Primary finding
Probable cause
Improper lubrication of the horizontal stabilizer gearbox by company maintenance personnel. A factor was the manufacturer's inadequate service procedure.
Investigator assessment
Analysis narrative
The captain obtained no response to nose-up stabilizer trim during descent. Normal nose-down trim remained operable; alternate trim was not attempted. The crew reported a jammed stabilizer and landed with nose-down trim. Disassembly of the horizontal stabilizer control unit showed inadequate lubricant and extensive corrosion in a gearbox. The airframe manufacturer's procedure for replenishing the gearbox lubricant could result in underservicing. The operator observed a gearbox service interval which was 250% of the manufacturer's recommendation.
Source record
Factual narrative
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