During cruise at FL340 an Electronic Centralised Aircraft Monitor (ECAM) message STAB JAM appeared, there was a pitch excursion, the autopilot disengaged and the control law degraded to ‘Alternate Law’. The flight crew carried out the ECAM actions and the aircraft continued to its destination without further incident. The failure was probably due to water ingress into the trimmable horizontal stabiliser (THS) command transducer which migrated into the mini reduction gear, froze and damaged the gear.
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