Qantas's top pilot says there was no cause for concern after a bad case of "wake turbulence" on a recent flight from the United States to Melbourne involving a massive Airbus 380 plane.
Main causes of turbulence
- Most common is a sudden change in wind direction and speed
- Can also be caused by a sudden change in air temperature
- Wake turbulence happens when a large jet disturbs the air as they fly through it
QF94 was flying from Los Angeles to Melbourne on Sunday when it hit the bumps caused by another Qantas A380, which had left the same airport a few minutes before.
Janelle Wilson, a passenger on the flight, told the Australian newspaper that the experience left her "frightened".
"All of a sudden the plane went through a violent turbulence and then completely up-ended and we were nosediving," Ms Wilson said.
"We were all lifted from our seats immediately, and we were in a free fall.
"The lady sitting next to me and I screamed and held hands, and just waited, but thought with absolute certainty that we were going to crash."
Qantas's chief technical pilot, captain Alex Passerini, reviewed the data from the flight and said there was never any danger, as planes are built to deal with wake turbulence.
"The airplane typically cruises at a pitch attitude, as we call it, of about two-and-a-half degrees," he said.
"We know it pitched up about a degree, and then, as part of the return to normal flight at the right altitude, the nose dropped about three degrees.
"So the total sweep is very small, but we can understand that for someone sitting at the back, that has experienced this lovely smooth ride, to have this suddenly happen can be a little alarming."
Mr Passerini said the movement could give the impression of a nose dive, depending on where the passenger was sitting on the plane.
"Particularly if there's a negative G … that 'top of the roller coaster' … that unsettling feeling in your stomach," he said.
"If you're not used to it, depending on how much flying you do, and how sensitive your stomach is, that can exaggerate the feeling of pitching over, and exaggerate the movement."
He said the distance between the two planes was not the problem.
"The airplanes were separated well in excess of any minimum standard, which was 1,000 feet vertically," he said.
"And the trailing airplane was about 20 nautical miles, or 37 kilometres, behind the leading airplane — so they're a long way back.
"It was just one of those situations where the right conditions in the atmosphere lined up and the airplane encountered the wake."
What is wake turbulence?
Neil Hansford, an aviation expert, said wake turbulence is different to the more commonly experienced atmospheric turbulence.
"Wake turbulence is a disturbance in the atmosphere that forms behind the aircraft," he said.
"There are wingtip vortices that have a different affect to the jet wash.
"The jet wash, as you'd imagine, simply refers to the rapidly moving gasses coming from the jet engines, and it is extremely turbulent, but it doesn't last for long.
"The wing tip vortices, on the other hand, are much more stable and can remain in the air for up to three minutes after the passage of an aircraft."
Mr Hansford said more large aircraft, like A380s, in the skies is not making wake turbulence more common, but noise restrictions around airports is making it harder to avoid all kinds of bumps.
Noise abatement areas around airports require planes to climb quickly, level out and then begin climbing again once they have reached a certain point.
"All of these noise abatement procedures are making it harder and harder to avoid anything like atmospheric or wake turbulence," Mr Hansford said.