NTSB Identification: CHI93IA078.
The docket is stored on NTSB microfiche number 52814.
Scheduled 14 CFR operation of USAIR (D.B.A. operation of USAIR )
Incident occurred Tuesday, January 26, 1993 in DETROIT, MI
Probable Cause Approval Date: 08/26/1994
Aircraft: FOKKER F-28 MK 1000, registration: N452US
Injuries: 42 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

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.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

IMPROPER LUBRICATION OF THE HORIZONTAL STABILIZER GEARBOX BY COMPANY MAINTENANCE PERSONNEL. A FACTOR WAS THE MANUFACTURER'S INADEQUATE SERVICE PROCEDURE.

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