FAA Aviation Mechanic Airframe (AMA)Landing Gear SystemsEasy
A technician removes a main landing gear wheel and notices a small plug installed in the wheel hub near the tire bead area has melted, releasing air from the tire. What is the purpose of this component?
- ATo melt at a predetermined temperature and deflate the tire before a brake overheat causes an explosive tire failure
- BTo equalize pressure between the tire and the shock strut during servicing
- CTo seal the wheel half bolts and prevent air leakage during normal operation
- DTo provide a visual indication of correct tire inflation pressure
Show answer & explanationAnswer & explanation
Correct answer: A. To melt at a predetermined temperature and deflate the tire before a brake overheat causes an explosive tire failure
Fusible (thermal) plugs contain a low-melting-point alloy core that melts when brake heat conducts into the wheel, deflating the tire in a controlled manner before excessive heat can cause the tire or wheel to fail violently.
Why the other options are wrong
- B. Fusible plugs are unrelated to strut servicing.
- C. Wheel half bolts are sealed by O-rings, not fusible plugs.
- D. Inflation is checked with a gauge, not the fusible plug.
Fusible (Thermal) Plug
A safety device in a wheel hub containing a low-melting alloy that melts at a set temperature to deflate the tire and prevent explosive failure from brake overheating.
- Melts at a specific predetermined temperature
- Prevents explosive tire/wheel failure from brake heat
- Located in the wheel hub near the brake side
Memory trick: 'Fuse it before it blows' - the fusible plug sacrifices itself to save the wheel