Fuel leaking from the fuel flow transmitter that ignited on contact with the engine’s hot cases which resulted in an engine undercowl fire. The fuel leak resulted from the fuel flow transmitter end housing backing off from the main housing, creating a gap that allowed high pressure fuel to escape. Under certain assembly variances and operational load and temperature variations, the end housing joint may not be able to maintain the preload without eventually yielding, which results in the loosening of the joint and the resultant gap.

The probable cause of this incident was the United 1544 flight crew's inadvertent entry onto the active runway.