Created Friday, Aug 11th 2023 15:46Z, last updated Friday, Aug 11th 2023 15:46Z
An Etihad Boeing 787-9, registration A6-BLF performing flight EY-834 from Abu Dhabi (United Arab Emirates) to Hong Kong (China) with 168 passengers and 11 crew, was intercepting Hong Kong's localizer 25R in a left turn about 15nm before the runway threshold at 10:41L (02:41Z) when the aircraft deviated to the right of the localizer and descended below Minimum Sector Altitude of 4300 feet MSL. The aircraft subsequently corrected and joined the localizer about 11mn before the runway threshold and continued for a landing on runway 25R without further incident.
Hong Kong's AAIA reported on Mar 4th 2020 under the headline "Loss of Control - Inflight", that the occurrence was rated a serious incident and is being investigated by the AAIA. The UAE GCAA as well as the US NTSB have been notified on Sep 20th 2019 after the AAIA got notice of the occurrence on Sep 9th 2019. The AAIA anticipates the investigation will last 12 months.
A similiar occurrence had happened in July 2019, see 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.
