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THS Jackscrew design

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THS Jackscrew design

Old 19th Jan 2013, 04:33
  #41 (permalink)  
 
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So you want to rewrite history
I'm afraid you are the one attempting to rewrite history.
The fleet was grounded and they admit to finding atleast 3 more jackscrews on their way out
The fleet was never grounded. Alaska commenced voluntary inspections of the jackscrew on the 9th Feb, following advice from the NTSB that the jackscrew had been recovered from the ocean in a damaged condition. The inspections were complete by the following day, with two other aircraft found to have discrepancies. These two were the only ones grounded.
pilots started taking notice, and hence, no more crashes
No more crashes had nothing to do with the pilots, rather the maintenance deficiencies were rectified.

A word of advice. You are welcomed by one and all to make contributions. Just cease making out to be something that you are not. You are not a pilot, so please stop pretending you are one.

And cease telling professional aviators that they know not what they are talking about - especially in the derisive, language you are so fond of using. I refer to your contributions on subjects such as derate, flex, runway performance, implications of V1 etc etc in particular.

If you are out to log the record as the poster with the most aliases and bannings, please continue on your merry way.
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Old 19th Jan 2013, 06:47
  #42 (permalink)  
 
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Here is the wiki to Flight 261 may I suggest that you are sailing close to the wind, my friend.. take care

Alaska Airlines Flight 261 - Wikipedia, the free encyclopedia

1- They called dispatch for help, a solution...

'and on a shared company radio with operations and maintenance facilities at Los Angeles International Airport (LAX) discussed a jammed horizontal stabilizer and a possible diversion to LAX'

2- Dispatch told to continue...

During this time the flight crew had several discussions with the company dispatcher about whether to divert to Los Angeles, or continue on as planned to San Francisco. Ultimately the pilots chose to divert.[8] Later the NTSB found that while "the flight crew's decision to divert the flight to Los Angeles...was prudent and appropriate", nonetheless "Alaska Airlines dispatch personnel appear to have attempted to influence the flight crew to continue to San Francisco

3- (CVR) transcripts indicate that the dispatcher was concerned about the effect on the schedule ("flow") should the flight divert.[9]
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Old 19th Jan 2013, 07:12
  #43 (permalink)  
 
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My post #30
Further, the Safety Board concludes that Alaska Airlines dispatch personnel appear to have attempted to influence the flight crew to continue to SFO instead of diverting to LAX.
So you add absolutely nothing with your
dispatch personnel appear to have attempted to influence the flight crew to continue to San Francisco
I'm intrigued that you take Wiki (as good as it is most cases) should have precedence over and above the official NTSB report.
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Old 17th Feb 2013, 23:31
  #44 (permalink)  
 
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Horizontal Stabilizer

My 2 cents worth. First I like the post by Machinbird. When it comes to controls, if it doesn't feel right, land the plane. Had I been flying that DC-9, it would have been put on the ground much earlier. I wouldn't give a heck what the company wanted, I'm flying, not the company or anyone in the company.
About the design, if the hinge was placed at the leading edge of the stab and the screwjack at the trailing edge, this accident would not have happened. Why they designed it the other way around, I don't know.
Having said that, there is NO excuse for bad maintenance. People's lives are at stake. If I remember correctly, the FAA inspector did warn of shoddy work and was told to "shut up" or be transferred. People should have gone to jail over this incident. So what happened? Today, 4 people are going to jail over the 737 crash. There has to be accountability. The same for the Nation Air DC-8 crash. There should have been jail terms. Too many managers getting away with crap.
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Old 19th Feb 2013, 15:19
  #45 (permalink)  
 
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Originally Posted by thermostat View Post
My 2 cents worth. First I like the post by Machinbird. When it comes to controls, if it doesn't feel right, land the plane. Had I been flying that DC-9, it would have been put on the ground much earlier. I wouldn't give a heck what the company wanted, I'm flying, not the company or anyone in the company.
For what it's worth, they were planning to divert to LAX once they realised the problem was more serious than a simple electrical malfunction - unfortunately by then the damage was too severe and they ran out of time.

While the jackscrew/stab design was criticised in the NTSB report for not being "fail-safe", the fact is that because the DC-9's certification ("grandfathered" to the MD-80 series) was performed during an era where such designs could be permitted as long as maintenence schedules were strictly adhered to, the regulators had to allow it.

If I remember correctly, the FAA inspector did warn of shoddy work and was told to "shut up" or be transferred.
I'm pretty sure that the FAA inspectors just trusted the paperwork - the whistleblower in the Alaska case was one of their own senior engineers. The accident occurred after he had raised objections, but before his warning was heeded by the FAA. Despite his being completely in the right, he was (through inter-airline management collusion) effectively blacklisted from working in aviation ever again.
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Old 19th Feb 2013, 17:05
  #46 (permalink)  
 
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Thanks for your 2 cents worth Dozy. As you say they were planning to divert but ran out of time. That is why I said they should have landed earlier, long before LAX. LAX was too late as we now know.
Just because something is "certified" doesn't make it foolproof. there are a number of cases in aviation history where bad, but certified systems have killed people. The design is stupid. The screwjack should have placed at the trailing edge, not the leading edge, just as the rudder of a plane or boat is aft of the rudder post.
As far as the whistleblower is concerned, the mechanic unions should have made a stink and threatened to shut down the entire industry.
That's how I feel about it. Aviation is not the place to fool around. There is too much at stake.
Thanks.
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Old 19th Feb 2013, 18:27
  #47 (permalink)  
 
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Originally Posted by thermostat View Post
That is why I said they should have landed earlier, long before LAX. LAX was too late as we now know.
Where else could they have gone? Lindbergh in San Diego is a challenging approach at the best of times from what I've been told, and certainly not ideal with a potential control issue.

Just because something is "certified" doesn't make it foolproof. there are a number of cases in aviation history where bad, but certified systems have killed people.
Agreed.

The screwjack should have placed at the trailing edge, not the leading edge, just as the rudder of a plane or boat is aft of the rudder post.
You can't fit it aft of the rudder post because there's no room. I'm having a little trouble understanding this theory of yours - could you humour me and go into a little more detail?

As far as I can tell, mounting it aft would cause the same failure mode to force the stab to nose-up and stall the aircraft rather than nose-down into a dive.

As far as the whistleblower is concerned, the mechanic unions should have made a stink and threatened to shut down the entire industry.
In an ideal world yes - but we're talking about the middle of a recession, and I don't know if the engineer concerned was affiliated.

Aviation is not the place to fool around. There is too much at stake.
Agreed in principle, but real-world issues tend to cloud things.
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Old 19th Feb 2013, 21:26
  #48 (permalink)  
 
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Lindbergh in San Diego is a challenging approach at the best of times from what I've been told, and certainly not ideal with a potential control issue.
Agreed

As to the whistleblower getting the axe ... so much for whistleblower protection laws.

I note The Robe is banned.

The problem with trying to trouble shoot a problem in an aircraft is that if you don't actually know what is broken, or what the failure mode is that you are trying to mitigate, it is easy to make the wrong decision and potentially make a wrong move.

I've seen it in real life when an engine went wrong in a twin engined helicopter, and the pilot flying identified incorrectly the engine that was low power, and tried to fly on that engine before I corrected him and he got the right emergency throttle selected.

We could have torched an engine.

The gents in Alaska 261 were, in terms of trouble shooting, in the blind insofar as what their real problem was. That they had a flight control problem was not as accurate a problem statement as they had a flight control linkage problem ... a lot different than what they seemed to have begun trouble shooting for.
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Old 19th Feb 2013, 22:20
  #49 (permalink)  
 
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Originally Posted by Lonewolf_50 View Post
As to the whistleblower getting the axe ... so much for whistleblower protection laws.
I think the latest laws were written as a result of what happened there - too late to help the individual involved, sadly.

The problem with trying to trouble shoot a problem in an aircraft is that if you don't actually know what is broken, or what the failure mode is that you are trying to mitigate, it is easy to make the wrong decision and potentially make a wrong move.
Quite. As I said on another thread, Rule 1 is "Don't make it worse!".

I've seen it in real life when an engine went wrong in a twin engined helicopter, and the pilot flying identified incorrectly the engine that was low power, and tried to fly on that engine before I corrected him and he got the right emergency throttle selected.
The same problem reared its head on the Kegworth B734 with a much nastier outcome. Used to the B733 where AC bleed air came from the right engine only, the crew assumed that it was the right engine that was failing and shut it down. It was in fact the left engine that had lost and ingested blade debris. The B734 used bleed air from both engines, but this design change was not mentioned during conversion training.

The gents in Alaska 261 were, in terms of trouble shooting, in the blind insofar as what their real problem was. That they had a flight control problem was not as accurate a problem statement as they had a flight control linkage problem ... a lot different than what they seemed to have begun trouble shooting for.
Indeed - the problem first manifested as unresponsive trim, but everything else seemed to be OK. It'd be interesting to ask members who are or were Mad Dog crew how often trim problems cropped up on the line.
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Old 20th Feb 2013, 13:59
  #50 (permalink)  
 
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Originally Posted by DozyWannabe
Originally Posted by thermostat
The screwjack should have placed at the trailing edge, not the leading edge, just as the rudder of a plane or boat is aft of the rudder post.
You can't fit it aft of the rudder post because there's no room. I'm having a little trouble understanding this theory of yours - could you humour me and go into a little more detail?

As far as I can tell, mounting it aft would cause the same failure mode to force the stab to nose-up and stall the aircraft rather than nose-down into a dive.
I think I know what he means. After the screwjack was forcefully disconnected, had the hinge point not been so far aft on the stabilizer, it would not have been pushed against the next available mechanical stop, but would have swung freely, like a weather vane.

I don't know if I like that scenario better, btw., because it seems to leave the crew with no pitch control at all.
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Old 20th Feb 2013, 17:45
  #51 (permalink)  
PJ2
 
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Dozy, noske;

Concerning the MD83 Stabilizer accident there is a decent NTSB animation of the THS installation here.

I think a reversal of the hinge-point and the jackscrew mechanism arrangements, (hinge point forward, jackscrew aft),would permit a certain weather-cocking as per noske's comments, (or possibly flutter), but I think Dozy is correct in observing that making room for such an arrangement would be challenging, (though not impossible, given some of the variations of airplane designs extant!).

The design, (single jackscrew, aft hinge), is industry-proven as are the outcomes of not following established maintenance schedules and procedures. Frankly I don't think there is much to learn here except the obvious.

Regarding the flight crew there is no direct instruction to attempt to move a jammed stabilizer but nor in the manuals I have for the DC9 & DC8 are there procedures for handling a jammed stabilizer in cruise. Perhaps those flying the MD80 can comment.

David36 mentioned in post #8 the DC10/MD11 as having two jackscrews, I assume as an example of redundancy and mentioned the L1011 as having a "hydraulic" THS. There would be no jackscrew for the THS on the L1011 as the entire stabilizer moved, serving as both "elevators" and a "THS".

Last edited by PJ2; 20th Feb 2013 at 17:53.
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Old 21st Feb 2013, 04:08
  #52 (permalink)  
 
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Did anyone ever answer the OP's question? ....in a T-tail access is more difficult.
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Old 22nd Feb 2013, 13:08
  #53 (permalink)  
 
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As an aside- many vehicle-maintenance-lifts have used a jackscrew,sometimes on one leg only, using cables or chains to send the otherside/corners up.

When you're stood under 1 1/2 tons of metal,unprotected, it concentrates the mind

Invariably, a brass or Phosphor-Bronze nut winds up/down the Acme-thread with the attached carriage conttaining arms/bed.
Floating in that connection is a SECOND nut(often steel) which carries no weight. This can be arranged a short distance from the load-carrier, which, as it's threads wear, closes-up on the secondary, safety nut thus giving an instant visual indication. The safety-nut would not be fit to use regularly but would safely lower the vehicle if the mechanic should witness "jolt" "clonk" as the main nut threads stripped.

I.m amazed that, even back then, an aircraft was certified with no backup safety-nut. must have had more concientious maintenance mechanics back then!
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