What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
On climb out the aircraft received stab trim, mach trim, and stall fail caution messages at about 500’ AGL. The pilot continued to climb but could not engage stab trim or adjust it from the failed position. It took a significant amount of nose down pressure to maintain altitude and the autopilot was not available to assist. Quick reference handbook (qrh) procedures did not correct the issue. The crew declared an emergency and requested to return to the airport. While the first officer flew the aircraft the captain wiggled the stab trim disconnect switch and regained trim control. The aircraft landed and returned to the gate without further incident.
Prior to this event, on 08/11/2024 the aircraft received mach trim and stab trim caution messages while in flight. The messages were re-set by the pilot under direction of maintenance control and remained cleared (ref.
On 08/14/2024 during climb out both stab trims disconnected and mach trim disconnected at the same time. Qrh procedures were run. Both systems were re-set with no further issues for that flight. A reliability discrepancy was initiated for the next maintenance overnight visit for troubleshooting of repeat stab trim/mach trim caution messages (ref.
On 08/17/2024 mach trim and stab trim caution messages came on in cruise. Qrh procedures resolved the issue for the remainder of the flight. On taxi in, after engine #1 was shutdown, both messages reappeared. Repeat history was noted. The issue could not be duplicated but the stab/mach trim panel was replaced.
On 08/20/2024 in response to the discrepancy made after emergency landing, the captain’s stab trim disconnect switch was replaced.
The overnight troubleshooting visit did not occur until 08/22/2024, after the emergency landing on 08/20/2024. Troubleshooting determined stab trim switch replacement corrected the problem. Functional and operational checks showed no defects. Maintenance carry over item (mci) was removed and the aircraft released for service.
There have been no further issues related to this system.
As the FAA filed it
ON CLIMB OUT THE AIRCRAFT RECEIVED STAB TRIM, MACH TRIM, AND STALL FAIL CAUTION MESSAGES AT ABOUT 500’ AGL. THE PILOT CONTINUED TO CLIMB BUT COULD NOT ENGAGE STAB TRIM OR ADJUST IT FROM THE FAILED POSITION. IT TOOK A SIGNIFICANT AMOUNT OF NOSE DOWN PRESSURE TO MAINTAIN ALTITUDE AND THE AUTOPILOT WAS NOT AVAILABLE TO ASSIST. QUICK REFERENCE HANDBOOK (QRH) PROCEDURES DID NOT CORRECT THE ISSUE. THE CREW DECLARED AN EMERGENCY AND REQUESTED TO RETURN TO THE AIRPORT. WHILE THE FIRST OFFICER FLEW THE AIRCRAFT THE CAPTAIN WIGGLED THE STAB TRIM DISCONNECT SWITCH AND REGAINED TRIM CONTROL. THE AIRCRAFT LANDED AND RETURNED TO THE GATE WITHOUT FURTHER INCIDENT.
PRIOR TO THIS EVENT, ON 08/11/2024 THE AIRCRAFT RECEIVED MACH TRIM AND STAB TRIM CAUTION MESSAGES WHILE IN FLIGHT. THE MESSAGES WERE RE-SET BY THE PILOT UNDER DIRECTION OF MAINTENANCE CONTROL AND REMAINED CLEARED (REF.
ON 08/14/2024 DURING CLIMB OUT BOTH STAB TRIMS DISCONNECTED AND MACH TRIM DISCONNECTED AT THE SAME TIME. QRH PROCEDURES WERE RUN. BOTH SYSTEMS WERE RE-SET WITH NO FURTHER ISSUES FOR THAT FLIGHT. A RELIABILITY DISCREPANCY WAS INITIATED FOR THE NEXT MAINTENANCE OVERNIGHT VISIT FOR TROUBLESHOOTING OF REPEAT STAB TRIM/MACH TRIM CAUTION MESSAGES (REF.
ON 08/17/2024 MACH TRIM AND STAB TRIM CAUTION MESSAGES CAME ON IN CRUISE. QRH PROCEDURES RESOLVED THE ISSUE FOR THE REMAINDER OF THE FLIGHT. ON TAXI IN, AFTER ENGINE #1 WAS SHUTDOWN, BOTH MESSAGES REAPPEARED. REPEAT HISTORY WAS NOTED. THE ISSUE COULD NOT BE DUPLICATED BUT THE STAB/MACH TRIM PANEL WAS REPLACED.
ON 08/20/2024 IN RESPONSE TO THE DISCREPANCY MADE AFTER EMERGENCY LANDING, THE CAPTAIN’S STAB TRIM DISCONNECT SWITCH WAS REPLACED.
THE OVERNIGHT TROUBLESHOOTING VISIT DID NOT OCCUR UNTIL 08/22/2024, AFTER THE EMERGENCY LANDING ON 08/20/2024. TROUBLESHOOTING DETERMINED STAB TRIM SWITCH REPLACEMENT CORRECTED THE PROBLEM. FUNCTIONAL AND OPERATIONAL CHECKS SHOWED NO DEFECTS. MAINTENANCE CARRY OVER ITEM (MCI) WAS REMOVED AND THE AIRCRAFT RELEASED FOR SERVICE.
THERE HAVE BEEN NO FURTHER ISSUES RELATED TO THIS SYSTEM.