Boeing uncommanded nosewheel steering events
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Boeing uncommanded nosewheel steering events
TSB Board concerned that runway overruns may continue if more is not done to understand uncommanded nosewheel steering events on Boeing aircraft
Montreal, Quebec, 5 November 2013 – The Transportation Safety Board of Canada (TSB) today released its investigation report (A10Q0213) into the 30 November 2010 runway excursion of an American Airlines Boeing 737-800 at the Montreal/Pierre Elliott Trudeau International Airport.
The aircraft was on a flight to Montreal, Quebec from Dallas, Texas with 113 people aboard. The aircraft landed normally on the wet runway in a crosswind. As the aircraft was slowing down, it veered, uncommanded by the crew, towards the left side of the runway. The captain, the pilot flying, tried using the rudder and the nosewheel steering tiller to steer the aircraft back to the runway centerline. Although the aircraft heading started to return back towards the runway heading, the aircraft continued to travel towards the left and exited the runway surface. There were no injuries, and damage to the aircraft was minor.
Investigators found that the uncommanded veer to the left of runway centerline was likely due to a jam in the nosewheel steering system. Following the occurrence, investigators did not find any anomalies with the nose-gear wheel system, as the jam likely cleared up. The flight crew did not receive any indication that a problem existed with the nose-gear steering system, nor are there any written procedures to manage a nosewheel steering problem of this kind. The aircraft’s flight data recorder (FDR) does not record parameters from the nosewheel steering system, thus making it difficult to determine when and how problems with nosewheel steering occur.
There have been 11 similar occurrences reported involving various Boeing aircraft types in the past 21 years throughout the world. The cause of these uncommanded nosewheel steering occurrences remains uncertain, despite post-event examinations and other efforts to analyze them. The manufacturer’s safety review process has deemed these occurrences to be an acceptable risk given their remoteness, and the manufacturer has not taken further action to correct them. As their cause is uncertain, and because little is being done to better understand the problem, the Board is concerned that there remains a risk for runway excursions to occur.
Following the accident, American Airlines now discusses this occurrence as part of recurrent training for its flight crews. This training is given to the flight crews to raise awareness of the possibility of a runway excursion due to a nosewheel steering problem after landing.
The TSB is an independent agency that investigates marine, pipeline, railway and aviation transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.
For more information, contact:
Transportation Safety Board of Canada
Media Relations
Transportation Safety Board of Canada - Aviation Investigation Report A10Q0213
Montreal, Quebec, 5 November 2013 – The Transportation Safety Board of Canada (TSB) today released its investigation report (A10Q0213) into the 30 November 2010 runway excursion of an American Airlines Boeing 737-800 at the Montreal/Pierre Elliott Trudeau International Airport.
The aircraft was on a flight to Montreal, Quebec from Dallas, Texas with 113 people aboard. The aircraft landed normally on the wet runway in a crosswind. As the aircraft was slowing down, it veered, uncommanded by the crew, towards the left side of the runway. The captain, the pilot flying, tried using the rudder and the nosewheel steering tiller to steer the aircraft back to the runway centerline. Although the aircraft heading started to return back towards the runway heading, the aircraft continued to travel towards the left and exited the runway surface. There were no injuries, and damage to the aircraft was minor.
Investigators found that the uncommanded veer to the left of runway centerline was likely due to a jam in the nosewheel steering system. Following the occurrence, investigators did not find any anomalies with the nose-gear wheel system, as the jam likely cleared up. The flight crew did not receive any indication that a problem existed with the nose-gear steering system, nor are there any written procedures to manage a nosewheel steering problem of this kind. The aircraft’s flight data recorder (FDR) does not record parameters from the nosewheel steering system, thus making it difficult to determine when and how problems with nosewheel steering occur.
There have been 11 similar occurrences reported involving various Boeing aircraft types in the past 21 years throughout the world. The cause of these uncommanded nosewheel steering occurrences remains uncertain, despite post-event examinations and other efforts to analyze them. The manufacturer’s safety review process has deemed these occurrences to be an acceptable risk given their remoteness, and the manufacturer has not taken further action to correct them. As their cause is uncertain, and because little is being done to better understand the problem, the Board is concerned that there remains a risk for runway excursions to occur.
Following the accident, American Airlines now discusses this occurrence as part of recurrent training for its flight crews. This training is given to the flight crews to raise awareness of the possibility of a runway excursion due to a nosewheel steering problem after landing.
The TSB is an independent agency that investigates marine, pipeline, railway and aviation transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.
For more information, contact:
Transportation Safety Board of Canada
Media Relations
Transportation Safety Board of Canada - Aviation Investigation Report A10Q0213
Last edited by JammedStab; 11th Jan 2014 at 16:14.
Unlike some runway departures on the BAe146 which were caused by one of the pilots leaving a Coca Cola can underneath the nosewheel steering handle which then got jammed......................However, I am sure that this could never happen in a Boeing.
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Not on a Boeing?
Being presented with my lunch on a very quick turnround, fortunately at Base, with so many other matters requiring my attention, sloppy eating resulted in my fork slipping from my hand and bouncing across the control column, hitting something else and slithering, handle first, down the very slim gap between the nosewheel steering gear and the surround. It promptly disappeared. Talk about four candles.....!
So it seems as if it could, indeed, happen on a Boeing.
So it seems as if it could, indeed, happen on a Boeing.
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Lost a very nice (metal/engraved) pen in a 737 cockpit one day. Spent the whole of the next turnaround (45 min ) trying to find it. . . . finally, a nice gift for the engineers on the next C check.
I suspect though, that this is something more mechanical/hydraulic . . . Boeing have kept this buried almost as well as the rudder problems (BTW B737 pilot since 1989 & no desire to fly an A320 thanks
) but DO wish Boeing could be less "solicitor friendly" & more "pilot friendly" . . .well, I can dream. 
I suspect though, that this is something more mechanical/hydraulic . . . Boeing have kept this buried almost as well as the rudder problems (BTW B737 pilot since 1989 & no desire to fly an A320 thanks
) but DO wish Boeing could be less "solicitor friendly" & more "pilot friendly" . . .well, I can dream.
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Once had to apply an excessive force to the tiller on a 767 to overcome the plastic water bottle FO had stowed behind his tiller.Bottle exploded,no de-brief required..lessons learnt.....blah
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Wet runway, sidewinds, looong fuselage forward of MLG which has lots of wheels and weight.....could the relatively small, lightly-loaded (in comparison) nose gear have possibly aquaplaned?...especially as directional control began to re-establish, coincidental with reducing-speed.
when one looks at the complex tread-pattern of motorcars and the somewhat simpler, but deeperpattern on HGV tyres and compares them with aircraft tyres which are expected to maintain an adequate contact-patch and directional stability, at more than twice the road-vehicle's speed, it's not a huge leap of the imagination.
when one looks at the complex tread-pattern of motorcars and the somewhat simpler, but deeperpattern on HGV tyres and compares them with aircraft tyres which are expected to maintain an adequate contact-patch and directional stability, at more than twice the road-vehicle's speed, it's not a huge leap of the imagination.
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Which leads me to a question I have asked myself of late. . . all Scandi countries (& Germany ) recommend, or mandate by law , the fitting of Winter tyres on cars , yet. . . .I use exactly the same tyres to land a 737 in Malaga in Summer @ 37c as I do to (try to ) land one in February in Tromso with braking action that is (as advised by the Norwegian CAA ) at best "unreliable" am I missing something here
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If you add tread and use softer rubber snow/ice/slush, you might have too much friction on other surfaces, ie generating excessive heat, then if you land your snow tires somewhere with hot temperatures, possibly more blowouts...just thinking out loud. Cars rarely travel to different climates. Cars also don't have reversers. The added complexity in managing spares etc...it's probably a mix of logistical and cost issues that outweigh possible (small) benefits.
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I had this happen many years ago on a 757. On take off, fortunately, at low speed, the aircraft veered left. The takeoff was aborted and we stopped before we transited into the boondocks. Full right rudder had been applied to no effect. There were no obstructions to the controls and no obvious reason why it happened. We returned to stand and engineering found no fault. We departed with no further problems.
I am sure there are experts here who will tell me, how we could have done better and that our beer cans got trapped in the rudders. I bow to their superior knowledge as I only have in excess if 10,000hours on the airplane and it must have been my imagination.
I am sure there are experts here who will tell me, how we could have done better and that our beer cans got trapped in the rudders. I bow to their superior knowledge as I only have in excess if 10,000hours on the airplane and it must have been my imagination.
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bluedonk, hell yeah, what the 
did you know ? ? 
deptrai, yep, it is not an easy one, not at all, particularly when flying (lets say) South of Spain to North of Norway ,+25/-25 is possibly the extremes, but, if we look worldwide in LH operation that is probably chickenfeed, but it is a problem, like aerodynamic deterioration after de-icing, that has been conveniently "ignored" for decades.)
did you know ? ? deptrai, yep, it is not an easy one, not at all, particularly when flying (lets say) South of Spain to North of Norway ,+25/-25 is possibly the extremes, but, if we look worldwide in LH operation that is probably chickenfeed, but it is a problem, like aerodynamic deterioration after de-icing, that has been conveniently "ignored" for decades.)
On take off, fortunately, at low speed, the aircraft veered left.
Over the years, I've investigated a number of such events during takeoff - without exception they were due to thrust asymmetry - clearly obvious in N1/EPR splits when we checked the DFDR.
I worked 737 classics for a while - with the hydromechanical engine controls there is often miss-match in the engine accel rates which will give a thrust asymmetry during the takeoff throttle push. If memory serves, we determined it was appropriate to move the engine stabilization N1 higher prior to engaging the A/T (70% N1?) and the problem largely went away.
FADEC engines accel very uniformly, so that part of the issue is pretty much gone on the newer airplanes.
Since I've been working 747, we sometimes see "idle stagger", where the pilot - while gripping all four throttles - inadvertently staggering the throttles enough that one or more engines are above idle. When they advance the throttles, the engine(s) that are already above idle accel much quicker. The procedure of an A/T takeoff is to 'stand up' the throttles to obtain ~ 1.10 EPR or 40% N1, allow the engines to stabilize, then hit TOGA (or manually advance to TO). What I've seen is the pilots are occasionally careless about the 'stabilize' part, hitting TOGA before all four engines have caught up.
All that being said, it's unlikely to have anything to do with the Montreal event. I'm with Cockney - suspect crosswind/aquaplaning rather than a mechanical problem. I to have wondered about the lack of meaningful tread on aircraft tires...
Bluedonk, just curious, Rolls or Pratt on your 757?
Over the years, I've investigated a number of such events during takeoff - without exception they were due to thrust asymmetry - clearly obvious in N1/EPR splits when we checked the DFDR.
I worked 737 classics for a while - with the hydromechanical engine controls there is often miss-match in the engine accel rates which will give a thrust asymmetry during the takeoff throttle push. If memory serves, we determined it was appropriate to move the engine stabilization N1 higher prior to engaging the A/T (70% N1?) and the problem largely went away.
FADEC engines accel very uniformly, so that part of the issue is pretty much gone on the newer airplanes.
Since I've been working 747, we sometimes see "idle stagger", where the pilot - while gripping all four throttles - inadvertently staggering the throttles enough that one or more engines are above idle. When they advance the throttles, the engine(s) that are already above idle accel much quicker. The procedure of an A/T takeoff is to 'stand up' the throttles to obtain ~ 1.10 EPR or 40% N1, allow the engines to stabilize, then hit TOGA (or manually advance to TO). What I've seen is the pilots are occasionally careless about the 'stabilize' part, hitting TOGA before all four engines have caught up.
All that being said, it's unlikely to have anything to do with the Montreal event. I'm with Cockney - suspect crosswind/aquaplaning rather than a mechanical problem. I to have wondered about the lack of meaningful tread on aircraft tires...
Bluedonk, just curious, Rolls or Pratt on your 757?
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Inflight refueling and tire cange.
Capt Play.
You just invented inflight tire service, crewchange, next,,,?
To somone that has an idea about winter ops, maybee ,wellcomm to my world.
Sentence deleted .. perhaps we can be a little less confrontational ? JT
You just invented inflight tire service, crewchange, next,,,?
To somone that has an idea about winter ops, maybee ,wellcomm to my world.
Sentence deleted .. perhaps we can be a little less confrontational ? JT
Back in the 80's we had severe nosewheel shimmy problems on our 737-200's. On a take off from Manila very severe shimmy took place just as we reached take off thrust. There was a loud cracking noise in the nose-wheel area, we momentarily lost steering control and lost A system. Came to grinding halt from a maximum speed attained of about 30 knots.
The shimmy was so severe it broke the nosewheel scissors linkage which in turn snapped the A System Hydraulic line to the nose-wheel.
A few weeks later a similar severe shimmy occurred to another of our 737-200's soon after touch down. Both nose wheel tyres burst. If I recall correctly the defects were traced to faulty retreads on the nosewheels.
The shimmy was so severe it broke the nosewheel scissors linkage which in turn snapped the A System Hydraulic line to the nose-wheel.
A few weeks later a similar severe shimmy occurred to another of our 737-200's soon after touch down. Both nose wheel tyres burst. If I recall correctly the defects were traced to faulty retreads on the nosewheels.
Tyre tread patterns
The ground loading is much higher in aircraft than with cars.
737-800
Nose 185 psi
Main 205 psi[1]
Car 30 psi
This may well make fine tread features irrelevant.
Also the width of the tyres may well be even smaller proportionately to the load reducing the volume of water to be displaced. This presumably matters too.
Wet grip would probably not be a problem if your car had 1cm wide tyres running at 200 psi even if they were slicks.
[1] http://www.boeing.com/assets/pdf/com...ps/737sec7.pdf
737-800
Nose 185 psi
Main 205 psi[1]
Car 30 psi
This may well make fine tread features irrelevant.
Also the width of the tyres may well be even smaller proportionately to the load reducing the volume of water to be displaced. This presumably matters too.
Wet grip would probably not be a problem if your car had 1cm wide tyres running at 200 psi even if they were slicks.
[1] http://www.boeing.com/assets/pdf/com...ps/737sec7.pdf
Last edited by jimjim1; 12th Jan 2014 at 09:47. Reason: Typo
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Bluedonk, it sound more like a uncentered nose wheel steering, as in you may have centered the tiller, but didn't allow for enough time for the nose gear to drive back to center. Was in a rolling takeoff after a 90 deg lineup? Maybe little uphill during the turn with 40% already set, immediately when lined up toga-push?
Been there, done that. Took full rudder pedal and some tiller to keep it from going off to the side. Was close to rejecting too. Been extra careful since, to ALWAYS allow the aircraft to roll straight for some meters, AFTER releasing the tiller (to ensure the nose gear is in the same position commanded by the tiller), before pressing toga.
Been there, done that. Took full rudder pedal and some tiller to keep it from going off to the side. Was close to rejecting too. Been extra careful since, to ALWAYS allow the aircraft to roll straight for some meters, AFTER releasing the tiller (to ensure the nose gear is in the same position commanded by the tiller), before pressing toga.
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Wet runway with a crosswind brings to mind immediately the diagram of the reverse thrust vectors in such conditions, pretty little diagram if I recall.
Did they depart form a field with slushy deposits on the runway? Is it possible the nosewheel steering cables froze inflight in the U/C retracted position and the lowered gear then put a spurious off-centre demand to the NLG steering jacks?
A NG engineer should be able to state whether the cable rigging changes between the lowered and retracted positions.
The steering bypass handle has been known to stick in the partially disconnected position due to lack of lube and a very tight setting of the handle on the spindle. Try it on a number of your fleet during the walkround and report it as a snag, it should spring positively into the "normal" position once the bypass pin is removed.
Just a few thoughts from 9 years on the type, but I wait to be corrected as we're all still learning I hope.
Did they depart form a field with slushy deposits on the runway? Is it possible the nosewheel steering cables froze inflight in the U/C retracted position and the lowered gear then put a spurious off-centre demand to the NLG steering jacks?
A NG engineer should be able to state whether the cable rigging changes between the lowered and retracted positions.
The steering bypass handle has been known to stick in the partially disconnected position due to lack of lube and a very tight setting of the handle on the spindle. Try it on a number of your fleet during the walkround and report it as a snag, it should spring positively into the "normal" position once the bypass pin is removed.
Just a few thoughts from 9 years on the type, but I wait to be corrected as we're all still learning I hope.
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As I recollect it was a perfectly normal Departure. There were no adverse weather conditions. The engines were spooled up to 1.2EPR and balanced before EPR engaged. It was quite a violent left turn and full right rudder had no effect. I cannot remember what the tiller input was. I take the point of asymmetric power application, but that was not the case here. I have seen the effects of unbalanced power application and that was not the cause in this case. The EPR as I remember were normal, the aircraft path was not. It all happened very quickly but at low speed. There was no runway excursion but a sobering experience none the less, it gets your attention, when, with full right rudder the aircraft turns left.
I am sure there are sky gods out there who have an answer in the blame culture we are now part of, I do not. For many years I have asked what caused it, I have no idea. The rudder control problems on the 737 I think have some similarities. It took a long time to figure out there was in fact a technical problem. This is such a rare event, I have never seen it again with my 10000 hours on the airplane, but it did happen. It happened with an expierenced crew,familiar with the airplane, current, well trained, and well rested and in good ambient conditions. I post this hoping that someone will benefit. I am very circumspect now when power is applied and a reject even at low speed is something that requires attention. I was lucky but it had the potential for a very different outcome.
I am sure there are sky gods out there who have an answer in the blame culture we are now part of, I do not. For many years I have asked what caused it, I have no idea. The rudder control problems on the 737 I think have some similarities. It took a long time to figure out there was in fact a technical problem. This is such a rare event, I have never seen it again with my 10000 hours on the airplane, but it did happen. It happened with an expierenced crew,familiar with the airplane, current, well trained, and well rested and in good ambient conditions. I post this hoping that someone will benefit. I am very circumspect now when power is applied and a reject even at low speed is something that requires attention. I was lucky but it had the potential for a very different outcome.
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I didn't try to assign blame, just to give one possible explanation. As I said I have had it happen to myself. And, like you, now am much more careful, before setting t/o thrust... i.e. let the aircraft roll straight without tiller input, before pressing TOGA.
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How about - A couple of fuselage drains blocked & fwd toilet sink drain hose leaking causing a puddle of water that freezes in flight. This then restricts the NW Steering cables on landing, gradually thaws on the ground resulting in it all working again. Happens several times - access panels removed, puddle found, much head scratching before theory worked out.