Learn how to start a multi-engine piston aircraft, which engine goes first, the checks after ignition, and how to handle hot or flooded starts.
To start a multi-engine piston aircraft, follow its approved checklist: secure the aircraft, clear both propellers, configure fuel and electrical systems, prime and start the specified engine, verify oil pressure and charging, then repeat for the other engine. Keep RPM low and confirm both engines are stable before switching on avionics.
In real-world aviation, this is only the generic flow. The aircraft flight manual or pilot’s operating handbook takes priority because carburetted, fuel-injected and turbocharged twins can require very different pump, mixture and throttle settings. The underlying fuel-air-spark process is covered in our piston-engine start sequence and shutdown checks.
Typical multi-engine piston start sequence
A light piston twin is normally started one engine at a time, with the first engine stabilised before the second starter is engaged.
- Use the aircraft checklist. Confirm the parking brake or toe brakes are holding, chocks are used where appropriate, loose equipment is clear and nobody is near either propeller.
- Configure electrical power. Set the battery, alternator or generator switches, beacon and avionics exactly as specified. Avionics and unnecessary electrical loads are normally kept off during cranking, but integrated systems differ.
- Set the fuel system. Check quantity, select the approved tanks and verify each fuel valve. Crossfeed is normally not used for starting unless the aircraft checklist specifically calls for it.
- Position the engine controls. Identify the correct engine before touching its controls. Propeller levers are commonly full forward and throttles slightly open, while mixture position depends on the engine and whether it is cold, hot or flooded.
- Prime only as required. Use the primer or electric boost pump for the stated duration or number of strokes. Do not add extra prime merely because the engine did not fire on the first blade.
- Clear and crank the engine. Call “clear prop”, make a final visual check, select the required ignition setting and engage that engine’s starter. Observe the starter’s published cranking and cooling limits.
- Stabilise the running engine. Release the starter as the engine fires, set the specified low RPM and confirm oil pressure promptly. Check fuel pressure, charging indication and any abnormal noise, vibration, smoke or flame.
- Start the other engine. Repeat the correct procedure for that engine rather than assuming its settings are already right. Keep the first engine at low RPM while the second starter is operating.
- Complete the after-start checks. Confirm both engines are charging and indicating normally, then configure avionics, lights, pumps, cowl flaps and other systems according to the checklist.
Which engine should be started first?
Start the engine named first in the aircraft’s approved checklist; there is no universal left-first or right-first rule for piston twins.
The sequence may reflect battery-cable routing, hydraulic or pneumatic equipment, ground-power arrangements, or a manufacturer’s standard operating flow. The concept of a critical engine concerns aircraft handling after an engine failure and does not, by itself, determine starting order.
If a ground power lead, servicing equipment or boarding activity is near one nacelle, resolve that hazard before starting either engine. A different start order is not a substitute for a completely clear propeller area.
How does priming change for cold, hot or flooded engines?
Priming depends on engine design and temperature rather than the number of engines fitted to the aircraft.
| Engine condition | Typical checklist logic | Common mistake |
|---|---|---|
| Cold carburetted engine | Use the specified primer strokes and a slightly open throttle. | Overpriming or pumping the throttle, which can leave fuel in the intake and increase fire risk. |
| Cold fuel-injected engine | Use the boost pump, mixture and throttle in the specified priming sequence. | Running the pump too long after fuel flow is established. |
| Hot fuel-injected engine | Use the manufacturer’s hot-start procedure, often with a different mixture and pump sequence. | Applying the cold-start procedure and flooding the engine. |
| Flooded engine | Stop priming and use the published flooded-start procedure. | Adding more fuel after repeated unsuccessful starts. |
Primer quantity and boost-pump timing cannot safely be standardised across aircraft. Our explanation of how to prime without flooding a piston engine covers the signs of too much and too little fuel.
What should you check after each engine starts?
Oil pressure is the first essential indication, followed by stable RPM, fuel pressure and a functioning electrical charging source.
- Oil pressure: it must rise within the aircraft’s published time limit. If it does not, shut the engine down using the checklist.
- Electrical output: confirm the alternator or generator is online before relying on it to support the second start. A temporarily high charging indication can follow starter use, but it should behave as the aircraft manual describes.
- Fuel and engine instruments: check the indication for the engine just started, especially where one gauge uses a left/right selector.
- RPM and temperature: keep the engine at the stated warm-up RPM. Do not race the first engine simply to make the second crank faster.
- Leaks, smoke or fire: stop and apply the appropriate abnormal or emergency checklist. An engine fire during start is not handled by repeatedly trying the normal procedure.
Magnetos normally provide ignition independently once a piston engine is running, while the battery and starter perform different jobs during cranking. Our guide to the battery, starter, alternator and magneto relationship explains why a charging fault may not stop an engine immediately.
Why will only one engine start?
When one engine starts and the other does not, compare the controls and indications engine by engine rather than adding more prime automatically.
| Symptom | Likely areas to check | Correct response |
|---|---|---|
| Propeller does not turn | Battery state, master switch, starter circuit, engine selection or starter limits | Stop and use the checklist; do not repeatedly reset a tripped circuit breaker. |
| Engine cranks but does not fire | Fuel selector, fuel valve, ignition, mixture and priming sequence | Verify each setting for that engine before another attempt. |
| Engine fires and immediately stops | Mixture left at idle cut-off, throttle too closed or incomplete fuel-pump sequence | Return to the published start procedure rather than adding indiscriminate prime. |
| Strong fuel smell or visible fuel | Flooded induction system | Stop priming and use the aircraft’s flooded-start procedure. |
| Second engine cranks slowly | Weak battery, excessive electrical load, first alternator offline or starter overheating | Stop cranking, observe the cooling limit and diagnose the electrical problem. |
| No oil pressure after ignition | Lubrication or indication fault | Shut the affected engine down immediately according to the checklist. |
In a simulator, also check that engine-selection commands have not left only one engine active and that separate throttle, propeller and mixture axes are assigned correctly. If this happens in Microsoft Flight Simulator, follow these MSFS fuel, mixture and ignition fault checks before changing realism or assistance settings.
The decisive limits—primer quantity, starter duty cycle, oil-pressure rise time and hot-start technique—come from the specific aircraft checklist. A memorised generic flow helps organise the work, but it must never replace the type-specific procedure.