Definition
A federal regulation governing scheduled air carriers (airlines) that sets the weather conditions required at an alternate airport before that airport may be listed on a flight plan. The rule states that an alternate airport may be used only if current weather forecasts indicate, at the estimated time of arrival, that the ceiling and visibility at that airport will be at or above the alternate weather minimums specified in the carrier's operations specifications.
Plain English
An FAA rule for airline operations that says you can only name an airport as your backup landing airport if the weather forecast for that airport, at the time you'd actually arrive, is good enough to meet the airline's required weather minimums.
Context Anchor
Seen in instrument procedure and flight planning discussions about alternate minimums for commercial operators.
Derivation
CFR stands for Code of Federal Regulations, the official collection of U.S. federal rules. Part 121 is the section covering scheduled airline operations. The number 121.625 simply identifies this specific paragraph within that part. Knowing this helps you find and reference the rule quickly.
Why Pilots Care
Commercial pilots and dispatchers must verify these minimums to stay in regulatory compliance and ensure a safe diversion option exists.
Analogy
A regulation citation is like an address. “14 CFR” tells you the rulebook, “Part 121” tells you the neighborhood, and “§ 121.625” tells you the exact rule to read.
Intuition Check
Do not assume this rule applies the same way to every pilot or every flight. Part 121 applies to airline-style air carrier operations, not ordinary private flying under Part 91.
Example Sentence 1
When the dispatcher selected the alternate for the flight to Denver, she checked § 121.625 to confirm the forecast ceiling and visibility at the alternate met the required minimums for the estimated time of arrival.
Example Sentence 2
Because the destination was forecast below limits, the crew selected an alternate that satisfied 14 CFR Part 121, § 121.625.