Santa Ana, CA, USA
N615AS
Boeing 737-700
The flight crew experienced a jammed horizontal stabilizer trim actuator during the takeoff initial climb. The pilot reported that after takeoff, during climb out, the "STAB OUT OF TRIM" annunciator light illuminated. The crew disengaged the autopilot and found the electric trim control inoperative at both the pilot and co-pilot positions, and the manual trim control was jammed and immovable. The crew leveled the airplane at 13,000 feet and accomplished the "Stabilizer Out of Trim" and "Jammed Stabilizer" checklists to no avail. The crew declared an emergency with air traffic control, and made an otherwise uneventful landing at Los Angeles. According to the pilot, the trim manual control was jammed and immobile. Post flight examination revealed the horizontal stabilizer trim actuator motor was seized. The actuator motor was subsequently replaced with a serviceable unit, and the aircraft was ferried to Seattle for inspection. No other faults were found in the pitch trim system and the airplane was returned to service. Further examination of the actuator motor revealed that the motor was mechanically seized. According to a representative of Boeing Aircraft Company, with the motor seized, in order to manually trim the stabilizer, it would have been necessary for the flight crew to exert sufficient force on the trim wheel to cause the motor clutch to slip in addition to the force necessary to overcome normal system friction.
On October 10, 2001, at 1627 hours Pacific daylight time, Alaska Airlines flight 497, a Boeing 737-700, N615AS, experienced a jammed horizontal stabilizer trim actuator during the takeoff initial climb from the John Wayne Airport-Orange County, Santa Ana, California. The flight was destined for Seattle, Washington; however, the flight crew diverted to, and landed at, Los Angeles International Airport, Los Angeles, California, at 1658. The airline transport certificated pilot, the remaining 4 crewmembers, and 82 passengers were not injured, and the airplane was not damaged. The flight was operated by Alaska Airlines, Inc., under 14 CFR Part 121, as flight 497, a regularly scheduled domestic passenger flight. The flight was operating on a instrument flight plan and visual meteorological conditions prevailed. The pilot reported that after takeoff, during climb out, the "STAB OUT OF TRIM" annunciator light illuminated. The crew disengaged the autopilot and found the electric trim control inoperative at both the pilot and co-pilot controls and the manual trim control was jammed and immovable. The crew leveled the airplane at 13,000 feet and accomplished the "Stabilizer Out of Trim" and "Jammed Stabilizer" checklists to no avail. After conferring by radio with their company maintenance personnel at Los Angeles, the decision was made to land there. The crew declared an emergency with air traffic control and made an otherwise uneventful landing at Los Angeles. According to the pilot, maintenance personnel who met the airplane on arrival could not move the stabilizer control either and believed the actuator gearbox was jammed. In a subsequent company interview, on November 13, 2001, the pilot reiterated that the trim manual control had been jammed and immobile; neither he, the first officer (co-pilot) or the mechanics who met the flight, were able to force it to move. The pilot said he had trained for the jammed stabilizer emergency in the simulator; however, in the incident at hand he had applied "a lot more force" than was required in the simulator and was still unable to move the manual control. Post flight examination revealed the horizontal stabilizer trim actuator motor was seized. The actuator motor was replaced with a serviceable unit and the aircraft was ferried to Seattle for inspection. No other faults were found in the pitch trim system and the airplane was returned to service. Further examination of the actuator motor revealed that the motor was mechanically seized. According to a representative of Boeing Aircraft Company, with the motor seized, in order to manually trim the stabilizer, it would have been necessary for the flight crew to have exerted sufficient force on the trim wheel to cause the motor clutch to slip in addition to the force necessary to overcome normal system friction.
The failure of the stabilizer electric trim motor as a result of internal mechanical seizure.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
