Continental 737 Off Runway at DEN
am I the only one who would have expected to see the control column moved to the full forward position at the beginning of the takeoff roll, and held at least until aerodynamic control was sufficient to maintain solid nosegear contact with the ground?
Keep the aeroplane on centreline with rudder pedal steering and rudder. Keep a light forward pressure on the control column during the initial phase of take-off roll to increase nosewheel steering effectiveness. The rudder becomes effective between 40 and 60 kt. Above 80 kt, gradually relax the forward control column pressure.
747: Maintain runway centreline using rudder pedals. The rudder starts to become effective at about 50 kts. Keep the control column slightly forward of neutral.
757: During the initial take-off roll, release the tiller, and hold the column neutral. Do not push the column forward. Keep the aircraft on the centreline with rudder pedals. The rudder becomes aerodynamically effective at about 50 kt.
777: Light forward pressure on the control column during the initial phase of takeoff roll (below approximately 80 kts) will increase nose wheel steering effectiveness. Above 80 kts relax the forward control column pressure to the neutral position.
757: During the initial take-off roll, release the tiller, and hold the column neutral. Do not push the column forward. Keep the aircraft on the centreline with rudder pedals. The rudder becomes aerodynamically effective at about 50 kt.
777: Light forward pressure on the control column during the initial phase of takeoff roll (below approximately 80 kts) will increase nose wheel steering effectiveness. Above 80 kts relax the forward control column pressure to the neutral position.
In the Denver accident, things appear to have been going relatively OK below 80kts, so I'd suggest that although the elevator technique wasn't textbook, it didn't have much of a bearing on the departure from the paved surface...
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I don't remember seeing on thread this:
From the skid mark on the Runway surface just before leaving, the nose (single) stripe indicates a fully castered pair of tires (wheels) scrubbing at some angle off line, even close to ninety degrees.
From CVR: 'Snap, Snap'. The nose gear is directly under and between the pilots, was this noise the cables parting ?
Signs of wear on the wires, are other pilots overdoing tillering ? The radius of the nose tire scrubs is decreasing, indicating an increasingly tighter turn to the left. An accelerated turn shows the inability of controls to correct the track.
With all due respect, the Rudder traces don't jive with what is expected to arrest the decrease in heading in a crosswind TO. The nose should be light or neutral above 80 knots, but as the nose skid shows, there was some weight on the gear. The Reject call happened after leaving pavement? The lack of braking rubber affirms that, the main's mark is "skid" induced, not brake marks. Ineffective use of Rudder? Late RTO call?
Inappropriate Tillering? Mx issues with NG? Exceeded Xwind Limit? Microburst?
Lots of food for thought.
From the skid mark on the Runway surface just before leaving, the nose (single) stripe indicates a fully castered pair of tires (wheels) scrubbing at some angle off line, even close to ninety degrees.
From CVR: 'Snap, Snap'. The nose gear is directly under and between the pilots, was this noise the cables parting ?
Signs of wear on the wires, are other pilots overdoing tillering ? The radius of the nose tire scrubs is decreasing, indicating an increasingly tighter turn to the left. An accelerated turn shows the inability of controls to correct the track.
With all due respect, the Rudder traces don't jive with what is expected to arrest the decrease in heading in a crosswind TO. The nose should be light or neutral above 80 knots, but as the nose skid shows, there was some weight on the gear. The Reject call happened after leaving pavement? The lack of braking rubber affirms that, the main's mark is "skid" induced, not brake marks. Ineffective use of Rudder? Late RTO call?
Inappropriate Tillering? Mx issues with NG? Exceeded Xwind Limit? Microburst?
Lots of food for thought.
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Obviously, I quite agree with the recommendations contained in the Boeing documents …
…and perhaps my questioning of not having the control column “full forward” at the start of the takeoff roll may have been a bit “over the top.” Sorry. I tend to get pragmatic (to a fault) in light of some actions – or the absence thereof. My point was that with the potentials of having a somewhat questionable runway surface (i.e., the potential of having the existing crosswind blow some of the snow and ice across the runway) together with the fact that the crosswind was reasonably substantial, one would think that maintaining nosewheel steering effectiveness would have been uppermost on the minds of the flight crew. However, regardless of how you read “light forward pressure on the control column,” it would seem to me to suggest that a “light forward pressure on the control column” is what is being recommended. Looking again at the FDR traces for control column position, the control column is maintained at “zero” for the initial portion of the takeoff roll, even moving to slightly nose UP at one point.
Perhaps the effectiveness of the nosewheel steering had zero contribution to the departure from the runway … but I have seen more than my fair share of captains who believe that if rudder pedal activation of nosewheel steering is good, then surely tiller activation of the nosewheel has to be better. Unfortunately, in strong crosswind conditions (particularly those involving the possibility of slippery runway conditions) that is exactly bassackward! Recall the Tower Air B747 departure from the runway at Kennedy? Use of the tiller isn’t always the best course of action. If you have your right hand on the throttles, and you’re relying fully on rudder pedal steering, your left hand can easily provide whatever forward control column position necessary. However, if you have your right hand on the throttles and your left hand on the tiller, you’ll have a lot of trouble maintaining light forward pressure on the control column, unless you ask the F/O to provide that piece for you.
Keep the aeroplane on centreline with rudder pedal steering and rudder. Keep a light forward pressure on the control column during the initial phase of take-off roll to increase nosewheel steering effectiveness. The rudder becomes effective between 40 and 60 kt. Above 80 kt, gradually relax the forward control column pressure.
Perhaps the effectiveness of the nosewheel steering had zero contribution to the departure from the runway … but I have seen more than my fair share of captains who believe that if rudder pedal activation of nosewheel steering is good, then surely tiller activation of the nosewheel has to be better. Unfortunately, in strong crosswind conditions (particularly those involving the possibility of slippery runway conditions) that is exactly bassackward! Recall the Tower Air B747 departure from the runway at Kennedy? Use of the tiller isn’t always the best course of action. If you have your right hand on the throttles, and you’re relying fully on rudder pedal steering, your left hand can easily provide whatever forward control column position necessary. However, if you have your right hand on the throttles and your left hand on the tiller, you’ll have a lot of trouble maintaining light forward pressure on the control column, unless you ask the F/O to provide that piece for you.
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Feds: Captain Could Have Prevented Denver Accident
Looks like the NTSB has reported on the Denver accident:
Feds: Captain Had 4 Seconds to Prevent Accident - ABC News
Just before the plane left the runway there was a gust of 52 mph that, hitting the plane's tail, caused it to "weathervane" — turn until its nose was pointed into the wind, investigators said.
The pilot had twice applied the plane's right rudder during the first 12 seconds of the takeoff roll to correct its direction back to the right. But when a gust caused the plane to swing violently to the left, he reached instead for the tiller — which turns the nose wheel and was of no use under the circumstances — instead of reapplying the rudder to turn the plane back to the right, investigators said.
The pilot had twice applied the plane's right rudder during the first 12 seconds of the takeoff roll to correct its direction back to the right. But when a gust caused the plane to swing violently to the left, he reached instead for the tiller — which turns the nose wheel and was of no use under the circumstances — instead of reapplying the rudder to turn the plane back to the right, investigators said.
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How 5 seconds can change your career.......very fortunate no fatalities.
Released by NTSB at today's Board Meeting
Synopsis: NTSB Abstract AAR-10/04
Presentations: http://www.ntsb.gov/Events/2010/Denver-CO/presenta...
Final Report: http://www.ntsb.gov/Dockets/Aviation/DCA09MA021/de...
Released by NTSB at today's Board Meeting
Synopsis: NTSB Abstract AAR-10/04
Presentations: http://www.ntsb.gov/Events/2010/Denver-CO/presenta...
Final Report: http://www.ntsb.gov/Dockets/Aviation/DCA09MA021/de...
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I was surprised to see three math errors (2 orders of magnitude each) in the fifth paragraph of http://www.ntsb.gov/Dockets/Aviation...021/421357.pdf and repeated verbatim in Continental's report http://www.ntsb.gov/Dockets/Aviation...021/436811.pdf.
Another interesting tidbit: "57% of [United Airlines] crosswind takeoffs [in the set of operational data analyzed] in excess of 30 knots occurred at DEN." Think about that a moment. 57% from one airport. I wonder what percentage of all UA operations world wide in that data set departed from Denver? I'm betting a lot less than 57%.
Final thought: this is the second accident report in the past year where data mining of huge operational performance data sets has suggested that the conditions that setup the accident in question were statistical holes in one. (I'm thinking of the BA038 enroute temps as the other.) What does that suggest about the difficulties of reducing an already miniscule accident RATE when the causes are things that are so rare that anticipating / designing / testing / training them out is also such a statistical challenge? The existing sims don't train high and gusty crosswinds below 50' AGL in part because there isn't even a winds model to do it with. And what far more likely scenario do you not train to find the sim time to train this one?
Another interesting tidbit: "57% of [United Airlines] crosswind takeoffs [in the set of operational data analyzed] in excess of 30 knots occurred at DEN." Think about that a moment. 57% from one airport. I wonder what percentage of all UA operations world wide in that data set departed from Denver? I'm betting a lot less than 57%.
Final thought: this is the second accident report in the past year where data mining of huge operational performance data sets has suggested that the conditions that setup the accident in question were statistical holes in one. (I'm thinking of the BA038 enroute temps as the other.) What does that suggest about the difficulties of reducing an already miniscule accident RATE when the causes are things that are so rare that anticipating / designing / testing / training them out is also such a statistical challenge? The existing sims don't train high and gusty crosswinds below 50' AGL in part because there isn't even a winds model to do it with. And what far more likely scenario do you not train to find the sim time to train this one?
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FDR report
Plot 2, page 10-6.
http://www.ntsb.gov/Dockets/Aviation...021/418501.pdf
Does it appear that the heading was fairly steady until the rudder went back to/towards neutral?
Plot 2, page 10-6.
http://www.ntsb.gov/Dockets/Aviation...021/418501.pdf
Does it appear that the heading was fairly steady until the rudder went back to/towards neutral?
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I was surprised to see three math errors (2 orders of magnitude each) in the fifth paragraph of http://www.ntsb.gov/Dockets/Aviation...021/421357.pdf and repeated verbatim in Continental's report http://www.ntsb.gov/Dockets/Aviation...021/436811.pdf.
When rudder pedal use during takeoff (15-3 seconds before takeoff) on the B-737-500 is compared to other B-737 variants, the mean plus 2 standard deviations was 2.56 degrees, and the maximum input out of 7,747 flights was 5.47 degrees. Rudder inputs were larger for the –500 than for the NG model 737s, with the NG models showing smaller rudder pedal inputs. The longest (-900) showed a mean + 2 standard deviations rudder input of 1.76 degrees and a max of 4.3. B-757 models showed still smaller rudder pedal inputs.
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The procedure in the 737 operating manual for the takeoff roll is to keep the airplane on centerline with rudder pedal steering and rudder.
The tiller should NEVER be used on takeoff and this point should be made more explicit in the operating manual. It seems like an obvious point, but American Airlines had to add this to its operating manual following their A300 crash:
The rudder in a large transport airplane is typically used for trim, engine failure, and crosswind takeoff and landing. A rudder input is never the preferred initial response for events such as a wake vortex encounter, windshear encounter....
Instructions in the operating manual would be slightly less direct than a placard next to the tiller.
Not to be Used for Directional Control During Takeoff or Landing
The tiller should NEVER be used on takeoff and this point should be made more explicit in the operating manual. It seems like an obvious point, but American Airlines had to add this to its operating manual following their A300 crash:
The rudder in a large transport airplane is typically used for trim, engine failure, and crosswind takeoff and landing. A rudder input is never the preferred initial response for events such as a wake vortex encounter, windshear encounter....
Instructions in the operating manual would be slightly less direct than a placard next to the tiller.
Not to be Used for Directional Control During Takeoff or Landing
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The tiller should NEVER be used on takeoff and this point should be made more explicit in the operating manual.
Had the Captain of the accident aircraft previously used the tiller during takeoffs? (Did the NTSB ask that question?)
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weekend ppl:
When the present Denver Airport was first proposed there was a fair amount of discussion about the subjective observations of pilots who used old Denver Airport (Stapleton) that during significant TRW activity, the cells were often stronger in the area of the new airport than over Stapleton and to the mountains to the west.
If, in fact, this has any validity perhaps the same could be said for strong winter winds.
Another interesting tidbit: "57% of [United Airlines] crosswind takeoffs [in the set of operational data analyzed] in excess of 30 knots occurred at DEN." Think about that a moment. 57% from one airport. I wonder what percentage of all UA operations world wide in that data set departed from Denver? I'm betting a lot less than 57%.
If, in fact, this has any validity perhaps the same could be said for strong winter winds.
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aterpster makes a good point. Even the local Indian tribes knew that this was not a good place to erect a tepee, let alone conduct a cross wind take-off.
A few years ago many aircraft were damaged by hail stones, what next; a tornado?
A few years ago many aircraft were damaged by hail stones, what next; a tornado?
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I don't have enough hands to keep the ailerons into the wind, one hand on the throttles and then use the tiller. The tiller is not even in my mind when I do X-wind take offs (or landings).
Same as the rudder is disconnected from my mind if I get an unexpected roll in flight. What is wrong with ailerons?
Same as the rudder is disconnected from my mind if I get an unexpected roll in flight. What is wrong with ailerons?
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Mile High Club
Tell you what group,
Denver is one of those cities where escape from rotor clouds and mountain wave is impossible if you fly in there long enough. I thought the old Stapleton airport was worse since it was closer to the rockies causing the turb. They would "sand" the several feet of packed snow and gusts were occasioned which exceeded the limits of all aircraft.
There I was, young Falcon 20 co-pilot at night roaring down the North runway with a brand new Captain on his first trip and we swopped ends going sideways down the runway. Full rudder didn't help. Instinctively, I aborted the takeoff slamming both throttles to idle, because there was little doubt in my mind we were going to wind up in a snow bank.
The Captain may have been dicking with the tiller (I'm not sure) which above 60 knots can only do two undesirable things:
On a dry runway: saw-off the nosetires.
On a wet or icy runway: nothing at all!
Once we skidded to a wild stop and started breathing again, he looked at me, and I looked at him and we knew, we had almost lost it.
I said: "Ya know, we almost ended up out there in the infield, and it's a pretty good dropoff in places".
He said: "Yep, well now that we've had our practice abort, tell em we want to try it again..."
He was one hell of a nice guy, but not a very good pilot.
That's also what we did on the 747 on ice, slam thrust levers to idle hold full rudder and not recommence rev/thrust until directional control was regained.
It's all you can do at high speeds. Otherwise, you have a growing diagonal vector off the runway. Obviously, under V1 you should abort. And on many jets at low speeds on ice the tiller starts skidding and you must use differential brakes and sometimes a little differential power; you now know that the takeoff is going to be dicey. Most jets the pilot not flying holds full down elevator on the roll to dig the nosewheel into the clutter a little better, (may make the tiller effective), then, once he gets the final power set, and pilot flying feels the pedal steering becoming effective, his hand comes off the tiller: Never to return to it!
Advanced landing technique when you're forced to land over crosswind limits due to fuel exhaustion: Reverse harder on the downwind engine (don't try to modulate it or you'll loose it; just set it one or two knobs higher than the upwind engine.. It will double your effective rudder. This is an ATP airmanship emergency thing. You're not going to find it in the book. (Not sure if you can do it anyway in the latter french pushbutton machines.)
Denver is not for kids. United of course, as you recall, had their famous pre-"wind shear" B-727 experience in the 80's? where they took off, got hit by the mountain wave, applied full meltdown power and still did not clear the obstacles on the end (dry microburst.) They hit an approach light pole, but didn't realize it until climb-out because the airplane wouldn't pressurize (because it had a huge pole stuck through the belly tail section). I saw the video on it years later.
But why fly to Denver in the winter time at all? Just be senior and fly to the islands every day!
Crunch - out
Denver is one of those cities where escape from rotor clouds and mountain wave is impossible if you fly in there long enough. I thought the old Stapleton airport was worse since it was closer to the rockies causing the turb. They would "sand" the several feet of packed snow and gusts were occasioned which exceeded the limits of all aircraft.
There I was, young Falcon 20 co-pilot at night roaring down the North runway with a brand new Captain on his first trip and we swopped ends going sideways down the runway. Full rudder didn't help. Instinctively, I aborted the takeoff slamming both throttles to idle, because there was little doubt in my mind we were going to wind up in a snow bank.
The Captain may have been dicking with the tiller (I'm not sure) which above 60 knots can only do two undesirable things:
On a dry runway: saw-off the nosetires.
On a wet or icy runway: nothing at all!
Once we skidded to a wild stop and started breathing again, he looked at me, and I looked at him and we knew, we had almost lost it.
I said: "Ya know, we almost ended up out there in the infield, and it's a pretty good dropoff in places".
He said: "Yep, well now that we've had our practice abort, tell em we want to try it again..."
He was one hell of a nice guy, but not a very good pilot.
That's also what we did on the 747 on ice, slam thrust levers to idle hold full rudder and not recommence rev/thrust until directional control was regained.
It's all you can do at high speeds. Otherwise, you have a growing diagonal vector off the runway. Obviously, under V1 you should abort. And on many jets at low speeds on ice the tiller starts skidding and you must use differential brakes and sometimes a little differential power; you now know that the takeoff is going to be dicey. Most jets the pilot not flying holds full down elevator on the roll to dig the nosewheel into the clutter a little better, (may make the tiller effective), then, once he gets the final power set, and pilot flying feels the pedal steering becoming effective, his hand comes off the tiller: Never to return to it!
Advanced landing technique when you're forced to land over crosswind limits due to fuel exhaustion: Reverse harder on the downwind engine (don't try to modulate it or you'll loose it; just set it one or two knobs higher than the upwind engine.. It will double your effective rudder. This is an ATP airmanship emergency thing. You're not going to find it in the book. (Not sure if you can do it anyway in the latter french pushbutton machines.)
Denver is not for kids. United of course, as you recall, had their famous pre-"wind shear" B-727 experience in the 80's? where they took off, got hit by the mountain wave, applied full meltdown power and still did not clear the obstacles on the end (dry microburst.) They hit an approach light pole, but didn't realize it until climb-out because the airplane wouldn't pressurize (because it had a huge pole stuck through the belly tail section). I saw the video on it years later.
But why fly to Denver in the winter time at all? Just be senior and fly to the islands every day!
Crunch - out
Last edited by Captain-Crunch; 17th Jul 2010 at 02:17. Reason: corrected "rudder becoming effective" to: "pedal steering becoming effective" per other readers.
Per Ardua ad Astraeus
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Originally Posted by C-C
He said: "Yep, well now that we've had our practice abort, tell em we want to try it again..."
EGMA:
I was there that day (as SLF). It was June 2001. We were #2 for takeoff.
I watched the #1 plane launch into the black cloud that was making its way down the runway, then all hell broke loose. I always wondered what his ride was like, and if he had to return to land. I can't understand why he would start his take off roll into something that looked very much like a tornado marching its way toward us.
As for us, it felt like the plane (737) was being beat up with baseball bats. I saw large numbers of baseball size hailstones hit the wings. After the tempest passed (about 10 min) there were several large dents in the wings. The captain wisely opted for a return to the gate over the protests of several idiots in the rear of the plane.
The storm grounded all the aircraft that were at the gates that day in Denver. Half of United's fleet of BAe 146s were grounded due to the damage. Many of the un-sheltered cars in the parking lots had broken windows. They all needed body work due to the dents.
Conclusion: Denver is no place for rookies. Weather there can be treacherous.
A few years ago many aircraft were damaged by hail stones, what next; a tornado?
I watched the #1 plane launch into the black cloud that was making its way down the runway, then all hell broke loose. I always wondered what his ride was like, and if he had to return to land. I can't understand why he would start his take off roll into something that looked very much like a tornado marching its way toward us.
As for us, it felt like the plane (737) was being beat up with baseball bats. I saw large numbers of baseball size hailstones hit the wings. After the tempest passed (about 10 min) there were several large dents in the wings. The captain wisely opted for a return to the gate over the protests of several idiots in the rear of the plane.
The storm grounded all the aircraft that were at the gates that day in Denver. Half of United's fleet of BAe 146s were grounded due to the damage. Many of the un-sheltered cars in the parking lots had broken windows. They all needed body work due to the dents.
Conclusion: Denver is no place for rookies. Weather there can be treacherous.
Last edited by Piper_Driver; 16th Jul 2010 at 16:27.
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Most jets the pilot not flying holds full down elevator on the roll to dig the nosewheel into the clutter a little better, (may make the tiller effective), then, once he gets the final power set, and pilot flying feels the rudder becoming effective, his hand comes off the tiller..
Perhaps we do need a placard next to the tiller explaining its proper use. The 737 operating manual says to hold light forward pressure on the control column and maintain directional control with the rudder pedals. Nowhere does is say to use the tiller until the rudder becomes effective. The rudder pedals will turn the nose wheel up to 7 degrees, if that is not enough to keep you on centerline, then you probably should discontinue the takeoff.
This is standard operating procedure, you will find it in the book.
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777Yank
you are right. (except for the typo...petals? pedals)
once the plane is aligned with the runway for takeoff ( or landing) you should not use the tiller.
I read the short version of the report. tower doesn't give winds, captain gave up on the rudder.
well, all of this can be traced to events about 30 years ago. deregulation of the industry and the controller strike. controllers use to have quite a bit of aviation experience as pilots(done personally), the replacements were just shoved through and something was lost in the translation...I watched the weather go crappy at CLT about 16 years ago...no warning of bad wx and bam a crash of a DC9 due to microburst. sky was GREEN...extreme rain...my DC9 was shaking AT THE GATE!
Nothing on the RADIO warning pilots.
and with de regulation, I've seen pilots get hired at majors that I would hire to flight instruct in a C152. The rudder is often the least understood flight control...more training...more experience...better flying.
once the plane is aligned with the runway for takeoff ( or landing) you should not use the tiller.
I read the short version of the report. tower doesn't give winds, captain gave up on the rudder.
well, all of this can be traced to events about 30 years ago. deregulation of the industry and the controller strike. controllers use to have quite a bit of aviation experience as pilots(done personally), the replacements were just shoved through and something was lost in the translation...I watched the weather go crappy at CLT about 16 years ago...no warning of bad wx and bam a crash of a DC9 due to microburst. sky was GREEN...extreme rain...my DC9 was shaking AT THE GATE!
Nothing on the RADIO warning pilots.
and with de regulation, I've seen pilots get hired at majors that I would hire to flight instruct in a C152. The rudder is often the least understood flight control...more training...more experience...better flying.