ASN Wikibase Occurrence # 234492
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| Date: | Sunday 29 September 2019 |
| Time: | 08:31 UTC |
| Type: |  Boeing 787-9 Dreamliner |
| Owner/operator: | Virgin Atlantic Airways |
| Registration: | G-VOWS |
| MSN: | 37974/373 |
| Year of manufacture: | 2015 |
| Fatalities: | Fatalities: 0 / Occupants: 249 |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | Hong Kong -
 Hong Kong
|
| Phase: | Approach |
| Nature: | Passenger - Scheduled |
| Departure airport: | London-Heathrow Airport (LHR/EGLL) |
| Hong Kong-Chek Lap Kok International Airport (HKG/VHHH) | |
| Investigating agency: | AAIA |
| Confidence Rating: |  Accident investigation report completed and information captured |
Flight VS206 was on intermediate approach near position RIVER and established on the localizer of runway 25R, descending to 4,500ft, when it deviated significantly to the right of the extended runway track. It therefore proceeded below the applicable MSA before ATC instructed the flight to go-around. Subsequent approach to the same runway was uneventful.
Within a few weeks similar incidents occured, to another Virgin flight, Etihad and Ethiopian Airlines. All incidents occured at approximately the same position and were of the same aircraft type.
The investigation team found that this serious incident was caused by a software problem embedded in the flight control module (FCM) of the autoflight director system (AFDS).
The Boeing 787 Autoflight Function (AFF) contains a Consistent Localizer Capture (CLC) control law that reduces the risk of Localizer (LOC) course overshoot in autopilot-engaged approaches that requires a large turn (40 degrees) onto the LOC course.
CLC provides the Boeing 787 with ILS performance consistent with a Ground-Based Augmentation System (GBAS) Landing System (GLS) approach. Using Global Positioning System (GPS) and runway information from the flight management function. CLC will turn the aircraft towards the LOC course before the LOC is within parameters for capture. In order to maximize the chance of capturing the LOC in one turn. “LOC” will annunciate on the FMA when a CLC turn begins and remain annunicated through the transition to LOC capture. Normally, CLC will automatically transition to the LOC capture control law when the LOC is within parameters to capture and “LOC” will continue to be visible on the FMA.
However, depending on the geometry and groundspeed of the approach, CLC may activate for such a short time that the three FCMs fail to synchronize the engaged autopilot mode and fail to transition to the LOC capture mode. This may result in the aircraft turning to a LOC intercept angle of approximately 20 degrees and flying through the LOC on this track, rather than properly capturing the LOC.
“LOC” will remain on the FMA despite the failed capture and, in some circumstances, the aircraft may begin descent down the glideslope while 20 degrees off of the LOC course.
Cause
The LOC course deviation was caused by the software failure of the CLC auto-flight function in the AFDS.
Accident investigation:
 |
|
Sources:
reports of similar occurrences:
https://www.thb.gov.hk/aaia/eng/investigation_reports/index.htm
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 29-Mar-2020 06:44 | Edwin | Added |
| 29-Mar-2020 06:48 | harro | Updated [Source] |
| 19-Aug-2023 09:23 | harro | Updated [[Source]] |
Corrections or additions? ... Edit this accident description
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