What happened
On 29 September 2019, a Virgin Atlantic Airways Boeing 787-9, registration G-VOWS, was conducting a scheduled passenger flight from London Heathrow to Hong Kong International Airport. While performing an Instrument Landing System (ILS) approach to Runway 25R, the aircraft encountered a significant deviation from its intended path.
As the aircraft attempted to intercept the localizer course at waypoint RIVER, the autoflight system failed to maintain the correct track. The aircraft overshot the localizer and drifted north toward higher terrain. During this deviation, the aircraft descended below the Minimum Sector Altitude of 4,300 feet. The flight crew identified the error and prepared for a missed approach, and Air Traffic Control subsequently instructed a go-around. No injuries were reported among the 235 passengers or 14 crew members, and the aircraft sustained no damage.
The investigation
The investigation examined the performance of the Autopilot Flight Director System (AFDS) and the behavior of the aircraft during the localizer capture phase. Investigators analyzed the flight data and the flight control electronics to determine why the aircraft failed to maintain the localizer course.
Findings
- The primary cause of the deviation was a software problem embedded in the flight control module (FCM) of the autoflight director system.
- The aircraft overshot the localizer course and drifted toward terrain while the autoflight system was engaged.
- The aircraft descended below the established Minimum Sector Altitude.
- No Enhanced Ground Proximity Warning System (EGPWS) alerts were triggered during the event.
Safety action
Following the investigation, several proactive measures were implemented by various aviation authorities and the manufacturer:
- Boeing updated the Aircraft Flight Manual (AFM) operating instructions and issued Alert Service Bulletins for the installation of updated software (FCE CBP 5.1) to resolve localizer capture anomalies.
- The Federal Aviation Administration (FAA) issued an Airworthiness Directive to mandate these manual changes.
- The Civil Aviation Department (CAD) of Hong Kong issued aeronautical information circulars and notices to airmen regarding the incident.
- Virgin Atlantic Airways issued notices to aircrew and incorporated the necessary service bulletins into their maintenance programs.