The takeoff from Honolulu was being performed by the Second Officer from the right control seat. This pilot was receiving promotional training under the supervision of the Captain. Weather conditions were reported as being fine. Because of a more favourable power decrement, the Captain had elected to use a Flaps 10 setting. Appropriate reference speeds as calculated for this particular takeoff were V1=148 knots; Vr=168 knots, and V2=176 knots. The body angle required at the completion of rotation was calculated to be 13 degrees. This target angle was expected to be reached by V2 as the aircraft passed through a nominal height of 35 feet. The stabilizer trim was set to 8.1 units nose-up, which was in accordance with a forward Centre of Gravity (CG) position. The subsequent flight was conducted without recorded incident. However, during a post-flight inspection at Vancouver, it was found that the aircraft had sustained damage to the undersurfaces of the rear fuselage. The damage was consistent with a tailstrike, although the flight crew had been unaware of such an occurrence. Flight Data Recorder analysis indicated that a tailstrike had occurred at Honolulu. Rotation for takeoff had been initiated at an airspeed of 157 knots. The elevator control input was initially held at an average setting, but the aircraft did not respond by lifting off at about 8 degrees as would have been expected. A further control input was made to achieve liftoff, during which a maximum body angle of 15 degrees was momentarily recorded. The average pitch change rate was calculated to be 3.1 degrees per second. It is estimated that with the mainwheels on the ground, the rear fuselage will contact the runway at a body angle of approximately 12 degrees. It was determined that although the initial elevator control input was consistent with a normal takeoff, the rate of pitch change was almost double the normal rate. It is considered that this was due to a characteristic of the aircraft which results in reduced elevator control pressures at forward CG positions, particularly when combined with a Flaps 10 setting. Company Operations Manuals note that elevator forces encountered during rotation when 8.5 or more units are required, will be approximately 40 to 50 percent of the elevator force experienced at lighter weights and mid or aft CG positions. The Second Officer had not previously experienced a takeoff under the existing weight and flap conditions, and was unaware of the comments in the Operations Manual relating to lighter elevator forces. It is possible that the tailstrike would not have occurred if rotation had been initiated at the correct speed. However, the reason that rotation was commenced 11 knots below the target speed could not be established.
