Individually Owned: 150,657
Corporate Owned: 137,281
O'hare Int'l Airport
Aircraft Accident/Incident Report
Chicago, Illinois 60666
Friday, April 7, 1995 17:10 CDT
NTSB Narrative Summary Released at Completion of Accident
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.
NTSB Probable Cause Narrative
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.
Event Information
| Type of Event | Incident |
| Event Date | 4/7/1995 |
| Event Day of the Week | Friday |
| Time of Event | 1710 |
| Event Time Zone | Central Daylight Time |
| Event City | CHICAGO |
| Event State | ILLINOIS |
| Event Country | -- |
| Zipcode of the event site | 60666 |
| Event Date Year | 1995 |
| Event Date Month | 4 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | |
| Event Location Longitude | |
| Event Location Airport | O'HARE INT'L AIRPORT |
| Event Location Nearest Airport ID | ORD |
| Indicates whether the acc/inc occurred off or on an airport | On Airport |
| Distance from airport in statute miles | 0 |
| Degrees magnetic from airport | 0 |
| Airport Elevation | 650 |
| Weather Briefing Completeness | Full |
| Investigator's weather source | Weather Observation Facility |
| Time of the weather observation | 1652 Central Daylight Time |
| Direction of event from weather observation facility (degrees) | 0 |
| Weather Observation Facility ID | ORD |
| Elevation of weather observation facility | 650 |
| Distance of event from weather observation facility (units?) | 0 |
| Time Zone of the weather observation | CDT |
| Lighting Conditions | Day |
| Lowest Ceiling Height | 1500 |
| Lowest Non-Ceiling Height | 0 |
| Sky/Lowest/Cloud Conditions | Unknown |
| Sky Condition for Lowest Ceiling | Overcast |
| Visibility Runway Visual Range (Feet) | 0 |
| Visibility Runway Visual Value (Statute Miles) | 0 |
| Visibility (Statute Miles) | 4 |
| Air Temperature at event time (in degrees celsius) | 6 |
| Dew Point at event time (in degress fahrenheit) | 3 |
| Wind Direction (degrees magnetic) | 40 |
| Variable Wind Indicator | Unknown |
| Wind Speed (knots) | 16 |
| Wind Velocity Indicator | Unknown |
| Wind Gust Indicator | Unknown |
| Wind Gust (knots) | 0 |
| Altimeter Setting at event time (in. Hg) | 29 |
| Density Altitude (feet) | -- |
| Intensity of Precipitation | Unknown |
| METAR weather report | -- |
| Event Highest Injury | None |
| On Ground, Fatal Injuries | 0 |
| On Ground, Minor Injuries | 0 |
| On Ground, Serious Injuries | 0 |
| Injury Total Fatal | -- |
| Injury Total Minor | -- |
| Injury Total None | 116 |
| Injury Total Serious | -- |
| Injury Total All | -- |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 5044 |
| NTSB Notification Source | -- |
| NTSB Notification Date | Apr 8 1995 12:00AM |
| NTSB Notification Time | 1745 |
| Fiche Number and/or location -used to find docket information | IMAGE |
| Date of most recent change to record | Dec 7 2000 4:12PM |
| User who most recently changed record | dbo |
| Basic weather conditions | Visual Meteorological Cond |
| FAA District Office | -- |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N9090U |
| NTSB Number | CHI95IA119 |
| Missing Aircraft Indicator | N |
| Federal Aviation Reg. Part | Part 121: Air Carrier |
| Type of Flight Plan filed | IFR |
| Flight plan Was Activated? | -- |
| Damage | Minor |
| Aircraft Fire | None |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | BOEING |
| Aircraft Model | 737-222 |
| Aircraft Series Identifier | 737-222 |
| Aircraft Serial Number | 19078 |
| Certified Max Gross Weight | 117000 |
| Aircraft Category | Airplane |
| Aircraft Registration Class | U.S. Registered/U.S. Soil |
| Aircraft is a homebuilt? | No |
| Flight Crew Seats | -- |
| Cabin Crew Seats | -- |
| Passenger Seats | -- |
| Total number of seats on the aircraft | 117 |
| Number of Engines | 2 |
| Fixed gear or retractable gear | Retractable |
| Aircraft, Type of Last Inspection | Continuous Airworthiness |
| Date of Last Inspection | Nov 24 1994 12:00AM |
| Airframe hours since last inspection | 794 |
| Airframe Hours | 51274 |
| ELT Installed | Unknown |
| ELT Activated | Unknown |
| ELT Aided Location of Event Site | Unknown |
| ELT Type | -- |
| Aircraft Owner Name | UNITED AIR LINES, INC. |
| Aircraft Owner Street Address | O'HARE INTERNATIONAL AIRPORT |
| Aircraft Owner City | CHICAGO |
| Aircraft Owner State | IL |
| Aircraft Owner Country | |
| Aircraft Owner Zipcode | 60666 |
| Operator is an individual? | -- |
| Operator Name | |
| Operator Same as Owner? | Yes |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | Yes |
| Operator Street Address | |
| Operator City | |
| Operator State | |
| Operator Country | |
| Operator Zip code | |
| Operator Code | UALA |
| Owner has at least one certificate | Yes - certificate holder |
| Other Operator of large aircraft? | No |
| Certified for Part 133 or 137 Operation | Unknown |
| Operator Certificate Number | -- |
| Indicates whether an air carrier operation was scheduled or not | Scheduled |
| Indicates Domestic or International Flight | Domestic |
| Operator carrying Pax/Cargo/Mail | Passenger Only |
| Type of Flying (Per_Bus / Primary) | Unknown |
| Second Pilot on Board | Yes |
| Departure Point Same as Event | Yes |
| Departure Airport Code | |
| Departure City | |
| Departure State | |
| Departure Country | |
| Departure Time | 1710 |
| Departure Time Zone | CDT |
| Destination Same as Local Flt | -- |
| Destination Airport Code | ATL |
| Destination City | ATLANTA |
| Destination State | GA |
| Destination Country | |
| Specific Phase of Flight | Takeoff |
| Report sent to ICAO? | -- |
| Evacuation occurred | -- |
| Date of most recent change to record | Dec 20 2002 12:42PM |
| User who most recently changed record | dbo |
| Since inspection or accident | -- |
| Event Location Runway Number and Location | 9L |
| Runway Length | 7967 |
| Runway Width | 150 |
| Sight Seeing flight | No |
| Air Medical Flight | No |
| Medical Flight | -- |