NTSB Issues Update On Continental 737 Accident In Denver

Minuteman

Minuteman

I HAVE STRONG OPINIONS ABOUT AUTOMOTIVE LIGHTING!
http://www.ntsb.gov/Pressrel/2009/090107.html

On December 20, 2008, at 6:18 p.m. mountain standard time, Continental flight 1404, a Boeing 737-500 (registration N18611), equipped with CFM56-3B1 engines, departed the left side of runway 34R during takeoff from Denver International Airport in Denver, Colorado. The scheduled, domestic passenger flight, operated under the provisions of Title 14 CFR Part 121, was en route to George Bush Intercontinental Airport (IAH), Houston, Texas. A total of 38 passengers and crew were transported to hospitals, and five were admitted. There were no fatalities. The airplane was substantially damaged and experienced a post-crash fire, which was located on the right side of the aircraft.

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 members of the flight crew have been interviewed. The accident flight was their first flight on the fourth day of a four-day trip. ...

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.

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. 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.

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.

...

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.

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.

...
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Probably a stupid question, but can you have a rudder hard-over on the ground? Has this ever happened? Would it be feasable that a hard-over could cause this? Can't think of another reason how a trained crew would let the airplane get away from them in this manner.
 
I think an interesting tidbit is the mention of the 32 sensors located around the field recording data every 10 seconds....that data is still being used to find the exact wind at the time of the accident.

So basically this initial report rules out some things rather than identifying the reasons leading to the accident. It doesn't look like it was engine failure or blown tire/s.

On a personal note this accident being so fresh in my memory, has impacted my take-off decision making regarding weather conditions etc. Even though this wasn't necessarily a weather related accident, it gets me thinking that adverse weather or runway conditions (contaminated, poor braking) can make a mechanical failure a much more difficult condition to handle.
 
WacoFan said:
Probably a stupid question, but can you have a rudder hard-over on the ground?
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I suppose in theory you could. Whether a fully deflected rudder at less than 120 knots would be enough to send an airplane off the runway is another question.
 
Didnt Boeing have some issued with the 737 rudder in the early 90s where they had to ground all 737 400 and 500 models?
 
As well as that United flight in Denver before the USAir accident and an Eastwind incident involving rudder reversal.
 
I believe those instances were on the 737-200. The -300, -400, -500, and NG has a different system. The hydraulics are different as well. I think a rudder hardover is highly unlikely in this case. I am starting to get a bad feeling about this.
 
Capt. Caucasian said:
I believe those instances were on the 737-200. The -300, -400, -500, and NG has a different system. The hydraulics are different as well. I think a rudder hardover is highly unlikely in this case. I am starting to get a bad feeling about this.
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The United and Eastwind incidents were -200s (not 100% sure on the Stinger Bee (love that callsign) one). USAir was a -300.
 
I have never heard of the term, "a rudder-hard-over". Anybody want to enlighten me?
Is just a pilot stomping on the rudder or is it something mechanical pushing the rudder hard over?
 
I have a bad feeling this accident had nothing to do with a mechanical issue. I'm just happy nobody was killed or seriously injured. We'll see soon what we can learn from this.
 
I'm guessing it does, but since I have never flown one: does the 737 nose wheel have the ability to go into a free caster mode?
 
Another 737 systems question-is the tiller steering inhibited above a certain speed? I thought I remember hearing that that is done on some transport category aircraft, but I could be wrong.
 
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