CALGARY - A day after an Air Canada jet plunged thousands of metres for 15 terrifying seconds on a flight from Victoria to Toronto, there was still no concrete evidence of what caused it to temporarily lose altitude and control.

Shaken passengers on Air Canada Flight AC190 described a sudden drop by the Airbus A319 jet which then rolled sharply to the left and right - violently pitching people, dishes and drink carts about the cabin. Ten people, including two crew members, were hurt but none seriously.

The Transportation Safety Board suggested "control problems" that might have been caused by turbulence, mechanical problems or a mistake by the flight crew. It's going to take a while before the cause is determined.

"This is not CSI," said board spokesman John Cottreau. "It's not just bing, bang, boom. There's an awful lot that goes on.

"We deal in facts. We don't deal in speculation. Sure, we can hypothesize, but those need to be scientifically examined and either proven or discounted."

Two safety board investigators are downloading information from the plane's black box, looking at the history of the aircraft and the takeoff. They're also asking for copies of air traffic control tapes. There will also be interviews with several people on the flight.

"This is a long, intense and thorough process."

Speculation that the jet hit severe turbulence is a favourite theory of many in the industry as evidenced by a fair amount of discussion on the aviation blog on the "Aviation Airline Forum" website.

"I suspect the originating event was turbulence and the flight control issues were a symptom, not a cause. We'll have to wait and see what the facts say," wrote VSPLAT in a discussion group called "A bad day for Air Canada."

"It is possible that the turbulence triggered what is known as a 'jet upset.' When an Airbus detects an upset, one of the things it automatically does is degrade the level of automation, in case the automation itself has triggered the fault. Most aircraft will kick the autopilot off if the aircraft attitude exceeds certain bank or pitch angles."

Turbulence can appear without any warning, explained an atmospheric scientist from York University.

"It was relatively high for clear air turbulence," said Peter Taylor. "You get these tropospheric folds every now and then which could produce something quite dramatic."

"Waves in the atmosphere break, and when they break they produce quite large amplitude and quite large-scale air turbulence which can cause the sort of dramatic impact on an aircraft...and you get a large loss of lift."

Taylor cautioned that he was only speculating and would need to see more data to make an educated guess, but he said the folds are common though usually not that large.

Air Canada spokeswoman Angela Mah said the airline is conducting its own "full-on investigation" and co-operating with the Transportation Safety Board.

"At this juncture it is extremely premature to talk about the circumstances surrounding Flight 190 or speculate on the cause," she said.

The good news is that all of the injured passengers and crew are out of hospital, she said.

"All passengers have departed for their final destinations. All the people that were in the hospital were discharged and our customers are all at their final destinations as we speak."

The safety board has released the aircraft back to Air Canada but it will remain out of service for the time being.

"We are still completing all of our maintenance checks to see if it is airworthy before it is returned to service," said Mah.

A Calgary aviation expert said there is no quick way to determine what was responsible. It could be mechanical error or turbulence.

"Honestly, at first I was a little bit frustrated because everybody said it's turbulence, but we really don't know," noted Mark Hanson, an air cargo pilot and a flight instructor at Mount Royal College in Calgary.

" It sounds like that's one of the options that it could have been, but there are thousands of things. We work very hard to keep an airplane flying straight and level and everything works against us. One of those things won momentarily and so who knows what it is?"

Air turbulence is a fact of life for pilots. And despite sophisticated instrumentation on today's aircraft it can strike without warning, although that doesn't happen often.

"It can. It's very, very rare but obviously this is an exceptional incident because how many millions of miles were flown Thursday and there's one incident we are talking about."

There were 88 people aboard Flight AC190.

On Friday, emergency crews were again called to Calgary International Airport after Air Canada Flight 286 reported pressurization problems enroute to Calgary from Vancouver.

Mah said the flight landed safely, no one needed medical treatment and no one was hurt.

"On the approach into Calgary, the pilot received an indication of cabin depressurization but there was no need to deploy oxygen masks," Mah told the Calgary Sun.

The Airbus 320 with 24 passengers and six crew members aboard then descended to a lower altitude as a precaution, she said.

"Because there was backup pressurization, at no time was anyone in danger."

She said an in-flight mechanical problem was detected.

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