Definition
An electrically driven fuel pump installed in addition to the engine-driven fuel pump. It is used to supply fuel pressure for engine starting, as a backup if the engine-driven pump fails, and during critical phases of flight such as takeoff and landing. It is controlled by a switch in the cockpit.
Plain English
A second fuel pump, run by electricity, that the pilot can switch on. It helps start the engine and acts as a backup so fuel keeps flowing if the main pump quits.
Context Anchor
Seen in fuel-injected engine starting procedures, fuel pressure checks, and emergency checklist steps for low fuel pressure.
Derivation
Auxiliary' comes from the Latin auxilium, meaning 'help' or 'aid.' The name fits — this pump is the helper that supports or stands in for the main engine-driven pump.
Why Pilots Care
Maintains fuel flow to the engine, preventing power loss or engine stoppage if the primary pump malfunctions.
Intuition Check
Do not read auxiliary as “unimportant” or “optional.” Here it means a supporting pump that may be required by the checklist in specific situations.
Example Sentence 1
Before starting the engine, the pilot turned on the auxiliary fuel pump to build fuel pressure.
Example Sentence 2
With the engine-driven pump failed, the auxiliary fuel pump kept fuel pressure steady for the remainder of the flight.