Learn what an aircraft electric fuel pump does, when to switch it on, when to leave it off, and why the POH or checklist always decides.
In Aviation & Real-World Flying, an aircraft electric fuel pump moves fuel from the tanks towards the engine and maintains positive fuel pressure. Depending on the design, it primes the system for starting, backs up an engine-driven pump, helps suppress fuel vapour, or runs continuously. Use it only when the aircraft checklist specifies.
What does the electric fuel pump actually do?
An electric fuel pump raises fuel pressure and keeps fuel flowing through the aircraft's fuel system. In a typical piston aircraft, it supplies or assists the engine-driven pump; it does not normally meter the final fuel-air mixture. That job belongs to the carburettor, fuel-injection servo, electronic controller or turbine fuel control.
The switch label helps identify the pump's purpose:
- Auxiliary or boost pump: feeds the engine, commonly for starting, selected flight phases or backup operation.
- Transfer pump: moves fuel between tanks or into a collector tank and may not feed the engine directly.
- Primary electric pump: provides the engine's normal fuel supply in aircraft without an engine-driven pump.
A running pump cannot overcome every fuel-system problem. A closed selector, empty selected tank, blocked line, failed valve or uncovered pickup can still stop the flow. Our explanation of how pumps, selectors and aircraft attitude affect usable fuel covers that distinction.
When should you switch an aircraft electric fuel pump on?
The Pilot's Operating Handbook (POH), Aircraft Flight Manual (AFM) or approved checklist is the deciding authority because pump procedures vary sharply between aircraft and even between variants of the same model.
| Situation | Typical purpose | Main caveat |
|---|---|---|
| Before engine start | Build pressure or prime a fuel-injected engine | Use the specified mixture, throttle and pump sequence; excessive priming can flood the engine. |
| Take-off and landing | Back up the engine-driven pump during critical phases | Common in some low-wing aircraft, but not a universal procedure. |
| Changing fuel tanks | Maintain pressure while changing the selected tank | Use it only if the checklist directs; a transfer pump is not necessarily an engine boost pump. |
| Hot-weather or high-altitude operation | Increase inlet pressure and reduce fuel vapour formation | The aircraft must be approved for this use. |
| Low fuel pressure or engine-driven pump failure | Provide an emergency or abnormal backup supply | Follow the complete checklist rather than operating the pump in isolation. |
| Turbine aircraft normal operation | Pressurise feed manifolds and prevent pump cavitation | Several boost pumps may run throughout the flight or be controlled automatically. |
A mistake we see constantly in simulators is copying one aircraft's pump procedure to another. A fuel-injected Cessna 172 may use its auxiliary pump mainly for priming, while another light aircraft requires its boost pump for take-off and landing. Our worked fuel-injected Cessna 172 starting sequence shows why the pump and mixture order matters.
Leave the pump off whenever the normal checklist calls for it to be off. Do not improvise by switching it on during a flooded start, suspected fuel leak, engine fire or electrical-smoke event; a pump can worsen a leak or fire, and the applicable emergency checklist may require it off.
Can an electric fuel pump keep the engine running?
Yes, but only if it is designed and rated as a backup to the engine-driven pump. A priming-only or transfer pump may not provide the pressure or flow required at high power.
If the checklist calls for the pump after low fuel pressure, rough running or power loss, confirm the selected tank and watch the fuel-pressure or fuel-flow indication. Switching on a pump while the selector remains on an empty tank will not solve the underlying problem. If pressure returns, do not treat that as a repair; follow the checklist's landing guidance.
Why does the fuel pump not work in a flight simulator?
In a simulator, an apparently inactive pump usually comes down to the wrong procedure, missing electrical power, an interrupted fuel path or simplified aircraft-system modelling.
- Identify the pump type. Check whether the control operates a boost, transfer, priming or primary pump and confirm the exact aircraft variant.
- Supply electrical power. The battery or required electrical bus must be live, and a modelled circuit breaker must be set.
- Open the fuel path. Confirm usable fuel, the correct tank selection and any required fuel shut-off valve position.
- Use the correct starting sequence. Pump, mixture and throttle order can differ between cold, hot and flooded starts. Our complete cold-and-dark start flow shows where boost-pump operation normally fits.
- Check indications, not just sound. Look for pressure or fuel-flow changes. Hearing a pump hum does not prove that fuel is reaching the engine, while some simulated pumps produce no audible sound at all.
If the switch moves but pressure never changes despite a valid configuration, the aircraft may simplify or omit that part of the fuel system. Also check for conflicting control bindings that immediately return the virtual switch to its previous position.