When do you
need an alternate for a departure airport in airline operation?
Answer: If the weather conditions at the takeoff
airport are below the landing minimums in the certificate holders operations
specifications for that airport, an alternate airport that meets alternate
airport weather requirements must be designated for the flight.
For two engine aircraft, the alternate must be within
one hour from the departure airport at normal cruising speed in still air with
one engine inoperative. For three or four engine, the alternate must be within
two hours.
