FAA Flight Instructor Airplane (FIA)Aircraft Systems and InstrumentsEasy
A pilot operating a high-performance normally aspirated engine leans the mixture aggressively while climbing at high power and reduced airspeed. What engine condition is this operation most likely to cause?
- AVapor lock
- BHydraulic lock
- CCarbon monoxide poisoning
- DDetonation
Show answer & explanationAnswer & explanation
Correct answer: D. Detonation
Leaning excessively during high-power, low-airspeed climbs raises combustion temperatures and cylinder pressures, promoting detonation—uncontrolled, spontaneous explosion of the fuel-air charge ahead of the normal flame front. Detonation can cause severe engine damage if not corrected by enriching the mixture and reducing power/CHT.
Why the other options are wrong
- A. Vapor lock relates to fuel boiling in fuel lines, usually from heat after shutdown, not leaning in flight.
- B. Hydraulic lock involves liquid in a cylinder before start, unrelated to mixture leaning.
- C. CO poisoning results from exhaust leaks into the cabin, not mixture setting.
Detonation
Uncontrolled, explosive combustion of the fuel-air mixture in the cylinder, occurring after normal ignition but before the flame front arrives, caused by excessive heat and pressure.
- Common causes: low-octane fuel, excessive lean mixture at high power, high manifold pressure with low RPM
- Can cause severe engine damage (holed pistons)
- Corrected by enriching mixture, reducing power, and increasing airspeed for cooling
Memory trick: LEAN + HOT + HIGH POWER = BOOM before the spark's turn.