Turbulence/windshear/microburst

An RAAF C130 Hercules transport aircraft was conducting touch and go circuits using runway 05. The pilot of VH-LOB called for taxy clearance for runway 05 at 1500.22, (time in hours minutes and seconds.) After establishing the distance remaining for an intersection departure as 1190 metres the pilot requested and received approval for an intersection departure.

At 1502.20 the pilot was cleared to line up on runway 05. A clearance for take-off was given at 1502.59 and the pilot quickly applied take off power and commenced the ground roll. The lightly loaded aircraft was soon airborne. The landing gear and then the flaps were retracted. Suddenly the aircraft rolled very rapidly to the left and pitched nose down. Despite application of full opposite aileron and rudder and nose up elevator the pilot was unable to prevent the aircraft from descending left wing down into the ground to the left of the runway.

The investigation concluded that the accident was due to an encounter with wake turbulence from the C130. Under the Manual of Air Traffic Services (MATS) instructions the minimum separation between a light aircraft making an intersection take off behind a medium aircraft, was three minutes. This standard was required to be applied by the air traffic controller at Wagga.

Information provided by the RAAF indicated the C130 was making consistent circuits, with the base call given just after the base leg turn was commenced. They indicated the time from making the call until the aircraft touched down, was 80-90 seconds. After a short ground roll power was re-applied for take-off and lift off was achieved an estimated 150-180 metres beyond the taxiway intersection from which the take off in VH-LOB was commenced.

The time between base calls on the last four approaches for the C130 averaged four minutes and 28 seconds, with all being within eight seconds of this average. The last base call by the C130 crew was at 1459.42, some three minutes and 17 seconds before VH-LOB was cleared for take-off. Considering the C130 crew's estimate of 80 to 90 seconds to touchdown from this call, the indications were that the three minute separation standard was not met.

The controller said that the C130 base leg calls were given when the aircraft was halfway around base leg. He also estimated the time from these calls to touchdown was 30 seconds and to lift off was one minute. On the touch-and-go landing immediately before the accident, the controller believed that the C130 touched down 12 to 15 seconds past the hour, at about the time VH-LOB taxied. Under MATS provisions the controller is allowed to anticipate that the standard will exist at the time of lift off. In the controller's opinion he had the required three minutes separation. He did not, and was not required to, record any times so these estimates could not be verified.

The Civil Aviation Authority (CAA) published an Aeronautical Information Circular (AIC) H 11/1991, on wake turbulence hazards and characteristics. This AIC was still current at the time of the accident. It stated that wake turbulence vortices (there is one from each wing) start at rotation for lift off and end at touch down. These vortices tend to sink until close to the ground and then move sideways at about five knots.

The vortice from the right wing moves to the right, while that from the left wing moves to the left. The light wind conditions existing at the time of the accident, probably resulted in the right-wing vortice remaining above the runway. The AIC stated that in stable conditions wake vortices can exist for in excess of three minutes.

From the available evidence it has not been possible to conclusively establish whether the required separation of three minutes existed at the time VH-LOB took off.

Significant Factors

The following factors were considered relevant to the development of the accident:

1. The light wind conditions that existed at the time probably resulted in the right wing vortice remaining over the runway.

2. Wing tip vortices generated by normal operations in the C130, persisted long enough and were of sufficient intensity to cause a control loss in VH-LOB.

On 8 November 2013, the captain and first officer operating a Qantas Boeing 767 aircraft, registered VH-OGU, prepared to conduct a scheduled passenger service from Melbourne, Victoria to Sydney, New South Wales. The crew obtained the relevant weather information, with no requirements for holding fuel or an alternate indicated.

During the descent into Sydney, the crew switched on the seatbelt sign at about 10,000 ft above mean sea level (AMSL). At about the same time, they observed lightning to the right of the aircraft’s track, with a corresponding red return on the aircraft’s weather radar display.

At about 2026 Eastern Daylight-savings Time, while on approach and descending through 4,200 ft AMSL, the aircraft encountered moderate turbulence for about 2 minutes. At about 3,000 ft AMSL, the crew elected to discontinue the approach, and conducted a missed approach. During the subsequent climb, passing about 4,200 ft AMSL, the aircraft encountered severe turbulence.

The crew reported that full go-around power was required to maintain altitude and speed, and they experienced difficulty controlling the aircraft. In the cabin, one passenger sustained a serious injury; one passenger sustained a minor rib injury and a third passenger sustained a minor injury from an iPad.

After orbiting for about 20 minutes, the crew commenced an approach to runway 16 Right. Passing about 5,000 ft AMSL, the aircraft again encountered severe turbulence and was difficult to control, and the crew again conducted a missed approach and commenced a turn to the north.

At about 2127, based on the remaining fuel quantity and the turbulence on the approach to Sydney, the crew declared a ‘PAN’ and elected to divert to Williamtown, New South Wales.  The aircraft landed at Williamtown with fuel reserves intact.

This incident serves as a timely reminder to passengers to safely stow any carry-on baggage, laptops, iPads and other items correctly, as they can become projectiles during turbulence if not properly secured.

Aviation Short Investigation Bulletin - Issue 26

On 23 September 2013, the crew of a Boeing 777-3ZGER aircraft operated by Virgin Australia, registered VH-VPE (VPE) conducted a scheduled passenger flight from Brisbane, Australia to Los Angeles, United States. At about 0305 Coordinated Universal Time in the cruise at flight level (FL) 310 and flying in clear air the aircraft encountered abrupt severe turbulence.  The flight crew turned on the seat belt sign, reduced the speed of the aircraft and requested from air traffic control a descent to a block altitude from FL310 to FL 290.

At the same time, the cabin crew had begun the meal service and the seat belt signs were turned off. Cabin crew members reported being thrown around the cabin by the turbulence with two of the 12 cabin crew hitting their heads on the aircraft cabin ceiling. Food and catering equipment were spread over seats, passengers and the aisles with the rear section of the aircraft affected the most. All passengers were seated at the time with their seat belts on. One passenger reported a sore neck and another passenger reported a burn injury as a result of a spilt hot meal. There were no reported injuries to the four flight crew.

This incident is a timely reminder for passengers to keep their seatbelt fastened when seated, pay attention to the safety demonstration and any instructions given by the cabin crew and read the safety information card in the seat pocket.

Aviation Short Investigation Bulletin - Issue 28

The ATSB was advised of two turbulence related events that occurred on 5 July 2013 and 7 July 2013, involving VH-VZY and VH-QOP respectively.

VH-VZY

On 5 July 2013, a Boeing 737 aircraft, registered VH‑VZY, departed Perth, Western Australia on a scheduled passenger service to Canberra, Australian Capital Territory. While descending through 8,000 ft, the aircraft encountered severe turbulence for about 2 minutes. The flight crew reported that they experienced difficulties with maintaining their assigned altitude of 7,500 ft for about 1 minute and the aircraft descended to 7,200 ft. A cabin crew member positioned in the rear of the aircraft sustained minor injuries.

VH-QOP

On 7 July 2013, a Bombardier DHC-8-402 aircraft, registered VH-QOP, was being operated on a scheduled passenger service from Wagga Wagga to Sydney, New South Wales.

During the cruise, while in clear conditions, maintaining flight level (FL) 210, the aircraft experienced severe turbulence. The turbulence ceased for about 2 seconds and moderate turbulence was then experienced. The aircraft pitched upwards by 5°, the right wing dropped by 7°, and the airspeed increased by about 20 kt. The seat belt sign was turned on. Overall, the turbulence encounter lasted for about 6 seconds. It was reported that a passenger sustained a broken or dislocated ankle, and a cabin crew member sustained an ankle injury.

Research conducted by the Australian Transport Safety Bureau (ATSB) identified that 99 per cent of people on board an aircraft receive no injuries during a typical turbulence event. However, passengers and cabin crew not wearing a seat belt can be thrown around without warning.

Aviation Short Investigation Bulletin - issue 23

On 10 May 2013, at about 2000 Eastern Standard Time, a Sunstate Airlines Bombardier DHC‑8‑402 aircraft, registered VH‑QOD (QOD), departed Townsville on a scheduled passenger flight to Cairns, Queensland. 

About 20 minutes into the flight, the aircraft was in the cruise at FL 180 and flying in clear air when the aircraft encountered light turbulence. The captain immediately switched on the seat belt sign. A second later, the aircraft encountered abrupt severe turbulence.

 The autopilot disconnected and the captain, as pilot flying, assumed manual control of the aircraft. The flight crew reduced the speed of the aircraft to below the turbulence penetration speed. The turbulence event lasted about 10 seconds, during which time the aircraft climbed about 400 ft above the cruising altitude. The flight crew then re-engaged the autopilot and returned the aircraft to the assigned level.

The weather radar did not show any significant weather for the entire flight. Both members of the cabin crew were standing when the aircraft encountered the turbulence and impacted the roof before falling to the floor. Both sustained head injuries and one was knocked unconscious.

The aircraft landed in Cairns about 20 minutes later, without further incident and the cabin crew were transferred to hospital.

In this event, all passengers were seated with their seat belts fastened, even though the seat belt sign had been switched off earlier. The fact that none of the passengers were injured highlights the benefits of keeping your seatbelt fastened during the flight.

Cabin crew are at greater risk of injury during turbulence encounters as they are moving around the cabin and not seated with a seat belt fastened.

Aviation Short Investigation Bulletin - Issue 23

On 13 September 2012, a Boeing 737 aircraft, registered VH-YIO (YIO), departed Bali International Airport (Denpasar), Indonesia on a scheduled passenger service to Brisbane, Queensland.

The aircraft became established in the cruise and the seat belt sign was turned off. Shortly after, the crew observed opposite direction traffic on the aircraft’s traffic alert and collision avoidance system (TCAS), about 1,000 ft above and slightly to the left. The crew observed the aircraft pass to the left. Airservices Australia surveillance data indicated the aircraft passed with about 0.9 NM lateral and 1,400 ft vertical separation.

Soon after, the First Officer reported that they felt ‘cobblestone’ like turbulence. The aircraft then experienced a wake induced roll, initially to the right to a maximum angle of 6.5° and then left to 40.4°, with a 40 ft loss in altitude. As the roll to the left commenced, the crew immediately responded by applying full right aileron deflection. 

Surveillance data indicated that there was about 2.1 NM lateral, and 1,400 ft vertical separation and the correct air traffic control separation standards were being applied at the time. Nil injuries were received.

This incident demonstrated the value of periodic recurrent training, allowing the crew to react to the wake turbulence encounter intuitively and promptly. Furthermore, it is a timely reminder of the benefits of having the seat belt fastened, even when the seat belt sign is turned off, so that injuries during a turbulence encounter can be minimised.

Aviation Short Investigation Bulletin – Issue 17

On 20 May 2011, a Qantas Airways Boeing 767-338 aircraft, registered VH OGR, was being operated on a scheduled passenger service from Melbourne, Victoria to Perth, Western Australia.

During the approach to runway 03 at Perth, the aircraft encountered turbulence over a 9 second period, with severe turbulence recorded for 3-4 seconds during that time; a go-around was conducted.

Two passengers, who were reportedly not wearing their seat belts at the time, sustained head injuries from coming into contact with a window reveal and an overhead locker. After landing, both passengers received medical attention, with one being transported to hospital.

As a result of this occurrence, the aircraft operator has advised the ATSB that they intend to present this incident at the Airservices Australia industry participation working group for discussion; to improve the dissemination of information relating to windshear events.

Generally, 99 per cent of people receive no injuries during a turbulence encounter; however, if passengers and cabin crew are not wearing their seatbelts, they can be thrown around without warning. Almost all in-flight turbulence injuries could be avoided by wearing a seatbelt and paying attention to any safety announcements made by the flight crew and cabin crew during the flight.

On 31 January 2011, a Boeing Company Aircraft 777-3ZGER, registered VH-VPH, was en-route from Phuket, Thailand to Melbourne, Victoria. When the aircraft was 170 NM north of Jakarta, Indonesia it encountered a period of sudden and unexpected turbulence. Six cabin crew members and four passengers received minor injuries.

At the time of the incident, the aircraft was established in the cruise and flying in cloud. The weather radar showed no significant weather in the immediate vicinity of the aircraft.

The flight continued to Melbourne where two cabin crew members consulted with paramedics, however no medical treatment was required.

The operator is considering including details of this occurrence in flight crew and cabin crew training to improve general crew awareness on the practical aspects of turbulence management and the importance of cabin discipline particularly relating to the handling of cabin equipment.

The operator is also considering changing a number of internal procedures to improve or standardise processes related to reporting injuries, providing support to crew in remote ports and assessing when crew are fit to return to duty.

On 16 February 2011, a Piper Aircraft Corporation PA-30 aircraft, registered VH-MAC, was being operated on a private flight from Coldstream, Victoria, to Canberra, Australian Capital Territory, via Strathbogie, Wangaratta Vic. and Albury, NSW, under the instrument flight rules. On board the aircraft were the pilot and one passenger. In preparation for the flight, the pilot had submitted a flight plan and obtained an aviation meteorological area forecast the previous evening.

After departure from Coldstream aerodrome, the pilot obtained clearance to 9,000 ft above mean sea level. While flying in light cloud and passing NE of Albury, tracking to Canberra, the aircraft encountered severe turbulence. After experiencing uncommanded climbs and descents continuously for nearly 35 minutes, while at times becoming inverted, the pilot saw terrain through a break in the cloud and flew clear of the cloud. The pilot then decided to divert to Albury and landed safely a short time later.

The pilot stated that in future, he would check the aviation area forecast prior to departure.