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EXCERPTS OF A THREAD ON TB 2000 Discussion Forum

Servomotors for Airline stabilizers - any experts out there?

http://hv.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=002TuT

greenspun.com : LUSENET : TimeBomb 2000 (Y2000) : One Thread

(snip)

...The following question and comments are from an embedded expert who I don't believe has been following this thread. Any comments?

"what about the stabilizer problems on the md series of planes? These servo motors which control the stabilizers pulse based on a timer which is chip based. The servo motor does not care about date, but may be a buffer overflow from that part of the chipset which does the date calcs anyway." -- md 80 series auxiliary questioner (md80series@remaining.questions), February 06, 2000. __________________________________________________________________________

Aha! Thanks md, glad to see someone has finally figured it out. I recall some programmers saying that even though a system may not need to use a date, it is sometimes written into the coding as a method of calculating time increments. If a non-compliant chipset like that were linked to the main computer showing a 2000 date, you'd eventually get buffer overflows, and that's why these things are all starting to happen around the same time. -- Hawk (flyin@high.again), February 06, 2000. ______________________________________________________________________

.... The Bulletin 1391 is a Pulse Width Modulated, single axis AC servo drive The 1391-DES digital drive has the same features as the 1391 series products, but takes advantage of a microprocessor-based control structure. -- Hawk (flyin@high.again), February 06, 2000. ______________________________________________________________________ (snip) .....Technology advancements in the MD-80 include aviation's first digital flight guidance system. -- Hawk (flyin@high.again), February 06, 2000. (snip)

_________________________________________________________________________

.... Thanks Hawk for all your contributions. Very interesting to say the least. That is quite an eyeopener that the MD-80 series includes "aviation's first digital flight guidance system". What other planes use digital guidance systems?

Wouldn't such digital guidance systems also include digital annual maintenance scheduling. If that is the case, then once a year a date would be accessed. Say that that date was January 1. Consider the possibility that the date had not been remediated correctly or at all or that it had failed to rollover. It could take weeks for the buffer to overflow if the date were incorrect.

Mikey noted that if the date sensitive software doesn't access the chip then it has no effect. I am not an embedded expert, but it would seem that at the time that annual maintenance scheduling kicks in, the chip would be accessed. -- md 80 series auxiliary questioner (md80series@remaining.questions), February 07, 2000. **************************************************************************

Response to a thread 2/17/2000 re Flight 261

Dear Sifting:

You posed two questions:

"If we are to believe that there could possibly be a link to date sensitive embedded chips, why are we now seeing this occur during the first few days of February?" and

"What could be the motivation for all of the real experts to avoid resolving these problems?"

It could be that the problems were triggered around the same time and that they all became evident about the same time. There could have been a number of weeks between the time the problems were triggered and the time that they got to a stage where they could cause failures.

I am not an expert, but here are three possible things that I have seen mentioned elsewhere that seem to me could have been involved:

1) buffer overflow 2) function overflow 3) annual maintenance scheduling (if scheduling functions are not Y2K compliant, and a date of 1900 comes up, that alone could shut down operations or trigger a failure).

As regards your second question regarding why experts would avoid looking into these problems, I would suggest several possibilities BEYOND the regular psychological barriers, bureaucratic constraints, and legal and insurance disincentives:

1) that few people have the training and expertise to troubleshoot the kind of interconnected set of problems that could have been involved with the Alaskan Airline crash;

2) that fewer still might be expected to found at the NTSB or FAA; and

3) that even fewer might be expected to be to be found on a maintenance crew.

What if this particular crash did involve a complex set of cascading problems, involving both mechanical and automated systems? And what if fewer than 50 people in the world had the training, expertise, and experience to sort out such a complex set of interconnected problems? ....Maybe, just maybe, we have reached a point when only a few people will be able to understand complex problems that require expertise in specialized and overlapping areas of technology. Maybe we have reached a day when others who need to understand what those few know, do not even know the right questions to ask, let alone have the understanding to recognize when an explanation is or might be relevant?

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http://www.egroups.com/group/humptydumptyy2k/1107.html? 1107 of 1606 4:31 PM Mon 7 Feb

Subject: FW: Something to consider about Alaska crash inve From: Ed Yourdon

Folks,

FYI -- I don't know the gentleman who cc-ed me on this message, and am in no position to verify its accuracy or credibility. But I think it's worth at least taking a quick pass through it to see if it sounds plausible. If so, perhaps you could send it on to someone who is more knowledgeable about aircraft, flight control systems, and so forth.

If there is someone in the group who can quickly and definitively put this "theory' to rest, let's do it right away. Obviously, comments from people with a background in the appropriate engineering fields would be most welcome.

Cheers, Ed [Yourdon]

----------

From: "Roman Mach" Date: Sun, 6 Feb 2000 08:48:57 -0800 To: Cc: Subject: Something to consider about Alaska crash investigation

Hi Byron Acohido:

I got your name from an article you wrote about the tail integrity of Flight 261 and saw you are an investigative reporter. http://www.seattletimes.com/news/nation-world/html98/plan_20000201.html

Given that, I want to present what I consider some interesting evidence, all circumstantial, about the crash that you may want to pursue, namely that there is a Y2K problem with the MD-80 series. As far as I know, and oddly so, I have not seen anyone yet propose the Y2K theory for this tragedy. The information I'm going to present is entirely based on conjecture as I have no other information about the crash than what I see in the news reports. I have no prior or current affiliation with Boeing or MD and have never worked on planes. I am also copying Ed Yourdon (Software and Y2K expert) as he may have some insight into what I have to say.

I think there is now enough evidence to make the following claim reasonable. I believe that the crash was a result of a Y2K problem with the plane's digital controller. Before you dismiss me as a scaremonger, I am a software engineer at an Internet firm and I headed up the Y2K efforts of our software systems at Saltmine. In the course of this process I became very adept and spotting potential Y2K problems or causes. I have also worked with hydraulic systems on boats and understand some of the hydraulic/mechanical issues that the plane could have experienced.

Here is the reasoning. You can accept it or reject it, but please give It some consideration:

1. In the words of a Boeing web site:

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

I don't know if this means that flight control surfaces are always under electronic control (i.e. fly-by-wire) or only when the autopilot is on, but in either case the plane is flown using electronic means at certain times, which means that the plane's control surfaces can change based on computer calculations.

http://www.boeing.com/commercial/md-80-90/index.html

2. The problem occurred with the Alaska Jet within minutes of 4:00pm PST January 31st 2000. So what, you say? Planes are configured to use what I believe is called 'Zulu' time, another term for GMT, or Greenwich time. This is because they need a reference point that stays constant when flying across time zones. It turns out that GMT = PST+8, so 4pm PST is midnight GMT or 0:00 in the plane's computer. Not only that, but in this case it also coincided with the "month rollover": 1/31/00 to 2/1/00.

It is conceivable that a software system on the plane may have been using the current (within seconds) date/time to help in navigation. If the software had a bug when doing a difference calculation between one month and the next then the resulting output could be bogus. Alternatively, someone may have patched specific lines of code in the software that only execute when the month becomes Feb 2000 - this is conceivable given that some programmers originally failed to account for the fact that Feb 2000 is a leap year. This code may never have been tested and may have crashed the software the moment it was input a date in Feb 2000 for the first time. It is also worth noting that most MD-80s were probably grounded during the Jan 2000 rollover, so this problem, if it also existed then, may never have been noticed during the first Y2K rollover event.

So how would a stabilizer jam? Simplifying greatly - A calculation is made in the autopilot that states where the plane should go in terms of heading angle is derived from the direction of flight, current date/time, and current (GPS, beacon or inertial) position. This value is then passed on to setting an angle for the stabilizer so that the plane is always moving towards its destination. If the date/time calculation fails because of a bug when the date reaches Feb 2000 the resulting number output could be anything; it may even be a number so large that when it finally is processed to set an angle for the stabilizer, the angle could be 90 degrees - something the stabilizer cannot reach, but it can certainly try and make it as close to 90 degrees as possible, which would probably be full extension of the stabilizer. The unexpected quick movement of the stabilizer to reach this extreme position could slam into mechanical stops and dislodge pipes, brackets or whatever, resulting in a mechanical jam that the pilots would be unable to deal with.

Here are specifics from MSNBC web site about the timing of the original problem:

http://www.msnbc.com/news/364560.asp

"At 3:55 p.m. PT, the plane, en route from Puerto Vallarta, was cleared to fly to San Francisco; it was the last routine transmission before the pilots indicated there was any problem.

At 4:10, the pilots acknowledged they were having difficulties and descended to 26,000 feet. A few seconds later, the flight descended to 23,750 feet and the pilots said they were having problems controlling the aircraft"

3. There have now been three planes with this problem, one has crashed and two have landed safely. News reports on the other two that had the problem:

Feb 2: http://www.msnbc.com/local/king/508850.asp

Feb 5: http://www.msnbc.com/news/364560.asp

When was the last time three planes all of the same make had essentially the same control surface problem within five days of each other and never before in their histories? The only two possibilities that I can come up with are identical faulty maintenance procedures or Y2K - the 4:00pm failure pushes me into thinking that this is a Y2K problem. Another oddity is that all three planes were on the west coast (California, Arizona, Reno) when they had the problem - maybe the software calculations fail if the date is greater than Feb 2000 and within a certain longitude window.

4. An MD-80 was known to have crashed years ago in China under the control of its autopilot - it landed short of the runway. This says that the autopilot can be a cause of a crash.

In any case, if my theory is correct, you should see the FAA ground all MD-80s very shortly or at least prevent them from flying on the West Coast.

I haven't presented this info to the NTSB since I don't know how to contact them, but I wouldn't be surprised if they are considering this angle also. At the minimum, I hope you found my email interesting and at the best, I hope that quick action is taken by the appropriate parties to prevent further loss of life.

thanks,

Roman Mach **************************************************************************** 2/25/2000? http://www.sacbee.com/news/calreport/calrep_story.cgi?N306.HTML Problems reported on 13 flights of MD-80 jetliners since Alaska Airlines crash

By TOM VERDIN Associated Press Writer

LOS ANGELES (AP) -- Pilots reported problems on 13 jetliners of the types ordered inspected following last month's crash of Alaska Airlines Flight 261, forcing three unscheduled landings this week alone.

Authorities, however, said there's nothing extraordinary about the number of reported problems: What's unusual is the public attention they are receiving since the Jan. 31 crash off the Southern California coast that killed 88 people.

The types of problems reported by pilots flying MD-80s, MD-90s and DC-9s are routine, officials said Thursday.

"You're just not noticing it for the other airplanes because everyone's focused on this one," said Paul Turk, a spokesman for the Federal Aviation Administration.

Three pilots reported problems with their horizontal stabilizers, the wing-like tail assembly that control a plane's vertical pitch and is the focus of the crash investigation.

On Wednesday, crew members on an Ontario, Calif.,-bound Delta Air Lines flight returned to Dallas after reporting apparent mechanical problems with the MD-90's horizontal stabilizer.

After the crash of the Boeing MD-83, the FAA ordered stabilizer inspections on more than 1,100 MD-80 and related series planes as well as MD-90s, DC-9s and Boeing 717s. Problems were found with 22 planes. The jackscrew, a bolt that drives the up-and-down motion of the wing-like stabilizer, was replaced in 18 airplanes.

Additional problems reported for MD-80s, MD-90s and DC-9s since the crash range from smoke in the cockpit to losing engine power.

On Monday, a Continental Airlines MD-82 made an emergency landing in Indiana after the crew reported trouble keeping the flight level. On the same day, an American Airlines MD-80 made an emergency landing in Tucson after one of its two engines failed.

A check by The Associated Press showed no reports associated with Boeing 717s since Jan. 31.

Reporting and checking such incidents is a daily occurrence for the nation's airline industry, Turk said.

"It's a very routine part of doing business, and the numbers you're showing for the MD-80 are pretty normal," he said.

The National Transportation Safety Board keeps track of such reports to spot any patterns, agency spokesman Terry Williams said.

He said the agency has not noticed a consistent problem since Jan. 31.

"As of this point, I'm not aware of any collective thing we're looking at in terms of these accidents," he said.

In some of cases, airline officials attributed the reports to overcautious pilots.

Just five days after the crash of Flight 261, an Alaska Airlines MD-83 returned to the Reno airport shortly after takeoff when pilots reported stabilizer trouble. Later, airline officials said they thought the pilots had overheated the mechanism's motor by running through several up-and-down cycles before takeoff.

Attention on one particular type of aircraft is common after a crash, heightened by cautious pilots and media outlets with piqued interest, industry observers said.

"The MD-80 has one of the very best safety records of all airplane models," Boeing spokesman John Thom said. "But for any airplane model ... that safety record doesn't have a lot of meaning to most people when there's been an air tragedy."

-- GICC Sysop (y2kgicc@yahoo.com), July 18, 2000


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