If any fusible plugs show signs of softening, they must all be replaced.

• A. Only the softened plug is replaced
• B. None
• C. Some
• D. All fusible plugs must be replaced

Answer: (D)

Fusible plugs are heat-sensitive safety devices in aircraft tires that relieve pressure by melting when the tire overheats, preventing a catastrophic tire failure. If you observe that a plug has softened, it shows the material has already undergone dangerous heat exposure and aged accordingly. The other plugs in the same tire assembly have likely endured the same conditions, so they’re probably weakened too. Replacing only the softened plug risks having another plug fail in service, which could lead to another overheat event or tire blowout. Replacing all fusible plugs ensures uniform protection and reliability across the entire tire assembly, making it the safest maintenance action.