Definition
A different plan a pilot prepares to follow when the original plan can no longer be flown safely or legally — for example, deviating around weather, diverting to another airport, or changing altitude or route to avoid a hazard.
Plain English
A backup plan. If the first plan stops working, this is what you do instead.
Context Anchor
Used in instrument flying and weather avoidance discussions, especially when a pilot needs to change plans because of clouds, storms, icing, or other unsafe conditions.
Derivation
‘Alternate’ comes from the Latin alternare, meaning ‘to do by turns.’ In flying, it points to a second option you can switch to when the first one no longer fits the situation.
Why Pilots Care
Having one ready prevents a pilot from continuing into unsafe conditions when the primary route becomes unusable.
Intuition Check
Do not read “course” here as only a compass direction. Here, “course of action” means the whole plan the pilot will follow, which may include changing route, altitude, timing, destination, or requesting help.
Example Sentence 1
When the line of thunderstorms grew across her route, she chose her alternate course of action and turned south to land at a nearby airport.
Example Sentence 2
When unexpected icing was encountered, the crew executed their alternate course of action and landed at the alternate airport.