Aviation safety investigations & reports

Wake turbulence event involving a Boeing 737, VH-YIO, 258 km SE of Bali International Airport (Denpasar), Indonesia, 13 September 2012

Investigation number:
Status: Completed
Investigation completed


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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

Download Final Report
[Download  PDF: 224KB]
Alternate: [Download  DOC: 615KB]
General details
Date: 13 September 2012   Investigation status: Completed  
Time: 1642 UTC   Investigation level: Short - click for an explanation of investigation levels  
Location   (show map): 258 km SE of Bali International Airport (Denpasar), Indonesia    
State: International   Occurrence type: Turbulence/windshear/microburst  
Release date: 23 April 2013   Occurrence category: Serious Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer The Boeing Company  
Aircraft model 737  
Aircraft registration VH-YIO  
Serial number 38714  
Operator Virgin  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Denpasar, Indonesia  
Destination Brisbane, Qld  
Last update 14 November 2018