2023-05 · NASA ASRS report 2001041
B737 flight crew reported the First Officer's pitch trim control moved the pitch trim in the opposite direction as intended after being replaced by Maintenance. The Captain assumed flying duties as the Captain's pitch trim control was working properly and the flight crew continued to destination airport.
Neither myself; nor First Officer noticed the direction of pitch trim wheel movement when testing the cutout function. Neither of us thought to actually look [that] the desired inputs on the pitch trim wheel corresponded with actual input. This incident could have easily been misidentified as an MCAS (Maneuvering Characteristics Augmentation System) activation in a MAX aircraft. We were shocked that a simple inadvertent switching of the wires could lead the pitch trim to work in opposite of pilot input.After Maintenance replaced the First Officer's pitch trim switch; no one noticed the pitch trim switch was trimming in opposite direction than commanded. Somehow; Maintenance and flight crew didn't notice until aircraft was airborne in critical phase of flight. First Officer correctly stated that he was having difficulty maintaining proper pitch during initial climb-out. I as Captain took control and because my pitch trim was operating correctly; managed to avoid a very serious undesired aircraft state. We were within a few seconds of that scenario with very little time to diagnose the issue with the aircraft.
We arrived at Gate XX ZZZ for the operation of flight ZZZ - ZZZZ. Upon arrival; Aircraft X was being worked on by Maintenance. We were advised to wait at the gate area as the mechanics were still onboard the aircraft. After being cleared onboard by Maintenance; we completed our preflight preparations/verifying that the trim and main elect stab trim switch worked. We received a new Maintenance Release; completed our briefings/checklist; and shortly departed from the gate. After receiving our final weights/verifying our final speed/trim settings; the Before Take-off Checklist was called for and completed. I was pilot flying; the takeoff roll and lift-off was normal. Shortly after takeoff; as I trimmed the aircraft to relieve control forces; I experienced the pressure on my yoke to be abnormal. I immediately advised the Captain and at that point; a control swap was made and I became the pilot monitoring. After getting to a safe altitude and engaging the autopilot; the Captain and I discussed what transpired. As the Captain did not experience any abnormalities after taking control; we did not declare an emergency and decided to continue on to ZZZZ. The aircraft flew normal enroute and landed safely in ZZZZ. To confirm what I felt during takeoff; the Captain and I discussed and decided to exchange controls in level flight disconnecting the autopilot as we were given descent between 6;000 to 4;000 ft. As I pitched and trimmed the aircraft; it was apparent that the trim was reacting opposite to my intended input. Controls were then transferred back to the Captain and a maintenance message sent.
More incidents for this aircraft family
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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