 The review board determined that the electrical power momentarily failed at 23 : 30 : 55 GMT , and found evidence of several electric arcs in the interior equipment . However , they were unable to conclusively identify a single ignition source . They determined that the fire most likely started near the floor in the lower left section of the cabin , close to the Environmental Control Unit . It spread from the left wall of the cabin to the right , with the floor being affected only briefly . 
