Definition
A secondary pump installed in an aircraft system to provide continued operation if the primary pump fails. In piston airplanes, this most commonly refers to an electric auxiliary fuel pump that supplies fuel pressure to the engine when the engine-driven fuel pump is inoperative or during phases of flight where redundancy is required.
Plain English
A second pump that takes over, or assists, when the main pump stops working or needs help. It keeps fuel (or another fluid) flowing to where the engine needs it.
Context Anchor
You may see this term in emergency procedures for engine trouble, fuel system checks, or low-altitude engine failure scenarios.
Why Pilots Care
Maintains control authority and allows configuration changes such as flap or gear extension during an engine-out emergency.
Intuition Check
Do not assume “backup” means the pump will automatically save the engine. It means there is a secondary pump available, but the pilot must know when and how to use it for that specific airplane.
Example Sentence 1
When the fuel pressure gauge dropped, the pilot switched on the backup pump and pressure returned to normal.
Example Sentence 2
The backup pump kept pressure to the rudder during the low-altitude engine failure drill.