When a Southwest Airlines flight attendant entered the cockpit during a flight and saw an iPad showing what appeared to be live footage from the plane’s lavatory, one of the pilots assured her it was a “top secret security measure”, according to court documents. Now, the airline denies there was ever a camera at all.

The flight attendant, Renee Steinaker, sued Southwest Airlines last year for emotional distress, negligence, invasion of privacy and sexual harassment. On Saturday, the airline said it would “vigorously defend the lawsuit”, claiming it had investigated the allegations at the time of the alleged incident, in February 2017, and had found no hidden camera.

“We can confirm from our investigation that there was never a camera in the lavatory,” Southwest Airlines said in a statement. “The incident was an inappropriate attempt at humour, which the company did not condone.”

Steinaker, who has worked as a Southwest flight attendant for decades, originally filed the lawsuit in 2018 in Maricopa County, Arizona, before the case was moved to Federal District Court in August, according to her lawyers.

One of the lawyers, Ronald Goldman, who has practised aviation law for nearly 50 years, said he had never seen a case like this before.

“The audacity of what happened is stunning,” Goldman said in an interview on Saturday. “This kind of conduct is so beyond the pale, in my opinion, that it jeopardised the safety of the flight and created a hostile work environment for the cabin crew.”

Lawyers for the pilots, Capt. Terry Graham and his co-pilot, Ryan Russell, did not respond to requests for comment on Saturday.

Steinaker was one of four flight attendants working on Southwest Airlines Flight 1088, which departed Pittsburgh for Phoenix on February 27, 2017. The plane, a Boeing 737-800, had lavatories in the front and back for the passengers and crew, according to court documents.

According to the complaint, about two and a half hours into the flight, Captain Graham asked for a flight attendant to come to the cockpit as he went to the lavatory. Southwest protocol requires that two crew members remain in the cockpit at all times.

Steinaker entered the cockpit, noticed an iPad mounted to the windshield next to the captain’s seat and saw what appeared to be a live-streaming video of Captain Graham in the lavatory, according to the complaint.

When questioned, Steinaker said, Russell admitted the video was from a functioning live-stream camera installed in the lavatory. He told Steinaker that cameras were a top-secret security measure that had been installed in the lavatories in all the airline’s 737-800 planes, the lawsuit alleges.

Russell then instructed Steinaker not to tell anyone about the recording or the camera, which he said was hidden so no one could find it. Steinaker then used her phone to take a picture of the iPad, which showed Captain Graham in the lavatory at the time, according to the complaint.

When the captain came back to the cockpit, Russell left to use the lavatory. Finding herself alone with Captain Graham, Steinaker confronted him about the cameras, but he refused to respond and blocked her view of the iPad, the lawsuit alleges.

Steinaker told the other flight attendants what had happened and showed them the picture she had taken of the iPad. When the plane landed in Phoenix, the two pilots immediately disembarked.