Jetstar A320 at Brisbane on Oct 13th 2011, weather and "immediate" forces aircraft into cumulonimbus and alpha floor
Last Update: May 24, 2012 / 22:34:07 GMT/Zulu time
About 30 seconds later the captain requested a turn to the right due to weather, the controller advised a turn to the right was not available due to traffic on the localizer and repeated the instructed to maintain their present heading and requesting to report as soon as they could accept a turn to the left. The crew observed an intense weather cell with heavy rain at their left.
Another 30 seconds later the controller instructed the A320 to "immediately turn left onto heading 170". The crew understood the instruction was to avoid a collision and complied with the instruction, which took them straight into the weather cell.
Shortly after rolling out at 170 degrees the crew experienced hail, heavy rain and a rapid reduction of airspeed, the autopilot disconnected when the aircraft reached the alpha floor protection speed, the first officer selected TOGA to arrest the aircraft's deceleration.
There was congestion on the radio frequency which delayed him requesting a heading change to get out of the cell. About 30 seconds after receiving the instruction to immediately turn left the crew requested an "immediate heading of 090", ATC advised they could expect the turn in 30 seconds, the crew repeated they needed the heading "NOW" and were cleared to turn onto 090. The aircraft subsequently flew clear of the weather and continued for a safe landing in Brisbane. No injuries occurred, the aircraft received no damage.
The Australian TSB released their bulletin reporting that the controller was responsible for departing and arriving traffic from/to Brisbane and to coordinate traffic clearance with adjoining airspace. The sector was busy with a large number of aircraft in a limited airspace when the weather rapidly deteriorated, the controller later commented that it had been the most "unworkable" situation he had experienced in 17 years of experience. A lot of aircraft were requesting deviations due to weather and it was very difficult to formulate a traffic sequence.
Following the incident the controller asked the shift supervisor to stop any more aircraft entering his airspace which returned his workload to manageable.
The ATSB annotated that it was the shift supervisor's duty to manage the overall workload of the area and hold traffic if a sector became too congested.
When the controller issued the "immediately turn left" instruction there was conflicting traffic about 10.2nm from VH-VGO descending from 5200 feet to 4000 feet while VH-VGO was maintaining 5000 feet.
The quick access recorder of VH-VGO showed after turning to heading 170 the aircraft encountered two vertical acceleration peaks of 1.5G and a minimum of 0.4G. At the same time the autopilot disconnected the thrust levers were placed into the TOGA detent, engines had already begun to accelerate prior to that in response to the airspeed decrease and autothrust commands.
The ATSB concluded their report with the safety message:
High workload can cause narrowing of attention and task fixation. This makes it difficult to continually assess the big picture and develop appropriate strategies. Effective workload management includes, for line controllers and supervisors alike; forward planning and seeking/providing assistance when needed.
In this incident, deteriorating weather combined with high traffic volume limited the options available to the controller to ensure separation.
The need for the controller to take immediate action to maintain separation, resulted in the use of phraseology which led the flight crew to believe that there was an imminent risk of collision and their subsequent turning into hazardous weather.
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This article is published under license from Avherald.com. © of text by Avherald.com.
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