What happened
On a cargo flight from Dayton, Ohio, to Toronto, Ontario, an Airbus A3/00 B4-203 operated by Express Net Airlines experienced a component separation while on approach to Runway 05 at Toronto/Lester B. Pearson International Airport. The flight, identified by registration N372PC, was being operated by a crew of three.
During the descent, the crew transitioned the flaps through several settings. At approximately 2129 local time, as the flaps were moved to the 25-degree position, the aircraft experienced significant aileron and rudder movement. Shortly thereafter, the flight crew disengaged the autopilot as the aircraft began to roll to the right. The pilot corrected the roll using left rudder input, and the aircraft completed the landing without further incident.
Following the landing, ground personnel notified the crew that the left centre inboard flap tab was missing. The detached component, weighing approximately 16 kg, was located in a retail parking lot in Mississauga, Ontario, roughly 7 nautical miles from the airport. The tab had struck and caused significant damage to an unoccupied parked vehicle.
The investigation
Investigators analyzed the flight data recorder and cockpit voice recorder, which showed no anomalies during the takeoff, climb, or cruise phases of the flight. The investigation focused on the structural failure of the flap tab hinge bracket.
Technical analysis revealed that the hinge bracket, which attaches the tab to the aircraft, failed due to low cycle fatigue. This fatigue originated from impact damage located on the bracket. Because this specific area is protected once the bracket is installed, the damage was likely sustained before or during the installation process and remained undetected during routine inspections.
Findings
- The hinge bracket failed after the crew selected the 25-degree flap setting during the approach.
- Pre-existing impact damage on the hinge bracket created a stress riser, allowing a fatigue crack to develop and progress over the component's service life.
- The separation of the flap tab caused the component to strike a vehicle in a populated area, though the separation itself did not significantly alter the aircraft's flying characteristics.