FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationMedium
An aircraft mechanic is inspecting a turbocharged reciprocating engine and finds the wastegate stuck in the fully closed position. What is the most likely operational consequence?
- AReduced manifold pressure at all altitudes, causing power loss
- BThe propeller governor will fail to maintain constant RPM
- CExcessive manifold pressure, potentially causing engine overboost damage
- DNo effect, since the wastegate only functions during engine start
Show answer & explanationAnswer & explanation
Correct answer: C. Excessive manifold pressure, potentially causing engine overboost damage
The wastegate controls how much exhaust gas bypasses the turbine to regulate turbocharger speed and manifold pressure. If stuck closed, all exhaust gas drives the turbine continuously, causing excessive boost and manifold pressure that can overboost and damage the engine.
Why the other options are wrong
- A. A closed wastegate increases, not decreases, manifold pressure since it forces all exhaust through the turbine.
- B. The wastegate is unrelated to the propeller governor system.
- D. The wastegate operates continuously in flight to modulate boost, not just at start.
Turbocharger Wastegate
A valve that controls the amount of exhaust gas bypassing the turbine, regulating turbocharger speed and manifold pressure to prevent overboost.
- Wastegate open = less exhaust to turbine = lower boost
- Wastegate closed = more exhaust to turbine = higher boost
- Stuck closed wastegate can cause dangerous overboost
- Controlled automatically or manually depending on system design
Memory trick: Closed gate traps all exhaust energy—turbine spins wild, boost goes wild