What happened
On the night of April 11, 2018, a Thai Airways International Boeing 747-400, registered HS-TGX, was performing a scheduled arrival at Tokyo International Airport. While executing a circling approach to Runway 16L, the aircraft descended to an altitude of approximately 304 feet, triggering a "TOO LOW TERRAIN" warning from the Enhanced Ground Proximity Warning System (EGPWS).
At approximately 23:52 JST, Tokyo Tower alerted the crew that their altitude was too low and queried if the runway was in sight. After the pilot confirmed the runway was not visible, the crew immediately initiated an emergency go-around to prevent a collision with the ground. The aircraft reached a minimum altitude of 282 feet during the maneuver. Following the emergency operation, the crew requested a new approach for Runway 22 and landed safely at 00:04 the following day. There were 384 people on board, including 365 passengers, and no injuries or aircraft damage were reported.
The investigation
The Japan Transport Safety Board (JTSB) examined flight data from the Quick Access Recorder (QAR) and EGPWS, as well as air traffic control communications and crew interviews. The investigation focused on the flight path during the VOR A approach and the crew's monitoring of the aircraft's descent. Investigators also reviewed the terrain database of the aircraft's EGPWS and the clarity of the airport's noise abatement flight course charts.
Findings
- The pilot in command (PIC) was focused on adjusting the lateral flight path and continued the descent without sufficient attention to the vertical path.
- The first officer (FO) failed to notice the dangerously low descent rate because his attention was concentrated on monitoring the lateral course.
- The aircraft's descent path became too low due to a lack of coordinated monitoring between the pilot flying and the pilot monitoring.
- Visual identification of the runway was hindered because the approach lights were obscured by the lights of nearby container piers and local town lighting.
- The EGPWS terrain database had not been updated to a version containing recent man-made object information, which might have provided an earlier obstacle warning regarding a nearby wind power plant.
Safety action
Following the incident, Thai Airways implemented several safety improvements, including upgrading the aerodrome qualification requirements for crew members and providing specialized simulator training for the VOR A approach. The company also updated the EGPWS terrain databases for its fleet operating in Japan and requested FMS navigation data updates to better facilitate the noise abatement flight course. Additionally, the Civil Aviation Bureau of Japan amended the airport's aeronautical information to provide clearer details regarding the noise abatement flight path.