What happened
On 2 March 2022, a United States Air Force F-16CG Fighting Falcon, bearing tail number 89-2035, was performing a takeoff from runway 05 at Aviano AB, Italy. The aircraft, assigned to the 555th Fighter Squadron, “the Triple Nickel,” was operating as the lead element of two aircraft for an air tasking order mission. During the takeoff roll, the pilot observed abnormal flight indications and the illumination of the anti-skid light.
As the aircraft became airborne, the left main landing gear wheel separated from the aircraft. While the pilot initially suspected a blown tire, subsequent inspections by a wingman and discovery of the detached wheel by airfield personnel confirmed the separation. Following recommendations from flight safety engineers and base supervision, the pilot executed a gear-up landing to safely recover the aircraft. The aircraft landed on its belly at approximately 13:41L, skidding along the runway. The pilot was uninjured during the incident.
The investigation
The investigation examined the mechanical failure of the left main landing gear assembly and the sequence of events leading to the separation. Investigators analyzed the wheel assembly, axle, and brake components, as well as maintenance records and personnel qualifications. The board reviewed the work performed by maintenance personnel during the assembly and installation of the wheel, which had occurred three days prior to the mishap.
Findings
- The primary cause of the mishap was the failure of the left outboard main landing gear wheel bearing.
- Excessive heat and friction from the failed bearing caused the bearing cone to soften and deform.
- Rotational forces caused the bearing cone to rotate around the fixed axle, eventually friction-welding the cone to the spacer.
- This fusion created enough force to fracture the anti-rotational tab on the spacer, allowing it to rotate counter-clockwise.
- The resulting movement sheared the locking tab on the wheel nut, causing the nut to loosen during the takeoff sequence and leading to the separation of the wheel.
- While the exact origin of the bearing's premature wear—such as potential contamination or pre-existing defects—could not be determined due to secondary damage, the board found no evidence of maintenance errors or improper assembly procedures.