A Toronto law firm has filed a $20-million class action lawsuit against Air Canada on behalf of the 95 passengers who suffered injuries after the plane they were on took a sudden plunge.

Air Canada originally told passengers that the plunge, on Flight AC878 between Toronto and Zurich in January 2011, was caused by unexpected turbulence.

But the Transportation Safety Board of Canada issued a report in April saying the terrifying episode happened when a co-pilot woke up and was confused enough to think the plane was about to collide with a U.S. military aircraft.

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Darcy Merkur, a partner with the law firm Thomson, Rogers in Toronto, told the CBC that if some passengers were not wearing their seatbelts, it would be 'a minor, minor impact on their entitlement.' (Thomson, Rogers)

Lawyer Darcy Merkur of the firm Thomson, Rogers, which filed the claim, says the passengers who have come forward "feel completely manipulated, completely lied to and they are pissed off; they want a corporation like Air Canada to be accountable for misleading them."

"We feel the suit was the right thing to do," says Ashlyn O'Mara who was on the flight, "there is a group of us."

In the class action suit filed in court Monday, Thomson, Rogers says that Air Canada covered up the cause of the incident. 

The suit has not been certified as a class action suit and the allegations have not been proven in court.

The suit names O'Mara of Toronto as a claimant. She has told CBC News that she had her seatbelt fastened and was awake when the plane plunged in the middle of the night.  

O'Mara told the CBC in an exclusive interview that part of the class action suit is about how passengers were treated by Air Canada.

"The company did not reach out to many of the passengers, including myself, to see if we were OK or to ask if there was anything they could do."

O'Mara also points out she is concerned about public safety and pilot fatigue. "It should be a wakeup call to everyone that something isn't right and that pilot fatigue is a serious problem that can affect anyone who flies."

If you have information on this story, please contact investigations@cbc.ca

With files from the CBC's Frederic Zalac and Mary Sheppard