AD Amdt-39-13879
Unsafe Condition
Reports of leaks caused by cracked bypass buttons that protruded beyond the internal o-ring seal, leading to a potential fire or explosion from a fuel leak.
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Required Actions
Install a bracket onto the fuel filter housing assembly to prevent a failed bypass button from protruding beyond the internal o-ring seal. Use specific Alert Service Bulletins (ASBs) for installation instructions. Perform a one-time inspection for proper gap adjustment if brackets were previously installed using certain ASBs.
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Compliance Time
Within 500 hours time-in-service or 6 months after the effective date of this AD, whichever occurs earlier.
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Affected Aircraft
Hamilton Sundstrand Power Systems Models T-62T-46C12 and T-62T-40C14 (APS 500R) APUs with fuel filter housing assemblies, part numbers 4951627, 4951960, or 4952039, installed. These APUs are installed on, but not limited to, Bombardier DHC-8-400 airplanes and Embraer EMB-135 and -145 series airplanes.
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Source: Official FAA Source ↗
Retrieved: Apr 6, 2026
Rights: U.S. Government Public Domain
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