What happened
During pushback from the gate, the left engine of the aircraft was started without any reported discrepancies. However, while attempting to start the right engine, several passengers observed torching behind the tailpipe. This caused a commotion among the passengers, and three of the four flight attendants reported seeing an orange glow either inside or outside the aircraft.
Although the captain reported no abnormal engine indications within the cockpit, he proceeded to secure the right engine. The captain then secured the left engine after noticing passengers on the ramp and observing the illumination of the entry door lights. During the event, a male passenger approached a flight attendant at door 2L and attempted to open the door by partially rotating the handle. While the door did not open completely, it was cracked open. The flight attendant eventually opened the door fully and locked it against the fuselage, allowing the male passenger and several other passengers to exit immediately. Passengers also evacuated through the 2R, 3L, and 3R doors after they were opened by a flight attendant.
The investigation
Analysis of the readout from the flight data recorder provided details regarding fuel flow during the engine start sequence. When the fuel cutoff switch for the right engine was in the "run" position, the recorded fuel flow was 1,69pend6 PPH. Within approximately two seconds of the switch being in the "run" position, the fuel flow increased to 3,136 PPH. The maximum recorded fuel flow reached 6,272 PPH, occurring two seconds before the right engine fuel cutoff switch was moved to the "cutoff" position, which was 24 seconds after the switch had been placed in the "run" position.
In comparison, during the start of the left engine, the recorded fuel flow was 544 PPH within four seconds of the fuel cutoff switch being in the "run" position. A review of the previous eight engine starts showed that fuel flows for both engines were nearly matched, with no recorded value exceeding 580 PPH within the first four seconds of the "run" position.
Findings
Flight crews are trained that during hot starts, fuel flow typically exceeds 700 PPH almost immediately. The engine start procedures checklist requires that an engine start be aborted if abnormally high or fluctuating fuel flow is noted.