By Simon Hradecky, created Tuesday, Apr 17th 2018 16:18Z, last updated Friday, Jul 31st 2020 16:20Z

A Thai International Airlines Boeing 747-400, registration HS-TGX performing flight TG-660 from Bangkok (Thailand) to Tokyo Haneda (Japan), was on a VOR/DME approach to Haneda's runway 16L when the GPWS activated at about 550 feet AGL while the aircraft was still tracking the VOR radial. The crew initiated an evasive maneouver in compliance with the GPWS alert, repositioned for another approach and landed safely on Haneda's runway 22 about 12 minutes after the GPWS alert.

Japan's TSB opened an investigation into the occurrence rated a serious incident.

On Jul 31st 2020 the JTSB released their final report concluding the probable causes of the serious incident were:

In this serious incident, it is probable that the Aircraft maneuvered an emergency operation to avoid crash into the ground because it came close to the ground surface in approach to Runway 16L at Tokyo International Airport.

It is probable that coming close to the ground was caused by the PICs concentration on modifying the lateral flight path, continuing descent without paying an appropriate attention to the descent path, and by the first officers unawareness of the too low descent path due to his concentration on monitoring the lateral flight path.


The JTSB reported the captain (39, ATPL, 10,746 hours total, 8,342 hours on type) was pilot flying, the first officer (33, ATPL, 4,007 hours total, 3,588 hours on type) was pilot monitoring.

The JTSB described the sequence of events:

The flight was smooth at take-off and in cruising. The FO attempted to reset FMS to approach the Airport in accordance with the instruction from the PIC after receiving ATIS B of the Airport; however, VOR A approach was not registered in FMS navigation data base. In dealing with that, after inputting DARKS ARRIVAL, the FO inputted SAZAN after DARKS, which was the final point of DARKS ARRIVAL and then created a FIX at a point 1 nm from Runway 16L threshold on the final leg to make them references course.

While flying over the final approach path (from DARKS to SAZAN), the FO offered the PIC that the FO would assist the PIC in finding the approach guidance lights, which were difficult to visually recognize from the left pilots seat of the PIC.

Asked by the PIC whether the FO could visually recognize the approach guidance lights ahead on the right when the Aircraft entered the down-wind leg while turning to the right after passing over SAZAN, the FO shifted his eyes from instrument monitors inside the aircraft to the outside, and he could not confirm the lights ahead on the right. However, the FO became aware that the width of down-wind leg was wide because he confirmed the lights that appeared to be the approach guidance lights ahead on the left. the FO advised the PIC that the lights should have been seen on the right side under ordinary circumstances, and shifted his eyes to the inside of the aircraft again to perform instrument monitoring. The PIC commenced base turn with turning left in an attempt to fly inside the designated flight course.

The FO performed call-out procedures in accordance with stipulations pertinent to stabilized approach when passing over 500 ft AFE. the FO called out 500 ft, STABILIZED because he could always visually recognize runway.

Then, while the FO was monitoring the flight path on the navigation display (hereinafter referred to as ND), the PIC attempted to intercept the point of 1 nm from Runway 16L threshold on the final leg; however, there was not enough airspace to allow the flight path to be modified because the Aircraft entered the inside excessively. Therefore, the FO pointed out to the PIC that it would be difficult to intercept the point.

At that time, there was advice from Tokyo Tower saying, Your altitude is too low, confirm, do you have Runway 16L insight? The PIC seemed to be concentrating on flying inside the designated flight course and modifying the course, and upon receipt of the advice, he commenced to search for Runway 16L. However, it seemed that the sight of Runway 16L was blocked by the container piers ahead on the left and the PIC could not visually recognize them.

When the PIC said, Negative, and the FO reported it to Tokyo Tower, EGPWS caution TOO LOW TERRAIN was enunciated, and the PIC executed a go-around.

The FO had experienced landing at the Airport; however, this was his first time VOR A approach, and he had not received simulator training.


The JTSB analysed:

It is highly probable that approach guidance lights ((1) in Appended Figure 1), which were thought to be ahead on the right of the Aircraft, was actually located ahead on the left due to the widened width of the down-wind leg as described in 3.4.4. Because of that, as described in 2.1.2 (1) and (2), it is probable that the PIC and the FO became aware, by seeing approach guidance lights ahead on the left ((1) in Appended Figure 1), that the Aircraft was flying outside the noise abatement flight course described in 2.8.3, and the PIC commenced the left turn as the base turn in an attempt to fly inside the noise abatement flight course.

Besides, as described in 2.1.2 (1) and as shown in Appended Figure 1, the PIC entered the down-wind leg and commenced the final descent for landing using VS mode of AP at 23:50:12. The position of the Aircraft at that time was 4.6 nm away in direct distance from the point of 1 nm short of 16L. So,it is highly probable that the timing to commence descending was too early. It is somewhat likely that this was due to that the final descent for landing commenced by the PICs guess without a clear picture for descent plan because of the wider width of the down-wind leg than he originally planned. OM of the Company pertinent to circling approach described in 2.10.2 (1) stipulates The final descent shall be started no earlier than where it fits into a normal approach angle. Although an accurate comparison cannot be made due to difference in actual flight course and noise abatement flight course, it is probable that an altitude of 1,100 ft should have been maintained in the downwind leg flight in order to land on Runway 16L at normal descent angle (3 o) as described in 2.11.

Besides, the PIC kept VS mode of AP after commencing descent until go-around; however, in view of FCTM pertinent to circling approach described in 2.10.2 (2), it is probable that the PIC should have disengaged AP and disconnected autothrottle at the time of commencing the final descent for landing.

In view of the limitations pertinent to the use of AP stipulated in FCOM in 2.10.5, it is highly probable that the PIC should have disengaged AP before reaching an altitude of 710 ft at the latest, more than 50 ft below MDA, followed by manual operation during the descent. It is highly probable that the FO should have advised the PIC to disengage AP when reaching the altitude through monitoring the altitude of the Aircraft.

As described in 2.1.2 (1) and (2), the PIC and the FO performed call-out procedures when reached 500 ft AFE in accordance with OM of the Company pertinent to stabilized approach described in 2.10.3. The PIC and the FO continued approaching because the Aircraft was in landing configuration at an appropriate speed and a descent rate, and Runway 16L was always visually recognizable; however, as shown in Appended Figure 1, the distance from the point where the Aircraft reached 500 ft AFE to the touchdown point on Runway 16L was as far away as 3.2 nm in direct distance (depression angle of 1.5 o), and accordingly, it is highly probable that Runway 16L was seen at a fairly shallow angle from the cockpit. It is probable that the Aircraft could have executed a go-around by judging that it deviated the stabilized approach criteria described in 2.10.3 at the point of reaching 500 ft AFE if the PIC and the FO recognized at that time that the descent path for landing on Runway 16L was too low to be appropriate.

As described in 2.1.2 (2), it is probable that the PIC concentrated on flying inside the noise abatement flight course and letting the Aircraft to fit into the final leg of Runway 16L, and continued descent changing the setting of AP descent rate between 200 and 500 fpm without paying an appropriate caution for the actual descent path. It is probable that this caused an excessive descent rate of the Aircraft leading to deviate from desirable flight path.

Furthermore, it is probable that the PIC temporarily became less attentive to visual recognition of Runway 16L from the time of passing over 500 ft AFE until he was advised by Tokyo Tower, Your altitude is too low, confirm, do you have. Runway 16L insight? because he was concentrating on modifying lateral flight path. Refering to OM of the Company pertinent to circling approach described in 2.10 (1), it is probable that the PIC should have grasped the positional relation with runway and the flight path of his own aircraft in circling approach by keeping visually recognizing Runway 16L or approach guidance lights used for landing throughout the entire path.

As described in 2.1.2 (2), the FO monitored on ND and pointed out to the PIC the lateral flight path of the Aircraft in the horizontal direction; however, it is probable that the FO was not aware that the descent path was too low because he was concentrating on monitoring the lateral flight path.

As stipulated in OM of the Company pertinent to task sharing described in 2.10.4, it is probable that the FO should have given the PIC as PF necessary advice by correctly grasping the flight path of his own aircraft through monitoring all instruments based on the recognition of his roles as PM.

As described in 2.1.2 (1) and (2), when advised by Tokyo Tower, Your altitude is too low, confirm, do you have Runway 16L insight? it is probable that the PIC was unable to grasp the position of Runway 16L because approach light beacon ((4) in Appended Figure 1) was not visually recognizable due to its mixing with the lights of the container piers ((5) in Appended Figure 1) located ahead on the left and the lights of the town.

It is probable that, immediately after the PIC told the FO, Negative and the FO conveyed it to Tokyo Tower, EGPWS caution TOO LOW TERRAIN was enunciated, and the PIC judged that the Aircraft came too close to the ground surface and instantaneously executed a go-around to avoid collision with it in accordance with OM of the Company described in 2.12.2.


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