The EgyptAir Boeing 777 was parked at gate F7 of Terminal 3 at Cairo airport on 29 July 2011, with preparations underway to operate flight 667.

As the last few of the 307 passengers were boarding, the flight crew in the cockpit heard a bang and a hissing sound coming from the right side console, immediately followed by smoke and flames.

[2]: 97, 109 According to the cockpit voice recorder, noises occur at 9:11:38 that the final report characterizes as "a pop is heard, followed by a hissing sound similar to the escape of pressurized gas".

[2]: 24  The fire erupted about 30 minutes after the first officer performed a test of the oxygen mask's function during the standard pre-flight checklist.

The captain’s side wiring was similar, except that sleeving was present on all airplanes inspected.

[2]: 61 Previous testing by the US National Transportation Safety Board following a 2008 cockpit fire on a Boeing 767 had found that flexible oxygen supply hoses could ignite if anti-kink springs along the oxygen supply hose were exposed to an electric current.

Further testing in conditions that increased the likelihood of ignition showed that 5 volts of direct current was not sufficient to destroy the hose.

Window grease in an oxygen-rich environment was another source of ignition that was investigated, but testing determined that the oxygen level did not impact the flashpoint, which was over 200 °F above the maximum theoretical temperature in that part of the cockpit.