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| Title: | Uncommanded roll and yaw, Douglas DC-9-34, April 30, 1998 |
| Micro summary: | This Douglas DC-9-34 experienced unusual yaw and roll behavior after takeoff. |
| Event Time: | 1998-04-30 at 1040 CDT |
| File Name: | 1998-04-30-US.pdf |
| Publishing Agency: | National Transportation Safety Board (NTSB) |
| Publishing Country: | USA |
| Report number: | CHI98IA169 |
| Pages: | 5 |
| Diversion Airport: | Lambert Saint Louis International Airport, St. Louis, Missouri, USA |
| Site of event: | St. Louis, MO |
| Departure: | Lambert Saint Louis International Airport, St. Louis, Missouri, USA |
| Destination: | Toronto/Lester B. Pearson International Airport, Mississauga, Ontario, Canada |
| Airplane Type(s): | Douglas DC-9-34 |
| Flight Phase: | Takeoff |
| Registration(s): | N928L |
| Operator(s): | Trans World Airlines |
| Type of flight: | Revenue |
| Occupants: | 44 |
| Fatalities: | 0 |
| Serious Injuries: | 0 |
| Minor/Non-Injured: | 44 |
| Other Injuries: | 0 |
| Diverted to: | Lambert Saint Louis International Airport, St. Louis, Missouri, USA |
| Executive Summary: | NTSB short summary: the yaw rate gyro of the Stab Aug Computer had been installed in a reverse position that was 180 degrees opposite from the correct position. NTSB synopsis: The flight experienced a flight control malfunction after takeoff. The flight declared an emergency and returned to the airport safely with no damage to the aircraft or injuries to the crew or passengers. The Captain stated: 'After takeoff the aircraft began to yaw and roll in a cyclic fashion left and right. I switched the yaw damper off and on to ensure that the yaw damper was on. Yaw and roll continued and appeared to increase in its yaw amplitude as the airspeed increased... I declared an 'Emergency' and requested an immediate return for a landing with the emergency equipment standing by... The landing was made in a normal fashion without damage to the aircraft or injury to anyone on board. Total air time was 6 minutes.' The Stability Augmentation Computer, Part 2587826-3, S/N 0270890 was inspected at the TWA Maintenance Facility. The inspection determined that the yaw rate gyro of the Stab Aug Computer had been installed in a reverse position that was 180 degrees opposite from the correct position. NTSB factual narrative text: On April 30, 1998, at 1040 cdt, N928L, a McDonnell Douglas DC9-34, being operated as Trans World Airlines flight number 732, from Saint Louis, Missouri to Toronto, Canada, experienced a flight control malfunction after takeoff. The flight declared an emergency and returned to Saint Louis. There was no damage to the aircraft and there were no injuries to the crew of 5 or 39 passengers. The flight was on an IFR flight plan and visual meteorological conditions prevailed. The Captain's report states: "After takeoff the aircraft began to yaw and roll in a cyclic fashion left and right. I switched the yaw damper off and on to ensure that the yaw damper was on. Yaw and roll continued and appeared to increase in its yaw amplitude as the airspeed increased... I declared an 'Emergency' and requested an immediate return for a landing with the emergency equipment standing by... The landing was made in a normal fashion without damage to the aircraft or injury to anyone on board. Total air time was 6 minutes." The Captain's full statement is an attachment to this factual report. The aircraft was a DC-9-34, S/N 48124. The Stability Augmentation Computer, Part 2587826-3, S/N 0270890 was inspected at the TWA Maintenance Facility in Kansas City, Kansas on May 27, 1998. Present at the inspection were personnel from TWA, FAA, NTSB, and Honeywell. See attached "Inspection Sign in Sheet". The inspection determined that the yaw rate gyro of the Stab Aug Computer had been installed in a reverse position that was 180 degrees opposite from the correct position. It was further determined that there is a correct "red alignment mark" and the gyro was not aligned with the red mark. There is a keyway; however, in this circumstance the pin was flush allowing the gyro to be installed in an incorrect manner. |
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