A line mechanic reports finding main tire/wheel assemblies with split or missing tie-bolt lock nuts on their B757-200 aircraft. Hydrogen embrittlement of lock nuts were noted as the cause of earlier failures and thought corrected; but now; similar failures are recurring.

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Attributes
ACN	1066342
Time
Date	201302
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Dusk
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Parked
Component
Aircraft Component	Main Gear Wheel
Person 1
Function	Technician
Qualification	Maintenance Airframe Maintenance Powerplant
Experience	Maintenance Technician 25
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural FAR

Narrative:

[This is in] reference air carrier maintenance computer system; item XXX01; on a B757-200 aircraft. One of the # 5 main wheel tie bolts had a broken nut. This is a recurring problem. About five years ago; we had problems with the tie-bolts breaking; now it is the nuts. Part failure of main tire/wheel tie-bolt lock nuts.

Original NASA ASRS Text

Title: A Line Mechanic reports finding main tire/wheel assemblies with split or missing tie-bolt lock nuts on their B757-200 aircraft. Hydrogen Embrittlement of lock nuts were noted as the cause of earlier failures and thought corrected; but now; similar failures are recurring.

Narrative: [This is in] reference Air Carrier Maintenance Computer System; Item XXX01; on a B757-200 aircraft. One of the # 5 main wheel tie bolts had a broken nut. This is a recurring problem. About five years ago; we had problems with the tie-bolts breaking; now it is the nuts. Part failure of main tire/wheel tie-bolt lock nuts.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.