Investigators are investigating whether the lithium batteries in the copilot's Apple iPhone 6S and iPad mini 4 could have caused the crash, according to this report:
Le Parisien - Crash d'EgyptAir : des experts se penchent sur des iPhone et des iPad (May 25, 2017)
I'm not literate in French, so my summary of the article is based upon Google's translation of the page. Footage from surveillance cameras at Roissy airport shows the copilot's iPhone and iPad mini atop the instrument panel:
Google's translation of the article says:
For personnel in the cockpit, it is forbidden to travel with these devices unless they are issued to the pilots by the company in the course of their work. For example, Air France or Transavia have a specific Nav / Aero tablet. "The cockpit plugs are not made to connect the toaster or the coffee maker. They are professional plugs, "says a source close to the file. Other European companies are careful to ensure that lithium batteries, which are considered unstable under certain conditions, are banned from the cockpits.
The investigators are acquiring "three iPad Mini wi-fi 3G model A 1455" and "three iPhone 6S, both new and used" and will test them by causing "a thermal runaway". Google translate explains:
After determining whether the appliances can catch fire, experts should cause this fire, in order to calculate the heat radiation produced and to analyze the soot and smoke that emanate. Through this expertise, filmed and recorded, investigators look to see if the tablet and the smartphone can catch fire spontaneously and, if so, under what conditions and at what speed; And ultimately to determine whether the combustion of the aircraft could have rendered the aircraft uncontrollable and / or asphyxiated the pilots.