Definition
An electrically driven backup fuel pump that pushes pressurized fuel from the tank to the engine, supplementing or replacing the engine-driven fuel pump when needed. It is used during engine start, takeoff, landing, switching tanks, and as a backup if the engine-driven pump fails.
Plain English
A small electric pump that helps push fuel to the engine. The pilot turns it on with a switch, and it backs up the main pump that the engine itself drives.
Context Anchor
Seen in fuel system discussions, engine starting procedures, takeoff and landing checklists, and emergency procedures for fuel pressure problems.
Derivation
‘Auxiliary’ comes from the Latin ‘auxilium’ meaning ‘help.’ ‘Positive pressure’ means it actively pushes fuel forward under pressure rather than relying on gravity or suction. The name describes its role: a helper pump that forces fuel toward the engine.
Why Pilots Care
Keeps the engine running if the engine-driven pump loses pressure or if fuel vapor forms at altitude, preventing an unexpected power loss.
Intuition Check
Positive does not mean “good” or “approved” here. It means the pump is creating pressure that pushes fuel forward through the fuel line.
Example Sentence 1
Before takeoff, the pilot turned on the auxiliary positive pressure pump and checked for a steady fuel pressure indication.
Example Sentence 2
At 12,000 feet the pilot activated the auxiliary positive pressure pump when a slight roughness suggested possible vapor lock in the lines.