NTSB Identification: CHI95IA045.
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Scheduled 14 CFR USAIR
Incident occurred Wednesday, November 23, 1994 in EVANSVILLE, IN
Probable Cause Approval Date: 05/16/1995
Aircraft: FOKKER F-28-4000, registration: N479AU
Injuries: 53 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 FLIGHT CREW REPORTED THAT WHILE DESCENDING FROM CRUISE IN PREPARATION FOR LANDING, THEY NOTICED THAT THE HORIZONTAL STABILIZER WAS NOT RESPONDING TO TRIM INPUTS. THE AUTOPILOT WAS DISENGAGED, AND BOTH NORMAL AND ALTERNATE MODES OF STABILIZER TRIM WAS ATTEMPTED WITHOUT SUCCESS. THE CREW FOLLOWED THE JAMMED STABILIZER APPROACH CHECKLIST, AND WAS ABLE TO EFFECT PITCH CHANGES BY BOTH CREW MEMBERS EXERTING FORCE ON THEIR CONTROL YOKES. POSTINCIDENT INSPECTION OF THE STABILIZER DRIVE ACTUATOR DISCOVERED NO HYDRAULIC LEAKS. THE ACTUATOR'S GEAR BOX WAS DRAINED, AND FOUND TO CONTAIN APPROXIMATELY ONE OUNCE OF MURKY, SLUDGE-LIKE HYDRAULIC FLUID. THE GEAR BOX IS REQUIRED TO BE FILLED WITH SEVEN OUNCES OF HYDRAULIC FLUID. THE ACTUATORS ARE SHIPPED FROM THE MANUFACTURER ESSENTIALLY DEVOID OF HYDRAULIC FLUID, WITH INSTRUCTIONS THAT THEY MUST BE FILLED PRIOR TO SERVICE.

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

the failure of company maintenance personnel to adequately service (fill) the horizontal stabilizer drive actuator with hydraulic fluid.

Full narrative available

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