Continental 737 Off Runway at DEN
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Shear (LBC)
Assume the worst, the xwind from the left disappears and is immediately replaced by one from the right, a net difference in direct xwind of close to sixty knots. Although the a/c probably couldn't T/O in a sustained 90 degree xwind of 60 knots, this new surmise isn't that. It could, in my opinion, recover from the configuration needed to offset the left x, then reconfigure to offset the new one from the right, and continue the T/O roll with no dire result. You're a met guy, possible? Flying through shear generally involves the Landing phase, but no reason not to entertain it on TO. What I've described is certainly plausible, but would mean some very strange wind action has gone unreported. Last month I landed in wind that was as much as 60 degrees left and 60 degrees right, gusting, with limits of 16 knots. The intimidating facet of shear on landing is A/S fluctuation, not heading discrepancies.
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crosswind limits
What I miss in the "crosswind might be a factor" assumption that part of the crosswind limitation is that when operated within crosswind limits the aircraft should remain controlable also after engine failure. Since there is no (reported) engine failure there is much more room for error, even outside crosswindlimits.
My bet is still something mechanical.
My bet is still something mechanical.
NTSB update today:
1) Engines were operating normally until they came in contact with ground due to landing gear collapse off runway. RH engine ingested snow and dirt, caught fire when fuel spilled on it after landing gear collapse damaged wing and fuel tank.
2) Bumps and rattles on CVR all occur AFTER departure from runway.
3) Captain (now interviewed after leaving hosp) says takeoff was normal and that the FIRST sign of trouble was the uncommanded veer to the left. He attempted heading correction with rudder, and then nose-wheel tiller, but neither worked.
No engine "bumps" from Flight 1404 until it veered off DIA runway : Local News : The Rocky Mountain News
Personally, I expect the winds will show up as at least a "factor" in the final report - with a mechanical primary cause that was exacerbated by the winds or brought on by the control deflections needed to correct for them.
1) Engines were operating normally until they came in contact with ground due to landing gear collapse off runway. RH engine ingested snow and dirt, caught fire when fuel spilled on it after landing gear collapse damaged wing and fuel tank.
2) Bumps and rattles on CVR all occur AFTER departure from runway.
3) Captain (now interviewed after leaving hosp) says takeoff was normal and that the FIRST sign of trouble was the uncommanded veer to the left. He attempted heading correction with rudder, and then nose-wheel tiller, but neither worked.
No engine "bumps" from Flight 1404 until it veered off DIA runway : Local News : The Rocky Mountain News
Personally, I expect the winds will show up as at least a "factor" in the final report - with a mechanical primary cause that was exacerbated by the winds or brought on by the control deflections needed to correct for them.
Last edited by pattern_is_full; 7th Jan 2009 at 21:43.
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Another News Story
The Denver Post's update has much the same info:
Experts: Crosswinds a factor in Denver air crash - The Denver Post
Experts: Crosswinds a factor in Denver air crash - The Denver Post
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airfoilmod,
I thought there was remarkably little "media bashing" in this thread.
So don't you start!
"... careened through open fields...." well, how would you have described it?
Occasionally, people forget that journalists have to describe events, not in technical terms that only make sense to a minute number of people, as in an NTSB report, but in a way that will evoke in the general public what it really meant to be there... and to have survived.
"Newspapers, bah." Most of us belong to the category who can read and sift.
Newspapers occasionally contribute something useful. Otherwise, we should let them get on with their job, which is .... selling newspapers.
CJ
I thought there was remarkably little "media bashing" in this thread.
So don't you start!
"... careened through open fields...." well, how would you have described it?
Occasionally, people forget that journalists have to describe events, not in technical terms that only make sense to a minute number of people, as in an NTSB report, but in a way that will evoke in the general public what it really meant to be there... and to have survived.
"Newspapers, bah." Most of us belong to the category who can read and sift.
Newspapers occasionally contribute something useful. Otherwise, we should let them get on with their job, which is .... selling newspapers.
CJ
I'm having troble reading an accepting the latest news reports. At this point I'm willing to accept as fact that the aircraft left the runway at 119 kts and then the bumps and the rattles occured as reported by the passengers and later confirme by the CVR.
However I just don't understand the timing of when and where the captain reportedly used the the nose wheel tiller as steering. My question has more to do with the reversion between rudder effectiveness and nose wheel tiller vs the event timings.
However I just don't understand the timing of when and where the captain reportedly used the the nose wheel tiller as steering. My question has more to do with the reversion between rudder effectiveness and nose wheel tiller vs the event timings.
LBC, rather than a wind shear causing problems, if there was a wind problem then wind gusts might be a more likely cause. The difference between the two is mean to peak intensity and speed of onset / decay; a horizontal gust being instantaneously more powerful.
Some good info in the references below; note how wind speed measurement can be inaccurate and the possible effects of gusts vs certificated max/demonstrated values.
If crosswind/gusts were a factor, then the vibration may have been due to nosewheel scrubbing.
The effectiveness of nosewheel steering at high speed depends on the nose leg loading, which is effected by elevator position, trim/cg, and airspeed.
Reduced load on the nose leg may enable the nose wheel to drift sideways (shudder) during a wind gust (aircraft nose yaws into wind); this is not normally a factor where the rudder is used correctly, it is increasingly effective as speed increases. An alternative or complementary cause could be over control of nosewheel steering (light loading/wet/slippery runway) so that again the nose wheel looses steering traction and shudders.
Thus to some extent it depends on piloting technique elevator positioning, use of nose wheel steering, and application of rudder.
In many aircraft, with speed above 80kts the rudder is the more effective control and nosewheel steering is not used. However, there is some indication that this variant of 737 depends on steering more than other aircraft; is this true?
Safety aspects of aircraft operations in crosswind.
Crosswind Certification - How does it affect you?
Some good info in the references below; note how wind speed measurement can be inaccurate and the possible effects of gusts vs certificated max/demonstrated values.
If crosswind/gusts were a factor, then the vibration may have been due to nosewheel scrubbing.
The effectiveness of nosewheel steering at high speed depends on the nose leg loading, which is effected by elevator position, trim/cg, and airspeed.
Reduced load on the nose leg may enable the nose wheel to drift sideways (shudder) during a wind gust (aircraft nose yaws into wind); this is not normally a factor where the rudder is used correctly, it is increasingly effective as speed increases. An alternative or complementary cause could be over control of nosewheel steering (light loading/wet/slippery runway) so that again the nose wheel looses steering traction and shudders.
Thus to some extent it depends on piloting technique elevator positioning, use of nose wheel steering, and application of rudder.
In many aircraft, with speed above 80kts the rudder is the more effective control and nosewheel steering is not used. However, there is some indication that this variant of 737 depends on steering more than other aircraft; is this true?
Safety aspects of aircraft operations in crosswind.
Crosswind Certification - How does it affect you?
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Thanks for the info, PEI_3721.
Without saying too much, I am fully aware of the LLWAS anemometer network at DEN. The first half of my career was spent developing the wind shear systems that are at DEN and at all the major airports in the US - and some overseas. The second half of my career has been spent studying turbulence (mainly in an aviation context), so I know a fair amount about wind gusts. I know just enough aerodynamics to be dangerous.
What I am not well-schooled in is the aerodynamics and control of aircraft taking off, so thanks for the link to the NLR document. Getting educated is always a good thing!
Without saying too much, I am fully aware of the LLWAS anemometer network at DEN. The first half of my career was spent developing the wind shear systems that are at DEN and at all the major airports in the US - and some overseas. The second half of my career has been spent studying turbulence (mainly in an aviation context), so I know a fair amount about wind gusts. I know just enough aerodynamics to be dangerous.
What I am not well-schooled in is the aerodynamics and control of aircraft taking off, so thanks for the link to the NLR document. Getting educated is always a good thing!
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AC Normal Until It Left the Runway?
This report says RTO initiated after departing the runway:
9NEWS.com | Colorado's Online News Leader | NTSB: Aborted takeoff came after plane left runway
and indicates that no failures are known prior to leaving the runway.
Similar updates in this story:
No engine "bumps" from Flight 1404 until it veered off DIA runway : Local News : The Rocky Mountain News
9NEWS.com | Colorado's Online News Leader | NTSB: Aborted takeoff came after plane left runway
and indicates that no failures are known prior to leaving the runway.
Similar updates in this story:
No engine "bumps" from Flight 1404 until it veered off DIA runway : Local News : The Rocky Mountain News
Last edited by repariit; 8th Jan 2009 at 03:14. Reason: Updated info
This article says the pilot tried to keep the plane on the runway by using rudder and tiller but couldnīt:
Pilot says he tried to keep airliner on runway - Examiner.com
Pilot says he tried to keep airliner on runway - Examiner.com
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Christiaan
If you've read my posts at all you must know I seldom slag the Press. Here, though, please read my post again; I quote the paper as posted by the paper. The syntax is so sloppy that it clearly implies, no says the a/c was continuing to accelerate as it "careened", etc. That is inexcusable, unless you think the pilot was continuing the T/O roll in the weeds. Bah again. rgds. AF
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RTO Initiated When?
Finn47 gave us the unedited information from the NTSB which shows "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".
The notion that RTO was initiated after 1404 left the runway (9News.com report above) is in error assuming "tire marks" are MG brake action. Looks like RTO happened 750 feet prior to leaving the runway.
It is unclear where 1404 was when the speed reached 119 knots. The speed was down to 89 knots when the berm tripped the FDR.
The notion that RTO was initiated after 1404 left the runway (9News.com report above) is in error assuming "tire marks" are MG brake action. Looks like RTO happened 750 feet prior to leaving the runway.
It is unclear where 1404 was when the speed reached 119 knots. The speed was down to 89 knots when the berm tripped the FDR.
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Some of the things you guys are saying are not clear.
1) The takeoff runway was 34R, and the winds were noted as 270 at 25 knots gusting to 32. Since the aircraft departed the runway to the left, and the wind was also from the left, how does crosswind factor in (thought clearly NTSB is interested in the crosswind)?
2) According to NTSB, the RTO sequence started after the aircraft departed the runway.
Assuming "which occurred" refers to event "rejection of the takeoff by the flight crew" and not event "commanded into reverse thrust", if the RTO sequence was started AFTER the aircraft departed the runway, what caused the tire marks prior to the runway departure? ABS failure (if equipped)?
1) The takeoff runway was 34R, and the winds were noted as 270 at 25 knots gusting to 32. Since the aircraft departed the runway to the left, and the wind was also from the left, how does crosswind factor in (thought clearly NTSB is interested in the crosswind)?
2) According to NTSB, the RTO sequence started after the aircraft 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.
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Dear flightsafety
Are you a pilot?
I ask, because as a pilot you should know that an airplane weathervanes INTO the wind...hence: crosswind from the LEFT, aircraft goes to the LEFT.
Quite simple, isn't it?
Are you a pilot?
I ask, because as a pilot you should know that an airplane weathervanes INTO the wind...hence: crosswind from the LEFT, aircraft goes to the LEFT.
Quite simple, isn't it?
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Tire marks might be from the side load on the main gear tires and have nothing to do with brake application.
Nose tire marks might also be from side loads, especially after the nosewheel steering was used.
Nose tire marks might also be from side loads, especially after the nosewheel steering was used.