Incident Overview
On an unspecified date, a DC-9-51 aircraft sustained a separation of the left outboard (#1 main) wheel and tire assembly during takeoff. The separated wheel struck and dislodged a section of the airport's perimeter wall. The wall panels subsequently hit a vehicle on a nearby road. The wheel itself also impacted another vehicle. No injuries were reported. The flight continued to its intended destination and landed without incident.
Post-Incident Examination
After the incident, the separated tire assembly was found to be pressurized, and its hubcap remained intact. Under the hubcap, the axle nut was intact. Examination of the interior portion of the #1 axle revealed intact internal threads. The anti-skid transducer adapter was found loosened inside the axle's threads, having backed out 4 1/2 turns from its proper position. A gap was designed to exist between the adapter and the nut. The axle nut was found to be in contact with the adapter when the adapter was in the backed-out position.
Maintenance History
The tire on the affected wheel had been replaced on October 1, 1999. During that replacement, mechanics installed the wheel following the procedures in manual 32-40-1. A review of that manual indicated that its steps did not include a caution for mechanics to verify the proper depth of the adapter.
Background on Anti-Skid Transducer Installation
In DC-9-20 through 40 series airplanes, the anti-skid transducer assemblies were initially secured using safety wire. Service Bulletin (SB) 32-111 was later issued to replace the safety wire method with a set screw method. The subject airplane had the SB 32-111 modification incorporated prior to its delivery to the airline.
Post-Incident Actions
Subsequent to the incident, the manufacturer issued temporary service bulletins to the affected airplane's 32-40-01 maintenance manuals, adding a caution for mechanics to check the depth dimension of the transducer adapter with reference to applicable technical data.