SDR 2014FA0000005

Service difficulty report · Lock Nut · Bell 407

Difficulty date: January 7, 2014
Submitted: January 7, 2014
Operation: General aviation
Make and model: Bell 407
Aircraft time: 8,265 hours
Engine: Allsn 250C47B
Engine time: 8,040 hours, 11,063 cycles
System (JASC): 6510 · Tail Rotor Drive Shaft
Part: Lock Nut
Condition: Broken
Location: Oil Cooler Shaft
Stage of operation: TO
How discovered: O
Nature of condition: E
Precautionary procedure: C

As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.

What was found

DURING TAKEOFF, CREW EXPERIENCED A SUDDEN, MASSIVE, AND CONTINUOUS VIBRATION. MAINTENANCE INVESTIGATION DETERMINED THAT THE SELF-LOCKING CASTELLATED NUT, SECURING THE FORWARD OIL COOLER DRIVE SHAFT BEARING HOUSING TO THE AIRFRAME MOUNT HAD A TOOTH FRACTURED OFF ALLOWING THE NUT TO ROTATE AND LOOSEN TORQUE.

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