Wednesday, January 07, 2009

Continental Flight 1404 Accident at Denver: NTSB Factual Update

NTSB logoThe U.S. National Transportation Safety Board (NTSB) has just issued a factual update on the runway excursion and crash of Continental Airlines Flight 1404 at Denver International Airport last month. Readers will recall that the aircraft, a Boeing 737-500 (registration N18611), departed the left side of runway 34R during its take-off roll, ultimately crashing into a ravine and catching fire. There were no fatalities, although 38 of those on board were injured. The entire right side of the aircraft was severely damaged by fire.

The accident happened on Dec. 20, 2008 at 6:18PM local time. The aircraft had been departing Denver for George Bush Intercontinental Airport, Houston, Texas.

The NTSB Update issued today presents factual information about the accident gathered thus far. Here are the highlights:

Inspection of the runway following the accident revealed that it was bare and dry and free of debris. The first tire marks were found about 1,900 feet from the runway threshold.

The aircraft exited the runway at about 2,650 feet from the runway threshold, continued across a snow-covered grassy drainage basin area, and crossed a taxiway and a service road before coming to rest about 2,300 feet from the point at which it departed the runway.

On the night of the accident, the majority of air traffic was arriving at the airport from the south and departing from the airport to the north.
Both pilots were aware of the crosswind conditions, having been advised by Air Traffic Control (ATC) that winds were 270 degrees at 27 knots just prior to takeoff.

The weather observation (METAR) in effect for Denver International Airport nearest the time of the accident was reported to be winds at 290 degrees and 24 knots with gusts to 32 knots, visibility of 10 miles, a few clouds at 4000 feet and scattered clouds at 10,000 feet. The temperature was reported as -4 degrees Celsius.

Wind data has been obtained from the airport's low-level wind shear alert system (LLWAS), consisting of 32 sensors located around the field, which record wind speed and direction every 10 seconds. This information will be used to determine a better estimate of the actual crosswind component at the time of the accident.
Crew Interviews
Both members of the flight crew have been interviewed.

The accident flight was their first flight on the fourth day of a four-day trip.

The Captain, the pilot flying, had accumulated a total of about 13,000 hours, with about 5,000 in the 737. The First Officer had flown about 7,500 hours in his career with about 1,500 hours in the 737; he was the pilot monitoring.

Both pilots remarked that all appeared normal until the aircraft began to deviate from the runway centerline. The Captain noted that the airplane suddenly diverged to the left, and attempts to correct the deviation with the rudder were unsuccessful. He stated that he briefly attempted to return the aircraft to the centerline by using the tiller to manipulate the steering of the nose gear but was unable to keep the aircraft on the runway.

Two Continental pilots who had flown the aircraft into Denver on the previous flight were passengers on the accident flight. Neither of the pilots was aware of any anomalies on the inbound flight and reported that all the aircraft's systems had operated normally.
Data Recorders
Bumping and rattling sounds audible on the Cockpit Voice Recorder (CVR) have been time-correlated with the Flight Data Recorder (FDR) and were found to have occurred as the airplane exited the runway and travelled through the grassy areas adjacent to the runway.

The aircraft reached a maximum speed of 119 knots, and it was traveling at 89 knots when the CVR and FDR stopped recording.

The airplane's Quick Access Recorder (QAR) and other electronics were retrieved and sent to the NTSB laboratory in Washington. The QAR, which records aircraft data, often has more parameters or information of higher fidelity than the Flight Data Recorder (FDR). Additional items, such as flight control and nosewheel steering actuators, were also removed from the airplane for testing and evaluation.

Physical inspection of the engines and information from the FDR has not indicated any evidence of pre-impact malfunctions with either engine. The FDR data shows that number one engine power was reduced before that of the number two engine during the accident sequence, and examination of the engine indicates that this reduction is consistent with snow and earth ingestion as the airplane departed the runway.

The FDR data also shows that both engines were commanded into reverse thrust following rejection of the takeoff by the flight crew, which occurred after the aircraft had already left the runway.
Landing Gear and Controls
A preliminary examination of the rudder system revealed no abnormalities or malfunctions.

The main landing gear and brakes, which had separated from the aircraft during the accident sequence, were found in good condition by visual examination. There were no signs of hydraulic leaking or flat spots on the tires.

The flight deck controls and corresponding control surfaces were found to be in the takeoff configuration.
Aircraft Cabin
There was no obvious damage to the passenger seats, which were found secured on their tracks. The safety belts all appeared intact although some showed evidence of fire damage.

Some components of the crew seats and restraint systems have been removed for further examination.
Evacuation Details
The three flight attendants indicated that there were no problems with the escape slides and that the emergency exit lights were brightly illuminated.

All occupants exited the airplane via the left side doors and overwing exits. The
flight attendants reported that the passenger who opened the overwing exit did so very quickly and easily. After a bottleneck of people developed by the left overwing exit, a Continental Airlines pilot, who was a passenger on the flight, directed passengers out via the doors.
The aircraft wreckage has been moved from the accident site to a secure area on the ramp, where the NTSB is continuing its examination.

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