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In response to media enquiries concerning a loss of separation incident between two aircraft that occurred on September 18, a spokesman for the Civil Aviation Department (CAD) today (September 27) gave the following response:
At 1.13pm on September 18, with inclement weather lying 30 to 50 nautical miles from Hong Kong International Airport (HKIA) from the southwest to the southeast blocking the approach paths to HKIA and causing extensive delays to arriving aircraft, a loss of separation incident involving a Dragonair A330 and a Cathay Pacific Airways B777 took place 37 nautical miles southwest of the airport while they were holding for their arrival sequence.
The A330 was holding at 22,000 feet together with five other aircraft at lower levels when the B777 was inbound from the north to the same area for holding. The crew of the B777 reported having only 10 minutes' holding fuel, and a same company aircraft then offered to swap its landing slot. While attempting to rearrange the holding sequence, the controller detected the conflict of the A330 and B777 aircraft at the same level and immediately instructed both aircraft to make a left turn when they were about 8.5 nautical miles (about 16 kilometres) apart. The B777 responded in accordance with the air traffic control (ATC) instruction. As the A330 was already in a right turn, it did not respond as per ATC instructions. Crews of both the A330 and the B777 were in visual contact with each other and were aware of the relative position of the other aircraft as well as able to maintain safety of their aircraft during the turn. To further provide vertical separation, the controller then instructed the B777 to climb to a higher level while the aircraft were about 4 nautical miles (about 7.5km) apart. There was no response from the B777 crew and preliminary investigation indicated that the crew of the B777 did not get the climb instruction.
About 17 seconds later, the A330 reported "TCAS climb" and the B777 reported "TCAS descent". (The term "TCAS" refers to the Traffic Collision Avoidance System.) They passed at 1 nautical mile (2km) in diverging turns with increasing vertical separation. The standard separation applicable is 5 nautical miles (horizontal separation) or 1,000 feet (vertical separation). As the avoiding actions by both aircraft were executed in a controlled manner and both pilots had the other aircraft in sight well in advance, there was no risk of collision.
On a normal day, there are typically eight controller working positions for the Approach Control Sectors in the Air Traffic Control Centre. In anticipation of the traffic complexity due to bad weather, one additional working position was opened up (for a total of nine) on September 18, and 13 controllers were on duty to man the nine positions in managing the air traffic. The staffing provision was considered sufficient to meet the traffic level.
The controller involved has worked with ATC over 14 years and has more than five years of experience in the Approach Rating. The controller had three work shifts in the preceding seven days and had just returned from a day off. After a one-hour break, the controller had worked for about 10 minutes before the occurrence. Therefore, fatigue was not likely to be contributory to the occurrence. After a rest and debriefing on the occurrence, the controller involved has resumed operational duties. Preliminary investigation indicated that the controller had taken appropriate corrective actions to ensure safe operations well before the separation was reduced to below the standard and in accordance with the laid down procedures. All actions by the controller were conducted in a calm and timely manner throughout the occurrence.
The CAD is conducting an investigation with the airline operators concerned. Although there was no risk of collision during the occurrence, the CAD will conduct a comprehensive investigation into all aspects, including ATC procedures, manning arrangements during bad weather, flight crew operations, TCAS operation procedures, etc.
Ends/Tuesday, September 27, 2011
Issued at HKT 15:23
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