Definition
Airports or landing locations, other than the intended destination, that a pilot identifies in advance as suitable places to land if the planned destination becomes unusable due to weather, equipment, or other operational reasons.
Plain English
Backup airports the pilot has chosen ahead of time in case they cannot land where they originally planned.
Context Anchor
Seen in instrument weather flying when fog may make the destination hard to see, closed to landing, or unsafe to continue toward.
Derivation
From Latin alternus, meaning 'one after the other' or 'every other.' An alternate is the next choice in line — the place you go if the first option doesn't work out.
Why Pilots Care
Ensures a safe place to land remains available if conditions at the destination deteriorate.
Intuition Check
Do not read “alternate landing sites” as just any place an aircraft could physically touch down. In this context, it means suitable backup landing places that the pilot has considered ahead of time and can realistically use.
Example Sentence 1
With fog forecast at the destination, the pilot selected two alternate landing sites along the route before departure.
Example Sentence 2
When visibility dropped due to fog, the crew diverted to the nearest preselected alternate landing site.