ASN Wikibase Occurrence # 359158
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| Date: | Friday 7 April 1995 |
| Time: | 17:10 LT |
| Type: |  Boeing 737-222 |
| Owner/operator: | United Airlines |
| Registration: | N9090U |
| MSN: | 19078/106 |
| Year of manufacture: | 1968 |
| Total airframe hrs: | 51274 hours |
| Engine model: | P&W JT8D-7B |
| Fatalities: | Fatalities: 0 / Occupants: 116 |
| Aircraft damage: | Minor |
| Category: | Serious incident |
| Location: | Chicago, IL -
 United States of America
|
| Phase: | Initial climb |
| Nature: | Unknown |
| Departure airport: | |
| Atlanta, GA (KATL) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
THE LEFT OUTBOARD MAIN WHEEL SEPARATED FROM THE AIRPLANE ON TAKEOFF. THE AIRPLANE WAS LANDED WITHOUT FURTHER INCIDENT. INVESTIGATION REVEALED THAT THE OUTER BEARING FAILED. HEAT AND MECHANICAL DAMAGE WERE CONSISTENT WITH INADEQUATE LUBRICATION. PRE-EXISTING MECHANICAL DAMAGE COULD NOT BE DETERMINED. THE WHEEL BEARING HAD ACCUMULATED 349 LANDING CYCLES SINCE INITIAL INSTALLATION, AND 219 CYCLES SINCE A BRAKE CHANGE. IT COULD NOT BE CONFIRMED THAT THE BEARING HAD BEEN REPACKED WITH GREASE SINCE INITIAL INSTALLATION. AN UNKNOWN QUANTITY OF GREASE HAD MIGRATED AWAY FROM THE BEARING CAVITY DURING OPERATION. AVERAGE CYCLES BETWEEN 737-200 WHEEL CHANGES PERFORMED BY THE OPERATOR WERE 259, AND WORLDWIDE ACCORDING TO BOEING WERE 200. AN OPTIONAL OUTER GREASE SEAL TO RETAIN GREASE WITHIN THE BEARING WAS NOT INSTALLED. THE BEARING AND WHEEL ASSEMBLY MANUFACTURERS STATED THAT AFTER 150 CYCLES, LUBRICATION PROPERTIES OF GREASE RAPIDLY DEGRADE.
Probable Cause: the inadequacy or deterioration of lubricating grease in the wheel bearing, which led to the total bearing failure and subsequent loss of the wheel. Factors were the insufficiently defined procedures for repacking the bearing, along with an insufficient method of retaining lubricant within the bearing.
Accident investigation:
 |
|
Sources:
NTSB CHI95IA119
History of this aircraft
Other occurrences involving this aircraft
| 26 June 1988 | N9040U | United Airlines | 0 | Salisbury, MD | |
non |
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 15-Mar-2024 07:36 | ASN Update Bot | Added |
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