Definition
A notation, marked by the symbol 'A NA' on an instrument approach chart, indicating that the airport may not be used as an alternate when filing an IFR flight plan. The restriction is typically due to factors such as the absence of weather reporting, lack of approach monitoring, or unreliable navigational aids during certain hours.
Plain English
This airport is not allowed to be listed as your backup airport on an IFR flight plan. If your destination weather is bad, you must pick a different alternate.
Context Anchor
Seen during IFR preflight planning, especially in approach chart notes and alternate minimums listings.
Derivation
“Alternate” means “the other choice,” and “minimums” are the lowest allowed conditions. “Authorized” means officially allowed. Together, the phrase says the lowest allowed backup-airport conditions have not been officially approved for that airport or procedure.
Why Pilots Care
It changes how you calculate fuel and route options for flights that require an alternate airport.
Intuition Check
Do not read “not authorized” as “the airport is closed” or “the approach can never be flown.” Here it means you may not use it as your planned IFR alternate.
Example Sentence 1
While planning the IFR flight, the pilot noticed 'Alternate Minimums are Not Authorized' on the approach chart and chose a different airport as the alternate.
Example Sentence 2
Because Alternate Minimums are Not Authorized at the destination, the pilot selected a different alternate airport with better weather.