Flight 261 Hypothesis Rebutted

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In rebuttal to an earlier thread on this forum discussing the cause of the crash of AS 261. My updated timeline: (times are PM Pacific Standard Time) 1:37 Takeoff from Puerto Vallarta
1:44 Altitude 7500 feet, autopilot engaged
1:57 Altitude 29000 feet, autopilot disengaged
2:00 Aircraft at 31000 feet
3:50 Loop point on CVR, earliest time of cockpit audio available. 1 hour and 53 minutes since autopilot disengagement @ 1:57 (No, the CVR was not "activated" at this point.)
3:55 Last routine contact with ATC, instructed to maintain 31000 feet continuing to San Francisco
3:55 Autopilot engaged
4:09 Primary trim actuator runs to the nose down position in about 6 seconds, and the autopilot disengages. The aircraft starts first dive.
4:10 Crew reports to ATC its control difficulties
4:11 Crew reports to ATC its plans to troubleshoot
4:14 Crew advises troubleshooting in progress
4:15 Crew requests clearance to LAX
4:17 Last contact with ATC. Clearance granted to LAX. Crew advises plans to lower flaps at 10000 feet
4:20 Aircraft begins final, fatal dive
4:21 Tragic end of flight, all on board lost

This timeline was obtained from information contained within several articles, including one from Aviation Week and Space Technology. When the B-2 stealth bomber was first unveiled, the government intended only to allow photographs from the front of the aircraft. This magazine flew overhead and took a photo from above. An obvious tool of TPTB. From the AW&ST article :
Several pilots said there must have been a problem for the autopilot to be off for such a long time in cruise. It commands stabilizer trim via the alternate trim motor.

Note the pilot's didn't limit the problem to the autopilot. Later in the article, talking about the trim runaway at 4:09 PM The trim moved at about the 0.33 deg./sec. rate of the primary motor, according to an investigative source. The significance of this speed is that it moved at more than 3 times the speed of the alternate motor, which is the one commanded by the autopilot. And no, the mythical Paula Gordon overflowing buffers didn't make the alternate motor move faster than that, nor did they rewire the aircraft to control the primary motor. If you doubt the more than 3x difference in speed, then here's a quote from an Air Safety Week article with detailed explanations of how the stabilizer trim works: Two small toggle switches located behind the throttle quadrant operate the alternate system. The smaller alternate electric motor moves the stabilizer more slowly, at a rate of about a tenth of a degree per second, but it does maintain function. The alternate system is connected to a different electric power supply. Obviously the trim runaway was in the primary system which is NOT controlled by the autopilot. And in response to a certain irrational doomer who fancies himself a bird of prey and who has accused a number of people of lying...... As with most aircraft stabilizer trim arrangements, the primary system consists of two switches on the yoke. One switch releases an electric motor clutch brake and the other signals power to the electric motor for up or down movement of the stabilizer. The primary system moves the stabilizer at a rate of about one-third of a degree per second. As an added safety feature, both switches must be moved in the same direction. Should the switch wires burn up from arcing, a "suitcase"-shaped handle on the console enables the pilot to actuate cable controls to the primary electric motor, thereby maintaining the ability to trim the aircraft with the primary motor.
Hmmm.... No mention of digital servo drives. So, let's review the conclusions of the previous forum thread:

The DFGC was sending faulty instructional signals to the auto pitch trim relays causing the stabilizer actuator motor to operate erratically. NOT!!!!!

Cause of faulty signals sent from DFGC: Microprocessor failure. NOT!!!!!

Cause of microprocessor failure: 90% likelihood of year 2000 non-compliance. WRONG!! 0/NONE/NADA % likelihood of year 2000 non-compliance.
No disagreement with the following statement on the earlier thread.
(Disclaimer: Any information other than that referenced by the provided links is conjecture on my part, as witnessed by my name at the bottom of this post. I have absolutely no experience, knowledge, or intelligence in the field of aviation, and this conclusion is based only on information that was available to me. (until presented with a more credible explanation, this is TTAIKI...the truth as I know it :-) ....

-- Hawk (flyin@high.again), February 14, 2000
No, we don't know yet what caused the crash of AS 261. I suspect that it will be the result of a series of failures: electrical, mechanical, and human any of which eliminated would mean that the aircraft had not crashed. There is enough information in the referenced articles on which to base some rational, informed speculation on the cause. In the end the NTSB will do the best job that they can with the information they are able to obtain and will be the ones to provide the best explanation. Whatever the cause, the tragic loss of 88 lives on AS 261 was NOT the result of a non-compliant chip. However Hawk and his flock of irrational doomers will continue to believe that it was.

-- Mikey2k (mikey2k@he.wont.eat.it), February 16, 2000

Answers

Apologies for the formatting. Apparently the Greenspun software interacts with hand-entered HTML tags in ways that aren't obvious. But I'll figure it out.

No, not a Y2k computer bug, nor was the crash of AS 261.

-- Mikey2k (mikey2k@he.wont.eat.it), February 16, 2000.


Mikey2k, Get On down Son! Ya doing the homework! You Go Guy!

-- Research (done@forus.com), February 16, 2000.

.We here are interested in y2k, and if flight 261 looks like y2k, smells like y2k, and sounds like y2k it probably is y2k!

-- ,-, (comma@dash.comma), February 16, 2000.

1:44 Altitude 7500 feet, autopilot engaged 1:57 Altitude 29000 feet, autopilot disengaged

Autopilot used for 13 minutes...

2:00 Aircraft at 31000 feet 3:50 Loop point on CVR, earliest time of cockpit audio available. 1 hour and 53 minutes since autopilot disengagement @ 1:57 (No, the CVR was not "activated" at this point.) 3:55 Last routine contact with ATC, instructed to maintain 31000 feet continuing to San Francisco 3:55 Autopilot engaged

K.. They used the autopilot for 13 minutes before thay turned it off.... before they got to altitude?..... flew for 1 hour and 58 minutes on manual, then engaged the autopilot again...

4:09 Primary trim actuator runs to the nose down position in about 6 seconds, and the autopilot disengages. The aircraft starts first dive.

14 minutes after turning on the AP the aircraft starts first dive, AP disengages... first implys they pulled out of it....

4:10 Crew reports to ATC its control difficulties 4:11 Crew reports to ATC its plans to troubleshoot 4:14 Crew advises troubleshooting in progress

They aren't troubleshooting Mech problems, they are flipping switches...

4:15 Crew requests clearance to LAX 4:17 Last contact with ATC. Clearance granted to LAX. Crew advises plans to lower flaps at 10000 feet 4:20 Aircraft begins final, fatal dive

Looks to me like they flipped the wrong switch :-(

-- Casper (c@no.yr), February 16, 2000.


My dear Mikey,

A Throughly thought out posting and research. But it still holds that the Jack Screw had to have "augered" out the threads of the gimbal nut. Causing said gimbal nut to become a sliding "collar" on the Jack Screw. And, when the stabilizer abruptly "slid" down on the Jack Screw, throwing the plane's tail into a downward thrust unexpectedly. There was not enough time for any one to increase thrust in order to keep the air craft from raising it's nose up for a steep climb. And the resulting stall.

In any such manuver, it is nearly always a set program, the air craft reaches a set attitude (nose wise) and the plane heels (slips sideways) over to the side in a half roll (180 degrees), simply because it does not have the power to continue the climb.

With the forward edge of the stabilizer in it's extreem down ward position, the plane now in an upside down position...The stabilizer would have hurtle the air craft into the sea.

Your research is excellent, but then the research the Hawk has offered so far, is just as compelling. And there are all those other aircaft ( of the same series-make-or model) that are suddenly having problems also.

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

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

-- Shakey (in_a_bunker@forty.fet), February 16, 2000.



Shakey, perhaps the scenario you describe of the actuator failure could have happened during the final fatal dive. The NTSB briefing describes a sharp nose down maneuver initially during the dive.

Your idea of the gimbal nut threads has possibility. However, I believe what I've presented has eliminated the possibility that the autopilot did this, if the "augering" idea turns out to be true.

-- Mikey2k (mikey2k@he.wont.eat.it), February 17, 2000.


Mikey, you posted some interesting information. Frankly, I have no idea whether you or Hawk are right.

I do have one question:

According to the report from Aviation Now you cite in your research:

At roughly 3:55 p.m., the autopilot was re-engaged.

At about 4:09:20, when the aircraft was straight and level at 31,000 ft. and 301 KCAS, the trim started moving for about 6 sec. to the full 2.1-deg. nose-down position, and the autopilot disengaged.

The trim moved at about the 0.33 deg./sec. rate of the primary motor, according to an investigative source.

That means its initial position would have been about zero deg., which is typical for cruise.

The aircraft started descending at about 7,000 fpm., or three times a normal descent rate, Hall said.

According to the report, it looks like the primary motor was being used while the autopilot was engaged in which case your 3x speed/alternate motor theory makes no sense.

Where did you get the information that an alternate motor is employed when the autopilot is engaged?

Any clarification would be appreciated.

-- Carl Jenkins (Somewherepress@aol.com), February 17, 2000.


It makes no sense to you that trim will move at the primary motor speed with the autopilot engaged because you've limited your possibilities to Y2k bugs in the autopilot. Open up your thinking to consider other possibilities.

I rechecked my "question". The discusssion of primary vs alternate speeds and which one the autopilot are included and even hotlinked, unless of course your browser has a Y2k bug.

-- Mikey2k (mikey2k@he.wont.eat.it), February 17, 2000.


Great thread!!

Actual debates involving research and polite discourse are so few and far between here. Mikey's post shows some work and thought, as did shakey's opposing viewpoint in an earlier thread. Both were well thought out and showed some engineering aptitude.

One thought to ponder: Every plane in this category is being watched carefully by every airline now - unscheduled landings to triple-check ground crew maintenance is understandably going to increase.

-- Bemused (and_amazed@you.people), February 17, 2000.


Mikey, My mind is open. I have come to no conclusion. You have failed to answer my question. Where, exactly is the quote, that ties the "alternate motor" to the auto-pilot. The quote from your source make it appear that the "primary motor" was engaged while the auto pilot was turned on.

Read your post, snd the report you quoted.

Quit begging the question with personal remarks that do not reflect my personal opinion and respond adequately, or consider your hypothesis refuted.......

-- Carl Jenkins (Somewherepress@aol.com), February 17, 2000.



Where, exactly is the quote, that ties the "alternate motor" to the auto-pilot.

Right here:

Several pilots said there must have been a problem for the autopilot to be off for such a long time in cruise. It commands stabilizer trim via the alternate trim motor.

-- (here@you.go), February 17, 2000.


Please accept my respectful ignormaus nods, and reserved judgment.

-- Squirrel Hunter (nuts@upina.cellrelaytower), February 17, 2000.

Thanks here@go, that does raise some interesting questions. Is the report concerning which motor is empolyed by the autopilot accurate? Anybody know? Is Mikey's observation about the 3x speed significant?

-- Carl Jenkins (Somewherepress@aol.com), February 17, 2000.

Is the report concerning which motor is empolyed by the autopilot accurate?

Since it comes from Aviation Week magazine, I'd say "probably."

Is Mikey's observation about the 3x speed significant?

It certainly seems so to me, but I'm not an aviation expert.

-- (here@you.go), February 17, 2000.


The problem was mechanical in nature-----get over it!!!

Roberto De Avionico

-- Roberto De Avionico (mainman@iserv.net), February 17, 2000.



Something I would appreciate info on--in modern airplanes, when the auto-pilot is disengaged, is "manual control" truly manual--ie, do the flight control surfaces respond via mechanical and hydraulic connections to the pilot's "driving" or is it "fly-by-wire"? If it is fly-by-wire, are there microprocessors involoved or is fly-by-wire an "old fashioned" servo+actuator (ie, no computer).

-- (nemesis@awol.com), February 17, 2000.

Carl, perhaps I accused you unfairly of being predisposed toward a non-compliant computer as the cause. But I have to wonder, since you greet my explanation with skepticism. Not that I'm offended by someone being skeptical of my post, but if I were to re-read Hawk's threads would I find the same degree of skepticism?

I believe that I've answered both of your questions in my original post to this thread. But let me take the opportunity to emphasis the point.

The stabilizer moved at the rate of the primary motor. Since the autopilot is not connected to the primary motor but instead to the much, much slower alternate motor, then the autopilot did not cause the runaway. The cause of the primary motor's moving is a subject for discussion, but the autopilot is not the culprit. If you wish to speculate on what cause the primary motor to move, then a re-read of the articles I referenced may provide some basis for a realistic scenario.

In fact I imagine that the autopilot attempted to drive the trim to oppose the runaway but the net effect would only have been to slow the net movement down slightly.

Since the flight crew was in contact with maintenance on the ground, I would speculate that the ground crew suggested something to try which would have been OK on the ground but not so great in the air. If this is true, it was the aircraft commander's responsibility to veto it. I imagine they had their hands full trying to fly the aircraft, navigate the aircraft, coordinate with ATC, and troubleshoot at the same time.

-- Mikey2k (mikey2k@he.wont.eat.it), February 17, 2000.


Mikey, Thanks for the insights. I appreciate you being straightforward and leaving out the other stuff. I am neither a doomer or a polly. I am posting information about events that appear to be akin to those predicted to be y2k related prior to CDC. If I sounded skeptical of your posts, it is because many "pollies" seem to be carrying water for corporations and doing apologetics for government screwups. Some of the "doomers" get carried away with their rhetoric as well. An honest debate and airing of information is very positive, even when we disagree. I just wish the insults between those who disagree would tone down and that we could treat each other respectfully.

-- Carl Jenkins (Somewherepress@aol.com), February 18, 2000.

Carl, I also prefer an exchange on the issues rather than an exchange of insults. But I may continue to chide you from time to time about your clipping service.

As far as anyone on this forum being a shill for anyone else, I doubt it. Even if Boeing, NTSB were handed Hawk's identity on a silver platter, I doubt they'd find him worth even the time of even their retained law firm's most junior associate to write a cease and desist warning letter.

If anything, Hawk is a shill of the government. He has seized on the most discredited scenario prior to the rollover, that of planes falling from the sky, and is publicizing it.

I believe that a Y2k bug could yet surface, but it won't be in an airborne system. If it does, Hawk could only discredit any reporting of it.

-- Mikey2k (mikey2k@he.wont.eat.it), February 18, 2000.


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