Boeing 747-338, VH-EBW (QF16)

QFI6, a Boeing 747, had departed Bangkok for Melbourne and was tracking southbound on airway G463 at flight level (FL) 290. The aircraft was in contact with Bangkok Area Control Centre (BKK ACC) Sector 3 on 135.5 MHz. Sector 3 was a combined radar and procedural control sector. At 0212:54 QF16 reported passing ALGOR at FL290, estimating KABAS, the flight information region (FIR) boundary, at 0221. Just prior to reaching KABAS, the aircraft would pass the intersection of G463 and B219 at KATKI. These positions were all located beyond radar coverage, over international waters, within the procedural control portion of BKK ACC Sector 3 airspace.

A Korean registered Boeing 747, KAL362, had departed Kuala Lumpur for Seoul, tracking via B219 at FL270. Approaching KANTO, located to the west of KATKI, the aircraft was transferred to the BKK ACC. The crew of KAL362 contacted Bangkok Sector 3 on 135.5 MHz and reported passing KANTO at FL270, estimating KATKI at 0219, and requesting climb to FL290. The next reporting position was SINMA, to the east of KATKI. At 0217:20 Bangkok Sector 3 cleared KAL362 to climb to FL290. KAL362 reported leaving FL270 for FL290. At 0220:21 the pilot in command of QF16 advised the Sector 3 controller of having received a traffic alert and collision avoidance system (TCAS) traffic advisory (TA), and that the aircraft had been climbed to FL300 to avoid a collision with KAL362, but was now descending to FL290.

The crew of QF16 had received a TCAS TA, followed by a resolution advisory (RA) commanding a climb to avoid climbing traffic some 800 ft below. Each crew sighted the other aircraft. The KAL362 crew also received a TCAS TA, followed by a TCAS RA commanding a descent. The crew of KAL362 did not report a traffic confliction.

An investigation carried out by Aeronautical Radio of Thailand Ltd, the Thai air traffic control organisation, indicated that KAL362 was incorrectly given a clearance to climb to FL290 by the Bangkok Sector 3 controller, and that the crews of both QF16 and KAL362 were acting in accordance with the clearances issued to them. The minimum required distance between the aircraft was 1,000 ft vertical separation, or a lateral separation of not less than 15 minutes between their estimated times of arrival at KATKI, the intersection of their intended flight routes.

In accordance with ICAO Aircraft Accident and Incident Investigation Annex 13, paragraph 5.3, the circumstances of this occurrence provide for the State of Registry to institute and conduct any necessary investigation. After consultation with the Korean authorities it was agreed that BASI would take responsibility for the ongoing investigation.

The procedural controller was responsible for issuing clearances to aircraft under procedural control, as was the case in this event. The role of the radar controller was to pass on the clearance to the aircraft. By not consulting with the procedural controller, the radar controller bypassed the established system of control, leading to a breakdown in safety.

The configuration of the Sector 3 console provided insufficient space to adequately display all relevant flight progress strips. As a result, controllers had developed the habit of removing strips at the earliest opportunity, thereby creating the potential for vital information to be missed.

The KANTO flight progress strip for KAL362 should have been retained on the procedural board until the crew reported at SINMA, the next position. The removal of the KANTO strip by the radar controller removed the only reminder available to all controllers that the intended tracks of KAL362 and QFI6 would cross.

Inclusion of the KATKI position on all flight progress strips for aircraft using the intersecting routes would have enabled controllers to more readily assess separation requirements in the procedural airspace. If the strips had required the KATKI position it is probable that the details for QFI6 and KAL362 would have been displayed under the same designator on the board, allowing controllers to recognise the potential conflict.

The inability to monitor the control frequency while conducting coordination reduced the likelihood of the procedural controller maintaining a complete appreciation of the disposition of traffic.

The reason why the crew of QFI6 did not hear the transmissions regarding KAL362 climbing to the same level, while operating on the same frequency within direct line of sight, could not be determined.

The design of the Sector 3 console did not allow for all relevant flight progress strips to be displayed.
The radar controller removed the KANTO flight progress strip after the KAL362 crew reported at that position.
The procedural controller did not hear the request for climb to FL290 by the crew of KAL362.
There was no requirement for the display of KATKI on flight progress strips for all aircraft using the intersecting routes.
The radar controller did not consult with the procedural controller prior to instructing the crew of KAL362 to climb to FL290.
The radar controller did not ensure that vertical separation was maintained between KAL362 and QF16 while the aircraft were in an area of conflict
The crew of QF16 did not hear the request and subsequent approval for KAL362 to climb to FL290.

Air Traffic Control services

Sector 3 was responsible for the provision of air traffic control in that part of the Bangkok FIR to the south of Bangkok, and for associated portions of the Phnom Penh and Ho Chi Minh FIR'S. The Sector 3 console had three positions: a radar control position with a radar display located on the left, a procedural control position in the centre, and a radar assistant position on the right. The radar controller was responsible for separating all aircraft in the sector. This included aircraft outside radar coverage. The Sector 3 procedural controller was responsible for issuing clearances using procedural control, and assisting the radar controller with flight progress strip (FPS) marking and coordination. The procedural controller was required to notify the radar controller of any changes that would affect procedural separation.

The radar controller was the only position with facilities to transmit and receive on the control frequency of 135.5 MHz. The procedural controller could monitor the frequency, but required the radar controller to transmit control instructions to aircraft operating under procedural control.

The console had been originally designed for operations utilising a flight data processor for aircraft flight information, without the need for flight progress strips. As a result, the radar operator and assistant radar positions were not fitted with flight progress strip bays. The flight data processor had subsequently proved to be less effective than planned and the sector had reverted to using flight progress strips. This required the radar and the radar assistant consoles to be fitted with temporary strip holders.

A high level of interaction and cooperation was required between the radar and procedural controllers to effectively manage the sector's airspace. The flight progress strips for each aircraft were required to be retained in the procedural display until the crew reported at the next position. This was to enable controllers to observe that an aircraft was in transit between the previous and next positions. However, due to limited space to display the strips, the Sector controllers had developed a habit of removing flight progress strips at the earliest opportunity to make space for new strips.

The strip for QFI6, annotated for the portion of the route from ALGOR to KABAS, did not include an estimate for KATKI. There were two strips for KAL362: one annotated for the portion of the route before KANTO, and one for KANTO to SINMA. The KANTO strip for KAL362 was located in the same bay as the KABAS strip for QF16. The radar controller removed the KAL362 KANTO strip from the bay after the crew reported at that position, prior to the SINMA position.

When the crew of KAL362 requested climb from FL270 to FL290, the radar controller scanned the flight progress strips at the procedural position. There was a SINMA strip for KAL362, but no other strip to indicate a possible conflict. SINMA was located east of the route of QF16. The procedural controller was carrying out coordination duties at the time, and did not hear the climb request. The radar controller then issued a clearance for the crew of KAL362 to climb to FL290, without consulting with the procedural controller.

Crew awareness

The crew of QFI6 were using the same control frequency as KAL362 when the crew of that aircraft reported at KANTO, and were subsequently approved to climb to FL290. There were reports of radio interference on that frequency, including reports of interference from aircraft operating at lower levels. The crew of QF16 did not recall hearing the crew of KAL362 request climb to FL290, nor the amended clearance and readback.

Local safety action

As a result of their investigation into the occurrence, Aeronautical Radio of Thailand Ltd has proposed to:

Issue a local instruction to prevent controllers approving climb and descent for aircraft operating in the area adjacent to the FIR boundary, or in those areas where crews of aircraft conduct frequency changes.
Issue a local instruction requiring the inclusion of the KATKI position on flight progress strips for all aircraft using the intersecting routes.
Amend the aeronautical charts to have KATKI annotated as a compulsory reporting point for routes G463 and B219.
Review all route intersections in the FIR similar to the KATKI position and amend existing procedures if required.
Review the procedural control facilities, including the provision of adequate flight progress strip bays, and the capability for continuous control frequency monitoring by the procedural controller.