Incident Overview
While an aircraft was parked at the gate, the flight crew heard a muffled explosion and observed flames emanating from a vent near seat 3-D. The location of the fire prevented the crew from returning to the cockpit to notify airport fire rescue (CFR) and illuminate the emergency floor lighting. Passengers and crew evacuated the aircraft. The second officer, who was the last to leave, could not reach the rear airstairs and exited via an emergency window after experiencing difficulty locating an exit due to smoke.
Maintenance and Preflight Events
During preflight, a mechanic noted a low passenger oxygen supply and replaced the oxygen cylinders. While exiting the electrical equipment bay, the mechanic saw a white flash engulf the oxygen system flow control unit. He attempted to notify CFR of the fire using a handheld radio, but was unsuccessful.
Maintenance History
The passenger oxygen system had six low-oxygen-quantity maintenance write-ups in the previous 30 days. However, the company's automated trend analysis program did not flag the system because of the job title of the person entering the write-ups. An inspection of Delta Air Lines' fleet revealed 35 oxygen system leaks on other aircraft.