Alternates & Weather Minima
Alternates & Weather Minima is a core knowledge area on the Aircraft Dispatcher FAA written exam. This hub collects our 7 in-depth, ACS-aligned alternates & weather minima articles — each written in plain English and grounded in the official FAA handbooks. Work through them below, then drill the topic with practice questions.
The 1-2-3 Rule: When a Destination Alternate Airport Is Required
The 1-2-3 Rule determines when Part 121 air carriers must list a destination alternate airport on the dispatch release, based on ceiling and visibility forecasts for the destination.
Selecting a Takeoff Alternate Under 14 CFR 121.617
Under 14 CFR 121.617, Part 121 operators must designate a takeoff alternate when the departure airport weather falls below certain visibility or ceiling thresholds, ensuring a safe diversion option if the aircraft cannot return after departure.
Domestic Destination Alternate Weather Minima Under 14 CFR 121.619
14 CFR 121.619 sets the destination alternate weather minima domestic air carriers must meet when filing an alternate airport, requiring ceiling and visibility thresholds that vary based on whether the airport has a precision or non-precision approach.
Flag Operations Alternate Requirements and the 6-Hour Rule (121.623-.625)
Flag operations under 14 CFR 121.619–625 establish when alternates are required on international dispatch releases, including the unique 6-hour rule that can eliminate the alternate requirement under specific weather conditions.
Choosing an Alternate: Approach Capability, NOTAMs, and Field Condition Factors
Selecting a legal alternate airport requires matching approach capability, weather minimums, and real-time field conditions — a critical dispatch skill governed by 14 CFR 121.619–.625.
Deriving Alternate Airport Weather Minima Under 14 CFR 121.625
14 CFR 121.625 governs how air carriers derive alternate airport weather minima, requiring specific ceiling and visibility standards based on approach type and airport equipment before a dispatcher can legally file a location as an alternate.
Exemption 3585 and Eligible-Alternate (ETOPS-Equivalent) Minima
Exemption 3585 allows eligible U.S. domestic carriers to file certain airports as alternates using ETOPS-equivalent reduced weather minima, provided specific aircraft, route, and maintenance approval criteria are met under 14 CFR 121.619–.625.
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Articles are original summaries grounded in the public-domain FAA handbooks and cite their source. ACS-aligned study aids — not a substitute for the official handbooks or regulations.