ASN Wikibase Occurrence # 147083
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| Date: | Sunday 22 October 1995 |
| Time: | 16:09 UTC |
| Type: |  Boeing 737-236 |
| Owner/operator: | British Airways |
| Registration: | G-BGJI |
| MSN: | 22030/693 |
| Year of manufacture: | 1980 |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | None |
| Category: | Incident |
| Location: | 15nm NW of Bournemouth, Dorset -
 United Kingdom
|
| Phase: | En route |
| Nature: | Test |
| Departure airport: | London-Gatwick Airport (LGW) |
| London-Gatwick Airport (LGW) | |
| Investigating agency: | AAIB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The crew reported at 13:30 at Gatwick to carry out a post-heavy maintenance check, test flight on the aircraft. The first officer (F/O) completed the external check, while the commander completed the 'Flight Deck Preparation' items of the aircraft checklist. A Standby (STBY) Rudder system check was carried out with no abnormalities noted and during taxi before take-off, the Yaw Damper indicator showed normal response to turns. When the aircraft was in straight and level flight at FL200 with an indicated airspeed of 290 kt, Autopilot and Autothrottle engaged and Yaw Damper ON, the aircraft experienced roll/yaw oscillations.
The Flight Data Recorder (FDR) showed that the Autopilot and Autothrottle were disengaged, and the commander reported that the Yaw Damper was switched OFF but the crew were unable to stop the oscillations. A MAYDAY call was broadcast at 16:09. The crew had the impression that the bank angle would have continued to increase had opposite roll control inputs not been applied. A descent was made to around FL75 and as the airspeed was allowed to reduce towards 250 kt the oscillations began to decay rapidly and stopped. The total duration of the roll/yaw event was about seven minutes. A low speed handling check was carried out, and it was found that the aircraft handled well at a speed 150 kt, with Flap 15° selected and with the landing gear down.
It was decided to return to London Gatwick Airport in this configuration, and the MAYDAY was downgraded to a PAN. The crew recovered the aircraft to Gatwick without further incident.
PROBABLE CAUSE: "(i) Contamination of the connector on the Yaw Damper Coupler, in the Electronic and Equipment Bay, by an unidentified fluid had occurred at some time prior to the incident flight and compromised the function of its pin to pin insulation.; (ii) Sufficiently conductive contaminant paths between certain adjacent pins had affected the phase and magnitude of the signals transmitted to the Yaw Damper Actuator, thereby stimulating a forced Dutch Roll mode of the aircraft.; (iii) The location of the Electronic and Equipment (E&E) Bay, beneath the cabin floor in the area of the aircraft doors, galleys and toilets made it vulnerable to fluid ingress from a variety of sources.; (iv) The crew actions immediately following the onset of the Dutch Roll oscillations did not result in the disengagement of the malfunctioning Yaw Damper system."
Accident investigation:
 |
|
Sources:
1. Flight International 29.11-05.12.95(11)
2. Air Safety Week11.12.95(3)
3. AAIB Aircraft Incident Report No: 1/98 at https://assets.publishing.service.gov.uk/media/5422f507ed915d1371000555/1-1998_Boeing_737-236_Advanced_G-BGJI.pdf
4. CAA: https://siteapps.caa.co.uk/g-info/rk=BGJI
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 26-Jul-2012 07:20 | harro | Added |
| 09-Jun-2016 20:05 | Dr.John Smith | Updated [Location, Source, Narrative] |
| 09-Jun-2016 20:06 | Dr.John Smith | Updated [Narrative] |
Corrections or additions? ... Edit this accident description
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