Boeing 737-222 N9090U

Summary

On 7 April 1995 at about 22:10 local time, a Boeing 737-222 registered N9090U was involved in an incident near Chicago, Illinois, United States. 116 people were on board and nobody was injured. The aircraft was slightly damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

7 April 1995 at 22:10

Classification

Incident

Location

Chicago, Illinois, United States

Nearest airport

O'hare Int'l Airport (ORD)

Coordinates

Not recorded

Aircraft

Boeing 737-222

Registration

N9090U

Category

Airplane

Engines

2

Operator

Not recorded

Operating rule

Part 121: Air Carrier

Purpose of flight

Unknown

Phase of flight

Not recorded

Route

Unknown → Atlanta

Aircraft damage

Minor

Weather

VMC

Light

Day

NTSB number

CHI95IA119

Nobody was injured.

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.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.