A Boeing 747-400 was enroute from Los Angeles to Melbourne, cruising at FL320 in a south-westerly direction on airway R576 in the Oakland Flight Information Region. A McDonnell Douglas MD-11 departed Honolulu and was climbing in an easterly direction to FL350. The aircraft were on converging tracks.
The Honolulu Air Traffic Control Facility was responsible for providing positive separation between the aircraft. The radar separation standard was 5 NM lateral, or 1,000 ft vertical.
A controller subsequently recognised that, without intervention, the tracks of the two aircraft would come within 5 NM when less than the required vertical separation existed. The controller instructed the MD-11 crew to "...fly heading 020 ..." to change the aircraft's track. The crew responded by broadcasting "... Air 205, now right, right heading...". The controller did not clarify the required turn direction, and then instructed the B747 crew "...fly 180, vectors on traffic". Those instructions were passed 60 seconds and 49 seconds respectively, prior to the aircraft passing each other.
The B747 crew correctly read back the instruction to fly 180 degrees. Immediately after receiving that instruction, the crew received a traffic advisory alert from the aircraft's traffic alerting and collision avoidance system (TCAS). The alert was followed by a TCAS annunciation of a resolution advisory (RA) to descend. The crew advised air traffic control, "... heading 180 and TCAS descent", as they descended the aircraft, in accordance with standard operating procedures. The crew had the MD-11 in sight for the duration of the incident.
Analysis of the continuous data recording plot indicated that the MD-11 did not commence the left turn until after the aircraft had passed. There was no indication that the B747 turned onto a heading of 180 degrees. A minimum of 700 ft vertical separation existed when there was less than 5 NM between the aircraft. An infringement of separation standards had occurred.
The MD-11 crew apparently misunderstood the instruction to fly heading 020 as "right" heading 020 degrees. A right turn would have been confusing to the crew as the aircraft was tracking approximately 090 degrees. The direction of turn onto a new heading would normally be flown via the shortest arc distance; in this case, a turn onto a heading of 020 degrees would normally involve a left turn. Thirty-three seconds later the MD-11 crew sought confirmation that a left turn to heading 020 degrees was required.
The crew of the B747 may not have turned as instructed due to their response to the TCAS alert, and their visual observation of the conflicting traffic. It could not be established whether standard separation would have been achieved if one or both crews had turned their aircraft when instructed to do so.
There was no evidence that the controller applied the principle of separation assurance in the control of these aircraft. Rather, the controller had relied on aircraft performance to achieve separation.
Local safety action
The Honolulu Air Traffic Control Facility completed mandatory team briefings for all personnel on the circumstances of this occurrence. All operational personnel were briefed on maintaining awareness, scanning, and vectoring with increased emphasis placed on operational supervision.
|Date:||15 January 2001||Investigation status:||Completed|
|Time:||1200 hours UTC|
|Location:||106 km NE Maui, (OGG), (VOR)|
|State:||International||Occurrence type:||Loss of separation|
|Release date:||17 December 2001||Occurrence class:||Airspace|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
Aircraft 1 details
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Melbourne, VIC|
Aircraft 2 details
|Aircraft manufacturer||McDonnell Douglas|
|Damage to aircraft||Nil|
|Departure point||Honolulu, Hawaii|