Continental 737 Off Runway at DEN
Join Date: Jan 2006
Location: US
Posts: 2,205
Likes: 0
Received 0 Likes
on
0 Posts
Flight Safety -
Agreed about the effectiveness of the rudder at 119 kts but the abort didn't start until after departing the runway. With takeoff power set the a/c would have been accelerating up to, or even after, departing the runway. So more important is what was the speed of the a/c at the time it started to swing to the left? That's the ability of the rudder to provide crosswind control.
Another factor to consider, were the nosewheels providing traction or were they overloaded by slip angle? All on our crosswind takeoffs are done with balanced traction and the tracking stability provided by the nose wheel traction forward of the C.G. Imagine doing a crosswing takeoff and at a unknown speed losing nosewheel traction (ie, like the sim 'icy runway' traction)? That would drastically reduce the a/c's crosswind limits.
Interesting investigation.
Agreed about the effectiveness of the rudder at 119 kts but the abort didn't start until after departing the runway. With takeoff power set the a/c would have been accelerating up to, or even after, departing the runway. So more important is what was the speed of the a/c at the time it started to swing to the left? That's the ability of the rudder to provide crosswind control.
Another factor to consider, were the nosewheels providing traction or were they overloaded by slip angle? All on our crosswind takeoffs are done with balanced traction and the tracking stability provided by the nose wheel traction forward of the C.G. Imagine doing a crosswing takeoff and at a unknown speed losing nosewheel traction (ie, like the sim 'icy runway' traction)? That would drastically reduce the a/c's crosswind limits.
Interesting investigation.
Last edited by misd-agin; 9th Jan 2009 at 14:44. Reason: incomplete sentence
Join Date: Jan 2009
Location: alameda
Posts: 1,053
Likes: 0
Received 0 Likes
on
0 Posts
I agree with the poster that the NTSB probably already knows what caused this accident.
IF(say again IF) it were a rudder hardover/jam...the NTSB IS PROBABLY trying to figure out how to get it fixed without grounding every 737 under their jurisdiction.
IF it were mishandling of the tiller, one simply must wonder why a pilot would use the tiller at this speed. ( I know the abovementioned John Cox, and don't like him...but I agree with his view on the tiller)
IF it were a wind gust within the operational limits of the 737, one must question pilot skill...OR must demand a new test of the 737 crosswind limits.
SO far, no one has mentioned the concept of momentary or subtle incapacitation of the crew. IF I were the copilot and saw the plane drifting off the centerline, I sure would speak up and if , after two communications without captain response, I would take the plane from the captain. (we have a two communication rule at our airline).
AND if the rudder went nuts (hardover) and I wanted to keep the plane on the runway, I would have used assymetric thrust to keep the plane on the runway...in this case idle or reverse right and maintain forward thrust on left.
I've flown for the airlines for many years and have seen some pretty sloppy crosswind technique especially on takeoff.
I would hope that the exact position of the stab trim and the exact loading of the aircraft would soon be made public. Can you all imagine if the plane had a nose down trim or was incorrectly loaded? The plane might have gotten very light on the mains and was running along on the nosewheel... think of the consequence to that.
regards from the heart of the golden west...
IF(say again IF) it were a rudder hardover/jam...the NTSB IS PROBABLY trying to figure out how to get it fixed without grounding every 737 under their jurisdiction.
IF it were mishandling of the tiller, one simply must wonder why a pilot would use the tiller at this speed. ( I know the abovementioned John Cox, and don't like him...but I agree with his view on the tiller)
IF it were a wind gust within the operational limits of the 737, one must question pilot skill...OR must demand a new test of the 737 crosswind limits.
SO far, no one has mentioned the concept of momentary or subtle incapacitation of the crew. IF I were the copilot and saw the plane drifting off the centerline, I sure would speak up and if , after two communications without captain response, I would take the plane from the captain. (we have a two communication rule at our airline).
AND if the rudder went nuts (hardover) and I wanted to keep the plane on the runway, I would have used assymetric thrust to keep the plane on the runway...in this case idle or reverse right and maintain forward thrust on left.
I've flown for the airlines for many years and have seen some pretty sloppy crosswind technique especially on takeoff.
I would hope that the exact position of the stab trim and the exact loading of the aircraft would soon be made public. Can you all imagine if the plane had a nose down trim or was incorrectly loaded? The plane might have gotten very light on the mains and was running along on the nosewheel... think of the consequence to that.
regards from the heart of the golden west...
Guest
Posts: n/a
Hornet
very succinct and to the point. I was squeamish about positing pilot mishandling, and have (and will) continue to have complete faith in the crew, until the need to change my opinion becomes obvious. My question is, did I miss a report/release targeting tillering as a possible cause? My post yesterday I put together without the benefit of seeing such a release, was there one?
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
Thanks misd - good post IMO. Once again, however, I have to caution against 'believing' the US press based on recent coverage of this accident.
1) The first para (your red) is written to 'suggest' an error by the crew, is it not?
2) The second para (blue) 'heightens' this titillating hint.
3) Para 4 (red/blue) is misleading, unless the NTSB have changed their initial statement which you quote later.
From our 'experts' Kev and John onwards, we gain little. It is stated by the NTSB that the rudder WAS being used first and therefore there was little else left for the crew other than the tiller except diff thrust and mainwheel brakes.
I would like to know about c of g, although even with a well-aft c of g, again the rudder should have coped with normal deviations.
There is always the possibility that a rudder hard-over to the left occurred, which could cause the swerve to the left with an increasing force as airspeed increases. I am assuming also that the 'rudder fine' steering function would not be affected by a hydraulic hard-over but is driven by pedal position - anyone confirm?
NB Whilst making a cuppa while composing this, a few more 'supportive' posts have appeared, so I'm a bit late at the gate.
1) The first para (your red) is written to 'suggest' an error by the crew, is it not?
2) The second para (blue) 'heightens' this titillating hint.
3) Para 4 (red/blue) is misleading, unless the NTSB have changed their initial statement which you quote later.
From our 'experts' Kev and John onwards, we gain little. It is stated by the NTSB that the rudder WAS being used first and therefore there was little else left for the crew other than the tiller except diff thrust and mainwheel brakes.
I would like to know about c of g, although even with a well-aft c of g, again the rudder should have coped with normal deviations.
There is always the possibility that a rudder hard-over to the left occurred, which could cause the swerve to the left with an increasing force as airspeed increases. I am assuming also that the 'rudder fine' steering function would not be affected by a hydraulic hard-over but is driven by pedal position - anyone confirm?
NB Whilst making a cuppa while composing this, a few more 'supportive' posts have appeared, so I'm a bit late at the gate.
Guest
Posts: n/a
Nose heavy
If nose heavy, hornet, and a slight deviation to the left occurred, the pilot may have attempted to "lighten the nose" by pulling the yoke, reloading the mains, and bouncing. ohoh pio. A sequence of cg "corrections" could have caused things to deteriorate quickly. Which way were the two nose wheels pointing, when, and which was the direction of the deposition of rubber, and when. The FDR knows all, and has told all. The result of the investigation is at hand, one thinks.
Guest
Posts: n/a
Deviation Left
As reported by the pilot. Causes? Rudder malfunction or sloppy ruddering.
Nosewheel turns a/c. At 115knots (~) n/w malfunction or sloppy heading.
A nose gear with steering authority at this velocity is unacceptable, mechanical or humanical.
Nosewheel turns a/c. At 115knots (~) n/w malfunction or sloppy heading.
A nose gear with steering authority at this velocity is unacceptable, mechanical or humanical.
Join Date: Jan 2001
Location: Dallas, TX USA
Posts: 739
Likes: 0
Received 0 Likes
on
0 Posts
Rogue Wind Gust
Was in the shower this morning and starting thinking about the possibility of a rogue wind gust. Denver is east of a large mountain range, and the wind was from the west and gusting that day. Then I found these.
NOAA weather history link (wind related) for Denver for Dec 20th, throughout the years.
NWS Denver/Boulder, CO - Denver/Boulder Wx History
New York Times article from 1991, referring to an earlier wind related UAL 737 crash at Colorado Springs.
Violent Rogue Wind Emerges in Search for Clues to Air Crash - New York Times
Edited to add: Found the NTSB link for the UAL 737 accident in March 1991. Probable cause listed as rudder servo valve failure.
DCA91MA023
NOAA weather history link (wind related) for Denver for Dec 20th, throughout the years.
NWS Denver/Boulder, CO - Denver/Boulder Wx History
New York Times article from 1991, referring to an earlier wind related UAL 737 crash at Colorado Springs.
Violent Rogue Wind Emerges in Search for Clues to Air Crash - New York Times
Edited to add: Found the NTSB link for the UAL 737 accident in March 1991. Probable cause listed as rudder servo valve failure.
DCA91MA023
Last edited by Flight Safety; 9th Jan 2009 at 16:09.
A nose gear with steering authority at this velocity is unacceptable, mechanical or humanical
Guest
Posts: n/a
Limiting scope
A/C operate in three axes. For the most part, myself included, focus has been on a/c heading, yaw. On the recorder and its accelerometers, pitch and roll would complete the picture. Most (all?) accidents begin at a place that could have been avoided, whether in design (overheated servo cylinder, 737 rudder, eg.) or flight management, cg? The Rudder is a "trimming" device, and , believe it or not, is not a critical control (for the most part). Given the correct runway, a 737 could launch with a gust lock pinning the rudder neutral. What makes it interesting on this thread is how people take information in and craft their comments. One thing I know now that I'm retired and reasonably conversant with the net is that it is
(as ever) virtually impossible to judge a book by its jacket.
lomapaseo-
I think that's my point. That's why the tillering is important, sir
(as ever) virtually impossible to judge a book by its jacket.
lomapaseo-
I think that's my point. That's why the tillering is important, sir
Last edited by airfoilmod; 9th Jan 2009 at 16:31. Reason: Response to lomapaseo
Guest
Posts: n/a
DCate
I read 10k total and 4k in type, and yes, tillering suggests something bad has already occurred.
The captain's reason for the onset of the accident was perfunctory and without elaboration (reportedly). This suggests that he doesn't know what happened (could be), or he ain't sayin'. Either way, I give him the benefit of the doubt.
The captain's reason for the onset of the accident was perfunctory and without elaboration (reportedly). This suggests that he doesn't know what happened (could be), or he ain't sayin'. Either way, I give him the benefit of the doubt.
Join Date: Sep 2008
Location: MI
Posts: 570
Likes: 0
Received 0 Likes
on
0 Posts
"January 7, 2009
NTSB ISSUES UPDATE ON CONTINENTAL 737 ACCIDENT IN DENVER
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. The Captain, the pilot flying, had accumulated a total of about 13,000 hours, with about 5,000 in the 737. The First Officer had flown about 7,500 hours in his career with about 1,500 hours in the 737; he was the pilot monitoring."
-----------------------------------------------
Well, guess we gotta split the difference!
Either way, I don't see him using the nosewheel steering under NORMAL situations.
NTSB ISSUES UPDATE ON CONTINENTAL 737 ACCIDENT IN DENVER
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. The Captain, the pilot flying, had accumulated a total of about 13,000 hours, with about 5,000 in the 737. The First Officer had flown about 7,500 hours in his career with about 1,500 hours in the 737; he was the pilot monitoring."
-----------------------------------------------
Well, guess we gotta split the difference!
Either way, I don't see him using the nosewheel steering under NORMAL situations.
airfoilmod;
Enjoying your contributions...
A thought on the nosewheel/crosswind discussion...as potential "causes", I know you're not positing same but exploring out loud), I am pondering the use of the tiller, the relative coarseness, depending upon skill and finesse and also runway roughness, of any resulting steering angle, a "skipping" nosewheel and the fact that nosewheel steering is, (of course), always available through the rudder pedals and lastly, the increasing effectiveness of the rudder as CAS increases, really lastly, certification issues re demonstrated crosswinds.
As I mentioned in an earlier post, when the airplane was introduced the A320's steering handle and the rudder pedals used to disconnect from the nosewheel steering at around 75kts but when the industry complained about "excursions" in high crosswinds, they re-programmed it to, I believe, 105kts and it worked much better. I have had experience under both regimes and the airplane did take dirty darts towards the weeds at 75kts in high crosswinds but, although one certainly knew when the nosewheel steering disconnected, it wasn't a control problem in my experience.
Where I'm going with this is, I am not at all convinced that use of the tiller, in and of itself to control direction or correct untoward direction, would result in an excursion. A skipping nosewheel would not, on it's own, cause, or result, in a heading diversion to the left - rather, other forces greater than the reducing nosewheel traction at higher nw angles that cannot be countered by the use of appropriate rudder, could cause a diversion to the left, and once again we are into "test pilot territory" because the crosswinds were below the demonstrated limits for the airplane.
Likely we're talking the same thing - perhaps a slightly different way of expressing it.
"Rogue gusts?" More possible now than when we first began this thread but not at all proven. I agree - the causes are likely known now through the recordings and the experienced analysis of the data.
Enjoying your contributions...
A thought on the nosewheel/crosswind discussion...as potential "causes", I know you're not positing same but exploring out loud), I am pondering the use of the tiller, the relative coarseness, depending upon skill and finesse and also runway roughness, of any resulting steering angle, a "skipping" nosewheel and the fact that nosewheel steering is, (of course), always available through the rudder pedals and lastly, the increasing effectiveness of the rudder as CAS increases, really lastly, certification issues re demonstrated crosswinds.
As I mentioned in an earlier post, when the airplane was introduced the A320's steering handle and the rudder pedals used to disconnect from the nosewheel steering at around 75kts but when the industry complained about "excursions" in high crosswinds, they re-programmed it to, I believe, 105kts and it worked much better. I have had experience under both regimes and the airplane did take dirty darts towards the weeds at 75kts in high crosswinds but, although one certainly knew when the nosewheel steering disconnected, it wasn't a control problem in my experience.
Where I'm going with this is, I am not at all convinced that use of the tiller, in and of itself to control direction or correct untoward direction, would result in an excursion. A skipping nosewheel would not, on it's own, cause, or result, in a heading diversion to the left - rather, other forces greater than the reducing nosewheel traction at higher nw angles that cannot be countered by the use of appropriate rudder, could cause a diversion to the left, and once again we are into "test pilot territory" because the crosswinds were below the demonstrated limits for the airplane.
Likely we're talking the same thing - perhaps a slightly different way of expressing it.
"Rogue gusts?" More possible now than when we first began this thread but not at all proven. I agree - the causes are likely known now through the recordings and the experienced analysis of the data.
Guest
Posts: n/a
PJ2
My feeling is:
Tillering at the speed we assume is not standard and suggests a problem.
My belief is not that the n/g input didn't work, but that it did. What does a pilot do with a heavy jet very close to V2 that smartly changes heading? Rudder, of course. The Captain says that was "not effective."
OK. Tiller? NO. Not me. How invested are you in the TO? It is at this point in the Roll I'm loudly saying Abort. An a/c that isn't tracking is a no go. If the tiller is an effort to maintain/DC while shutting down, fine. The word so far is that abort got yelled after leaving concrete. The a/c was doing what it was supposed to do, predictably. T/O thrust, but no rudder? OK I'll just turn into the wind and fly, like I was built to. My question, and Strike me dead if someone thinks I'm faulting crew, the information so far leads one to ask why, w/o DC, the Roll continued. Assuming less than V2.
Loss of directional control:any change in heading that cannot be corrected with the appropriate control input. See, the captain has said the a/c diverted from centerline, he applied Rudder, and IT DIDN'T WORK.
So would he have taken off with an inop rudder? No. Would he continue a T/O with one? 64 dollars.
Tillering at the speed we assume is not standard and suggests a problem.
My belief is not that the n/g input didn't work, but that it did. What does a pilot do with a heavy jet very close to V2 that smartly changes heading? Rudder, of course. The Captain says that was "not effective."
OK. Tiller? NO. Not me. How invested are you in the TO? It is at this point in the Roll I'm loudly saying Abort. An a/c that isn't tracking is a no go. If the tiller is an effort to maintain/DC while shutting down, fine. The word so far is that abort got yelled after leaving concrete. The a/c was doing what it was supposed to do, predictably. T/O thrust, but no rudder? OK I'll just turn into the wind and fly, like I was built to. My question, and Strike me dead if someone thinks I'm faulting crew, the information so far leads one to ask why, w/o DC, the Roll continued. Assuming less than V2.
Loss of directional control:any change in heading that cannot be corrected with the appropriate control input. See, the captain has said the a/c diverted from centerline, he applied Rudder, and IT DIDN'T WORK.
So would he have taken off with an inop rudder? No. Would he continue a T/O with one? 64 dollars.
Last edited by airfoilmod; 9th Jan 2009 at 18:52.
Join Date: Jul 2008
Location: buenos aires
Age: 77
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
steering
The pedal nose wheel steering became inop when nose gear shock strut is extended until 2.5 inches from the top. An defective state off the shock strut , ( low oil ,bubles ) and a rear CG may relif load over the nose an extended the strut . If you operate the tiller in this condition the mecanism( the centering cams) can be damaged .
Guest
Posts: n/a
Which is why pitch
Enters into the problem of finding an answer. If the nose gear leaves the deck, centers, derotates in other than centered heading, (or centered and dropped onto a skidding surface) it may fail. I still am curious why one might think tillering might be a solution to loss of DC? I don't think cg enters into it; unless it was way out, the airspeed was sufficient to lighten the nose or load it. The wandering radome should be sufficient cause to consider a slow taxi back to the gate or MOC, not a minor nuisance to be corrected non-standard, and continue. (which is not what I think occurred). AF
(I'll just keep going here, nobody else?)
(I'll just keep going here, nobody else?)
Join Date: Dec 2008
Location: SoCal
Age: 65
Posts: 31
Likes: 0
Received 0 Likes
on
0 Posts
Clarification
Cut and pasted from NTSB update (my comments)
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, (750 Feet from Event to edge of runway)
The aircraft reached a maximum speed of 119 knots, (location of AC not known but assume that throttles are at max)
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.
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.
(So from the numbers, from Event on the runway to the edge of the runway is between 4 and 5 seconds if you assume 110 Kts. Call it one second to recognize Event and apply rudder, apply more and more in the next second still accelerating. In 3 seconds you are 20 degrees left of desired heading. Now grab the tiller. Now I don’t know the B-737 but that sounds like a last ditch Oh Crapiola attempt to save to me and I have maintained a few AC. I have not seen any timing numbers for the Abort but guess it came as they entered the dirt. The purpose of this post is to bring the above excerpt together for reactions in the time allotted to the people in command.)
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, (750 Feet from Event to edge of runway)
The aircraft reached a maximum speed of 119 knots, (location of AC not known but assume that throttles are at max)
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.
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.
(So from the numbers, from Event on the runway to the edge of the runway is between 4 and 5 seconds if you assume 110 Kts. Call it one second to recognize Event and apply rudder, apply more and more in the next second still accelerating. In 3 seconds you are 20 degrees left of desired heading. Now grab the tiller. Now I don’t know the B-737 but that sounds like a last ditch Oh Crapiola attempt to save to me and I have maintained a few AC. I have not seen any timing numbers for the Abort but guess it came as they entered the dirt. The purpose of this post is to bring the above excerpt together for reactions in the time allotted to the people in command.)