No obvious culprit in Continental 737 excursion at Denver: NTSB

By John Croft

New NSTB information on the runway excursion by a Continental 737-500 departing the Denver International Airport the night of 20 December reveals no obvious failure mechanism that would have caused aircraft to depart the left side of the runway.

Of the 115 occupants on the aircraft, 34 were transported to hospitals and five were admitted after the aircraft crossed a snow-covered grassy drainage basin area and crossed a taxiway and a service road before coming to rest 2,300ft from the point where it left the runway. Despite a post-crash fire on the right side of the aircraft, no passengers or crew were killed.

Pilots of Flight 1404, departing Denver for Houston, told NTSB investigators that "all appeared normal until the aircraft began to deviate from the centreline" on the 1818h departure on Runway 34R. Winds were recorded from 290 degrees at 24kt with gusts to 32kt, presenting a left crosswind condition for the departure.

The captain further told investigators that the airplane "suddenly diverged" to the left and "attempts to correct the deviation with the rudder were unsuccessful." The pilot also stated that he "briefly attempted to return the aircraft to the centreline" using the tiller mechanism.

While the cockpit voice recorder (CVR) had revealed that the pilots called for a rejected takeoff after "bumping and rattling" sounds were heard, further analysis of the flight data recorder and correlation with the CVR show that the rejected takeoff occurred after the aircraft left the side of the runway, says the NTSB. The bumping sounds occurred after the aircraft left the runway as well.

A preliminary examination of the aircraft's rudder system revealed no abnormalities, the board states, and the main landing gear and brakes, which had separated from the aircraft during the accident sequence, were found to be in "good" condition by visual inspection. There were no signs of hydraulic leaking or flat spots on the tires, investigators explain.

Data from the aircraft's flight data recorder (FDR) show no evidence of pre-impact malfunctions with either engine. But power on the number one engine was reduced before power reduction of the second engine in the accident sequence. Examination of the number one engine indicated the power reduction was consistent with ingestion of snow and earth as the 737-500 departed the runway.

The board's findings show both engines were commanded into reverse thrust following the rejected takeoff.

© Reed Business Information 2009