Learn how to start a piston aircraft engine safely, including cold, hot and flooded starts, oil-pressure checks and common fault diagnosis.
To start a piston aircraft engine correctly, use the aircraft’s approved checklist: secure the aircraft, complete pre-start checks, confirm the propeller area is clear, configure fuel, mixture and throttle for the engine’s condition, engage the starter, then verify oil pressure immediately. The POH procedure always overrides generic advice.
In aviation and real-world flying, there is no universal control sequence. Carburetted and fuel-injected engines need different priming methods, while hot weather, altitude and the engine’s recent operating history can change the correct mixture setting. Use the Pilot’s Operating Handbook (POH) or Aircraft Flight Manual (AFM) for that aircraft and engine combination.
What is the correct piston-engine starting sequence?
A correct generic sequence is to make the aircraft safe, establish fuel and electrical power, prime only as required, clear the propeller, crank within the starter limits and confirm normal engine indications.
- Secure the aircraft. Complete the pre-flight inspection, set the parking brake and use chocks where required. Seat belts, loose objects and cockpit controls must be clear of anything that could interfere with the throttle or flight controls.
- Configure the cockpit. Select the prescribed fuel tank, open any fuel shut-off valve and set electrical equipment as the checklist directs. Non-essential avionics are normally left off during cranking to reduce electrical load and protect the equipment.
- Set the engine controls. Position the mixture, throttle, fuel pump and primer for a cold, hot or flooded start. Aircraft with a constant-speed propeller commonly start with the propeller control forward, but the checklist remains decisive. Our explanation of mixture and propeller-control operation covers what these controls are doing inside the engine.
- Clear the propeller. Check the entire propeller arc visually and call “clear prop” loudly enough for people nearby to hear. Treat every propeller as live even when the magnetos appear off; a defective ignition-grounding circuit can leave an engine capable of firing.
- Engage the starter. Turn on the beacon where fitted, hold the brakes, select the required ignition position and crank. Do not exceed the starter’s operating and cooling limits specified in the POH.
- Stabilise the engine. When it fires, release the starter, confirm that the ignition switch returns from
START, and set the lowest suitable stable RPM. Avoid an immediate burst of power, especially with a cold engine. - Check the instruments. Confirm oil pressure within the published time, then check charging output, fuel pressure, warning lights and other engine indications. Shut down if oil pressure does not rise normally.
This sequence assumes an electric starter. Hand-swinging a propeller is a separate, high-risk operation requiring an approved procedure, suitable aircraft, competent assistance and specific training.
For a familiar type-specific example, our worked Cessna 172 sequence covering start, pre-flight, flight and landing shows how the general principles fit around a complete operating checklist. Individual Cessna 172 models still differ, so use the documentation for the actual aircraft.
Does a cold, hot or flooded engine need a different start?
Yes—engine temperature and fuel-system design determine how much fuel is needed before cranking and how it should be introduced.
| Engine condition | Typical starting logic | Common mistake |
|---|---|---|
| Cold, carburetted | Use the specified number of primer strokes and a slightly opened throttle if directed. | Over-priming or pumping the throttle, which can flood the engine and leave fuel in the induction system. |
| Cold, fuel-injected | Use the boost pump and mixture controls in the exact sequence and duration specified by the manufacturer. | Running the pump too long or applying a carburetted-engine technique. |
| Hot, fuel-injected | Use the dedicated hot-start procedure to manage vapour and residual fuel. | Adding a full cold-start prime, making an already rich condition worse. |
| Flooded | Stop adding fuel and use the POH’s flooded-start procedure, commonly involving idle cut-off and a more open throttle. | Continuing to prime. Be prepared to retard the throttle promptly because the engine may start at high RPM. |
| High-density altitude | Use the starting mixture position specified for the conditions. | Assuming full rich is always correct; an excessively rich mixture can prevent the engine from firing. |
A mistake we see constantly is repeating the same unsuccessful start while adding more prime each time. If the first normal attempt fails, stop and identify whether the engine lacks fuel, has too much fuel, lacks ignition or is cranking too slowly.
Why does a piston engine crank but not start?
A piston engine that turns normally but does not fire usually has an incorrect fuel, mixture, throttle or ignition configuration.
- No sign of firing: check fuel quantity and selector position, mixture setting, ignition selection and whether the prescribed prime was completed.
- Strong fuel smell or fuel draining from the induction system: suspect flooding. Stop priming and use the approved flooded-start procedure.
- Fires and then stops: check mixture position, throttle opening, fuel-pump use and fuel selection. Do not keep the starter engaged after the engine fires.
- Slow or laboured cranking: stop before overheating the starter or flattening the battery. Cold oil, a weak battery or an electrical fault may require maintenance or approved external power.
- Backfiring, abnormal mechanical noise or repeated kickback: discontinue the start and have the ignition timing and engine examined rather than trying again.
Do not repeatedly reset a tripped circuit breaker or manipulate controls at random. Observe the starter duty cycle and investigate the failed condition before another attempt.
What should you do if the engine catches fire during start?
An engine fire during start requires the aircraft’s emergency checklist immediately. Many piston-aircraft procedures use continued cranking to draw flames into the engine, followed by fuel and mixture isolation if it does not start, but the control order varies by aircraft.
If the fire persists, secure the engine and electrical system as directed, evacuate and use suitable firefighting equipment from a safe position. Do not taxi or continue operating an aircraft after a suspected induction or engine fire until it has been inspected.
What must be checked immediately after the engine starts?
Oil pressure is the first critical indication after start, followed by starter disengagement, stable RPM and normal fuel and electrical-system readings.
- Confirm oil pressure rises within the POH limit; shut down promptly if it does not.
- Verify that the starter has disengaged and the ignition switch is in its normal running position.
- Set a low, stable RPM and allow a cold engine to warm without unnecessary high power.
- Check charging output, fuel pressure, warning lights and vacuum indications where fitted.
- Turn on avionics only after the electrical system is stable, unless the aircraft checklist specifies otherwise.
- Lean the mixture for ground operation when approved, particularly where spark-plug fouling is likely, and restore the required take-off setting during the before-take-off checks.
The magneto check, carburettor-heat check and full engine run-up belong at the prescribed run-up stage rather than being improvised immediately after starting.