Image copyright Getty Images Image caption A pilot a told a flight attendant that a hidden camera was a "top-secret security measure", a lawsuit alleges

A Southwest Airlines flight attendant has filed a lawsuit accusing two pilots of livestreaming a plane's toilet on hidden camera.

Renee Steinaker alleges she caught the pilots during a 2017 flight from Pittsburgh to Phoenix.

Captain Terry Graham asked her to sit in the cockpit with co-pilot, Ryan Russell, while he used the toilet, the suit alleges.

Ms Steinaker alleges she saw an iPad showing live video from the toilet.

The pilots and Southwest Airlines have denied there was a camera filming passengers and crew members in the toilet. The airline said the incident was "an inappropriate attempt at humour".

Ms Steinaker alleges that Mr Russell told her to keep quiet about the camera, which he said was a "top-secret security measure".

The flight attendant reported the incident to the airline, but alleges that a supervisor ordered her not to talk to anybody about what happened.

The pilots were not sanctioned by Southwest Airlines and continue to pilot commercial flights for the airline, according to the suit.

"The allegations [in this lawsuit] frame conduct that is outrageous," Ronald Goldman, a lawyer representing Ms Steinaker, told the BBC.

How have the airline and pilots responded?

In a statement, Southwest Airlines told the BBC that the airline "does not place cameras in the lavatories of our aircraft".

Initially, the American airline declined to comment further on the lawsuit. But in a later statement, the airline said it had investigated the allegations and found there was never a camera in the toilet.

"Southwest will vigorously defend the lawsuit," the airline said. "When the incident happened two years ago, we investigated the allegations and addressed the situation with the crew involved.

Image copyright Getty Images Image caption The incident allegedly happened during a 2017 flight from Pittsburgh to Phoenix

"We can confirm from our investigation that there was never a camera in the lavatory; the incident was an inappropriate attempt at humour which the company did not condone."

The BBC has requested comment from the lawyer representing the pilots.

In their written response to the complaint, Mr Russell and Mr Graham admitted an iPad was in the cockpit, but denied all other allegations, CNN reported.

What does the lawsuit allege?

Around two hours into the flight, on 27 February, 2017, Mr Graham asked Ms Steinaker to sit in the cockpit while he went to the toilet, the suit alleges.

According to Southwest Airlines policy, at least two staff members are required to be in the cockpit at all times.

Mr Russell admitted the camera was livestreaming "with a panicked look on his face" before advising Ms Steinaker not to tell anyone about "this new security measure", the suit alleges.

The cameras were a "top-secret security measure" installed in all the airline's 737-800 planes, Mr Russell allegedly told the flight attendant.

Sceptical of Mr Russell's explanation, Ms Steinaker took a photograph of the iPad with her phone, the suit states.

When Ms Steinaker complained, a supervisor allegedly told her to keep quiet about it because "if this got out, if this went public, no one, I mean no one, would ever fly our airline again".

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Ms Steinaker's lawsuit seeks at least $50,000 (£38,000) in damages from Southwest Airlines and the pilots.

Mr Goldman said his client had been "significantly harmed" by the alleged conduct, which caused her "severe emotional distress".

The lawsuit was initially filed in Maricopa County, Arizona, but has been moved to US District Court in Arizona. No trial date has been set.