NTSB Identification: CHI00IA009.
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Scheduled 14 CFR NORTHWEST AIRLINES INC.
Incident occurred Thursday, October 14, 1999 in CHICAGO, IL
Probable Cause Approval Date: 05/09/2001
Aircraft: McDonnell Douglas DC-9-51, registration: N766NC
Injuries: 105 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
A DC-9-51 sustained a left outboard main (#1 main) wheel and tire assembly separation on takeoff. That wheel impacted and dislodged the airport's perimeter wall and impacted a vehicle on a nearby road. The wall panels impacted another vehicle. No injuries were reported. The flight landed without incident at its intended destination. That tire assembly was found pressurized and its hubcap was found intact. Its axle nut was found intact under the hubcap. The interior portion of the #1 axle was examined and its internal threads were found intact. The anti-skid transducer adapter was found loosened inside the axle's threads and backed out 4 1/2 turns. A gap was designed to exist between the adapter and the nut. The axle nut was found to contact the adapter when the adapter was backed out to the position as found. The tire was changed on October 1, 1999. The mechanics installed the wheel in accordance with manual 32-40-1. That manual was reviewed and its steps did not caution mechanics to check for the proper depth of the adapter. DC-9-20 through 40 series airplane's anti-skid transducer assemblies were initially secured in position through safety wire. Service Bulletin (SB) 32-111 was issued to incorporate a set screw method in lieu of safety wiring the anti-skid transducer in place. This airplane's SB 32-111 modification was incorporated prior to its delivery to the airline. Subsequent to the incident, the manufacturer issued temporary service bulletins to the affected airplane's 32-40-01 maintenance manuals, cautioning mechanics to check the depth dimension of the transducer adapter with reference to the applicable technical data.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The landing gear's wheel separation due to the improper installation of the wheel by company maintenance personnel using incomplete maintenance steps, and the maintenance steps not listed in the manufacturer's manual. Factors were the airport perimeter wall and the vehicles. Full narrative available
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