Engine Starting Procedures

2.engine-start-procedures. Engine Starting Procedures

Engine starting is one of the most safety-critical phases of ground operations. A mismanaged start can result in a propeller strike, hydraulic lock, fire, runaway aircraft, or injury to bystanders. The Airplane Flying Handbook emphasizes that the Pilot's Operating Handbook (POH) or Airplane Flight Manual (AFM) is the authoritative source for the specific start procedure — but a set of universal principles applies to virtually all reciprocating-engine airplanes.

Pre-Start Considerations

Before the master switch comes on, the pilot must:

• Complete a thorough preflight inspection, with particular attention to fuel quantity and grade, oil level, and any obvious leaks or damage.
• Position the airplane on a firm, level surface clear of loose gravel, sand, snow, or debris that the prop wash could blow into other aircraft, hangars, or people.
• Set the parking brake and/or chock the wheels. Verify the brakes hold by applying toe pressure.
• Visually clear the propeller arc. Open a window or door and shout "CLEAR PROP!" loudly, then pause two to three seconds before energizing the starter to give anyone nearby time to respond.
• Ensure all passengers are briefed and seat belts are fastened.

Typical Cold-Start Sequence (Carbureted Engine)

A representative procedure for a normally aspirated, carbureted four-cylinder engine such as a Lycoming O-320 in a Cessna 172:

1. Seat belts and shoulder harnesses — fastened.
2. Brakes — held.
3. Mixture — IDLE CUTOFF.
4. Throttle — closed, then primer applied per POH (typically 2–4 strokes when cold, 0–1 when warm). Lock the primer.
5. Throttle — cracked open approximately 1/4 inch (about 1000 RPM target).
6. Propeller area — CLEAR.
7. Master switch — ON.
8. Beacon/anti-collision light — ON (signals to ramp personnel that the engine is about to turn).
9. Fuel pump (if installed) — ON for high-wing gravity-fed Cessnas this is usually not required; for low-wing aircraft (Pipers, Cirrus, etc.) the boost pump is normally ON for start.
10. Ignition switch — START. Release to BOTH as soon as the engine fires.
11. Mixture — advance smoothly to FULL RICH as the engine catches (or per POH).
12. Oil pressure — verify in the green within 30 seconds (summer) or 60 seconds (winter). If no indication, shut down immediately to prevent engine damage.
13. Set throttle to a warm-up RPM of 1000–1200.
14. Avionics master — ON only after the engine is stabilized to protect solid-state equipment from voltage spikes.

Hot Starts and Flooded Starts

A hot start (engine recently shut down) typically requires little or no priming because residual fuel vapor is plentiful. Excessive priming creates a flooded condition.

If the engine is flooded — indicated by a strong fuel smell, fuel dripping from the cowl, or failure to fire after a normal attempt — the standard clearing procedure is:

• Mixture — IDLE CUTOFF
• Throttle — FULL OPEN
• Crank the starter for several blades (typically 3–5 seconds)
• As the engine fires, retard the throttle and advance the mixture to RICH

Cold Weather Starts

When ambient temperatures are below approximately 20°F (-7°C), preheating the engine is strongly recommended. Cold oil cannot circulate, and starting a cold-soaked engine accelerates wear, can cause hydraulic lock in radial engines, and may damage starter components. External preheat warms the oil sump and cylinder heads to operating-friendly temperatures before the first revolution.

Fuel-Injected Engines

Fuel-injected engines (such as the IO-360 in a Cessna 172S) use a slightly different sequence: mixture rich, throttle cracked, fuel pump ON until fuel flow stabilizes, then pump OFF, mixture to idle cutoff, and crank — advancing the mixture as the engine fires. Hot starts on injected engines are notoriously difficult due to vapor lock; the POH technique must be followed precisely.

Hand Propping

Hand propping should be attempted only when absolutely necessary and only by pilots trained in the procedure. A qualified pilot must be at the controls with brakes set, the airplane should be chocked, and the person at the propeller must brief the cockpit pilot on every command ("Brakes and contact," "Contact," "Switch off").

Post-Start Checks

After a successful start, the pilot verifies:

• Oil pressure rising into the green arc.
• Ammeter showing a charge (positive indication).
• Vacuum/suction or electrical attitude system online.
• Engine RPM stable at 1000–1200 for warm-up.
• All annunciator lights clear.

Never taxi until oil pressure is confirmed normal and engine instruments are stabilized in their operating ranges.