Continental Airlines Flight 1404

Investigation

The aircraft's black boxes (data and sound) were recovered from the wreckage in usable condition. The cockpit voice recorder did not reveal any apparent problem until 41 seconds after the aircraft's brakes were released, just before takeoff. At that point, a bumping or rattling sound could be heard, and the crew aborted the takeoff four seconds later. Both recorders stopped working six seconds after that (before the plane came to a stop). At one point during the sequence, the plane's speed reached 119 kn.

When interviewed, First Officer Levang told investigators that he was unaware of any problem until the plane was traveling between 87 and 90 kn, when it moved away from the runway's centerline and made a "sudden left turn." He indicated that Captain Butler, who was too badly injured to interview with officials when the investigation began, was flying at the time. Both the captain and first officer had clean safety records when the crash occurred and were experienced pilots.

Wheel marks left on the ground, and initial reports from passengers and firefighters indicate that the plane was airborne briefly. When during the sequence the fire started is unclear. No snow or ice was on the runway, but 31 kn crosswinds were happening at the time.

The flight crew who flew the aircraft to Denver prior to the incident flight was also on board, though not on duty, and reported having no difficulties with the plane during their previous flight. It had suffered an engine failure and subsequent emergency landing in 1995, after which both engines were replaced, but was otherwise undamaged in that incident.

Initial speculation suggested that the plane could have suffered a landing gear malfunction that might have resulted in a wheel lockup during the takeoff roll, leading to the runway excursion. National Transportation Safety Board (NTSB) officials said that when the takeoff began, the aircraft's engines appeared to be functioning properly, its tires were inflated, and the brakes did not appear as if they had failed or otherwise malfunctioned, concluding that the landing gear did not cause any problems.

On July 17, 2009, focus had shifted to a possible large gust of wind or a patch of ice. Captain David Butler stated: "My speculation is that we either got a big, nasty gust of wind or that, with the controls we had in, we hit some ice." He also stated that he stopped pushing on rudder controls because they had stopped working. The winds were reported at about 24 to 27 kn from the northwest with gusts up to nearly 32 kn just before the airliner began its takeoff roll northward down a north–south runway. The 737 has a crosswind limitation for takeoff of 33 kn on a dry runway.

Contrary to the "average" wind data reported to the incident pilots, the NTSB investigation found that a sensor at one end of the runway showed a crosswind of 40 kn, with analysis showing the airplane was hit with a peak gust crosswind of 45 kn. In addition to being much higher than the data reported to the pilots as they prepared for takeoff, this was also much higher than the airline industry used in pilot training. The NTSB also received a report analyzing 250,327 departures involving 737-500s and found that only four of those departures (less than 0.002%) had experienced a crosswind above 30 kn, meaning that for a commercial pilot to have real-life experience with crosswinds anywhere near the velocity that hit Continental Airlines Flight 1404 that day was nearly impossible. The NTSB believes that this is why the pilot believed that his rudder controls were not working, deciding not to push the rudder anymore and to focus instead on other inadequate remedies to the situation.

On July 13, 2010, the NTSB published that the probable cause of this accident was the captain's cessation of right rudder input, which was needed to maintain directional control of the airplane, about four seconds before the excursion, when the airplane encountered a strong and gusty crosswind – with a contributing factor of inadequate crosswind training for extreme wind gusts in the airline industry. A further contributing factor was no requirement for the air traffic control system to provide sufficient wind information to the air traffic controllers (ATCs) and pilots. In response to the NTSB report, the Federal Aviation Administration required the airline industry to adjust the crosswind training protocols for pilots, and required ATCs to provide multiple sources of wind information, rather than averages, to pilots.