FAA Commercial Pilot Airplane (CAX)Aircraft SystemsMedium
A pilot flying a turbocharged airplane with a fixed-position wastegate notices the manifold pressure oscillating up and down by several inches without any throttle input, particularly during climb power settings. This phenomenon, caused by the interaction between exhaust gas flow, turbocharger RPM, and throttle position, is best described as?
- ATurbo lag
- BCompressor surge
- COverboost
- DBootstrapping
Show answer & explanationAnswer & explanation
Correct answer: D. Bootstrapping
Bootstrapping is a self-sustaining manifold pressure fluctuation that occurs in some turbocharged systems because a change in manifold pressure changes exhaust flow, which changes turbocharger speed, which further changes manifold pressure — creating a feedback loop. Turbo lag is a delay in boost response, compressor surge is a stall-like bang from disrupted airflow, and overboost is exceeding maximum rated manifold pressure.
Why the other options are wrong
- A. Turbo lag is a response delay, not an oscillation cycle.
- B. Compressor surge produces an abrupt stall/bang, not smooth oscillation.
- C. Overboost is exceeding a pressure limit, not a fluctuation pattern.
Bootstrapping
A manifold pressure oscillation in turbocharged engines caused by a feedback loop between exhaust flow, turbo speed, and manifold pressure.
- Common with older fixed or manually controlled wastegates
- Manifests as MP rising and falling without throttle movement
- Modern automatic wastegate controllers largely eliminate it
Memory trick: Boots keep bouncing the boost.