Definition
A backup switching device or procedure that automatically transfers a system, circuit, or service to an alternate path when the primary path fails or becomes unavailable.
Plain English
A backup switch that takes over if the main one stops working, so the system keeps running.
Context Anchor
Seen in aviation abbreviation lists and notices about airport or system equipment status.
Derivation
From the everyday phrase 'fall back,' meaning to retreat to a secondary position when the first one fails. The 'switch' is the device that makes the changeover happen automatically.
Why Pilots Care
It provides an immediate way to keep essential flight functions working after a primary system failure, supporting continued safe flight.
Intuition Check
Do not read “fall back” as something physically falling backward. Here it means “use the backup option.”
Example Sentence 1
When the primary transmitter failed, the fall back switch routed traffic to the standby unit without interrupting service.
Example Sentence 2
During the preflight, the instructor pointed out the FBS location so the student would know how to restore manual heading mode if needed.