What happened
On 18 October 2019, a Virgin Atlantic Airways Boeing 787-9, registration G-VBOW, was performing a scheduled passenger flight from London Heathrow to Hong Kong International Airport. While executing an Instrument Landing System (ILS) approach to Runway 25R under visual meteorological conditions, the aircraft's autoflight system intercepted the localizer at waypoint RIVER.
As the aircraft attempted to capture the centerline, it overshot the intended heading and began diverging from the localizer course toward the terrain to the north. The crew noticed the deviation and, recognizing that the aircraft was not turning onto the runway path, the pilot flying disengaged the autopilot and took manual control. The pilot successfully re-established the aircraft on the correct heading approximately 12 nautical miles from the runway threshold, and the flight landed without further incident. There were no injuries and no damage to the aircraft.
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 flight data, which showed that while the localizer pointer movement appeared slow, the aircraft's flight path deviated significantly from the centerline. The team also reviewed maintenance history and the software architecture of the flight control systems.
Findings
- The primary cause of the flight path deviation was a software problem embedded in the flight control module (FCM) of the autoflight director system.
- The aircraft's automated system failed to maintain the localizer course after interception, leading to a heading overshoot.
- No warnings from the Enhanced Ground Proximity Warning System (EGPWS) were triggered during the deviation.
- The flight crew responded appropriately by transitioning to manual flight to correct the course.