Incident Details
An aircraft was on final approach to Chicago O'Hare International Airport when a structural failure of the number three flap track occurred. The pilot experienced significant uncommanded roll and yaw but regained control of the aircraft and executed an uneventful landing.
Damage
The aircraft sustained substantial damage to the left wing, left inboard flap assembly, left inboard spoilers, and the spoiler support beam.
Investigation Findings
The investigation revealed a history of flap track cracking problems associated with stress corrosion and design inadequacy. A design change of the member was accomplished in 1971 by the manufacturer, but flap tracks of the earlier design were allowed to remain in service on 239 aircraft. The airworthiness directives and service bulletins applicable to this particular structural member were found to be not adequate in methodology and periodicity to ensure crack detection, and they do not require inspection for the cause of the crack-corrosion pits.