Photo: Aerial photo of wreckage, from NTSB AAR 10/04, figure 2.

Eddie Sez:

We tend to focus our simulator training on engine failures, systems-related emergencies, and the obvious weather challenges. Weather in the simulator is usually summed up by "hot and heavy" or "ice and rain." We don't do a lot of realistic crosswind training and probably none of that realistically deals with gusts. Wind shear training boils down to a series of programmed problems. In other words, we train to what we are technologically able to train to in the box.

This mishap was caused by a captain who had a lack of finesse with the rudder on a very gusty crosswind which increased unpredictably due to windshear. The crosswind, the gust, the wind shear should not have ended up with the aircraft departing the runway laterally. A pilot with a reasonable amount of experience should have been able to handle it all. But we never test our captains under realistic conditions because we don't know how to do that in a simulator. We simply hope the pilot has seen enough of this before we hand him or her the keys to a multi-million dollar jet and the lives of passengers. The only solution would seem to be this: experience. But if you lack that experience, perhaps researching a few mishaps and talking to pilots who have this under their belts. My advice (for what it is worth):

  • When in doubt, wait it out. In this case the winds went from 11 knots to over 25 in just a few minutes. Perhaps in a few more they could exceed the airplane's limits (they did not in this case) or die down.

  • Just because everyone else is using the selected runway doesn't mean they are right. If the runway is wrong, say so on the radio. That can change things immediately. I was once at LaGuardia and was given the choice of using the runway everyone else was or waiting an hour. I said, on ground control frequency, "I will have to wait, a fifteen knot tailwind is against the limitations in my flight manual and just about every flight manual I've ever read." Once it was on tape, every airliner on frequency requested the runway be changed. And it was.

  • When applying rudder on takeoff for a crosswind, you will usually need most of it when at low speed and a decreasing amount as you accelerate. Put what you think you need at the beginning of the takeoff roll and wait a few seconds before changing it.

  • When adjusting your rudder input, add or subtract in small increments and wait a second.

  • If you are making rudder reversals you are doing something wrong.

  • Most importantly: you need to fly the airplane starting with brake release. Even when stationary, a wind means every air foil on the airplane is generating a force and you need to make sure that force is pointed where you intend.

One last note. The captain had a very good record and was probably genuinely surprised by the outcome of this takeoff. It is vitally important that we pilots acknowledge the fact we "don't know what we don't know." We must always be in learn mode and the best way to do that once you think you have the game mastered, is to research mishap reports from other pilots who also thought they had the game mastered.

What follows are quotes from the relevant regulatory documents, listed below, as well as my comments in blue.


Accident Report


Narrative

Figure: Continental Airlines 1404 Wind / Rudder / Heading / Lateral load, from NTSB AAR 10/04, figure 1.

[NTSB AAR 10/04, ¶1.1]

  • The pilots stated that they taxied toward runway 34R without event. About 1812, the DEN air traffic control (ATC) tower (ATCT) ground controller instructed the pilots to monitor the DEN ATCT local controller’s frequency while awaiting takeoff clearance. At 1814:27, the DEN ATCT local controller cleared the accident pilots to taxi into position on runway 34R and hold (to ensure adequate separation behind the airplane that took off on runway 34R at 1814:20). The pilots taxied onto the runway and completed the before-takeoff checklist while they held in position on the runway. According to CVR data, at 1816:16, one of the pilots commented, “what are the winds?” The accident captain noted to the first officer, “looks like...some wind out there.” The first officer replied, “yeah,” and the captain stated, “oh yeah, look at those clouds moving.”

  • At 1817:26, the DEN ATCT local controller told the accident pilots that the wind was from 270° at 27 knots, assigned a departure heading of 020°, and cleared them for takeoff on runway 34R. (In their written statements, both pilots noted that although the wind velocity had increased from the 11 knots that had been reported by the ATIS, the tower-reported wind was still within the airline’s published crosswind guideline of 33 knots for a clear, dry runway like runway 34R.) The first officer acknowledged the clearance, and, as they began the takeoff roll, the captain stated to the first officer, “alright...left crosswind, twenty ah seven knots...alright look for ninety point nine.”
  • The 90.9 refers to the engine takeoff setting.

  • At 1817:49, the CVR began recording the sound of increasing engine noise. The captain stated that, as the airplane accelerated, he shifted the primary focus of his attention from the thrust levers to outside visual references, keeping the airplane on the runway centerline. Meanwhile, according to post accident interviews, the first officer’s attention was primarily focused on monitoring the engine instruments, consistent with company policy. At 1818:04, the first officer advised the captain that the power was set at 90.9 percent. The first officer stated that after the power was set, he shifted his attention to monitoring the airspeed so that he could make the standard airspeed callouts, the first of which was at 100 knots.

  • During the airplane’s initial acceleration along the runway centerline, information from the flight data recorder (FDR) indicated increasing right rudder pedal inputs, while the control wheel and column and their respective control surfaces were at their neutral positions. At 1818:07, as the airplane accelerated through about 55 knots, the airplane’s heading began to move left, and the FDR recorded the beginning of a large right rudder pedal input that peaked at 88 percent of its available forward travel about 2 seconds later. This 88-percent right rudder pedal input was followed by a substantial reduction, reaching about 15 percent by 1818:09.75. Almost simultaneous with the onset of this large rudder pedal input, the FDR began to record a left control-wheel input. The nose of the airplane moved to the right; however, at 1818:10, as the airplane was accelerating through about 85 knots, the airplane’s nose reversed direction and began moving back to the left at a rate of about 1° per second. This leftward movement of the nose continued for about 2 seconds and was accompanied throughout its duration by another substantial right rudder pedal input. This second large right rudder pedal input peaked at 72 percent of available forward displacement at 1818:11.75 and a speed of more than 90 knots and then decreased again, reaching 33 percent at 1818:13.25.
  • The NTSB report notes the pilot over corrected during his first application and then took out too much rudder. Things were complicated by the fact the gusty winds were changing during these rudder inputs. But even if the winds were steady, the rudder movement shows very poor technique. For a steady crosswind pilots should apply a little less than they think necessary and wait. If more is needed it can be, if less is needed a portion of the amount used should be taken out, not all of it. For a gust crosswind these techniques are even more important. With the reduction from most of the rudder to almost none of the rudder, the pilot also risks a rapid rudder reversal which can overstress the vertical fin.

  • During this second large right rudder pedal movement (at 1818:12), the airplane’s left turning motion slowed for about 1 second, and then the nose began moving rapidly to the left again. A fraction of a second later (at 1818:13.25), the right rudder pedal was abruptly relaxed (reaching its neutral position about 1 second later). At 1818:13.5, the CVR recorded one of the pilots exclaiming, “Jesus,” and, at 1818:13.6, the FDR recorded the beginning of a transition from left control wheel input (consistent with crosswind takeoff technique for a left crosswind) to right control wheel input (crossing the control wheel’s neutral point at 1818:14). Although the pilot briefly made a small right rudder pedal input at 1818:14.25, the FDR did not record any more substantial right rudder pedal inputs as the airplane continued to veer to the left.
  • The control wheel input to the right is an indication of panic. More about this: Pilot Psychology / Panic.

  • At 1818:15, the CVR recorded the first officer saying, “oh [expletive].” At 1818:17, the CVR began to record the sound of increasing background noise as the airplane left the runway, and, at 1818:21, the captain called to reject the attempted takeoff. FDR data showed engine power reductions, as well as activation of the brakes. Thrust reverser deployment began about 3 seconds after the airplane left the runway.

  • The investigation revealed that the airplane departed the left side of runway 34R about 2,600 feet from the approach end and crossed taxiway WC and an airport service road before coming to a stop on a heading of about 315° in an area just north of DEN aircraft rescue and firefighting (ARFF) fire station #4. The airplane was still moving at a speed of about 90 knots when electrical power was lost, and the FDR and CVR stopped recording at 1818:27. Post accident interviews with passengers and crewmembers, as well as evidence from the crash site, indicated that, as the airplane crossed the uneven terrain before coming to a stop, it became airborne, resulting in a jarring impact when it regained contact with the ground.

  • According to the captain, after the airplane left the runway and he subsequently initiated the rejected takeoff, they were “along for the ride.” Both pilots stated that there were a couple of “very painful” bumps before the airplane came to a stop. They indicated that they were somewhat dazed or “knocked out” for 1 or 2 minutes after the airplane stopped and made no immediate attempts to get up or leave the cockpit. The first officer stated that he could hear activity from the cabin and considered making an announcement, but he was hindered because the cockpit was completely dark. By the time the pilots left the cockpit, the cabin crew, assisted by some deadheading pilots, had evacuated all of the passengers. The first officer and a deadheading captain were the last to exit the airplane.

Analysis

[NTSB AAR 10/04, ¶1.5.1]

The captain had a flawless record, but we don't know about his gusty crosswind capability. Simulator technology doesn't really test pilots realistically and it isn't a training item in most curricula.

[NTSB AAR 10/04, ¶1.7]

[NTSB AAR 10/04, ¶1.10.4]

One can debate the tower's role in runway selection and the role they played in providing wind information that may not have been the most pertinent of several to choose from. The winds were changing so rapidly it may not have made a difference, given the captain's stick and rudder performance. (More about that soon.)

[NTSB AAR 10/04, ¶1.16.1.2]

[NTSB AAR 10/04, ¶1.16.2.1]

[NTSB AAR 10/04, ¶2.2]

[NTSB AAR 10/04, ¶2.2.1]

[NTSB AAR 10/04, ¶2.3.2.2]

[NTSB AAR 10/04, ¶3.1]


Probable Cause

[NTSB AAR 10/04, ¶3.2]


See Also

Abnormal Procedures & Techniques / Windshear

Pilot Psychology / Panic


References

NTSB Aircraft Accident Report, AAR-10/04, Runway Sode Excursion During Attempted Takeoff in Strong and Gusty Crosswind Conditions, Continental Airlines Flight 1404 Boeing 737-500, N18611, Denver, Colorado, December 20, 2008