Event Details

Title:Uncommanded roll to the left, Boeing 737-3B7, August 5, 1995
Micro summary:Uncommanded roll to the left during descent for this Boeing 737-3B7.
Event Time:1995-08-05 at 1000 EDT
File Name:1995-08-05-US.pdf
Publishing Agency:National Transportation Safety Board (NTSB)
Publishing Country:USA
Report number:MIA95IA194
Site of event:Charlotte, NC
Departure:Albany International Airport, Albany, New York, USA
Destination:Charlotte/Douglas International Airport, Charlotte, North Carolina, USA
Airplane Type(s):Boeing 737-3B7
Flight Phase:Descent
Type of flight:Revenue
Serious Injuries:0
Other Injuries:0
Executive Summary:

NTSB short summary:

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.

NTSB synopsis:

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.

NTSB factual narrative text:

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.
Learning Keywords:Operations - Maintenance
Operations - Upset - Uncommanded or excessive Roll
Systems - Flight Control System
Close match:Uncommanded roll, Serious incident on March 20, 2001 at Frankfurt/Main, to Airbus Industrie A320-200
Excessive right aileron required on Boeing 737-400, EI-BXB, at Dublin Airport
Uncommanded roll, Boeing 737-236 Advanced, G-BGJI
Flight control system failure, Report on the incident to Airbus A320-212, G-KMAM, London Gatwick Airport, on 26 August 1993
Aileron control cable failure on a Boeing 737-3TO on takeoff at Seattle, September 27, 1997
Uncommanded roll, Douglas DC-8-71F, December 14, 2001
Uncommanded roll, McDonnell Douglas DC-9-15, July 12, 1997
Uncommanded roll during cruise, Airbus A320-211, April 28, 1995
Uncommanded roll and yaw, Douglas DC-9-34, April 30, 1998
Control difficulties, McDonnell Douglas MD-11, October 21, 1998
Reduced roll capability, Boeing 747-422, April 1, 2003
Roll control difficulties, McDonnell Douglas MD-11F, N583FE, January 15, 2003


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