FAA Aviation Mechanic Powerplant (AMP)Turbine EnginesMedium
A technician examines a turbine engine's main shaft where it passes through a stationary case section. A series of thin circumferential knife-edge ridges on the rotating shaft are positioned very close to a stationary honeycomb or abradable lining. What is the primary purpose of this labyrinth seal arrangement?
- ATo accelerate bleed air flow and generate additional engine thrust
- BTo restrict air or oil leakage between rotating and stationary sections while tolerating slight rubbing contact without seal damage
- CTo direct cooling oil jets onto the turbine disc through the labyrinth passages
- DTo create a rigid metal-to-metal contact seal that completely eliminates all air and oil leakage
Show answer & explanationAnswer & explanation
Correct answer: B. To restrict air or oil leakage between rotating and stationary sections while tolerating slight rubbing contact without seal damage
Labyrinth seals use closely spaced knife-edges against an abradable lining to create a tortuous, restrictive path that minimizes (but does not eliminate) leakage of air or oil, while allowing brief rubbing contact during thermal growth without damaging the rotating shaft.
Why the other options are wrong
- A. Labyrinth seals are not designed to generate thrust.
- C. Labyrinth seals control leakage; oil cooling of turbine discs uses separate passages/jets.
- D. Labyrinth seals restrict, not completely eliminate, leakage; they are non-contact or light-contact by design.
Labyrinth Seal
A non-contact (or light-contact) seal using rotating knife-edges against an abradable stationary lining to minimize air or oil leakage in a turbine engine.
- Reduces, but does not fully eliminate, leakage across rotating/stationary interfaces
- Abradable lining allows brief rubbing without seal damage
- Common at compressor/turbine disc interfaces and bearing compartments
Memory trick: Labyrinth seal = a maze that slows leaks but never fully blocks them