MD-11
Maintenance Airframe; Maintenance Powerplant
Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Manuals; Procedure
General safety concern to raise awareness of recent safety of flight issue. Three incidents of nose wheel bearing failure on Company MD-11 aircraft have occurred within the last 10 months [on three separate aircraft at 3 separate locations]. Through our software I do not see this happening prior to 11/XX/16. This issue happens at high speed during takeoff and landing. Douglas MD-11 nosewheel installation and design is unique to all other Company fleet types. My observations are as follows:1) MD-11 nose wheel final torque is the lowest of all Company fleet 25ft/lbs. Initial torque is also comparatively low. 2) Axle sleeve that contains both inner and outer bearing races (possibly migrates).3) Tang washer part# ACG7220-1 contains a small 90 degree lip. This lip must fully seat in narrow channel made by axle and axle sleeve. 4) Tang washer is a snug fit circumferentially (possibly cocks sideways during installation). 5) Safety bolt does not go through axle. Douglas MD-11 nose gear design is cantered and set back further. During hard turns heavy side loads occur on the wheel and axle in the direction of the turn.
The reporter stated he's been in the industry over 30 years and this is the first time he has seen nose wheel bearings fail. The reporter stated since the beginning of the year he has seen 4 failures. The reporter also stated that flight crews would write this up as a nose wheel vibration or shimmy and the mechanic would find the nose wheel bearings completely destroyed and the wheel leaning against the strut. The reporter stated that he doesn't have any idea of what caused the failure and only suspects that the wheel shop is installing incorrect bearings. The reporter stated since he wrote the report he has changed his mind suspecting the tab washer as being a problem.
MD-11 Maintenance Technician reported 3 incidents of nose wheel bearing failures.