On July 29 2011 an Egyptair 777-200 Flight MS667 Reg SU-GBP was preparing for departure at Cairo Apt and had just finished boarding when the cockpit crew oxygen system malfunctioned and started an intense fire on the RHS of the cockpit.
Everybody evacuated safely through the still-connected passenger bridge through doors 1L and 2L, and the fire was brought under control by the airport fire dept but not after melting huge holes in the exterior acft skin and causing severe damage to the entire fwd section of the plane.
The accident report in the link above is a very sobering read if you imagine the incident happening 60 mins later as the 777 has departed and at altitude.
There would be no time to talk to the ground, and very little time for the crew to effect a descent before smoke/heat/depressurization took everybody out