CHARLOTTE, NC, USA
N396US
Boeing 737-3B7
THE CAPTAIN REPORTED THAT DURING DESCENT THROUGH 12,000 FEET WITH THE 'A' SYSTEM AUTOPILOT ENGAGED AND WITH AN AIRSPEED OF 250 KNOTS, THERE WAS AN UNCOMMANDED ROLL TO THE LEFT. HE DISENGAGED THE AUTOPILOT AND ROLLED THE THE AIRPLANE TO WINGS LEVEL FLIGHT, THEN CONTINUED THE FLIGHT WITH THE AUTOPILOT OFF. POSTINCIDENT EXAMINATION OF THE AIRCRAFT REVEALED AN INTERMITTENT ELECTRICAL CONNECTION IN AN 'A' AUTOPILOT CIRCUIT, DUE TO PIN CONNECTOR(S) BEING PUSHED OUT OF PLACE ON THE FLIGHT CONTROL COMPUTER SHELF CONNECTOR. ONE OF THE PINS WAS IN THE AILERON POSITION SENSOR EXCITATION CIRCUIT. THE 'A' FLIGHT CONTROL COMPUTER HAD BEEN REMOVED AND REINSTALLED THE DAY BEFORE THE INCIDENT TO INSPECT THE RACK FOR FLUID CONTAMINATION.
On August 5, 1995, about 1000 eastern daylight time, a Boeing 737-3B7, N396US, operated by USAir, Inc., as flight 7, a 14 CFR Part 121 domestic passenger flight from Albany, New York, to Charlotte, North Carolina, had an uncommanded roll to the left while descending to land at Charlotte. 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 78 passengers were not injured. The flight originated from Albany, New York, on August 5, 1995, about 0833. The captain stated that during descent through 12,000 feet at 250 knots airspeed, the "A" autopilot system was on LNAV and level change. The aircraft shuttered and then rolled to the left to a 30-degree bank angle. He disengaged the autopilot and rolled the aircraft level. The flight was continued with the autopilot off. Postincident investigation revealed the "LO" side of the roll sensor excitation from the "A" autopilot system flight control computer (FCC) to the "A" aileron autopilot actuator LVDT and "A" airleron postion sensor was intermittently open due to a socket pushed out of the locked position in the connector. Intermittent contact of this socket with its pin in the connector could cause airplane roll oscillations. The "A" system FCC had been removed and reinstalled the day before the incident to inspect the connectors for contamination. See attached Boeing Commercial Airplane Company report.
IMPROPER INSTALLATION OF THE 'A' SYSTEM FLIGHT CONTROL COMPUTER BY COMPANY MAINTENANCE PERSONNEL, WHICH RESULTED IN PIN CONNECTOR(S) BEING PUSHED LOOSE AND SUBSEQUENT MALFUNCTION OF THE AUTOPILOT.
Source: NTSB Aviation Accident Database
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