What happened
During takeoff, a DC-9-51 experienced the separation of its left outboard main (#1 main) wheel and tire assembly. The detached wheel struck and dislodged panels from the airport's perimeter wall. The moving wheel then impacted a vehicle traveling on a nearby road, while the dislodged wall panels subsequently struck another vehicle. There were no injuries reported as a result of the incident. Following the separation, the flight continued and landed at its intended destination without further incident.
The investigation
Investigators examined the separated tire assembly and found it was still pressurized with the hubcap remaining intact. The axle nut was also found to be intact beneath the hubcap, and the internal threads of the #1 axle showed no damage. However, the anti-skid transducer adapter was discovered loosened within the axle's threads, having backed out 4 1/2 turns.
While a gap is designed to exist between the adapter and the nut, the investigation determined that the axle nut was in contact with the adapter when it was in its found position. Records indicated the tire had been changed on October 1, 1999, with mechanics performing the installation according to manual 32-40-1. A review of that manual revealed it lacked instructions for mechanics to verify the proper depth of the adapter.
Historically, anti-skid transducer assemblies on DC-9-20 through 40 series aircraft were secured using safety wire. This specific aircraft had previously undergone modification via Service Bulletin (SB) 32-111, which implemented a set screw method instead of safety wiring.
Findings
- The anti-skid transducer adapter had backed out 4 1/2 turns from its proper position.
- The maintenance manual used for the tire change did not include a requirement to check the depth of the transducer adapter.
- Following the event, the manufacturer issued temporary service bulletins for the 32-40-01 maintenance manuals to instruct mechanics to verify the transducer adapter depth dimension against technical data.