Created Friday, Aug 11th 2023 15:47Z, last updated Friday, Aug 11th 2023 15:47Z
A Virgin Atlantic Airways Boeing 787-9, registration G-VOWS performing flight VS-206 from London Heathrow,EN (UK) to Hong Kong (China) with 235 passengers and 14 crew, was on an ILS approach to runway 25R at about 16:31L (08:31Z) when ATC cleared the flight to 4500 feet MSL and intercept the localizer. After the aircraft established on the localizer the aircraft veered to the right off the localizer and descended below minimum safe sector altitude until ATC instructed a go around. The aircraft landed safely on the second approach about 18 minutes later.
On Mar 6th 2020 Hong Kong's AAIA reported under the headline "Loss of Control - Inflight" the occurrence was rated a serious incident and opened an investigation.
According to Mode-S Data transmitted by the aircraft the aircraft passed the highest point of terrain, the peak of Tai Mo Shan at 3277 feet MSL, about 0.3nm south at about 3700 feet MSL (corrected for QNH).
There had been other similiar occurrences, see Incident: Etihad B789 at Hong Kong on Sep 7th 2019, veered off localizer and descended below safe height on ILS approach and Incident: Ethiopian B788 at Hong Kong on Jul 18th 2019, loss of control on ILS approach.
Also see the later similiar incident Incident: Virgin Atlantic B789 at Hong Kong on Oct 18th 2019, deviated from localizer and descended below minimum safe altitude, which also shows a Boeing bulletin addressing the issue.
On Aug 11th 2023 Hong Kong's AAIA released their final report into this occurrence as well as three more similiar occurrences concluding the probable cause of this serious incident was:
The LOC course deviation was caused by the software failure of the CLC autoflight function in the AFDS.
The AAIA analysed:
During the investigation of this occurrence, another operator encountered a similar occurrence on the B787 at VHHH on 7 September 2019. The flight data of this flight was sent to Boeing, the aircraft manufacture, for analysis. These two occurrences appeared to be identical and Boeing was able to determine the root cause.
Evaluation of the flight data suggested that the CLC AFF initiated the turn towards the RWY 25R LOC, as LOC annunciated the active roll mode.
After the CLC AFF had initiated the turn, the A/P transition to the LOC mode did not occur. This resulted in the aircraft HDG stabilised 20 degrees short of the LOC course and flying through the LOC course on this track, rather than properly capturing the LOC.
The recorded flight data was consistent with the LOC capture anomaly of the AFDS as described in the FTD 787-FTD-22-20001.
The LOC course deviation observed was due to the LOC capture anomaly of the AFDS.
The FTD stipulated that the issuance of a Flight Crew Operations Manual Bulletin and related FAA AD 2020-24-04, associated with the software modification released by Boeing via Alert SB B787-81205-SB270053-00 addressed this anomaly.
