Qantas B738 and Virgin Australia B738 near Sydney on Jan 8th 2012, separation not ensured

Last Update: June 25, 2012 / 13:15:15 GMT/Zulu time

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Incident Facts

Date of incident
Jan 8, 2012

Classification
Incident

Airline
Qantas

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

Radar display at activation of STCA (Graphics: ATSB)The Australian Transportation Safety Board released their final report stating the occurrence controller assumed duties for two sectors about 30 minutes prior to the incident. Adverse weather prevailed prompting many flight crews to request to divert from assigned flight pathes, a number of aircraft were in holding patterns in neighbouring sectors. According to AIPs standard flight levels had to be used, the controller however was permitted to assign non-standard flight levels when required by traffic or operational necessities. Adverse weather was assumed to meet such requirements.

VH-VZS was holding in the neighbouring northern sector at FL330. About 15 minutes after assuming duties the controller coordinated with his collegue to release the aircraft out of the holding and send it on towards Sydney at FL330. At that time VH-VUJ was climbing through FL184 in the neighbouring southern sector. 5 minutes later the southern collegue coordinated VH-VUJ indicating the aircraft was on a heading of 350 degrees diverting around weather and was climbing towards FL300, a southbound aircraft at FL310 did not permit to climb the aircraft higher. VUJ subsequently contacted the occurrence controller reporting heading 350 and requesting to maintain that heading for at least another 45nm due to weather. The controller advised that a higher level would become available only after 45nm. The crew subsequently requested and was approved heading 340 degrees due to weather.

Another minute later VZS contacted the occurrence controller and requested to divert 10nm to their right due to weather, which was approved. The two aircraft were now on reciprocal headings with a vertical separation of 3000 feet, the controller had two other aircraft on his frequency and engaged in coordinating holdings and weather diversion requirements with adjacent controllers and made numerous transmissions on his frequency to that theme.

Six minutes after VZS reported on frequency VUJ reported clear of weather, distance between VUJ and VZS was 78.5nm at that point. VZS requested another weather related diversion, numerous transmissions occurred to determine the position and the impact on the arrival route into Sydney. 3 minutes after that request the controller cleared VUJ to climb to FL330, the two aircraft were 32.7nm apart. Although separation criteria were not yet infringed, separation was no longer assured. VUJ requested a heading of 040 due to weather which was approved.

56 seconds after VUJ had been cleared to FL330 the short term collision alert (STCA) activated at the controller's work place, the aircraft were separated by 2200 feet vertical and 17.5nm at that point at a closing ground speed of 920 knots. Three seconds later the controller instructed VZS to immediately turn right 30 degrees and instructed VUJ to maintain FL310 and to turn right onto a heading of 070. Both crews acknowledged their instructions, VUJ reported descending to FL310. Minimum separation was 1600 feet vertical and 10nm horizontal, a loss of separation did not occur.

Two minutes after VUJ was cleared to FL330 the aircraft passed each other at 1900 feet vertical separation.

The ATSB reported the controller had 38 years of experience as air traffic controller and 13 years in controlling the particular sector. He said in post incident interviews he had not identified the possible conflict until the activation of the short term conflict alert. The compromised separation recovery techniques utilized were effective and prevented the loss of separation.

The ATSB released following:

SAFETY MESSAGE

This incident highlights the need for awareness of the effects of high workload and sustained task complexity on performance, and the importance of taking regular breaks, and monitoring performance during such periods.

While the use of conforming levels is not always possible due to operational circumstances such as weather, the utilisation of conforming levels by both flight crew and ATC, whenever possible, provides an integral system defence against the loss of vertical separation between aircraft on reciprocal tracks.

In this incident, the air traffic controller attributed their prompt and effective resolution of the detected conflict to experience and to having received compromised separation recovery training. Those actions highlight the benefit and importance of regular, appropriate training in providing an integral defence for the management of such situations.
Incident Facts

Date of incident
Jan 8, 2012

Classification
Incident

Airline
Qantas

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

This article is published under license from Avherald.com. © of text by Avherald.com.
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