MD-80 Spirit Air, twice dives, just past midnight : LUSENET : TimeBomb 2000 (Y2000) : One Thread

The MD-80, first fully digital aircraft, seems to have a problem(s) occuring just after midnight Greenwich time. This incident occured with flight 683 (Ft Myers FL - Detroit MI). It's not listed on their website but a call to them gave info that it takes off 6:50pm and lands 9:50PM. Articles states incident occured about 1.5 hrs before landing, or about 8:30PM or 1:30 GMT. Here's the link:

The Alaska plane also was reported to have had it's trouble a bit after midnight. It looks a bit like an embedded chip problem MIGHT be at fault here, but I seriously doubt we'll ever learn the truth about it.

Not unlike TWA 800.

-- Programmer Farmer (looking@for.truth), February 20, 2000


Jeez, this is getting tiring.

The MD-80 is not the world's first all digital aircraft. It has a digital flight control system but not fly by wire controls. The Boeing 777 is the first fly by wire commercial aircraft. Heard of any of these falling out of the sky lately?

The Spirit MD-80 had problems because the plane was overweight for the altitiude it was trying to attain. There's nothing I've read that has any reference to a date.

As a general rule, don't fly any airline that has more letters in it's name than it has years of existence.

-- Jim Cooke (, February 20, 2000.

Were there MD 80 "incidents" December 31? Hmmm...

-- Total Doomer (, February 20, 2000.


Some of us are CLEARLY reaching. HARD. I don't have a problem with bona fide date related stuff but this MD-80 thing is WAY beyond rational thought.



-- Chuck, a night driver (, February 20, 2000.

Jim said...

"The MD-80 is not the world's first all digital aircraft."

Boeing says...

"Technology advancements in the MD-80 include aviation's first digital flight guidance system."

It doesn't have to be manual fly-by-wire to have a problem. It is fly-by-wire while on autopilot, which is probably 80% of most flight times. This is worse than manual fly-by-wire because everything is being controlled by the computer, which could easily go bezerk like it did on flight 261 and so many others since.

-- Hawk (flyin@high.again), February 20, 2000.

Chuck, maybe so, but humour us, okay? Eventually the debate/discussion may help to clear the air (pardon the pun). I'm looking hard for concrete proof one way or another, but for some strange reason these airlines do not post their airplanes' electronics charts online (G). And don't even think about sending me to Honeywell's site!

Jim, just a quick request about what you said. First, are you saying "fully" (digital aircraft) is the same as "all?" Since you obviously have a strong working knowledge of the terminology, perhaps you'd be willing to describe for the non-technical person the difference between the expression "fly by wire" and "computer guided." For example, I realize it has to do with hydraulics, but a clarification of the differences would be really helpful. And enlightening.

Second, in the article at which discusses Spirit Airlines Flight 685 and not 683 as in the first post here, it is mentioned that ATC gave them clearance to go to 35,000 ft (too high for their weight) but it is not clear who desired that level nor why. How does the system that indicates their safe weight for various flight levels work?


-- Rachel Gibson (, February 20, 2000.

Rachel, I'm sure these self-proclaimed "experts" on this forum will go off with all kinds of details to impress us, but I'm going to save a lot of time and use a very simple analogy.

You have no doubt played computer video games, right? Fly-by-wire is like playing the game while you have control over it, with your hands on the joystick. Your movements are being translated through the digital controls and the response is observed on the screen.

Most of these games, while you are not playing them, will continue to run through random scenarios by themselves. This is equivalent to the autopilot, where the computer program is actually controlling what you see on the screen (not random of course, but providing feedback to itself on which it bases its next movements). In either case, the control signals are transmitted through a digital system, so there really isn't a hell of a lot of difference.

-- Hawk (flyin@high.again), February 20, 2000.

Rachel, this topic has been the source of much discussion and has generated numerous threads. The idea that the autopilot caused the crash of AS261 has been disproven in this thread.

In the end it seems that people believe what they want to believe. If you want to believe that Y2k caused this crash, then you can listen to the simple-minded explanations of Hawk who has admitted that he has no aviation experience. But who has called liars others who do because they don't support his baseless "theories".

-- Mikey2k (, February 20, 2000.

Everyone looks to autopilot.

Ever see those jack screws? There are two computer controlled servo motors in the green box at the bottom.

These are pulsed motors, or used to be, which meant they needed a timing chip. Maybe not any more

-- pliney the younger (, February 20, 2000.

Now you got it! The faulty timing chip is either in the digital servo drive box, or the autopilot, and I think the autopilot had something to do with the error because it has the date function built into it. The servo drive could also have a date function chip in it but I don't know that for certain.

-- Hawk (flyin@high.again), February 20, 2000.

If you have any links (Hawk doesn't count) that indicate digital servo drive outside the autopilot in the MD-80, please provide the links here.

The articles on which I based my rebuttal thread indicate nothing more than simple DC motors. The DC-9 design from which the MD-80 is derived is 35 years old. Not many digital servo drives back then.

-- Mikey2k (, February 20, 2000.

Here's another example of Mikey2k putting words in peoples mouths:

"In the end it seems that people believe what they want to believe. If you want to believe that Y2k caused this crash, then you can listen to the simple-minded explanations of Hawk who has admitted that he has no aviation experience.

Most of us have a big ???? with regard to the MD80 problem. It appears you have made up your mind that it is not date related.

After reading the many threads on the subject it appears you have NO hands on experience in even flying paper airplanes. I'll stick with Hawk's thoughts on the matter.


-- Ray (, February 20, 2000.


Just ignore the trolls. You and I and everyone else on this forum knows that I have provided diagrams showing the digital servo drives that the autopilot uses for flight guidance controls. The plane was on autopilot when the errors occurred.

-- Hawk (flyin@high.again), February 20, 2000.

Please do not jump down on me too hard, but I must ask a question.

?????Assuming the jack screw WAS controlled by embedded chips in the servo motors or even IF the auto-pilot was defective, How would this account for the Jack-screw nut being completely reamed out????

-- Tommy Rogers (Been there@Just a, February 20, 2000.

Ray, you are one the people I had in mind when I wrote that.

If you were given an MD-80 to tear apart in search of non-compliant embedded chips, you still would believen them there after you had torn the aircraft into pieces no bigger than a grain of sand.

-- Mikey2k (, February 20, 2000.

Hawk, let me answer this question, eventhough I'm just a moron, I know very well from my own industry, when a PLC see a date function involving 00 and the external clock or date function is more than 00 the PLC's response is to open a digital gate or close a digital gate, BUT, if the function at that time of digital response happens to be in running operation ... the PLC continues to drive the function until it seizes... inotherwords, if the servos continued to receive the false information that the motors would continually run...eventually shearering off the nut like a lathe out of control.

-- SB Ryan G III (, February 20, 2000.

Hi Tommy, Jim, Hawk and everyone,

Here's a message I posted on c.s.y2k regarding this discussion. (I hope it formats okay)


Paul LeBlanc wrote:

>> MD-80s disbelieving passengers told everything was all right


Thanks for the article.

I have a problem or two with what's written and I wonder if there are any large aircraft experts here who could explain some things.

>> Feb. 19  Richard Aussicker was relaxing in his aisle seat as Spirit Airlines Flight 685 cruised toward Detroit on Jan. 30 when he sensed a growing vibration throughout the cabin. Louder and louder, he remembered, almost like driving down one of those washboard roads. The plane dived precipitously, but leveled off. Then came more vibration and another dive. <<

Okay, I take these to be 'facts' as seen by one person.

>> What Aussicker and the other passengers of the Fort Myers-to-Detroit flight did not know was that they probably came as close to falling from the sky in an aerodynamic stall as any airline passengers have ever come without dying. In a stall, airflow over the wings is disrupted, destroying lift and causing the plane to fall. But stalls at normal cruising speed are almost unheard of. <<

Again, okay. I pretty much know what stalls an aircraft.

>> On Flight 685, the pilot inexplicably flew the plane too high for its weight, sources close to the investigation said. <<

This doesn't exactly make sense. Wouldn't an aircraft, during a climb, need more and more power to sustain the climb if it was "too heavy?" Wouldn't the pilot(s) have noticed? Didn't the low airspeed indicators/alarms work?

Why would the pilot have again tried climbing if he had stalled once? He's a slow learner?

The plane 'vibrated' (4-30 Hz range feels like a vibration). Assuming that this is an MD-80 class commercial jet, what could cause this vibration?

>> When the plane landed, the crew then failed to notify airline mechanics that they might have overstressed the engines in recovering, according to the airline and federal investigators. <<

Overstressed the engines? Climbing 'too high' would have overstressed the engines (as well as pulling out of a dive).


My suspicion is that the vibration came from a servomotor (affecting the control surfaces) that was 'hunting' to achieve the proper setting, but couldn't. That is, some part was worn to the point that the exact setting needed couldn't be found, because the part was worn at that exact setting.

So the servomotor would pass the setpoint and get to an area where the part wasn't worn -- only to reverse direction because it was too far. The servomotor would repeat this action in the opposite direction, and repeat the cycle. This cycle could be in the frequency range where it would be felt as a vibration.

Eventually the servomotor would become overheated, and fail to function until cooled. If an attempt to hold the 'bad' setpoint was attempted too often, the servomotor would burn out.

What if the servomotor was controlling the horizontal stabilizer? If an aircraft was normally flown at a certain altitude (or air density), a part (the jackscrew and nut) could wear at a specific setting that holds the plane in the correct attitude. This wear could then cause the 'hunting' situation, and if the pilot (or autopilot) tried to hold that attitude and altitude, the servomotor would overheat and stop working, causing loss of control (and a dive).

The solution is to fly the aircraft at an altitude where the setpoint was out of the part's worn area.

My guess is that something like this happened. The aircraft was flying normally, burning up fuel and loosing weight. The autopilot was adjusting the horizontal stabilizer for the loss of weight (even though the fuel used is at the center of gravity, there will be a tiny adjustment needed) and the servo setpoint came into the range of the worn area of the part. Then the vibration started as the servo system tried to find the correct position. Then the servo overheated.


I can't imagine what a date could have to do with this situation -- but, I've seen some amazing implementations of servo controls.

-- Dean -- from (almost) Duh Moines (CDP, KB0ZDF)

-- Dean -- from (almost) Duh Moyn (, February 20, 2000.


Regardless of what others may call you, you're obviously not a moron at all. You're very perceptive, as I can see by your excellent analysis of what happened on flight 261.

The NTSB is either dumber than mud or they are concealing the fact that they too are looking at the control systems for the cause. To say that the jackscrew and the nut were the cause of this problem is like saying the tires are responsible when the engine explodes.

I think they know that, but they also know that your average American idiot is stupid enough to believe it. As long as they tell them it has been fixed, so they don't have to worry about taking that trip to Hawaii, they simply don't care if it doesn't affect them.

-- Hawk (flyin@high.again), February 20, 2000.

Ryan, a few questions:

What industry are you in?

What position do you hold in your industry? That is, what are your qualifications to state how PLC's work in your industry? Have you actually written code for the PLC's?

Why exactly are dates used in control functions in your industry?

Do you know for a fact that the motors are strong enough to cause mechanical damage if driven continuously into a stop, or is this just a supposition?

Do you have any background in the aviation industry? Do you have any qualifications to state how a date function would be used in an aircraft? If so, please provide details.

-- Mikey2k (, February 21, 2000.

Wow! I don't even know where to start.

The Digital Flight Guidance system does what is sounds like - it provides digital information to the aircraft for things like heading, altitude, and time to destination. It does not act like the controler for a video game! The first all digital CONTROL system (not guidance), or fly by wire, is on the Boeing 777. It's even called the "flying video game" by pilots. If there was ever going to be an embedded systems failure on a commercial aircraft, it would happen on a 777. There are about 200 777's flying right now. Anybody heard of a problem with them?

The idea that a servomotor will make an aircraft shake enough to be noticeable is really rather pathetic. No servomotor is anywhere big enough to cause this. Now, a stall will make the aircraft shake violently and this appears to be the case in the Spirit incident. Palnes have been stalling since the Wright brothers first flight. Why do we find it necessary to come up with these bizarre explanations when simple physics provides an answer?

I don't know what caused any of the MD-80 problems and NONE of us will know (or at least have enough information to make a best guess) until the NTSB releases its report. It seems very unlikely to me that this ia an electronic failure compared to a mechanical failure but I don't know for sure. Anyone saying they know for sure the cause of an accident before all the data is in is likely to be proved a fool.

-- Jim Cooke (, February 21, 2000.


I certainly don't feel that any particular type of experience is necessary to be intelligent or good at deductive reasoning, so please don't feel that it is necessary to reply to any attempts by trolls to conduct some kind of Spanish Inquisition. Here is some more recent evidence that seems to verify that you could be correct...

More damage discovered on part from Alaska Airlines Flight 261

WASHINGTON (CNN) -- National Transportation Safety Board investigators have found additional damage to a mechanical part suspected in the crash of Alaska Airlines Flight 261 last January, which killed all 88 people aboard.

The NTSB said Friday that threads had been stripped from a gimbal nut that helped control the aircraft's horizontal stabilizer and on the lower stop nut, and there were impact marks on the outside of both nuts.

"The board will try to determine if those impact marks -- as well as the stripping of both nuts' threads -- were made before the aircraft contacted the water or after," NTSB Chairman Jim Hall said in a statement.

Investigators also say now that the lower stop nut was stripped of its thread.

The plane, an MD-80 series, had radioed Los Angeles International Airport reporting trouble with its horizontal stabilizers just before it crashed into the Pacific on January 31. The horizontal stabilizers control an airplane's pitch, allowing its nose to point up or down.

Navy finishes mapping debris field

Also, the NTSB said the U.S. Navy has completed mapping the wreckage area off the California coast and has been directed to accelerate salvage operations next week.

In addition to the gimbal nut, investigators in Washington are studying the jackscrew assembly that it was attached to. The gimbal nut works with the jackscrew to control the up and down movement of the horizontal stabilizer.

Investigators are trying to determine how the gimbal nut threads were stripped and why strips of metal were found wrapped around the jackscrew.

"You can look at the metal," said aviation consultant Lee Dickinson. "You can look at the material and get an idea of whether something was pre-existing or whether something was a result of the crash itself."

Details of jackscrew investigation

Sources familiar with the investigation said the jackscrew assembly on the Alaska Airlines plane was believed to be the original unit, installed when the jet was built.

Investigators want to know if there may have been a damaged batch of jackscrew assemblies at the point of manufacture, or if maintenance practices such as lubrication may have contributed to the problems.

The board said it will also be examining grease samples from each unit to identify specific products being used and to determine compatibility between those products and to detect possible contamination. The work is expected to take several weeks.

They're also looking at the effects that extreme temperature changes might have on the mechanical parts. Flight 261 was flying a route from Puerto Vallarta, Mexico, to San Francisco when it crashed.

Other jackscrews arrive for inspection

Hall also said the NTSB will examine five newly received gimbal nut-jackscrew assemblies discovered to have problems during last week's FAA mandated inspection of more than 1,000 MD-80 series jetliners in the U.S. commercial fleet. More suspect assemblies were expected to arrive.

The assembly on Flight 261 was supplied to McDonnell Douglas by the Peacock Company of Norwalk, California, on June 28, 1990 The entire jackscrew assembly was manufactured and assembled in the United States, contrary to earlier reports.

As the Navy operation to bring up other parts of the plane accelerates, the remaining parts of the tail section and flight controls attached to the wings and cockpit area are among the sections of the aircraft expected to be recovered.

So far, the remains of 49 of the 88 people aboard the plane have been recovered from the ocean and identified by the Ventura County Medical Examiners Office, according to officials.

-- Hawk (flyin@high.again), February 21, 2000.

Hawk, you're doing a really, really good job of ignoring me. Keep up the good work!!!!!

-- Mikey2k (, February 21, 2000.

HAWK, Thanks... but I didn't even read that nonsense from y2kmike or whatever his or her name is... well not until I read your follow up about NOT having to qualify myself to him/her... but I couldn't finish the rubbish he/she was directing to me so I didn't, whenever I see names like mikey2k, imso,ladylogic, ...well you know...when you see their names or handles you quickly dismissed their comments/ramblings of being any value whatsoever to this forum or life itself. I make it a habit to look at the author before reading the comment/message...this saves me the time of reading junk and the possibility of lashing out in anger for What? I guess the best thing is to ignore what would disrupt and tear down...and embrace what will build up and solve... We've had some problems just recently... in the last couple of months with machinery that is controlled by SCADAs, PLCs, and DCSs that have run away due to date sensitive failures. Even though we designed and built this systems, and did the remediation work on them, many y2k failures are inevitable because some technical problems are not discernable prior to a failure, then others you can see clearly that while discernible, they weren't within our operations jurisdiction to control and correct... With the thousands and thousands of embedded systems we find that inputing of corrupt data for instance from a Supervisory Control unit (SCADA)can be as damaging as a PLC failure to close a valve which is driven by a servo motor of some kind...the failure in our industry of just one valve could rupture lines carrying lethal substances ...etc. We should not overlook that government is lying big time about what is happening...and we must know that whistle blowing on our industries can cause death (i.e., Ron Brown, Foster, etc.) or dismissal from your job, or family harrassed by government police etc. We must be careful about letting government agents and idiots on this forum to draw our attention from the focus that brings us here...that is we are a family and nation still...we believe in the American foundations...but unfortunately they really don't exist anymore because we let these trolls and pollys as you call them take over and destroy a great nation under the guise that we need to get their permission to breath and practice freedom of speech. As for the aircraft problems we as a world are being victimized with presently... I really don't know if we will be able to get the whole picture... I know that government is lying to us because they rule us...and anything we do find outside our own forum and discussion that may come from government will most likely be a lie of some kind in part or whole. The failure of computerized systems is the major present danger in this world... thousands are dying and millions will... because some people will never cease to do anything they can for power and money and pleasure...and then the sad thing is many of their victims are the same who we call trolls and pollys, because they have swallowed the lie and have hardened their hearts to only believe what the elite tell them to believe and do...

Anyway, I know I got off the subject...but for future reference, if I make a comment or contribution to this forum and some goofball says something afterwards, chances are that I do take the time to read it

-- SB Ryan G III (, February 21, 2000.

HAWK, I was in a hurry and forgot to reread...but when I did I need to make this following correction: In the last paragragh I wrote was: "...if I make a comment or contribution to this forum and some goofball says something afterwards, chances are that I do take the time to read it" It should have read: "...if I make a comment or contribution to this forum and some goofball says something afterwards, chances are that I DO NOT take the time to read it


-- SB Ryan G III (, February 21, 2000.

In 1959 I had a forced landing due to engine failure in an aircraft built in 1945. I guess I should have checked for imbedded chips before takeoff?

-- Roy (bushwhacker@north, February 21, 2000.

Ryan, you've ended up answering my questions anyway.

Yep, don't let anyone ever, ever, ever confuse you with the facts.

-- Mikey2k (, February 21, 2000.

Hmmm... S.B, your stuff is the biggest BS 've read since RC the oil fact, he sounds very, very, similar....

I know about PLCs, and SCADAs, and ....frankly sir, you barely know enough to fool only those who don't.

I appreciate the facts presented here by Mikey and Mr. Cooke. Regards,

-- FactFinder (, February 29, 2000.

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