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AAL A-300 accident

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AAL A-300 accident

Old 6th Feb 2004, 14:43
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AAL A-300 accident

A bit simplistic in it's presentation (it is a general public newspaper), the article's main point is, IMHO, valid.......a scenario that few pilots were (1) aware of, (2) trained for.

Jet's design may have caused crash
By Alan Levin, USA TODAY
WASHINGTON - A scientist hired by federal investigators has concluded that
the design of an Airbus jet may have contributed to the wild side-to-side
motions that tore its tail loose and sent it plunging into a New York City
neighborhood in 2001.
The scientists' report, recently made public with other findings from the
investigation, signals that the National Transportation Safety Board (NTSB)
is considering whether the jet itself could be partly to blame for the
accident that killed 265 people.

The NTSB has not yet concluded what caused American Flight 587 to crash into
Queens shortly after takeoff Nov. 12, 2001. It was the second-worst airline
crash in U.S. history. A spokesman for the agency declined to comment on the
scientist's report. Airbus, however, says its data will show that the jet in
the accident, the A300-600, was not at fault.

If the NTSB cites the jet's design in its findings, that could prompt a call
for changes in the way the government certifies the design of rudders on all
aircraft. It also could affect the legal battle between American and Airbus
over which company should pay damages in lawsuits filed by victims'

Using too much rudder

Investigators have long since concluded that the co-pilot of Flight 587
triggered the accident by repeatedly punching the jet's rudder back and
forth, according to NTSB documents. The rudder is a movable panel at the
rear of the jet's 27-foot-tall tail fin. It swings the nose of the aircraft
right or left but is so powerful that it can damage the tail fin if misused.

Several sources familiar with the crash investigation told USA TODAY that an
intense debate is underway over the underlying reasons for a pilot to make
such severe rudder movements on a routine flight. The NTSB is expected to
release its findings this spring.

Some argue that blame lies with the pilot and American's training program,
which taught pilots to use the rudder in an emergency. Pilot groups and Amer
ican insist that is not true.

But others suspect that the rudder system on the A300-600 - which moves with
less pressure from the pilot than any other large jet - was at least partly
to blame. Foot pedals on the floor of the cockpit move the rudder.

The scientist hired by the NTSB, Ronald Hess, writes in his report that the
Airbus accident is "consistent" with a rare phenomenon in which a pilot
essentially loses control of a plane because he or she is tricked by the

Hess is an aeronautical engineering professor at the University of
California-Davis. He says that on an A300-600, a pilot could apply more
rudder than intended because its pedals are so sensitive, particularly at
higher speeds. This could cause the pilot to slam the jet from side to side
while intending to straighten it.

A similar situation could occur in a car. A driver who suddenly swerves to
avoid debris in the road might overcorrect and skid in the other direction
if the steering is difficult to control. That could trigger a series of
increasingly larger skids back and forth.

Many other factors have been cited to explain why co-pilot Sten Molin turned
the flight into a terrifying ride that fatally damaged the jet.

Another American pilot who had flown with Molin told the NTSB that he
believed the co-pilot had used too much rudder on a previous flight.

American taught its pilots to use rudder to help stabilize a jet if they
felt it was going out of control. Federal regulators had warned that the
training was dangerous, NTSB records show. The records also show that
American's flight simulators also distorted the way a rudder works on a real

The airline says its training was the same as other airlines and had no role
in the accident.

In addition, virtually no airline pilots knew before the accident that they
could damage a jet by moving the rudder from side to side at such a speed.

Airbus officials, meanwhile, have attacked the theory that their rudder
could be flawed.

The European jet manufacturer, which last year delivered more planes than
Boeing for the first time, says its data show Molin put far more pressure on
the rudder pedals than was needed.

That suggests he would have caused similar extreme motions on any jet model,
company officials say. A report filed by French accident investigators, who
represent Airbus' interests in the case, also disputes Hess' report.

The A300-600 and the A310, a similar model that shares the same rudder, have
flown 16 million hours since being introduced in the early 1980s, and "there
has never been an issue with rudder pressure," says Airbus spokesman Clay

About 460 of the two models are used around the world. In the USA, only
American carries passengers on the jet.

Out of control on Flight 587

A few minutes before takeoff on Flight 587, co-pilot Molin pushed down on
one rudder pedal and then the other, the plane's data recorder shows. They
each moved 4 inches and required 65 pounds of pressure to depress as far as

The rudder performed perfectly in this preflight check. But the check might
have given Molin a distorted idea about how the pedals worked at higher

Just 85 seconds after Flight 587 lifted off, as the jet flew at 290 mph, the
pedal moved only 1.3 inches and required half the pressure to swing the
rudder as far as possible, according to tests after the accident. This was
when Molin began the series of extreme rudder movements that tore the
vertical fin off the tail.

Like all rudder pedals on commercial jets, a pilot must push with about 20
pounds before the rudder on the A300-600 moves. Pedals are designed this way
so that pilots don't move the rudder accidentally.

But after the A300-600's rudder begins to move, it requires far less
pressure to swing the rudder an equal distance than on other types of jets.
At 290 mph, a pilot who had begun to move the rudder need only add 10 pounds
to the pedal to swing the rudder all the way to one side.

By comparison, the similar-sized Boeing 767 requires 63 pounds of additional
pressure to move the rudder as far as possible.

Rudder sensitivity

The Airbus A300-600 jet requires significantly less force
from pilots to move its rudder than other large jets. The higher the value,
the more a rudder moves when a pilot applies equal pressure to foot pedals
on the cockpit floor. A report filed with federal crash investigators says
that the A300-600's rudder controls may have contributed to a 2001 accident
because it is so sensitive. Airbus officials say the rudder controls had
nothing to do with the accident.

Rudder sensitivity comparisons:

A300-600: 0.93
McDonnell Douglas MD-11: 0.273
Boeing 777: 0.214
Boeing 747: 0.197
Boeing 767: 0.127

Sources: National Transportation Safety Board, University
of California at Davis aeronautical engineering professor Ronald Hess.
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Old 6th Feb 2004, 17:36
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The FO had gained a fair few hours on the A300-600 so it wasn't like he wasn't used to the feel of the rudder. Suggesting that the B767 requires more force to swing the rudder from side to side did not have an impact on the FO's reaction in an A300-600 as he had 1) only been flying the A300-600 in his recent career and 2) never flown the 767.
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Old 6th Feb 2004, 18:09
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I remember, in my alcohol abused brain, that the airline's policy was the use of rudder doublets, contrary to the manufacturer's advice! Also, that the pilot used full deflection rudder!

Maybe I am just a bit long in the tooth but every aircraft that I have flown has been subtley different - that's why you do a type conversion!!

Sounds like a case of "should have tried harder at school"!

Repeated mishandling leading to fatigue failure are the words that we are looking for - IMHO
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Old 7th Feb 2004, 00:14
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I don't know if I've previously made a post on Pprune where I've expressed feelings as strong as this, but...

The design of the A300-600 rudder system is stupid. All airliners need to progressively limit rudder travel to reduce the forces on the vertical fin as the airspeed increases. But the way Airbus chose to do this on this aircraft is dumb.

To move the rudder in an emergency, here's the required thought processes for both an A300-600 and a 767.

Problem - I have an attitude emergency at 290 kts. and I need to move the rudder. I might have to perform a rudder doublet (move the rudder to one side then the other), so how much pressure and travel do I impart to the rudder at this speed so I don't create full deflection, in case I need to perform a rudder doublet?

A300-600 Answer - Let's see, at this speed, the rudder pedal travel is 1/3rd of the low speed travel (1.3 inches/4 inches) for full deflection, and the required pedal pressure is 1/2 that required at low speed for full deflection. I have to successfully work this out while I'm in the middle of this emergency.

767 Answer - The same as always at any speed. Nothing to work out, do the same as you always do.

Now tell me if you don't think the A300-600 rudder design, isn't just out of its mind stupid.
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Old 7th Feb 2004, 00:36
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Fight Safety Check here; http://www.pprune.org/forums/showthr...hreadid=118064 before you declare designs stupid. Also see and read the IFALPA link.
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Old 7th Feb 2004, 00:38
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Yep, a few years ago agressive use of the rudder was all the rage in the sims here in the U.S. Some of it was in the wake of 737 rudder malfunctions causing upsets. The idea was that using full rudder would speed unusual attitude recovery, which it does if the tail doesn't fail (and you don't get lost and kick the wrong one). I can see where the FO may have got the idea to try to kick his way out of some wake turbulence.
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Old 7th Feb 2004, 06:15
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new one on me.."rudder doublet"
unless of course there is an airplane out there which occasionally has a rudder reversal problem???
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Old 7th Feb 2004, 07:47
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Sweeper, OK, rudder reversal...that's what I meant.

The "rudder doublet" meaning (as I intended it), refers to 2 opposing movements in quick succession, as opposed to 2 opposing movements spaced farther apart in time. In nearly all uses of the word "doublet", there is the idea of referring to 2 things located close together.

Last edited by Flight Safety; 7th Feb 2004 at 08:00.
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Old 7th Feb 2004, 08:00
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I know a FDX A300 management pilot who attended AA unusual attitude training a few years before this accident. He confirmed to me their emphasis on rudder usage, saying the techniques taught seemed to come from a light aircraft aerobatic philosophy.

By the way, how long before 411 pipes up?
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Old 7th Feb 2004, 12:41
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Right now, Huck.

Ever since the early days of the B707, pilots have been taught ...use the rudder very carefully, on a large jet transport it is a very powerful control surface, especially at higher speeds.

It would seem that some bright new guy, in a position of 'authority' in some airlines' training department has/have decided to use the rudder in a very INappropriate way.

A few will never learn.
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Old 7th Feb 2004, 16:32
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I have to agree with those that question the ergonomics of the rudder control system. I think the reference to the 767 system was as an example of what the 'logical' or expected feel of the input/response should be during progressive rudder travel limitations.

Reduced pedal travel as the rudder deflection is limited is one thing, but the varying pedal forces during limitation appears to have no logical relation.

Beyond this, there is the lag between input and deflection, which can be clearly seen in the NTSB graphs. There are moments when the pedals are pushed one way while the rudder is still deflected the other way before it reacts. While this may be insignificant during typically smooth control inputs, this momentary lag will have significant effects on the pilot's feel for how the aircraft is responding to commands, even inspiring the pilot to make quicker and larger inputs, especially during relatively rapid reversals.

I'm not too sure how this lag compares to other large commercial aircraft, but if compared to a direct link system (cables/rods with no augmentation), it would appear to me to be a factor. I certainly would not be happy for any of my R/C planes to have such a input/response lag.

Another point is that the DFDR data collection periods for accelerations and other pertinent parameters are too far apart to have picked up the all the 'details' of the alleged wake turbulence, making it impossible to back-drive a simulater and experience exactly what Sten Molin felt the aircraft was doing.

Making any finite conclusions on whether he was right or wrong to make such input commands based on such incomplete evidence is just not right IMO.

BTW, it wasn't a 'fatigue failure'. The forces exceeded the ultimate design load of the structure. The big issue here is that the FARs only require the structure to withstand forces from a full (inc limited) rudder deflection, centering the rudder during the subsequent yaw deflection, and centering the rudder during yaw deflection + overswing. It does NOT certify tail structures for a rudder reversal during yaw deflection or yaw deflection + overswing. One has to ask 'why not?', since the chances of a rudder correction being made during a sudden gust, or specifically just when a sudden gust stops, seem quite high to me. Add in a bit of control system lag, and the circumstances of an aircraft in sideslip with an opposing or reversed rudder deflection are even higher.
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Old 8th Feb 2004, 01:46
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My apologies in advance for begin so focused on the design issue...

Managing the side forces on the vertical fin is THE central issue here, in regards to maintaining the structural integrity of the fin, as loss of the fin usually means loss of the aircraft.

We all know that the rudder's deflection angle has to be progressively limited as the airspeed increases, to keep the side forces generated by the rudder, within the design load limits of the vertical fin.

The design issue for me is how the rudder limiting system interacts with the pilot, to help or hinder the pilot's ability to correctly and accurately modulate those side loads.

As airspeed increases in the 767 design, the rudder limiting system does not affect the length of rudder pedal travel or the pedal forces required, but instead progressively limits the rudder's deflection angle at the fin. This system essentially maintains a constant relationship between the amount of rudder pedal travel and pedal force applied, to the amount of aerodynamic control force and side force being generated at the fin, regardless of the airspeed.

As airspeed increase in the A300-600 design, the rudder limiting system progressively and directly limits the amount of pedal travel and pedal force, thus resulting in the progressively limited deflection angle of the rudder at the fin. The problem with this system, is that NO constant relationship between pedal force and pedal travel to side forces generated at the fin, is being maintained here.

You can think of the human interface design problem presented here in terms of "modulation gain", where "gain" (normal use of the word, expressed as a ratio of controlling power to the amount of power being controlled) refers to the ratio of the amount of controlling power and movement of the pilot's legs, to the amount of side force begin generated by the pilot's control inputs.

In the 767 system, the control "gain" is basically constant, meaning the amount of force and travel appiled to the rudder pedals always produces the same amount of aerodynamic force and side force on the fin, regardless of the airspeed. So 50 percent pedal travel means 50 percent side force, at all airspeeds. This is a very intuitive system for the pilot.

In the A300-600 system, the control "gains" are screwed because the relationship between the amount of pedal force and travel to side force generated at the fin, is constantly changing with the airspeed. So if the pilot wanted to apply about 50 percent side force, he would have to know the airspeed, know the rudder pedal travel limit for that speed, then move the pedal 50 percent of that amount. As you can see, this system makes it much more difficult for the pilot to accurately modulate (or control) the amount of side force being applied at the vertical fin.

So the design question for me is, does the rudder limiting system help the pilot's ability to accurately and correctly manage the amount of side forces being applied to the vertical fin, while recovering from an attitude emergency? In the 767 system I think it does, because the control gains are constant. In the A300-600 system, I strongly believe it does not.

Up to now I've ignored the regulation issue. Many of use know the weakness of the regulations that specify the design load limit of the vertical fin, specifically how the regulatory design load limit is inadequate for a full rudder reversal at speed. If the regulation is ever modified to include greater strength for the vertical fin, I think it should also include a provision for rudder limiting systems that present constant travel and force gains to the pilot, so aerodynamic side forces and side loads on the vertical fin can be accurately controlled by the pilot.

Last edited by Flight Safety; 8th Feb 2004 at 23:22.
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Old 8th Feb 2004, 13:15
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I can not imagine any country certifying a two seater in which the fin would fail during a rudder reversal in a yaw oscillation. I guess the manufacturers of big A/c said that they did not need such strength because their planes would not be likely to get into such attitudes. Obviously they were wrong and the authorities should not have allowed that standard.

Question is will they do anything about it or will they just say: "Well only happens one in x million flights, uneconomic to fix" and will you or I be on the next flight it happens to?
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Old 8th Feb 2004, 13:24
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A better idea would be to tell pilots to keep their size twelves on the floor and absolutelyNOT use the rudder for which it was not intended.

This ain't rocket science...then again maybe it is for the newer guys who have been given duff gen.
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Old 8th Feb 2004, 15:49
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Would have thought if you'd got the type rating, you would be expected to be familiar with the vagaries of your aircrafts controls.

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Old 8th Feb 2004, 22:43
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Just What Initiated the Rudder Movement?

Sven Molin's feet allegedly performing a Tour de France sprint seem to be the focus of many posts in this new thread; and coupled with the paper-thin margins between breakout force and full deflection, and control system lags, they may eventually be demonstrated as the initiating cause.

So far I have not seen anything in this or previous threads or available NTSB documents to exculpate the yaw damper and/or rudder control system.

I'm waiting for Airbus to hire a 747 to generate a similar wake and fly the accident profile in a well-instrumented A300-600 -- flight test crew may insist on bang seats
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Old 17th Feb 2004, 07:14
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AAL A-300 accident

Reply to Ronald A. Hess Ph.D.
University of California-Davis
NTSB selected investigator on the AA 300 accident

Dear Sir:

The recent article in the February 6th issue of "USA Today", which includes excerpts from you own report, continues to infer that the co-pilot of American Airlines’ Flight 587, was the cause of the accident, through overuse of the aircraft’s rudder.

In fact, the co-pilot never had control of the rudder after it was struck by the 0.3 and the 0.4 G forces of the "Heavy" Boeing 747’s vortices! These forces, striking the large rudder surface area, broadside, broke the linkages to the rudder actuators! The rudder was then free floating, reacting to the rotating vortices striking it, alternately, first on one side and then the other. This whipping action of the rudder, back and forth was faster than any pilot would have ever commanded, even if he was physically able to do so!.

The final 0.8 G forces striking the large, vertical Fin surface area, broadside, induced an instantaneous YAW. The resultant massive inertia factor, sheared off both engines from their pylons, the vertical Fin from its support fitting, and broke the rudder into four pieces. The abrupt YAW also initiated an instantaneous
"Dutch Roll", into the ground.

Although the co-pilot used a full right aileron input to counter the steep left bank, there was no evidence that any rudder input was applied, to assist in an attempted recovery maneuver! THERE WASN'T ANY RUDDER INPUT AVAILABLE TO THE PILOT! THERE WASN'T ANY RUDDER!

This was the first accident, of this type, in 100 years!. It was a perfect "Join-up" on the center of a horizontal tornado! (The aircraft wake from the Boeing 747 "Heavy".). NASA states that the angular velocities in a vortex may be as high as 300’/sec.

William J. Sherriff
Capt. Ret.
American Airlines

Last edited by wsherif1; 18th Feb 2004 at 06:54.
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Old 17th Feb 2004, 08:14
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Sorry if I'm being a bit obtuse here, but why the hell should a pilot need to touch the rudders at this stage of flight?

In all my years of multi jet flying, the only time SIGNIFICANT amounts of rudder was needed was for real or sym asy flying!!???? And it would need to be significant to cause fin failure...
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Old 17th Feb 2004, 23:39
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The retired captain said:
In fact, the co-pilot never had control of the rudder after it was struck broadside, by the 0.3 and the 0.4 G forces of the "Heavy" Boeing 747’s vortices, which severed the linkages to the rudder actuators!
Anyone care to explain how vortices sever rudder actuator linkages? I don't think so.
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Old 18th Feb 2004, 00:00
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411A, I am with you all the way on this one.

In all my years of flying swept wing jet transport a/c I have NEVER heard anyone advocating use of rudder to correct a departure in ROLL!

OK far enough if you have got FULL aileron in and the a/c is still rolling (past the vertical let's say) you might start using a judicious amount of rudder to assist.

The "experts" can come up with all the data they like but, IMHO, this was an accident induced by incorrect training! What amazes me is that (apparently) nobody spoke up against teaching this method of control operation.
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