NTSB Recommendation re Airbus Rudder Travel Limits
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It seems to me there are a couple points left unaddressed. The B-52 was designed Sixty years ago; the picture is instructive in two ways. First, the Vertical Stabilizer failed up to but short of its roots in the fuselage, so that part is straightforward enough, and points to a shortcoming of modern airliners in general, and Airbus in particular, due to demonstrable failures in the VS/Fuse join.
The second point is obvious to anyone old enough to remember when a/c were built in one setting, not farmed out piecemeal to locations around the globe. Structure is addressed as a function of stress on a continuum, and in certificated airframes the stress must be SPREAD such that it cannot become focal and cause failure.
The lugs and brackets solution on the 300 is begging to be noticed, and discussed.
Secondarily, if a system such as the VS/Rudder is to fail, it must not fail at the Fuselage in any way prior to or in concert with Rudder separation.
The Rudder is of course a necessary control, but its utility can be sacrificed and must be, as has been noted in the 447 thread, before the V/S cuts loose: an aircraft cannot be flown with directional stability without a Vertical stabiliser.
The Rudder is a trimming device. Obviously it cannot perform as a control when yaw gets dicey, and certainly not with power that is all or nothing at all. Again, the Rudder must fail (separate) when its aspect is divergent from the Vertical plane such that it transmits load failure to the VS.
Of course the Rudder pulls out the VS forward mount first, the resistance of the Rudder is a lever that pushes the aft vertical spar DOWN and pulls the forward UP. This is the reason for the bottom trailing edge of the Rudder in 447 looking the way it does.
Back to Global modularity. No matter the strength of the join, the Vertical assembly with its uncommon power with its Rudder deflection at some speed will snap any mount proposed (patently). More continuity in the vertical and deeper spread of the fuselage resistance to control forces is demanded. Planting a Tail on an assembled Fuselage is not working.
edit for PJ2
I think it is necessary to think of the VS and the Rudder as separate systems; the Rudder must never be stronger than the VS mount. It is irrelevant to tout the strength of the Rudder here, if it was lost, the VS load would reduce and the VS would not separate. The Rudder caused the loss of the VS, directly. It would be embarrassing to land with a VS only, but not fatal. Wait til dark and send around a company flatbed to retrieve the Rudder.
bear (obviously with hindsight, all due respect)
The second point is obvious to anyone old enough to remember when a/c were built in one setting, not farmed out piecemeal to locations around the globe. Structure is addressed as a function of stress on a continuum, and in certificated airframes the stress must be SPREAD such that it cannot become focal and cause failure.
The lugs and brackets solution on the 300 is begging to be noticed, and discussed.
Secondarily, if a system such as the VS/Rudder is to fail, it must not fail at the Fuselage in any way prior to or in concert with Rudder separation.
The Rudder is of course a necessary control, but its utility can be sacrificed and must be, as has been noted in the 447 thread, before the V/S cuts loose: an aircraft cannot be flown with directional stability without a Vertical stabiliser.
The Rudder is a trimming device. Obviously it cannot perform as a control when yaw gets dicey, and certainly not with power that is all or nothing at all. Again, the Rudder must fail (separate) when its aspect is divergent from the Vertical plane such that it transmits load failure to the VS.
Of course the Rudder pulls out the VS forward mount first, the resistance of the Rudder is a lever that pushes the aft vertical spar DOWN and pulls the forward UP. This is the reason for the bottom trailing edge of the Rudder in 447 looking the way it does.
Back to Global modularity. No matter the strength of the join, the Vertical assembly with its uncommon power with its Rudder deflection at some speed will snap any mount proposed (patently). More continuity in the vertical and deeper spread of the fuselage resistance to control forces is demanded. Planting a Tail on an assembled Fuselage is not working.
edit for PJ2
I think it is necessary to think of the VS and the Rudder as separate systems; the Rudder must never be stronger than the VS mount. It is irrelevant to tout the strength of the Rudder here, if it was lost, the VS load would reduce and the VS would not separate. The Rudder caused the loss of the VS, directly. It would be embarrassing to land with a VS only, but not fatal. Wait til dark and send around a company flatbed to retrieve the Rudder.
bear (obviously with hindsight, all due respect)
Last edited by bearfoil; 9th Aug 2010 at 20:49.
Thread Starter
411a, PTH, Huck, thank you. I understand the use of rudder but I asked my question for a reason and the point is made in the responses: In fact there are NO circumstances where the rudder would be used as it was here - the rudder on a jet transport is never used in flight, period, except for those cases you describe - crosswinds, turn coordination and yaw damping.
The next question then needs to be asked: Before this accident and prior to awareness of the potential inability to finely modulate rudder response at high speed (Flight_Safety Post #28), what reason or evidence, at the time, would any manufacturer have to contemplate that the rudder would be used in this way? As PBL states, any design that fails at 30% above ultimate load, (and the A319 rudder withstood 29% above design limit load) would seem robust enough.
The QRH for the A320 has always been abundantly clear when rudder protections are lost due to various system failures: "Use Rudder With Care".
I think the key point in this is made by safetypee: "EASA’s reconsideration of their “position on the pilot training-out as being an efficient and sufficient measure to avoid any new hazardous situation … ” and “that crew use of rudder pedal inputs in upset encounters cannot be ‘trained out’ ” points towards a system change as being the only viable solution for a range of aircraft.
Essentially EASA has changed its view of the pilot’s contribution towards safety in situations involving aircraft with deficient systems, where the pilot through erroneous behaviour, contributes to an accident. This is a major advancement in safety thinking, but could have very wide ranging implications."
The next question then needs to be asked: Before this accident and prior to awareness of the potential inability to finely modulate rudder response at high speed (Flight_Safety Post #28), what reason or evidence, at the time, would any manufacturer have to contemplate that the rudder would be used in this way? As PBL states, any design that fails at 30% above ultimate load, (and the A319 rudder withstood 29% above design limit load) would seem robust enough.
The QRH for the A320 has always been abundantly clear when rudder protections are lost due to various system failures: "Use Rudder With Care".
I think the key point in this is made by safetypee: "EASA’s reconsideration of their “position on the pilot training-out as being an efficient and sufficient measure to avoid any new hazardous situation … ” and “that crew use of rudder pedal inputs in upset encounters cannot be ‘trained out’ ” points towards a system change as being the only viable solution for a range of aircraft.
Essentially EASA has changed its view of the pilot’s contribution towards safety in situations involving aircraft with deficient systems, where the pilot through erroneous behaviour, contributes to an accident. This is a major advancement in safety thinking, but could have very wide ranging implications."
Per Ardua ad Astraeus
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I have looked briefly at the NTSB stuff, but could someone help here? Has it been positively determined that the fin failed due to human 'cycling' rudder input or was the rudder input an attempt to control the a/c following some sort of fin failure? I have only seen the words 'probable' so far. The wmv shows rudder movement in line with pedal displacement until the supposed 'separation', but is that supposition or confirmed?
For what it is worth, I was always taught to keep my feet on the floor after take off when flying swept wing jet aircraft and only to reunite them with the rudder pedals on approach and landing.
Farting around with rudders was purely for take-off, landing and asymmetric flight only.
As one of my old mentors once put it, a bootfull of rudder could result, at best, in 380 gin and tonics being spilled and, at worst, serious damage which might bite you or the next chap to fly the aeroplane.
Sound advice I feel.
Farting around with rudders was purely for take-off, landing and asymmetric flight only.
As one of my old mentors once put it, a bootfull of rudder could result, at best, in 380 gin and tonics being spilled and, at worst, serious damage which might bite you or the next chap to fly the aeroplane.
Sound advice I feel.
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Originally Posted by kbrockman
neither did the Transat A310 loosing most of its stabilizer BTW.
PBL
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PBL
pbl
I am glad that you know all about transport category rudder certification. I guess I don't. Mind you I've taken 7 FAA written exams, gone to FlightSafety twice, been through ground schools at 3 regional airlines and one Major airline and have two type ratings.
nope...not once was I told that moving the rudder would shake the plane apart...never...not in 35 years of flying...until the Airbus/American tragedy.
so, for me, and other people like me who might not know, a placcard is cheap insurance.
Mind you also, that my last two jet transports had rudder limiters so I couldn't pull an airbus!
Mind you if the limiters failed, we had procedures to deal with the situation (including written instructions to limit rudder movement ).
And, as to using the rudder in flight...I've quite smoothly and happily initiated shallow turns in a transport jet using just rudder...it was nice to know how to use the rudder if needed!
I am glad that you know all about transport category rudder certification. I guess I don't. Mind you I've taken 7 FAA written exams, gone to FlightSafety twice, been through ground schools at 3 regional airlines and one Major airline and have two type ratings.
nope...not once was I told that moving the rudder would shake the plane apart...never...not in 35 years of flying...until the Airbus/American tragedy.
so, for me, and other people like me who might not know, a placcard is cheap insurance.
Mind you also, that my last two jet transports had rudder limiters so I couldn't pull an airbus!
Mind you if the limiters failed, we had procedures to deal with the situation (including written instructions to limit rudder movement ).
And, as to using the rudder in flight...I've quite smoothly and happily initiated shallow turns in a transport jet using just rudder...it was nice to know how to use the rudder if needed!
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PTH - the Airbus has a rudder limiter.
What a/c are/were you type rated on? They might have had the same rudder limiter design that the A300/310/320 have.
Anyone know if Airbus changed to the better standard on the A330/340/380?
NTSB concerned about rudder sensitivity on Airbus narrowbodies
NTSB believes a variable-ratio rudder travel limiter may provide better protection against high loads from sustained rudder inputs at high speeds than variable-stop systems since variable-ratio systems retain a relatively uniform response throughout the airspeed envelope, and require more physical effort from a pilot to produce cyclic full rudder inputs at high speeds
What a/c are/were you type rated on? They might have had the same rudder limiter design that the A300/310/320 have.
Anyone know if Airbus changed to the better standard on the A330/340/380?
NTSB concerned about rudder sensitivity on Airbus narrowbodies
NTSB believes a variable-ratio rudder travel limiter may provide better protection against high loads from sustained rudder inputs at high speeds than variable-stop systems since variable-ratio systems retain a relatively uniform response throughout the airspeed envelope, and require more physical effort from a pilot to produce cyclic full rudder inputs at high speeds
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pth,
yes, with all your experience it would surprise me greatly that you missed all the discussions and information distribution about rudder, certification of and use of, that followed the AA587 accident eight and a half years ago.
If, of course, I were to believe that. Which I don't. I can't see how an experienced professional pilot could be around any kind of discussion forum such as PPRuNe any length of time and have missed it. All of the people on the bluecoat list knew about it as soon as Dornheim broke the story, if not before.
PBL
yes, with all your experience it would surprise me greatly that you missed all the discussions and information distribution about rudder, certification of and use of, that followed the AA587 accident eight and a half years ago.
If, of course, I were to believe that. Which I don't. I can't see how an experienced professional pilot could be around any kind of discussion forum such as PPRuNe any length of time and have missed it. All of the people on the bluecoat list knew about it as soon as Dornheim broke the story, if not before.
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Hi guys, I know that the AA accident in New York involved aggressive use of rudders; what is your take on pilots who come on with a 15 to 20 degrees crab in a strong crosswind and then suddenly kick it straight at flare? What do you think would be the force even at the slow speed at flare?
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NTSB believes a variable-ratio rudder travel limiter may provide better protection against high loads from sustained rudder inputs at high speeds
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I have never flown with a pilot that puts their feet on the floor after takeoff. You have three controls, elevator, aileron and rudder. They control pitch, roll and yaw. Why not use the yaw control if it becomes necessary?
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I am just a light aircraft jockey but occasionally throw a Yak or a Slingsby around and know not to mistreat the rudder and that sturdy but ultimately fragile fin.
How is it that these professional guys were not aware that they could destroy their aircraft by being heavy footed? This is not an Airbus problem!
With respect!
How is it that these professional guys were not aware that they could destroy their aircraft by being heavy footed? This is not an Airbus problem!
With respect!
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If the RTLU is a "protection", AirBus has a duty to anticipate a Pilot trusting it, and perhaps blank out the possibility that a prot. could snarl and bite. The device is a PRTLU without a fully trained crew. But especially when aggressive recovery is trained in?
587 comes a little sharper into focus?
587 comes a little sharper into focus?
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I have never flown with a pilot that puts their feet on the floor after takeoff.
An Aileron roll in any swept wing jet without some feet would end up pretty interesting.
Rudder required with engine failure, or when landing in cross winds.
it is actually incredibly easy to break an airplane
the three least understood phenomena in the pilot community are:
1. The Stall
2. Operating Strength Limitations
3. Airplane performance
I'm NOT being funny or sarcastic in any way
the three least understood phenomena in the pilot community are:
1. The Stall
2. Operating Strength Limitations
3. Airplane performance
I'm NOT being funny or sarcastic in any way
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it is actually incredibly easy to break an airplane
But these guys were being asked not to do that and yet... (training...?)
I don't know and as I said, not a heavy metal man but...