2020

What is an Alternate Airport? When must a pilot file an Alternate Airport on an IFR Flight Plan?

Here's what you need to know.


An Alternate Airport is one that a pilot may divert to (when on an IFR flight plan) if weather does not allow that pilot to land at the original destination airport. Think of it as Plan B.


It is always smart to have an Alternate Airport! That way, the pilot has a Plan B if he or she is unable to land at the original destination for any reason. However, there are legal requirements for when a pilot MUST file an Alternate Airport and they have to do with weather criteria.

THE 1, 2, 3 RULE

Remember, the 1, 2, 3 Rule. Prior to filing an IFR Flight Plan, a pilot must check the weather at the original destination airport between 1 hour before the ETA to 1 hour after the ETA. During that time frame, the weather must be forecasted to be better than 2,000' ceilings and 3 SM of visibility. If the forecasted weather is less than 2,000' ceilings and/or less than 3 SM visibility, then the pilot must file an Alternate Airport.

1 - 1 hour before to 1 hour after the ETA

2 - At least 2,000' Ceilings and

3 - At least 3 SM Visibility


The pilot may still fly to the original destination airport with forecasted weather less than the 1, 2, 3 Rule and shoot the Instrument Approach to land. This legal requirement is for filing purposes. The FAA wants pilots to have a backup plan in case they are unable to land at the original destination.

Author - Nate Hodell

CFI/CFII/MEI/ATP - Creator of wifiCFI - Owner of Axiom Aviation Flight School.

This information is included in the Alternate Airports Lessons on wifiCFI. Sign up today to watch videos, listen to podcasts, take lesson quizzes, join live webinars, print lesson quicktakes, and more by clicking this link >

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