ORLANDO, FL, USA
N390US
Boeing 737-3B7
THE FLIGHT EXPERIENCED AN UNCOMMANDED ROLL TO THE LEFT DURING DESCENT FOR LANDING. THE FLIGHT CREW DISENGAGED THE AUTOPILOT AND YAW DAMPER, BUT REENGAGED THE YAW DAMPER SINCE THERE WAS NO APPARENT YAW PROBLEM. THE DESCENT WAS CONTINUED AND A LANDING WAS MADE WITHOUT FURTHER INCIDENT. EXAMINTATION REVEALED THE CONNECTOR PLUGS AND WIRING HARNESS TO THE E-1-2 AND E-1-3 SHELF DISCONNECT BRACKETS IN THE ELECTRONICS COMPARTMENT WERE CONTAMINATED WITH WATER AND A BLUE RESIDUE. THE SOURCES OF CONTAMINATION WERE WATER FROM A CURRENT MAIN CABIN DOOR LEAK AND BLUE RESIDUE FROM A PREVIOUS LEAK OF THE FORWARD LAVATORY.
On July 18, 1995, about 1630 eastern daylight time, a Boeing 737-3B7, N390US, registered to and operated by USAIR, Inc., as flight 855, a 14 CFR Part 121 scheduled domestic passenger service from Pittsburgh, Pennsylvania, to Orlando, Florida, experienced an uncontrolled roll to the left during descent for landing. Visual meteorological conditions prevailed at the time and an instrument flight rules flight plan was filed. The aircraft was not damaged and the airline transport-rated pilot, first officer, 3 flight attendants, and 115 passengers were not injured. The flight originated from Pittsburgh, on July 18, 1995, about 1504. The captain stated that about 65 nautical miles north of Ormond Beach, Florida, the flight was descending through 28,000 feet. The "A" autopilot system was on longitudinal navigation and vertical speed was selected for pitch control. The aircraft suddenly rolled hard to the left to about 25 degrees of bank angle. He overrode the roll with aileron control and returned the aircraft to wings level. The aircraft again rolled to the left and he disengaged the autopilot and yaw dampener. He reengaged the yaw dampener, left the autopilot off, and continued the flight to Orlando, without further incident. Examination of the aircraft showed the connector plugs and wiring harness to the E-1-2 and E-1-3 shelf disconnect brackets in the electronics compartment were contaminated with blue residue and water. The flight control computers and flight management computer mounts on these shelves. Evidence indicated the forward lavatory located above the electronics compartment had leaked at one time but was not currently leaking. Additionally, the main cabin door drain was found to not be properly sealed and water was leaking from the drain and dripping on to the wiring harness and migrating into the connectors. The flight control computer, and roll actuators were removed from the aircraft and tested. No failures which would cause an uncommanded roll were noted. For additional information see attached Boeing Commercial Airplane Company report, the Honeywell test report, and the FAA test report.
CONTAMINATION OF THE WIRING HARNESS AND ELECTRICAL CONNECTORS TO THE E-1-2 AND E-1-3 SHELF DISCONNECT BRACKETS IN THE ELECTRONICS COMPARTMENT, WHICH RESULTED IN AN ELECTRICAL FAULT AND AN UNCOMMANDED ROLL MALFUNCTION OF THE AUTOPILOT. A FACTOR RELATING TO THE INCIDENT WAS: INADEQUATE MAINTENANCE INSPECTION OF THE AIRCRAFT BY COMPANY MAINTENANCE PERSONNEL.
Source: NTSB Aviation Accident Database
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