Here’s the online version of a story aired on ABC tonight. The title phrase doesn’t appear in the text, but was used more than once on the broadcast about the Airbus crash last year where the rudder snapped off in flight.
Apparently, using the rudder too extremely or frequently can itself generate sufficient forces to destroy the rudder. The suggestion is that pilots be trained to reduce its use.
Maybe I’m an ignoramus, but doesn’t that suggest that the plane has a design problem? Sure, I suppose a hard rudder movement at top speed might not be a good idea, but this was moments after takeoff, at relatively low speed, possible in a attempt to stabilize the plane as it flew through another plane’s turbulent jetwash.
I’m not an engineer, but most planes have what’s called “maneuvering speed,” which is a range wherein you can input full, abrupt control surface movement without overstressing the airframe.
The article doesn’t bring this subject up, so I don’t know if they were above, below, or within this window. If they were within this speed, then my hunch is that the pilots didn’t do anything wrong and the cause is structural failure.
If a pilot is using the rudder without sufficient bank, the load of the turn overstresses the rudder, causing metal fatigue and possible failure. Usually bankless turns are done while on final approach, to line up with the runway in a crosswind.
Considering that the primary theory is material failure (the rudder was made of composites), a few too many bankless turns could well be at the root of the problem. Composites typically do not have the elasticity of metals.
The Airbus A300-600 in this case was well within the green arc - i.e. “manuvering speed”.
Yes, one should be able to ‘wag the tail’ at that speed.
Yes, the vert. stab. (to which the rudder is attached) snapped off.
Yes, the FAA then told all ATP’s (read: airliner-rated) pilots not to ‘wag-the-tail’, without mentioning the Airbus specifically.
No previous crash resulted in this limitation.
see www.ntsb.gov for details of the crash and investigation to date.
For those who know what it is, a flat spin is my guess.
opinion: bolting a massive composite structure to an aluminum one was a massive design flaw - such point loads in a composite matrix make me uncomfortable.
p.s. - I ran into a story that one of the stab. halves on that plane had serious delimination problems during manufacture, and the defect was not properly repaired.
p.p.s. - yes, I am watching this, and, no, I will never board an Airbus (or chopper, V-tail bonanza, and certain other craft)
I feel I should point out that “wake turbulence” (which is what the phenomena is called) can impose very high stresses on the airplane. The forces involved can cause damage to a following plane than wanders into the vortices (they’ve been described by such terms as “horizontal tornadoes”) However, 5 miles of separation is usually considered sufficient to avoid jet wakes. Now, it is possible that some freak weather condition resulted in unusually persistant wakes, but it’s unlikely.
Hmm… “bankless turns”… I think you’re confusing this with a “slip”, which might be described as a “turnless bank”, or perhaps a “crab”, which is neither bank nor turn.
Unless you’re getting into extreme situations, such as an emergency slip-and-descent, I don’t see how this is going to impose any more than the usual stress on the rudder. Since that manuver is usually reserved for airplanes that are on fire, perhaps stressing the rudder is not the highest on the list of immediate concerns.
I have seen damaged rudders caused by jamming the rudder full-force, but that’s an extreme manuver - you might find it in a plane used for spin training, or in one where the pilot had to make a sudden manuver to avoid a collision. The normal use of rudder for normal manuvers in all areas of flight should not cause “overstress” or damage. Since airliners are not used for stunt flying and are flown in such a controlled manner, this sort of damage is extremely rare.
In any case, it wasn’t the rudder that failed - it was the vertical stablizer, a non-moving part of the tail. It just isn’t right for a vert stab to fall off the tail of an airplane during a routine take-off. Either there’s a defect in the airplane, or a defect in the design. This sort of airframe failure is unprecedented in an airliner. I don’t know the exact stats, but even among homebuilt airplanes it’s largely unheard of. Snap off a wing, yes, or lose an elevator, but a vert stab?
Um, actually manuvering speed is not equivalent to the green ar — oh, nevermind. The essence is that the airplane wasn’t going fast enough that anything should have been overstressed.
Except that wake turbulence, on its own, case overstress a plane even if that plane is at manuvering speed or under.
Except that 5 miles following should keep an airplane out of wake turbulence.
In other words, that explanation doesn’t add up.
Nevermind there’s seldom, if ever, a reason to “wag the tail” anyhow…
Probably because the vert stab has never fallen off an airliner before, short of the airplane being bombed or shot at. That looks like a “we have to do SOMETHING to reassure and keep the public flying” sort of reaction.
Not sure they were high enough off the ground to give them enough time to establish one of those. I’m not an expert in spins (just experienced a few, that’s all) but you don’t go from “stall” (a condition where the airplane is unable to maintain enough lift to hold itself up in the air) to “flat spin” instantaneously. Yes, a turbulent wake could, in theory, so abruptly change the angle of attack of the wing that the airplane could stall, but again, you shouldn’t be encoutering that extreme a wake five miles behind the wake-generating airplane.
I share your concerns about the Airbus, but not on the V-tail Bonanza. It’s actually a very fine airplane, with a reputation sullied by too many doctors and lawyers buying more airplane than they could handle, not being sufficiently current in their skills, and allowing their egos to overcome their good judgement. Don’t blame the machines for the human failings of the people flying them.
As for choppers - I enjoy them, but yeah, they just aren’t as safe as airplanes, and when things go wrong, they go more wrong more quickly than on fixed wings.
A local sim pilot down at the airport approached one of our chopper pilots last summer with “Hey! I just bought a helicoptor sim program! It’s great!”
Chopper pilot: “Is it down for maintenance at least 75% of the time?”
Sim pilot (puzzled look): “No.”
Chopper pilot: “Then it’s not a very accurate simulation.”
Not nessesarly a design flaw. Your car (or mine if you don’t have one) has a stearing wheel that allows you (or me) to turn the wheel up to certain angle. If going down the hyway at 65mph and I were to turn the wheel to it’s extream the car is not going to remain on the road (well not in any controllable manner anyway) . Now this by itself may not break the stearing like it could on the rudder but then again neither of these things should ever happen.
With the car It’s really no big deal to add some extra steal to allow such activity (also we have static friction being greater then dynamic friction meaning the force against the strearing wheel is less when skidding then when driving - and road irriglarities) in a plane extra weight means lots of extra cost so there is much insentive to optimize.
IANAP, and IANAE, but to me it’s almost intuitive that a bank turn would be less stressful on the airframe than a rudder turn. Someone who really knows will hopefully correct me if need be–I think that in a rudder turn, force is exerted on the fuselage laterally toward the outside of the turn, just as when you turn your car you can feel a similar force acting on you. But if the pilot banks, then doesn’t the plane experience a greater perpendicular downward force, which, however, is nicely and evenly distributed under the aircraft?
I like to lurk on another board that is airline related. Of course we all know that The Straight Dope is the source for all info but you may find some interesting things about this accident here and here.
I don’t get your post, k2dave. If the plane was within maneuvering speed, any full deflection of the rudder should not pose any undue stress on the airframe. The vertical stab coming off could not have been a result of the pilot’s actions. So, assuming there was no collision with anything, it has to be a design flaw.
I don’t see an equiavalent to an automobile in this regard.
I think it would be the other way around, at least in terms of total stress. If you do a turn with 60 degrees of bank, the plane feels 2g’s Weight is distributed along the length of the fuselage, but it’s only supported by the attachment of the wings, so the fuselage has to be pretty strong to keep from bending along its full length. (60 degrees of bank would be pretty extreme for an airliner, but it makes for a nice round number. Less banking means less overall stress, but the description is similar.)
Turning with just the rudder doesn’t work very well. It’s a bit like driving on snow or ice, and even pilots call it a skid. You can use the rudder to point the plane left or right, but all your momentum is carrying you in a straight line. The plane will eventually take on its new direction, but it does so reluctantly, and doesn’t pull any noticeable g’s.
All of which may be beside the point; planes are specifically designed for banked turns. But they should be designed to let you use the rudder, too! My first flight instructor was showing me how to do a preflight walkaround inspection. At one point, he grabbed the wingtip and started shaking it up and down, it made the whole plane rock back and forth. I thought he was being a bit rougher than he had to be, but he said if the plane couldn’t stand up to that, he sure didn’t want to fly in it.
I saw something once that may be of some interest here. I did a college internship at the Museum of Flight at Boeing Field in Seattle. One day there seemed to be a little more activity than usual, and I saw the Boeing chase plane (an old F-86 painted in Boeing colors) take off. It came back escorting a 707. The 707 landed and it was missing the top 1/3 of its vertical stabilizer. (Safe landing, nobody hurt; good job, everybody.) I found out later what had happened. It was a plane Boeing was developing for the Navy. The designation was probably E-something, but it was based on a 707 airframe. It was for airborne communications and electronics, a bit like the AWACS but without the radome. Pictures that I’ve seen show some sort of antenna built into the top of the stabilizer, but you have to look closely to notice so it wasn’t very big. But it must have been big enough to make a difference. They’d had a fin break off a year before, and figured it was due to aero-elasticity, flutter and resonance. Which is a bit like the Narrows Bridge collapse, I gather; just the right forces at just the right speed can be a problem for just the wrong object. The flight I saw was one they sent up to see if they’d fixed the problem. They hadn’t.
Has anybody looked into that for the Airbus crash? I would think the composites behave much differently than metal in this regard, but could they have have hit just that one bad spot in the design?
Well my car analogy wasn’t the best but my point is that the rudder can physically move to it’s extremes at any time but in practice there should never be a reason to move the rudder to the extreme during normal crusing speed (this is what got me thinking of the stearing wheel - you would never turn it to the extreme during car crusing speeds - just for low speed turning - but you can)
Another analogy I could use is that you can physically floor a (well lets stick with a) car engine when it just cold starts up at -40F and drive it like a bat out of hell with no warm up time - it could work or might break doing that - it’s not a design flaw (well it could be a design flaw that just happened to break at that time) it’s opperator error.
Yessir, and that’s a valid concern. Just like the tendency of Cessna seats to hop backward on take-off, the nasty trait of Piper Tomahawks going into unrecoverable spins, and all the other “oops, we didn’t catch THAT in testing!” design flaws found in various species of aircraft since 1903.
Fact is, many people have flown Bonazas for many years with nary a problem. They are NOT a beginner’s aircraft, and require a conservative pilot who will fly it in a conservative manner. NOT some keep-up-with-the-Drs-Jones ego-driven test-pilot wannabe. Doesn’t mean every accident in a Bonaza is a result of that, but it has been a contributing factor in many cases.
I used to have a plane (AA-1A), which, if it went through 360[sup]0[/sup] of spin, could not be recovered (read: you’re dead).
That is very different than knowing that the tail is going to fall off, and wondering if you will be the crash which causes the next “oops, that fix didn’t work, try this” AD.
I am NOT talking about a bozo biting off more plane than he can handle - I’m talking about a defect which, if not fixed (and, it seems, there has yet to be a final fix (aside from destruction)) will kill the occupants.
IOW: the crash that killed Buddy Holly, The Big Bopper, and Richie Valens was pilot error (story was the plane had just gotten a new horizon, the pilot was tired and mis-read it).
the crashes in which the tail was found 1/2 mile from the rest of the wreckage are design failures.
p.s. Beech’s handling of the investigation and report of the tail failures was reprehensible.
p.p.s. - the 35 (“V” tail) was discontinued. the 36 (exactly the same bird, but with a conventional tail) was continued.
p.p.p.s. - you can fix the “Cessna sliding seat” problem by checking the security of the seat (I’d look for a STC, but that’s just me) - you can’t fix the fractured tail spar connections.
Ahem! When I was training, the Bell JetRanger was the safest single-engine aircraft around. (Not that I’ve ever flown one, though.) Besides If you need to land a heli off-airport, you don’t need a runway.
Erm… Well, there’s usually something available for rental. And that one time I was only delayed an hour while they put the rotor blades back on. (I pay special attention to any vibrations that day!)
Wasn’t that because the fuel went all the way out to the wingtips, creating a moment that could not be overcome by controls?
I think I remember reading that Traumahawks were designed with x-number of ribs in the wings, but Piper deleted some of them to save money. This caused the wings to twist excessively. Am I remembering correctly?
don’t know about the Tomahawks (there used to be 1 sitting abandoned at the local field - story was some idiot bought it and was going to use it as an instrument platform RIGHHHHTTT :rolleyes: )
The AA1’s problem was:
very short coupled
tiny rudder and elevators.
(although there were no baffles, the tank (an 8" dia x 1/8" wall steel tube which also served as spar) didn’t hold enough to worry about)
there just isn’t enough authority in the tail. I doubt it would be certificated today.
Tomahawks were originally certified as permitted to do spins. Problem was, the spin accident rate was always 6-8 times higher in the Tomahawk than any other primary trainer. There was a quite a bit of debate for a number of years as to why this was so. But the FAA line was that it was a pilot problem, not a plane problem. The aircraft had been certified properly, and safely spun in testing. But there was a growing number of pilots who were refusing to spin, or even fly, the airplane. Which was cheesing off the guys who were spinning their Tomahawks on a regular basis with no problem whatsoever.
Then, one day, a CFI candidate (spins are required for that rating) and a designated pilot examiner were performing the CFI checkride in a Tomahawk. They got to the spin part, and apparently, despite flawless spin recovery technique, the damn thing wouldn’t stop spinning. In the end, the CFI-candidate unbuckled and climbed up on top of the control panel which altered the weight and balance of the aircraft enough so that it came out of the spin. Two very shook up people landed the airplane and it was sent out for all kinds of tests. Because NOW the FAA believed there might be an airplane problem.
The final verdict was that, despite the production Tomahawks being made to the same specs, some would safely spin and some would not - and there was no way to know until you tried it. Yes, there was a lot of speculation about wing spars, but the fact was, if you lined up a bunch of Tomahawks some were potential spin-deathtraps and others were safe to spin and you just couldn’t tell by looking at them. Or examining those wing spars.
Needless to say, the spin authorization for that model was revoked.
And the popularity of the model - already on shakey ground - went way down.
Some of us fixed-wing folk have landed safely without runways as well - although I will admit that the off-field capabilities of fling-wings are superior in many ways.
Broomstick: Of course I don’t have the benefit of actually making a real emergency landing (although most of my heli landings have been off-airport).
One thing about slips: My dad routinely slipped his Cessna 172 and Cessna 182, just for fun. He’d intentionally come in high and do a “falling leaf” routine using full deflection of the control surfaces. It never damaged either airplane in the least. Slips are fun to do. I’ve done them for practice (just in case the flaps suddenly didn’t work or something), but for me it’s easier just to use those barn-door-sized control surfaces.
I’m no longer current. Helicopters are expensive to operate. Last year I was this close to buying one, but then I found out about the insurance premiums. Now I’ve decided to concentrate on buying a house, so a personal aircraft is farther away. When I am in the position where I can buy an aircraft, I think I’ll look into a C-172. Helis are fun, but fixed-wings are much more practical. F’rinstance, if I want to take a long trip I’d like something that flies faster than I drive.
