Definition
A backup option held in reserve in case the first chosen alternative also becomes unworkable. In aeronautical decision-making, it is the second fallback plan a pilot identifies when evaluating a course of action, used if the primary alternate cannot be carried out.
Plain English
A second backup plan. If your first backup doesn't work either, this is the one you switch to.
Context Anchor
Used in flight planning and decision-making discussions, especially when teaching pilots to think ahead before weather, fuel, daylight, or other conditions reduce their options.
Derivation
From Latin secundus, 'following' or 'second in order,' and alternare, 'to do by turns.' An alternate is one of two or more choices; a secondary alternate is the one you turn to second — after the primary alternate has been ruled out.
Why Pilots Care
It provides an extra safety margin when weather, mechanical problems, or other issues eliminate the first two landing options.
Intuition Check
Do not read alternate here as “every other.” In this context, an alternate is a backup option. Do not read secondary as “unimportant.” It means the next choice after the primary alternate.
Example Sentence 1
With thunderstorms forecast along the route, the pilot filed one alternate airport and identified a secondary alternate further south in case the first also went below minimums.
Example Sentence 2
During the cross-country briefing the instructor stressed identifying a usable secondary alternate before departure.