This is a repost from an earlier thread, I thought it needed more attention, so here it is:

Suppose, just suppose, that the autopilot were to get confused, beit buffers, or anything else. Is it possible that a plane could tilt its elevators slowly in the wrong direction, and compensate for it with the flaps on the wings, or anything else? This scenerio would explain why the plane suddenly nose dived when the autopilot was disengaged.

Although, not being at all familiar with planes and such, I may just be completly out of my league, BUT, sure sounds like a plossible scenerio.

Another would be this: If a part of an aircraft is capable of being on "autopilot", this means that it IS controlled by computer. Now the tricky part, just because you press a button that "turns it off", does it really mean that the computer is out of the "loop"?

If a system is capable of going into "autopilot", one switch, will not bring it back to a "manual" operation.

Manual is just that, no electronics, but this condition is impossible, because everything has to go through the "autopilot" computer, it may be that the computer no longer exercises control over certain functions, and it may be this is exactly what is happening (going wrong). Who is to say, or can say, that by turning off autopilot, the computer WILL NOT or DOES NOT exercise ANY influence on ANY control?

Any insight would sure enlighten me.

-- Electman (vrepair1@tampabay.rr.com), February 09, 2000

Answers

NO

NO

PLEASE PLEASE STOP!!!

Please stop this, it is getting insane, everybody and his 12 year old nephew is getting into the game, coming up with how aircraft fly.

No more making up off the wall speculation, before you know it no one will get into an aircraft again.

Why do people do this? Why speculate how something works and then run free with all kinds of scenerios based on that speculation? I'm banging my head on the table in frustration, doesn't ANYONE want to know how they really work? AAAARRRRGGGGG!!!!!!!!

-- Cherri (sams@brigadoon.com), February 09, 2000.

Excellent observation Electman, and my point exactly. This aircraft was only 8 years old, and was loaded with the latest digital electronics. Whether the autopilot has control or not, the movements initiated by the captain are nonetheless being relayed through the computer system. This is reinforced by the statement from Aviation Week saying that there is no way to manually control the stabilizer. There is definitely some very erratic Y2K malfunctions happening in most of these planes we are hearing about recently. I've never seen so many bizarre reports within one week, and there are going to be a lot more.

-- Hawk (flyin@high.again), February 09, 2000.

Cherri my dear you seem a little stressed this evening.

-- David Whitelaw (Dande53484@aol.com), February 09, 2000.

She can't take it when someone is smarter than her, especially a man.

-- Hawk (flyin@high.again), February 09, 2000.

Electman, this is going to sound like I'm flaming you, but I'm not really. I have no expertise in brain surgery and wouldn't waste a brain surgeons time discussing theories about how to rewire a nervous system. Your post shows a complete lack of understanding of the basics. My understanding comes from 27 years' experience with aviation including simulators, work on actual aircraft, flights while sitting in the jump seat, and avionics design. The most direct answer is that to answer all your questions would first require educating you to a level that can't be done in a forum post. Again I'm not flaming you, but I don't know where you're coming from and I have to wonder if you have a Y2k axe to grind like a certain birdbrain on this forum.

I think that plenty has been posted on other threads both by people who know what's going on and by people who think Y2k is at fault.

If you're really trying to understand how the MD-83 works, then you can read posts by Cherri, myself, and others who have aviation backgrounds. Also read other sites that we reference such as the NTSB. See if you can find a book in the library that explains aerodynamics and aircraft control systems.

But if you're a disappointed doomer who hoped his extensive preps would be necessary, then read Hawk's posts and swallow them whole.

-- Mikey2k (mikey2k@he.wont.eat.it), February 09, 2000.

Whether the autopilot has control or not, the movements initiated by the captain are nonetheless being relayed through the computer system.

WHAT COMPUTER SYSTEM? The movements initiated by the captain are relayed through what computer system? Are you saying that there is a computer system in that aircraft that everything is "computed" in and out of?

Is that what you think? Do you actually believe what you are saying? If so, then it is an assumption on your part, correct? Or do you have something to support the existance of this central computer?

-- Cherri (sams@brigadoon.com), February 09, 2000.

Electman, most of the self-proclaimed aviation experts like Mikey have only worked on what are now outdated relic aircraft in terms of technology. You are definitely on the right track.

Mikey, Cherri, and the rest o'dem "dumb ol' pilots" ought to go to the link provided by Rachel and read some very interesting comments by avaition experts currently working in the field, about the numerous problems inherent in the aviation computer systems.

-- Hawk (flyin@high.again), February 09, 2000.

My dear Mr. Electman,

Sir, if you where watching the media news tonight. You must have saw a segiment of it showing a "jack screw". I am sure, since your name suggests that you are either in the same feild as myself (or closely related to it). That you reconized that the stablizers on the air craft are using the same type of mechanical control system (and jack screw) as digitalized motor contoled valves do. And yes, there are embeded systems in the linkage (just as there is in any digitalized contol systems).

Mistress Cherri..Dear lady I am truely sorry if you have become distressed. And are you out on sympthy strike with the rest of the workers who went out today? As for flying in one of the things..The last one I rode on was on my return trip back from my father's funeral. I still remember the strange sounds ( to me) that the flaps (probably wrong deffinition) made every time the plane's wing changed. In any case, after I landed. My wife picked me up, and we had something to eat and made our hour plus drive to our home. Later that afternoon, I tuned in to the news..And the air liner I had rode on, had went down, the news said from a micro burst at the Dallas air port.

So, no...I do not ride one of the things (and does that ever drive the company up the wall..LOL).

"As for me...I shall finish the Game"!

~~~~~~~~~~~~~~~~~~~~~~~~~~Shakey~~~~~~~~~~~~~~~

-- Shakey (in_a_bunker@forty.feet), February 09, 2000.

Uh-oh, Cherri is really cracking under pressure. She's having another one of those flashbacks like she did last night. She thinks it is 1970 and she is back in Vietnam again. Look at her, she doesn't even know that airplanes use computers now. Wow, amazing.

Cherri my dear, you poor ole thing, you've been at this for days now and the stress is getting to you. Go lie down dear, and rest. When you wake up you'll be back in the year 2000 and you'll realize that computers are a real thing these days, not just a fantasy like in 1970.

-- Hawk (flyin@high.again), February 09, 2000.

My dear Mikey2K and mstress cherri,

I havebut one question for you two concerning the M-80 series air craft. Are they in part,or wholey flow by wire.

Does a hydralic motor, on an electric motor drive the screw? And I guess that is two questions, is't it..

"As for me ....I shall finish the Game"!

~~~~~~~~~~~~~~~~~~~~~~~~~Shakey~~~~~~~~~~~~~~~~~~~

-- Shakey (in_a_bunker@forty.feet), February 09, 2000.

My dear Mikey2K and mstress cherri,

I have but one question for you two concerning the M-80 series air craft. Are they in part,or wholey flow by wire.

Does a hydralic motor, or an electric motor drive the jack screw? And I guess that is two questions, is't it..

"As for me ....I shall finish the Game"!

~~~~~~~~~~~~~~~~~~~~~~~~~Shakey~~~~~~~~~~~~~~~~~~~

-- Shakey (in_a_bunker@forty.feet), February 09, 2000.

Fabulous thinking, Mr Electman. You are first in line for editing Mr Hawk's newsletter, "How Everything is Related to Y2K Even if There is No Evidence and How the Government Will Try to Kill You for Saying Anthing Different and How Even a Completely Uneducated Person Can See the OBVIOUS Y2K-Related Problem With a Piece of Machinery as SIMPLE as the Modern Aircraft".

-- Imso (lame@prepped.com), February 10, 2000.

Hey Shakey, how's it hangin'?

Let's first define what a "fly-by-wire" system would be. Sensors would convert the pilot's input into the the control stick into electrical signals which then are input into computers which then control the actuators driving the control surfaces. The MD-83, on the other hand, has mechanical linkages from the control stick to control valves on hydraulic actuators for the ailerons and elevators.

The jack screw, part of the trim actuator, is driven by electric motors which are controlled via switches and relays.

No computers on this type aircraft, compliant or not, between the pilots' controls and the control surfaces in the MD-83. And no reason that a fly-by-wire aircraft would have a date-dependant computer between the pilot's control and and the aircraft control surface. Aerodynamic effects are pretty much the same from day to day -- any differences are due to ... gas laws -- Boyles' Charles', etc.

-- Mikey2k (mikey2k@he.wont.eat.it), February 10, 2000.

My dear Mr. Mikey2k

Sir...My question, I seem to have not made clear. My concern, or attention was/is focused on the embedded systems. Like in micro prosessing chips.

Computers, and any thing made after 1980 has them. Can be remeadated. Software, if any, can be changed. There are GPS trackers on the aircraft for sure. And since there is a "jack screw" there is a (PLC/PROM/ROM) controller for the electric/ or hydralic motors also.

Control systems principals are the same, in every application. The black boxes, limit switches etc. are physically made different. But their intended applications are the same.. To perform a specfic task (with in a set parameter). Thank you for your respondse sir.

Well if it isn't stuck on himself Imso. I'd ask you how it was hanging. But there is doubt that it is at all.

"As for me...I shall finish the Game"!

~~~~~~~~~~~~~~~~~~~~~~~~Shakey~~~~~~~~~~~~~~~~~~~

-- Shakey (in_a_bunker@forty.feet), February 10, 2000.

A simple question to you aero types. Is the actuator motor torquey enough to strip a jackscrew?

-- Carlos (riffraff1@cybertime.net), February 10, 2000.

When are the experts going to tell us that the Alaskan Air Pilot also tried to commit suicide by deliberately plunging his aircraft into the ocean :)

-- Carl Jenkins (Somewherepress@aol.com), February 10, 2000.

Cherri, everything is fine according to you. So, I am having a hard time figuring out why you dog Hawk, who btw, blasts you in a way I wouldn't(no offense, Hawk-your business; she doesn't have to hear it if she chooses not to).

So, Hawk makes posts to this forum about planes. I honestly don't know if he is right or not. Based on character alone, I would choose Hawk. But, regardless of whether he is right or wrong, it still doesn't explain your obsession with him. Cherri knows Hawk is wrong. And Cherri, he is not going to wake anybody up but for the meager few of us doomers. So why do you expend so much time on him?

The Polly world is safe from Hawk so why your obsession with him, Cherri? It reminds me of Carville and Matalin. A match made in heaven?

-- Kyle (midtnbuddy@juno.com), February 10, 2000.

Shakey, you say you asked a question, which you did, and which I answered even your followup if you re-read my previous answer realizing that an embedded system is a classification of computer.

You've been around awhile, before microprocessors saw wide use. Were there actuators with jackscrews BM (before microprocessors). Just because a technology exists, does that mean that it is used in each and every possible application?

-- Mikey2k (mikey2k@he.wont.eat.it), February 10, 2000.

Carl,

"When are the experts going to tell us that the Alaskan Air Pilot also tried to commit suicide by deliberately plunging his aircraft into the ocean :)"

Yeah, I've been wondering the same thing. Sure looks like they're leading up to that, or at least a way to say that it was the pilot's fault. Anything to avoid spending the money to fix it.

Mickey Mouse,

"Just because a technology exists, does that mean that it is used in each and every possible application?"

We never said it is used in EVERY application, but does that mean that it is used in NONE of them? Your arguments are not nearly as credible as mine.

-- Hawk (flyin@high.again), February 10, 2000.

First, I have no Y2K axe to grind. I simply want to figure out what is happening, call it deductive reasoning, but to really "know" I need some answers to questions.

Mikey2k said "The MD-83, on the other hand, has mechanical linkages from the control stick to control valves on hydraulic actuators for the ailerons and elevators."

Now, while this may be true, then how is it possible for autopilot to function? If the autopilot takes control of the surfaces of the plane, then a computer IS involved, and it simply isnt just mechanical linkages, THERE IS AUTOMATION, SOMEWHERE. Is it that the control valves (hydrolics) are ALSO actuated by the autopilot? An autopilot DOES take control of the plane, it isnt as simple as tying a rope to the steering wheel, for heaven sakes!

I rode in a small plane, once, and it was on autopilot, it didnt matter if i turned the wheel, the autopilot was on, and my movements didnt affect flight... so much for just manual linkage... there is more involved, I would like to know what.

Now, on to another tid bit.

I know there is redundancy involved, lets focus on that there jackscrew.

No one has answered my question on whether or not the elevator can be placed in the wrong direction, slowly, and be compensated elsewhere.

Is it possible? If it is, then I will let you in on another suspicion of mine.

-- Electman (vrepair1@tampabay.rr.com), February 10, 2000.

Electman:

Part of the problem is the inexact terminology of "auto" and "manual". In terms of control systems, the meanings are slightly different than in everyday life. "Auto" means closed loop (i.e. feedback) control and manual means open loop. It has nothing to do with how the final actuator is linked up. Another important concept is "local" versus "remote". As an example, consider a tank level contoller that adjusts the opening of an outlet valve to maintain a constant level in the tank that may have a varying supply to it. In "Auto", the operator enters a tank level (say 10 feet) into the controller and the controller gets a measured feeback from a level indicator of what the actual level is and either opens or closes the valve depending on whether the level is higher or lower than the setpoint. In "Manual" the operator enters a valve position (say 60% open) into the controller and the controller moves the valve to that position and holds it there, whether the tank overflows or runs dry, until a new postion is entered. If the valve is operated by a motor, then, instead of entering a position, he would push either and increase or decrease button to make the motor move the valve to the desired position (remember this for later). In both "Auto" and "Manual" mode, the valve itself must be in "remote" mode, i.e. it gets its position setting from a remote location. In "local" (also known as 'hand'), the valve is disconnected from the controller an someone must manually adjust the hand adjustment at the valve itself.

Thus, an aircraft control system most likely does not have "local" mode capability for most things (but it could for some), but it certainly has a manual mode for all of the controls, i.e. when the autopilot is switched to the OFF position. And, contrary to Hawk's assertion above, when the autopilot is off, the signals to the final actuators do NOT go through the flight computer. He even provide a link to the Aviation Week news article in an earlier thread that clearly points this out. To move the stabilizer manually on the MD- 83, the pilot and FO have two thumb switches which activate the motor (not servomotor, just a plain old DC motor) that turns the jackscrew, one for forward and one for reverse direction on the motor. There is no computer involved, the pilot simply watches his display to see the angle of the stabilizer and releases the switch when it reaches the proper position. Note also that there are no calculations involved in any of the above that would have any need for a date or time.

Any control system is a combination of electrical and mechanical devices and very often computers or microprocessors. But that does not mean that all operations are done thorugh the computer at all times. In a true fly-by-wire aircraft like the 777, the pilot would not be able to use the increase/decrease functions to adjust the stabilizer -- he would have to enter a desired angle into his console which would then be passed to the controller for the stabilizer. But, that is clearly not the case here as Hawk has so graciously pointed out. It is a pity that he can only read a part of the links he provides and understand only of part of what he reads.

-- My Full Name (My@email.address), February 10, 2000.

This site shows the MD-80's systems, with diagrams. Hope it helps bring some light to this debate, i.e. "fly-by-wire", manual vs. autopilot etc., on this perticular plane.

(Click on the right arrow at the bottom to view next diamgram page.)

http://www.clouddancer. de/main/xfee.htm

-- Chris (catsy@pond.com), February 10, 2000.

Correction: click on the "systems" button in the frame at right, then click on the arrows at the bottom to flip pages.

-- Chris (catsy@pond.com), February 10, 2000.

Great link Chris! Lot's of good info.

Hey Chicken-Hawk! Help me out here! I can't seem to find the damned stabilizer servocontroller and servomotors in any of those schematics. Surely someone as brilliant as you will have no problem finding them and pointing them out to all us ignorant slobs! I mean, surely you would never post something that you were not absolutely 100% sure of, would you?

-- My Full Name (My@email.address), February 10, 2000.

Tried the site, its been busy, cant get in.

One question remains un-answered, please, someone answer it:

Is it possible for the elevators to slowly move into the wrong posistion and be compensated for by something else?

-- Electman (vrepair1@tampabay.rr.com), February 10, 2000.

Been to the site, there are NO schematics, only block diagrams, which are totally inadequate.

I think I'll stick with what I know, I do not know planes. But I do like to figure things out, but to do that would take me quite a bit of time and a whole bunch of books.

Guess I'll have to wait for the "offical word".

Regards

-- Electman (vrepair1@tampabay.rr.com), February 10, 2000.

Electman,

To your original question; "...that by turning off the autopilot,the computer will not or does not excercise any influence on any control"? When any autopilot I've ever worked with is switched off, power is removed from the output amplifier section of the autopilot system and the output signal lines are also "cut" by opening relays.

On most aircraft, part the "automatic flight contyols system" (AFCS) still functions because as well as being the autopilot, those same black boxes usually are the stabily augmentation and control force boost systems systems. In an emergency a crew can disable the stab aug system either completely or by individual axis. This is probably part of what was going on while the crew troubleshot the problem.

But if there was a mechanical failure of the jackscrew, it wouldn't matter what configuration the stab aug and AFCS was in. The fixed end of the hydrualic cylinders used to move the tail when control inputs would be flopping around and the tail would be moving on its own.

Think of a car or truck which uses the older steering box type of steering and what kind of steering problems you get when the idler arm goes bad. That or maybe trying to move a bulldozer blade when the end of the cylinder attached to the tractor frame is loose. Those two examples are about the best illustrations I can think of right now.

WW

-- Wildweasel (vtmldm@epix.net), February 10, 2000.

Is it possible for the elevators to slowly move into the wrong posistion and be compensated for by something else?

-- Electman (vrepair1@tampabay.rr.com), February 10, 2000.

That is a good question. Actually yes, if it happened while on autopilot then the trim would be compensated for. When the autopilot kicked off the adjustments would be lost and the pilot would have to make them manually. The G-forces alone could have stripped the threads on the screws, especially if they were aluminum (made that way for weight concerns) They were not designed to stand up to that strong a force. If one of the jack screws stripped suddenly, that could account for the noise that was heard and the aircraft spinning out of control so suddenly.

-- Cherri (sams@brigadoon.com), February 13, 2000.

Cherri,

Not bad logic for someone NOT in the know, huh?

Amazing what deductive reasoning can do...

I knew I was on to something when they talked of turning the autopilot on and off, and I belive I'm real close. I only hope that it is something mechanical, because if its not, just replacing the jackscrew wont solve the problem.

I can only go so far, because my knowledge of flight and systems is minimal at best, but I just have a sneaky suspicion on this one, and can't help but speculate.

-- Electman (vrepair1@tampabay.rr.com), February 13, 2000.

Let me clarify Cherri's answer. No matter how the trim system is mechanised in an aircraft, the pilot flies the control stick first to control the aircraft attitude, and if a constant force is required to do that he will adjust the trim in the direction to reduce the amount of force required. The trim position required for that will vary with airspeed, mach number, and center of gravity which changes depending on the aircraft cargo load and fuel burning off. It can also change with aircraft configuration such as lowering the flaps and landing gear (and the flaps were lowered just prior to the final fatal plunge). If some failure prevents the trim from adjusting, then the pilot will need to maintain force on the control wheel.

Trim is not moved to an absolute position except preparing for takeoff when it is moved to an estimated position for the moments after rotation and liftoff. After takeoff, trim is adjusted to reduce the control force needed.

An autopilot will control the elevator and trim in the same manner as the pilot. A servo engages and moves the elevator. If the autopilot senses that servo effort is required to move the aircraft, then it commands the trim to move in the appropriate direction. Now if the trim fails to move then the servo will need to deflect the elevator to maintain controlled flight. If this situation persists the autopilot should indicate a mistrim which should alert the pilot to be ready for the need to add force when the autopilot disengages.

The autopilot uses relays to control trim motion, and typically there is some mechanism to prevent a single failure from causing a runaway, or that a runaway can be overridden. I suspect that a failure occurred in AS261 which was a trim runaway but that when the autopilot was engaged and the trim started to runaway that the autopilot commanded motion in the opposite direction and this stopped the trim from moving.

The NTSB report says that simultaneous with autopilot disengagement (the autopilot no longer in control) and in six seconds that the trim ran to the stop. Actually that can't be, since the autopilot takes perhaps 1/10 of a second to disengage. I suspect that when the autopilot was disengaged the runaway fault was no longer cancelled.

What puzzles me is why the runaway was allowed to continue for 6 seconds without the crew stopping it. There should have been a trim- in-motion warning, and I understand the crew is trained on how to remove power from the trim actuator to prevent trim runaways from continuing too long.

A lot of this is speculation, and I expect the NTSB will determine the true cause. I speculate that there will be multiple causes of this accident where if any one were missing AS261 would have landed safely. I suspect both the trim control relays and a mechanical cause in the actuator itself.

-- Mikey2k (mikey2k@he.wont.eat.it), February 14, 2000.