Update on Continental crash in Denver: is it a first look event?

Posted on 02. Jan, 2009 by in Featured

A reader raised some very good points about the continental 737 crash in Denver:

1. Chip,
I saw the Airnav website posted winds gusting 280 degrees at 33 knots. Since this was runway 34R, it seemed to me that just a quartering left front crosswind that should not have that adverse of an impact on a 737. That’s why I’m inclined to believe it’s a blown tire (perhaps debris on the runway?). Do you know were they actually at V1 when they aborted? That taxiway they went off at is about 1/3 of the way down the runway…approx 4000 feet. Is that enough runway for a 737 to reach V1? I’m not a 737 pilot, just private, so I don’t know myself.

Excellent questions, let’s go to the charts: I checked the the Jeppesen 10-9 for the runway heading of the 34’s in Denver. They actually are set at 350 degrees magnetic. Large airports number sets of parallel runways differently to identify them. For example: DFW has 5 north/south runways all the same heading 354/174 degrees. Two are on the west side of the terminal complex and called/charted runways 36/18 left and right. The three on the east side are 35/17 left, center and right; even tho they all have the same heading.

Side note to non-pilots: All runways are charted/named according to their predominant magnetic heading; i.e. a runway with a heading of 273 degrees is runway 2 7 (two seven).

Also I’m not sure if the referenced wind is magnetic or true. If true we would have to adjust further for magnetic variation. For simplicity let’s assume it is magnetic. Referencing my cross wind chart for a 33 knot wind 70 degrees off of heading shows a cross wind component of 30 knots. The maximum cross-wind component for a 737 is 35 knots. I fly the MD-80, its max is 30. Having landed with a 30 knot crosswind I can tell you it is a hand full and a true limit IMO (the manual lists it as a demonstrated limit).

4,000 feet is more than enough runway to achieve a V-1 speed. SNA (John Wayne Airport) in LA is a 5700 foot runway. So the aircraft that operate there have to be able to accelerate to V-1 and then abort coming to a stop in the remaining runway.

Many things can affect a V-1 speed: flap setting, reduced power, weight of passengers and fuel, and meteorological conditions. The 737-500 was going to Houston; so given the pax load of approx 100 people and the fuel required to go to Houston and the speeds cited in the article. In my opinion they were at or past V-1 when the crew initiated the abort. At DEN the runways are very long, 3 4 right is 12,000 feet, thus a late decision to abort can be safely made and executed under normal conditions. The wind was not normal conditions IMO.

I keep going back to the wind; it is significant. I am starting to think that we may have one of those very rare first events that will dictate a new limit and training. The wingtips and their effect on takeoff in a crosswind, IMO will have to be looked at closer. The DC-9 (model 83) Operating Manual does not differentiate a cross wind limit between takeoff and landing. There is no reference to aborted takeoff wind limits or guidance. FAA aircraft certification follows a very strict set of procedures and requirements for all aircraft. If there is no limit/guidance for the DC-9 series I suspect there is none for the 737.

Why is this significant?

When a Captain initiates an abort (rejected takeoff) a series of automatic systems are activated. In the DC-9 (MD-80); when the Captain pulls the throttles to idle and deploys the thrust reversers; auto-brakes apply with maximum pressure, spoilers on the wing raise to 60 degrees. These all can affect directional control and thus are set for a zero wind condition. Which means they activate neutrally and thus can take out ANY CROSSWIND INPUTS initially, which must be then over ridden by the crew to maintain directional control. At 150 miles per hour things happen fast, and keep in mind that the V-1 is an INDICATED speed, DEN is 5,000 feet above sea level so the actual ground speed was faster than the reported abort speed. If a severe yaw developed or deepened, caused by the auto systems, with the wind near the cross-wind limits it could have been beyond the capability of the aircrafts flight controls to correct it. Below is a 747 rejecting a take off (wet runway), note the spoilers raised on the wing.

here is a close up of spoiler deployment:

The video below is from an AIRBUS flight test for certification, some things to note: 1. look at the wind sock, the wind was down the runway. 2. Watch the rudder (back panel of vertical tail) movement; the crew was fighting to maintain conrol with the wind down the runway. 3. Finally, keep watching the video, look at the smoke coming from the brakes. 3/4’s of the way through the tape they catch on fire and burn furiously.

For now the focus will remain on the noise which caused the crew to abort; however I think the real story will be the wing tipped 737’s ability in a crosswind abort to maintain directional control. I also think that it could lead to a review of take-off/abort cross-wind limits for all certified aircraft.

No Responses to “Update on Continental crash in Denver: is it a first look event?”

  1. Rick 3 January 2009 at 10:06 #

    It’s a fascinating theory you’re raising about the winglets, which I always had the impression they were thought to improve directional control even though their primary goal was to reduce drag.
    They’re supposed to finish removing the plane’s hull to a hanger today (Saturday), so we’ll be watching to see what that nose gear and it’s tires looks like.

  2. Rick 3 January 2009 at 11:12 #

    The more I think about your theory, the more I think you’re onto something with the wing tips or winglets. The thing that keeps coming back to my mind is the loud noises picked up on the voice recorder and “bumpy” ride descriptions by flight crew and passengers….all leading up to the abort decision. That bothers me a lot. That’s why I think some failure with the nose gear was a significant contributor in the chain of events. Do you have any thoughts about what might have caused the noises and the rough takeoff roll?

  3. Chip 3 January 2009 at 16:14 #

    Again your questions deserved an individual thread.

  4. Robert Hadow 11 March 2009 at 14:13 #

    You said, “I’m not sure if the referenced wind is magnetic or true.”
    All winds reported at an airport are reported with respect to magnetic north. Winds aloft are always reported with respect to true north. This is part of the Private Pilot body of knowledge.

  5. chip 12 March 2009 at 07:49 #

    I’m not familiar with the AIRNAV site and didn’t source it, I was answering a readers question. I don’t report absolutes unless I know it to be, had it been an airport ATIS or field report I would not have put in the caveot.

    “Winds aloft are always reported with respect to true north.” Not in the airlines, most use magnetic. My airline uses magnetic for all winds aloft so that the Tail/Head wind component can be used for planning. Be careful of absolutes; This is part of the Airline/Naval Aviator/Test Pilot body of knowledge.

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