What happened
On a flight from Kingston, Ontario, to Toronto/Lester B. Pearson International Airport, a de Havilland DHC-8 operated by Jazz Air Inc. experienced unexpected flight control behavior shortly after takeoff. The first officer, acting as pilot flying, noticed that the aircraft required unusual forward pressure on the control column to prevent a nose-up pitch. As the aircraft accelerated, the need for forward pressure increased, eventually requiring the first officer to request the captain's assistance to hold the column forward.
After reaching 4,000 feet, the crew declared an emergency. To address the difficulty, the crew activated the elevator pitch disconnect handle, which isolated the left and right elevators. This action restored normal control functionality to the captain's side of the system. The crew subsequently performed a flapless landing at Toronto without further incident.
The investigation
The investigation focused on the mechanical state of the elevator control system. Post-flight inspections revealed that part of a balance weight on the right-side elevator spring tab was missing, along with the two nuts intended to secure it. The investigation established that two bolts had migrated out of the remaining portion of the weight and became lodged on the top surface of the elevator. This physical obstruction held the spring tab in a trailing-edge-down position, creating the pitch anomaly.
Investigators also examined the maintenance history, noting that the spring tab had undergone balancing work approximately one month prior. It was determined that the securing nuts had likely been left loose following this adjustment. Furthermore, the investigation looked into why the subsequent independent inspection failed to identify the loose hardware and why the flight crew's training and checklists did not adequately prepare them for a "soft" control jam.
Findings
- The primary cause of the control difficulty was that the nuts securing the counter balance weight to the weight arm were not tightened.
- The loss of these nuts allowed the weight to partially detach, causing bolts to migrate and jam the elevator spring tab.
- The independent inspection performed on the aircraft was inadequate, as it failed to detect the unfastened nuts.
- Flight crew training and the Quick Reference Handbook (QRH) lacked sufficient guidance to identify the specific symptoms of a spring tab jam or to recognize the risks of overstressing the aircraft tail by accelerating during such an event.
Safety action
Following the occurrence, Bombardier Inc. issued an All Operator Message to increase awareness of "soft" jam possibilities in DHC-8 flight controls, advising crews to use the control jam checklist immediately without allowing the aircraft to accelerate. Additionally, Jazz Air modified its maintenance inspection forms and implemented new procedures to monitor and limit excessive overtime for maintenance personnel.