ASN Wikibase Occurrence # 240766
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| Date: | Saturday 30 December 2017 |
| Time: | 12:27 LT |
| Type: |  Airbus A320-232 |
| Owner/operator: | British Airways |
| Registration: | G-EUUW |
| MSN: | 3499 |
| Year of manufacture: | 2008 |
| Engine model: | IAE V2527-A5 |
| Fatalities: | Fatalities: 0 / Occupants: 148 |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | 20 NM northwest of Geneva Airport (LSGG) -
 Switzerland
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | London-Heathrow Airport (LHR/EGLL) |
| Genève-Cointrin Airport (GVA/LSGG) | |
| Investigating agency: | STSB |
| Confidence Rating: |  Information verified through data from accident investigation authorities |
British Airways Flight BA728 was descending towards Geneva, Switzerland when it encountered an area with turbulence, causing severe vibrations. At 12:27 local time, while crossing FL174 with an airspeed of 229 kt, the active Autopilot (AP) 2, Autothrust (A/THR) and both Flight Directors (FD) disengaged, and the fly-by-wire flight control system reverted to alternate law. The AP disconnection master warning was triggered, and the AUTO FLT YAW DAMPER SYS amber caution was displayed on the ECAM.
The flight crew informed ATC that they had some flight control problems and that they requested radar vectors but did not want to start the approach yet.
At 12:33 the flight requested to stay under radar vectoring and to maintain FL 110.
In the meantime the flight crew had started the checklist related to the ECAM message and the Flight Augmentation Computer 1 (FAC 1) was successfully reset at 12:35. Following the successful reset, normal law was recovered, and the flight crew regained A/THR and Flight Director 1 (FD1) but neither AP 1 nor AP 2 were available. In addition, the ECAM E/WD AUTO FLT YAW DAMPER SYS amber caution was replaced by the AUTO FLT YAW DAMP 2 amber caution.
The flight crew made a Pan-Pan call to ATC, stating "flight control system failures". The aircraft continued to hold as the pilots attempted to re-engage AP1.
At 12:51 the flight crew reported "ready for approach". The flight was ATCO vectored for an ILS approach to runway 23. After an ILS approach flown manually, the aircraft touched down at 13:05.
Conclusions
As flight BA728 was passing through a turbulent layer in icing conditions during descent to Geneva Airport, both FACs of the Airbus A320 simultaneously rejected all 3 IRs due to a significant lateral body acceleration, leading to the loss of the yaw damper function. As a consequence, the active Autopilot, Autothrust (A/THR) and both Flight Directors (FD) disengaged, and the flight controls reverted to alternate law.
The flight crew successfully reset FAC 1 which led to the recovery of one yaw damper, normal law, A/THR and FD 1. Since the FAC 2 was not reset, the landing capability of the aircraft remained limited to CAT 1 without AP and the subsequent ILS approach was flown manually with the A/THR engaged. There is no evidence showing that the resetting of FAC 2 would not have been successful. Such a reset would have enabled the flight crew to re-engage AP 1 and/or 2 and hence would have offered the option of an automatic landing, as required in low visibility conditions, for example.
However, the investigation also showed that it is generally not known by the pilots and not mentioned in the FCOM that in all cases the FMGC needs at least 2 IRs valid and consistent in each of the FACs to enable the re-engagement of one or both Autopilots. This means that if there is an AUTO FLT YAW DAMPER 1(2) fault due to 2 IRs rejections in one or both FACs, the APs are not available unless both FACs are reset. This is inconsistent with the status page that suggests the AP availability on the non-affected side.
Accident investigation:
 |
|
Sources:
STSB
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 01-Sep-2020 12:12 | harro | Added |
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