What happened
On a scheduled passenger and freight flight from Toronto/Lester B. Pearson International Airport to Vancouver, an Air Canada Boeing 747-433 Combi experienced a tail strike during its takeoff roll. The aircraft was carrying 243 passengers and over 31,000 kg of cargo.
As the aircraft accelerated, the nose began to pitch up uncommanded at approximately 120 knots. The first officer initiated rotation at 134 knots, which was roughly 11 knots below the calculated rotation speed. This steep, early rotation caused the underside of the aircraft's tail to strike the runway. The crew did not realize the strike had occurred during the takeoff roll, but they noted unusual flight characteristics during the climb, requiring significant nose-down stabilizer trim to maintain control. Upon arrival in Vancouver, an inspection revealed scraping and minor buckling to the lower fuselage near the auxiliary power unit access doors. There were no injuries to the 253 people on board.
The investigation
The investigation focused on why the aircraft's pitch attitude changed so significantly during the takeoff roll and why the rotation occurred prematurely. Investigators examined flight data recorder information, which showed that the nose began pitching up without any elevator input from the crew.
Technical analysis of the aircraft's loading process revealed that the ALPAC computer application, used to calculate weight and balance, had failed to correctly compute the weight moment for certain cargo pallets. This resulted in a center of gravity calculation that placed the aircraft within safe limits, when in reality, the center of gravity was actually beyond the aft limit of the flight envelope. Furthermore, the investigation looked into the cockpit environment, noting that the company's "silent cockpit" policy meant that airspeed callouts were not being performed by the pilot not flying.
Findings
- The tail strike was caused because the first officer rotated the aircraft too steeply and at a speed below the required rotation speed.
- The early rotation was facilitated by a far aft center of gravity and an incorrect stabilizer trim setting.
- The aircraft's center of gravity was actually beyond the aft limit, despite computer data indicating it was within limits.
- A recently modified loading computer application (ALPAC) contained an error in calculating weight moments for specific cargo pallets.
- The modifications to the ALPAC software had not been adequately validated or monitored after implementation.
- The first officer did not use sufficient down elevator input to keep the nosewheel on the runway during the takeoff roll.
- The captain, acting as the monitoring pilot, did not intervene to prevent the uncommanded pitch-up or the premature rotation.
- The lack of verbal airspeed callouts contributed to a lack of coordination regarding the aircraft's performance during the takeoff roll.