Flight History
On 18 July 2019 at 23:51 hrs, Ethiopian Airlines flight ETH 645, a Boeing 787-8 aircraft registered as ET-ASG, was conducting a scheduled passenger service from Manila Ninoy Aquino International Airport to Hong Kong International Airport (VHHH). The aircraft was cleared by Air Traffic Control (ATC) to proceed direct to waypoint RIVER and descend to 4,500 ft for an Instrument Landing System (ILS) approach to runway 25R.
With the autoflight system engaged, the aircraft began intercepting the localizer (LOC) at waypoint RIVER, 15 nautical miles from the runway. During the left turn to intercept from the south, the aircraft overshot the LOC course and continued deviating north towards terrain. The aircraft descended below the Minimum Sector Altitude (MSA) of 4,300 ft. No Enhanced Ground Proximity Warning System (EGPWS) warnings were triggered.
The flight crew noticed the deviation, and at 23:53:02 hrs the pilot flying disengaged the autoflight system and took manual control. ATC instructed a go-around. After a second approach to the same runway, the aircraft landed without further incident. There was no damage to the aircraft and no injuries.
Cause
The investigation determined that the serious incident was caused by a software problem embedded in the flight control module (FCM) of the autoflight director system. This software issue led to the abnormal localizer capture behavior, resulting in the overshoot and deviation.
Findings
- The aircraft was properly maintained and certified.
- The flight crew were qualified and followed standard procedures.
- The ILS and navigation aids were functioning correctly.
- No weather or communication issues contributed.
- The autoflight system had a latent software defect in the consistent localizer capture logic.
Safety Actions
In response, the Civil Aviation Department of Hong Kong conducted a comprehensive check of the ILS, issued an Aeronautical Information Circular, and communicated with Boeing and the FAA. Boeing issued a Flight Crew Operations Manual Bulletin and an Alert Service Bulletin to address the software issue. Ethiopian Airlines distributed flight safety information and incorporated the service bulletin.