Created Friday, Aug 11th 2023 15:42Z, last updated Friday, Aug 11th 2023 15:42Z
An Ethiopian Airlines Boeing 787-8, registration ET-ASG performing flight
ET-645 from Manila (Philippines) to Hong Kong (China) with 225 passengers and 10 crew, had been cleared for the ILS approach to Hong Kong's runway 25R, the aircraft was about to intercept the localizer from the south of the localizer beam. Shortly after passing the waypoint RIVER (15nm before the runway threshold), the aircraft was about 13nm short of the ruway threshold at 23:52L (15:52Z), the aircraft was observed descending through 3700 feet MSL about 1nm north of the localizer, about 0.3nm horizontally from a terrain peak rising up to 3277 feet MSL. ATC instructed the aircraft to immediately climb to 4500 feet. The aircraft subsequently performed a missed approach, positioned for another ILS approach and landed without further incident.
Hong Kong's Air Accident Investigation Authority (AAIA) rated the occurrence a serious incident and opened an investigation categorizing the occurrence a "loss of control in flight". The captain held an ATPL with type ratings on Boeing 777s and Boeing 787s and had accumulated 5,302 hours total and 3,082 hours flying experience on type. The US NTSB representing the state of aircraft design and manufacture and Ethiopia's Accident Investigation Bureau (EAIB) representing the state of registry and operation of the aircraft joined the investigation.
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.
Related Flight:
ET645,
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