What happened
During a scheduled airline flight, the crew performed a practice autoland approach to recertify the Boeing 757 for category 3 (CAT III) procedures. At the time of the event, weather conditions were good and not a contributing factor. The ILS runway 8 approach chart contained a notation stating the localizer was unusable from 0.8 nm to the threshold. As the aircraft approached the runway, it began to drift off the centerline at approximately three-quarters of a mile from the threshold, consistent with wind direction and the chart notation.
The flight crew did not notify air traffic control that they were conducting an autoland approach, as required by both FAA advisory material and the airline's flight operations manual. Following the drift, the first officer disconnected the autopilot to hand-fly the aircraft back to the runway centerline. This maneuver resulted in a prolonged flare. The aircraft eventually touched down approximately 4,000 feet from the landing threshold at a speed lower than nominal.
The investigation
An examination of the flight data recorder confirmed the aircraft's drift off the centerline and the subsequent flight path. Investigation into the horizontal stabilizer trim control system revealed that during the landing flare, the stabilizer moved to a position commanding full nose-up trim. Testing of the trim system showed no mechanical anomalies or malfunctions. However, an assessment indicated that the rate of trim change observed could only be achieved by operating the stabilizer trim switch on the control yoke or the levers on the center pedestal. During post-accident training, it was noted that the first officer's handling of the yoke could inadvertently activate the trim switch.
Findings
- The aircraft sustained substantial damage due to a tailstrike.
- The first officer's attempt to recover from the centerline drift led to a prolonged flare and a long landing.
- It is likely that the first officer inadvertently activated the full nose-up trim switch on the control yoke during the flare, causing abnormal control forces and an excessive pitch attitude.