The claimants operating theory suggests that an overheating iPhone 6s or tablet caused the crash that killed 66 people in 2016.

Several survivors of victims of the EgyptAir crash have filed a lawsuit against Apple, claiming that an iPhone 6S or iPad Mini belonging to the copilot overheated in the cockpit and caught fire, leading to the crash. The suit was first reported by gossip website TMZ .

EgyptAir Flight 804 was a flight from Paris to Cairo that crashed into the Mediterranean Sea on May 19, 2016, killing all 66 people aboard. Nearly two years later, the cause of the crash remains mysterious. Investigations continue, although many reports have stated that smoke had been detected on the plane.

Theories as to what caused the crash have run the gamut from terrorism to a fire that began in the plane's avionics bay.

Now, plaintiffs' attorneys think they've found a culprit for the mysterious crash: Apple. It's not clear how much money the suit is for, or what jurisdiction it was filed in.

Not much substance, and a hard road

Also unclear is how the plaintiffs plan to establish that the iPhone or iPad caused the crash, or how they may determine that the copilot's device was responsible.

A published investigation in early 2017 laid out the circumstantial case that a copilot had placed his iPhone and tablet on a glare-shield in the cockpit, as seen on CCTV cameras.

Experts pushed back on that theory. David Learmount, a former pilot and operations and safety editor at Flight International magazine, told The Daily Telegraph in 2017 that the theory was a "red herring," and far from the most plausible explanation.

"A phone bursting into flames just below the windscreen is a fairly spectacular thing to take place on a flight, and they would have told somebody on the ground. Nobody has mentioned this," Learmount said. "The key point is while there were warnings about the window heating systems, there were also smoke alarms in the toilet and avionics bay under the floor. How would the fire have got under there? It doesn't make sense."

Learmount believes that the computer in the avionics bay was damaged, and issued erroneous warnings to the pilot after a short-circuit or explosion.

There are no documented cases of an "exploding" iPhone causing a plane to crash. However, there were a couple of well-publicized incidents in 2016 in which smartphones either spontaneously combusted or otherwise began smoking on planes. One of them was in the news just weeks before the EgyptAir crash. None of those cases caused an explosion even remotely near large enough to threaten the plane itself or result in any fatalities.