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Topic: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: NWADTWE16
Posted 2012-07-05 22:15:36 and read 10551 times.

Im hoping to get some feedback from Maintenance or Pilots on this one. Ever since learning the final results of the AS 261 review it appeared to me that there was no solution except to 'grease the jackscrew'..which considering thats mandatory anyway doesnt really leave me comfortable flying on any of the series again. Im wondering if there was a 'fix' from Boeing/MD? and does the one jackscrew situation exist on all similar types..ie 717|MD90|MD82 etc?

http://www.youtube.com/watch?v=Tz25o8Oj6_Y

ALASKA 261 VIDEO

Topic: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: starrion
Posted 2012-07-05 22:47:15 and read 10454 times.

While I am not an aircraft mechanic, I believe the AS situation was caused by maintenance not being performed when it should have.

Parts wear out, and that is true on all aircraft. So I am not sure that there is justification for calling it a 'jackscrew issue' . If a part needs to be replaced or a part needs to be maintained and it isn't then any aircraft may be rendered unsafe.

Topic: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: ASFlyer
Posted 2012-07-05 23:09:19 and read 10364 times.

There was never really a "jackscrew issue" as much as there was a maintenance issue. The jackscrew should have functioned perfectly if it had been lubricated more often.

Topic: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: NWADTWE16
Posted 2012-07-05 23:17:27 and read 10325 times.

But there is just ONE , albeit large jackscrew holding the vetical stabilizers to the aircraft, correct? It appeared to me that the final word was that this was a design flaw in the sense that there is no back up measure should it not be maintained and therefor fail

Topic: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: SASMD82
Posted 2012-07-05 23:19:34 and read 10305 times.

Perhaps he (NWADTWE16) means the redundancy issue. The problem was (or actually is) that if the jackscrew fails, there is no alternative to move the vertical stabiliser.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: Max Q
Posted 2012-07-06 00:25:38 and read 10132 times.

Quoting NWADTWE16 (Reply 3):
But there is just ONE , albeit large jackscrew holding the vetical stabilizers to the aircraft, correct? It appeared to me that the final word was that this was a design flaw in the sense that there is no back up measure should it not be maintained and therefor fail

I think you mean the horizontal stabilizer.



I don't know what the final fix was.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: Starlionblue
Posted 2012-07-06 01:22:07 and read 10099 times.

Quoting NWADTWE16 (Reply 3):
But there is just ONE , albeit large jackscrew holding the vetical stabilizers to the aircraft, correct? It appeared to me that the final word was that this was a design flaw in the sense that there is no back up measure should it not be maintained and therefor fail

I don't think the DC-9/Mad Dog is alone in having a single jackscrew.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: atlamt
Posted 2012-07-06 04:01:36 and read 10058 times.

Quoting Starlionblue (Reply 6):

I don't think the DC-9/Mad Dog is alone in having a single jackscrew.

Not at all, every a/c I've worked on have a single jackscrew. The biggest difference is access. It's takes a lot more to get up to the jackscrew on a md80 then say a 737. Also once you are there the access is limited. That being said it's not a difficult job. In 15 years I've never found one with an issue. There are two different checks. The first and most frequent is a visual check and lubrication. The other is more involved and uses test equipment to measure any wear in the nut/threads, this is usually performed during a heavy maintenance visit.

The AS accident was a combination of factors. The time between inspections and lubes had been extended I believe several times. Also they had mixed grease types. This caused a reaction which formed an abrasive that wore the jackscrew faster. The test fixture AS used for measuring wear wasn't made to MD specifications and was inaccurate. Then when it was inspected and found to be worn out of limits a supervisor came in behind the mechanic and approved it as within limits.

Also the pilots emergency checklist and training now tells them not to attempt to move the jackscrew in a situation like this. Not to blame the AS261 crew they were doing what they were trained to do. But there is a chance that if they had not tried to move the jackscrew the nut should have held and they may have been able to land the a/c.

The MD80 jackscrew has no design flaw. When maintained properly there is nothing to worry about. It doesn't even cross my mind when I fly.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: Dalmd88
Posted 2012-07-06 07:30:12 and read 9961 times.

I second everything atlamt says. If they are maintained properly there is no problem. I've never had a second thought of flying on one of our MD80's. I know our program is very good. The only plane I had some questions about were the old 737 classics. I don't have a lot of confidence in the fix they had for the rudder issues that caused a few crashes. They are all gone from our system now so it's not an issue.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: tdscanuck
Posted 2012-07-06 08:50:46 and read 9904 times.

Quoting NWADTWE16 (Thread starter):
Ever since learning the final results of the AS 261 review it appeared to me that there was no solution except to 'grease the jackscrew'..which considering thats mandatory anyway doesnt really leave me comfortable flying on any of the series again

The solution was "grease the jackscrew PROPERLY, and do the freeplay check PROPERLY". In other words, do what the OEM told you to do and you don't have a problem.

Quoting NWADTWE16 (Thread starter):
Im wondering if there was a 'fix' from Boeing/MD?

The fix was "Do the proper maintenance." There is no problem if you do that.

Quoting NWADTWE16 (Thread starter):
does the one jackscrew situation exist on all similar types..ie 717|MD90|MD82 etc?

The "situation" exists on all modern jetliners except the L-1011, as far as I know. It's a much bigger situation than jackscrews...if you don't do the preventative maintenance properly *and* you don't do the check to identify failing preventative maintenance properly, something will fail.

Quoting NWADTWE16 (Reply 3):
But there is just ONE , albeit large jackscrew holding the vetical stabilizers to the aircraft, correct?

Yes, although the screw itself is structurally redundant.

Quoting NWADTWE16 (Reply 3):
It appeared to me that the final word was that this was a design flaw in the sense that there is no back up measure should it not be maintained and therefor fail

It's not a design flaw; the screw is structurally redundant. So is the nut, but if you wear all the threads out of both parts of the nut by not maintaining them for extended periods you defeat all the redundancy.

Quoting SASMD82 (Reply 4):
The problem was (or actually is) that if the jackscrew fails, there is no alternative to move the vertical stabiliser.

You don't need one; if the jackscrew fails the horizontal stabilizer gets stuck. During certification you have to prove you have enough elevator authority to fly the aircraft with the stabilizer stuck at the worst-case position. It sucks for the flight crew (they can't trim anymore) but they maintain control.

The problem on the AS MD-80 was that the nut failed; the stabilizer was no longer controlled by the jackscrew. That's supposed to be protected by having redundant nut threads but the poor maintenance took out both sets.

Tom.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: LH707330
Posted 2012-07-06 10:17:49 and read 9841 times.

Quoting tdscanuck (Reply 9):
Yes, although the screw itself is structurally redundant.

Tom, is it redundant in that it has bi-helical threads so that no single failure lets the nut slip (although it could jam)?

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: yeelep
Posted 2012-07-06 12:16:26 and read 9757 times.

Quoting atlamt (Reply 7):
Also they had mixed grease types. This caused a reaction which formed an abrasive that wore the jackscrew faster.

It was determined that the change of grease from Mobil 28 to Aeroshell 33 had no effect in the failure of the jackscrew. In fact the lab test results showed less wear with Aeroshell 33 grease. There were however, many procedural deficiencies made during the change over. Including a lack of follow up inspections, to check for possible accelerated wear due to the change in grease.

Quoting atlamt (Reply 7):
The test fixture AS used for measuring wear wasn't made to MD specifications and was inaccurate.

Yep, they were using a non conforming restraining fixture. However, inaccurate measurements can also easily be taken using the Boeing/MD fixture.

Quoting atlamt (Reply 7):
Then when it was inspected and found to be worn out of limits a supervisor came in behind the mechanic and approved it as within limits.

It was never out of limits as measured. Its endplay measured .040" which was the upper limit. The original planned action was to replace it, this was then changed to recheck the endplay. This was done five times with the result of a .033" endplay. With either measurement, the jackscrew was not out of limits and did not require replacement. If they had actually ordered and changed the jackscrew, it would have been possible, that had an overhauled jackscrew been used instead of new, it too could have had an end play of .040". Although I admit it would have been unlikely, there were no requirements in the overhaul manual to have lower endplay limits for a freshly overhauled unit.

Quoting Dalmd88 (Reply 8):
The only plane I had some questions about were the old 737 classics. I don't have a lot of confidence in the fix they had for the rudder issues that caused a few crashes.

Then you shouldn't have much confidence in the NG either, or probably the MAX in the future.

Quoting tdscanuck (Reply 9):
It's not a design flaw; the screw is structurally redundant. So is the nut, but if you wear all the threads out of both parts of the nut by not maintaining them for extended periods you defeat all the redundancy.

Yeah, but it has a single point failure mode. Maybe a design philosophy flaw.

Quoting SASMD82 (Reply 4):
The problem was (or actually is) that if the jackscrew fails, there is no alternative to move the vertical stabiliser.

I disagree, its not having an alternative method of restraint if both nuts fail.

As others have said there haven't been any design changes. The lube/inspection and endplay check intervals have been greatly reduced. The lube/inspection now requires an inspector. The lubrication procedures have been changed. The endplay results are now recorded and tracked to detect accelerated wear. I don't know if its required (old man memory) but when we performed the endplay check, we would have two mechanics do the check separately. Each performing it multiple times to ensure we were getting accurate readings. This would include removing the measuring and restraint fixture to eliminate the possibility of incorrect setup. Of course this was all done under the watchful eye of the inspector. There are other things that I'm sure I have forgotten, I haven't done a lube or insp. on one in probably 5 or 6 years.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: Roseflyer
Posted 2012-07-06 14:41:15 and read 9660 times.

Quoting NWADTWE16 (Thread starter):
Ever since learning the final results of the AS 261 review it appeared to me that there was no solution except to 'grease the jackscrew'..which considering thats mandatory anyway doesnt really leave me comfortable flying on any of the series again. Im wondering if there was a 'fix' from Boeing/MD?

Maintenance tasks are divided into 5 categories based on Maintenance Steering Group -3 analysis which has its origins back in the 747 design in the 1960s and was generated between NASA, Boeing, United Airlines and Pratt & Whitney. Based on failure effect, maintenance tasks are assigned a level of criticality. There are many tasks that are safety items, meaning that if the maintenance task is not performed, there will be an operational impact to the airplane which impacts safety. Items such as lubricating the jackscrew fall into this category.

Failure of the stabilizer control is a failure effect. It can be caused by many different things such as failure of the primary brake, secondary brake, ballnut, gimble, etc. Maintenance tasks are identified to address all failure modes and there are mandatory lubrications, visual inspections and operational checks. All of these are a part of the approved maintenance program that was generated from the MSG-3 analysis.

When an airline does not accomplish the requirements of maintenance, safety problems happen. The FAA is very strict regulating maintenance. They are heavily involved with Boeing and the airlines at determining when and where maintenance is required. Not accomplishing maintenance leads to big fines and can result in grounding airplanes. From time to time this happens at airlines where mistakes happen. Every airline is required to have an engineering department and approved maintenance program.

So overall, it is not about the airplane being unsafe. The MD80 is a certified design that has an approved maintenance program. What I would be cautious of is flying on any airline that is blacklisted by the EU or in a blacklisted country from EASA or an FAA Category 2 country because that means there is not adequate maintenance oversight. Maintenance is very important and I feel comfortable telling anyone to fly and not worry on EASA, FAA, or Transport Canada regulated airlines or airlines that are oversought by regulators approved by those three bodies, so most MD80s are safe, but I’d steer clear of airlines in category 2 countries (and some cat 2 countries might surprise you since airlines operating brand new airplanes are restricted such as Israel and Pakistan).

Quoting NWADTWE16 (Thread starter):
Im wondering if there was a 'fix' from Boeing/MD? and does the one jackscrew situation exist on all similar types..ie 717|MD90|MD82 etc?

Basically every airplane has a jackscrew. The design has dual threads so that one can fail and the other can take the load. There also is a primary and secondary brake to stop the stabilizer. On some planes there is an additional rod that can bear the load. However, as with any moving part, if it is not lubricated it will crack and fail. There are lubrication tasks that are required all over the flight controls system. The failure mode of stripping the jackscrew was satisfied by lubricating it and the primary failure mode is intended to be a jammed stabilizer rather than free floating stabilizer which is what happened on AS 261.

Quoting NWADTWE16 (Reply 3):
But there is just ONE , albeit large jackscrew holding the vetical stabilizers to the aircraft, correct? It appeared to me that the final word was that this was a design flaw in the sense that there is no back up measure should it not be maintained and therefor fail

There are quite a few parts that are called dual load path redundant parts. While they appear as a single piece, they actually are double the size necessary and have overlapping designs that can independently take the structural load. Also they are often separate pieces so that cracks cannot propagate through. Basically all the control rods in the primary control system work this way. There’s only one quadrant controlling the elevators and rudder. It’s all dual load path equipment. It is adequately redundant.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: Starlionblue
Posted 2012-07-06 17:00:02 and read 9596 times.

Quoting yeelep (Reply 11):
Quoting tdscanuck (Reply 9):
It's not a design flaw; the screw is structurally redundant. So is the nut, but if you wear all the threads out of both parts of the nut by not maintaining them for extended periods you defeat all the redundancy.

Yeah, but it has a single point failure mode. Maybe a design philosophy flaw.

Ok, but airliners have other single points of failure. If a wing spar snaps you're done. Some parts are not redundant. They're just designed never to fail if properly maintained.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: 737tdi
Posted 2012-07-06 22:58:54 and read 9478 times.

A few of these statements? were saying vertical stab. but, as said it was the horizontal. Alot of aircraft have single jackscrews, but as said they are certified to fly at the full deflection.

The statement made about the rudder failures was way off post but I'll address them. If you look at later history you will see aircraft that have had similar discreapancies. They were not due to the rudder, they were due to flap spindle failure. I guess you could say, IMO, the two fatal accidents were not caused by any rudder problem. Am I smarter then the NTSB or FAA. Nope, not in any way, but there have been exact inflight anomalies that have been proven to be flap spindle failures. I've seen it personally. Two broken spindles on the same outboard flap. What kind of roll/yaw is that going to induce on approach?? I just don't believe the rudder theory. Now that is my opinion. By the way that problem has been addressed and has been fixed.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: saafnav
Posted 2012-07-06 23:41:11 and read 9466 times.

How would you make the jack screw redundant by adding another one?

Assume the one binds... The other will be able to turn, but since the Stabilizer is bound the the stuck jack screw, nothing will be able to move?

Just a thought.

Erich

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: Starlionblue
Posted 2012-07-07 00:16:59 and read 9458 times.

Quoting saafnav (Reply 15):
How would you make the jack screw redundant by adding another one?

Assume the one binds... The other will be able to turn, but since the Stabilizer is bound the the stuck jack screw, nothing will be able to move?

Just a thought.

Erich

Yes quite. There really isn't any way to make it more redundant by adding more jackscrews. Ergo, you must make the jackscrew failsafe.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: larshjort
Posted 2012-07-07 03:02:17 and read 9399 times.

Quoting saafnav (Reply 15):
How would you make the jack screw redundant by adding another one?

Assume the one binds... The other will be able to turn, but since the Stabilizer is bound the the stuck jack screw, nothing will be able to move?

I think what some want is another jackscrew so that if one destroys the threads on the nuts, the other one still is in control. It wouldn't be a if they get since the aircraft is certified to fly with the stabilizer stuck at worst scenario.

/Lars

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: MD11Engineer
Posted 2012-07-07 03:45:01 and read 9391 times.

Quoting Starlionblue (Reply 6):
Quoting NWADTWE16 (Reply 3):
But there is just ONE , albeit large jackscrew holding the vetical stabilizers to the aircraft, correct? It appeared to me that the final word was that this was a design flaw in the sense that there is no back up measure should it not be maintained and therefor fail

I don't think the DC-9/Mad Dog is alone in having a single jackscrew.

Nope. The only aircraft I know, which have two jackscrews are the DC10 / MD11 (the Tristar uses hydraulic rams).

Quoting atlamt (Reply 7):
The AS accident was a combination of factors. The time between inspections and lubes had been extended I believe several times. Also they had mixed grease types. This caused a reaction which formed an abrasive that wore the jackscrew faster. The test fixture AS used for measuring wear wasn't made to MD specifications and was inaccurate. Then when it was inspected and found to be worn out of limits a supervisor came in behind the mechanic and approved it as within limits.

Shortly afterwards Boeing changed it´s specs for grease used on flight controls from MIL-G-23827B (e.g. clay based Aeroshell Grease 7) to the new Boeing spec BMS 3-33 (Lithiumsoap based Aeroshell Grease 33). Grease 7 had the drawback that it was absorbing water and then losing it´s lubrication properties over time, which Grease 33 does not.
Also Grease 33 fullfilled several other specs, so that the airlines only need to keep a stock of Grease 33 instead of several types of grease as before.
After studying the specs I have replaced various greases used on historical aircraft for our museum, and which are not obtainable anymore, with Aeroshell Grease 33.

Jan

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: MD11Engineer
Posted 2012-07-07 04:02:29 and read 9385 times.

Quoting Roseflyer (Reply 12):

So overall, it is not about the airplane being unsafe. The MD80 is a certified design that has an approved maintenance program. What I would be cautious of is flying on any airline that is blacklisted by the EU or in a blacklisted country from EASA or an FAA Category 2 country because that means there is not adequate maintenance oversight. Maintenance is very important and I feel comfortable telling anyone to fly and not worry on EASA, FAA, or Transport Canada regulated airlines or airlines that are oversought by regulators approved by those three bodies, so most MD80s are safe, but I’d steer clear of airlines in category 2 countries (and some cat 2 countries might surprise you since airlines operating brand new airplanes are restricted such as Israel and Pakistan).

That´s another thing:

Most mechanics hate lubing and it often gets delegated to the most junior ones. The grease stinks and you only need dilligence, but not a lot of brains for doing this job. You´ll get dirty and many grease pins are hard to reach. Still, it is extremely important to lube ALL grease fittings. Often those, which are hard to reach, or those which are blocked by hardened old grease get conveniently "forgotten". You´ll also have to make sure that you really pump enough new grease in to displace all the old grease and possibly water in the joints (I have seen main landing gear trunnion bearings where lots of water came out when I squeezed the grease in).
A while a go we had an aircraft where one of several aftflap mounts failed. It was discovered after landing and fortunately there was enough redundency in the design so that the flap did not seperate. The aircraft was grounded for a few days though in a remote place until they could install the spare part. An inspection reveilled that the flap fitting joint was bone dry and eventually seized, causing it´s attachment to break off.
When the aircraft came back, I checked ALL aftflap support fittings and found most of them dry, in some cases the grease pins missing. I ordered a complete relube of the whole flap system and instigated a fleet action (and inspection and lube of the whole fleet).

It also doesn´t help that many MROs or airlines save on lubing equipment and buy the cheapest grease guns, wqhich will squeeze the grease anywhere except into ther grease fitting. An industrial grade pneumatic grease gun with a long hose and fed from a bucket of grease makes the job much easier, cleaner and faster.

Also, many airlines due to costs do A-checks (where most regular lube jobs are carried out) outside, even in winter, when tghe grease has a consistency of wax and is very hard to get into the grease fittings.

Jan

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: 737tdi
Posted 2012-07-07 09:37:35 and read 9272 times.

Quoting MD11Engineer (Reply 18):
Nope. The only aircraft I know, which have two jackscrews are the DC10 / MD11 (the Tristar uses hydraulic rams).




Although an almost obsolete aircraft the DC-8 also uses two jackscrews driven by a single middle gearbox via chain drive. I have seen the middle gearbox fail. There are two sprockets inside that gearbox with shear pins and I had to fly to Portland OR. once to repair a stab. that one sprocket had failed. The horiz. stab. was full up on the left side and almost full down on the right. I had to use a couple of Chevy truck jacks to relieve the tension/weight of the stab. just to get the jackscrews loose. Many years ago.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: prebennorholm
Posted 2012-07-07 16:27:37 and read 9156 times.

Quoting yeelep (Reply 11):
Quoting Dalmd88 (Reply 8):
The only plane I had some questions about were the old 737 classics. I don't have a lot of confidence in the fix they had for the rudder issues that caused a few crashes.

Then you shouldn't have much confidence in the NG either, or probably the MAX in the future.

The rudder actuator system was substantially revised on the 737NG.

What is supposed to have happened at the 737 classic rudder hardover accidents, that same thing is by design impossible on the NG.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: NWADTWE16
Posted 2012-07-07 18:54:05 and read 9088 times.

Really great responses on this one..thank you to all. I just want to add, isnt the issue with the MD80 that with one jackscrew (others have one too as stated above) that the issue would be that the MD80 has its tail wings on top of the tail. Does that design make this issue more important to that aircraft or does it have no relavance?

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: jetmech
Posted 2012-07-07 19:35:15 and read 9075 times.

Quoting saafnav (Reply 15):
Quoting Starlionblue (Reply 16):

All the commercial types I have seen both A & B have had single jackscrews operating the tail plane. IIRC, on the Boeing at least, this single jackscrew is given redundancy by being constructed as two concentric tubes. The outer tube is threaded whilst the inner tube is unthreaded, thus, there is redundancy if either the outer or inner tube should structurally fail. I don't think there is redundancy for thread stripping, however, the Boeing jackscrew is different from the MD80 device.

The MD80 is an plain ACME design, where the threads of the screw and nut bear upon each other directly (hence the need for adequate lubrication). The Boeing item is of the re-circulating ball design, where the screw and nut threads are both configured as semi-circular recesses. The adjacent set of recesses form a cavity of circular cross section following a spiral path. This cavity is filled with ball elements, thus, there is no direct contact between the screw and nut.

http://www-mdp.eng.cam.ac.uk/web/library/enginfo/textbooks_dvd_only/DAN/threads/mechanics/recircBallBIG.jpg
http://www-mdp.eng.cam.ac.uk/web/lib...hreads/mechanics/recircBallBIG.jpg

As you can imagine, there would probably be less friction in the re-circulating ball design, however, jackscrew lubrication is still an important maintenance task for this type of design.

Regards, JetMech

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: Starlionblue
Posted 2012-07-08 02:07:17 and read 8994 times.

Quoting NWADTWE16 (Reply 22):
I just want to add, isnt the issue with the MD80 that with one jackscrew (others have one too as stated above) that the issue would be that the MD80 has its tail wings on top of the tail. Does that design make this issue more important to that aircraft or does it have no relavance?

Not really a difference with T-tails. Granted, since the stabilizer is further back it has more authority for a given size. But to compensate for this it is smaller.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: yeelep
Posted 2012-07-08 03:11:51 and read 9139 times.

Quoting prebennorholm (Reply 21):

Quoting yeelep (Reply 11):
Quoting Dalmd88 (Reply 8):
The only plane I had some questions about were the old 737 classics. I don't have a lot of confidence in the fix they had for the rudder issues that caused a few crashes.

Then you shouldn't have much confidence in the NG either, or probably the MAX in the future.

The rudder actuator system was substantially revised on the 737NG.

What is supposed to have happened at the 737 classic rudder hardover accidents, that same thing is by design impossible on the NG.

Not quite true, the NG rudder control system as originally delivered, up to line 1947, was essentially the same as the system on the Classics. AD2002-20-07 which has since been superseded by AD2007-03-07 required the redesign of the system for 737-100/200/300/400/500/600/700/800/900, incorporation was required by November 12 2008.
Dalm88 said he didn't have confidence in the fix for the rudder issues on the Classics. If that's the case, he shouldn't be confident in any current, past or possibly future 737 model.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: tdscanuck
Posted 2012-07-08 12:07:48 and read 8969 times.

Quoting LH707330 (Reply 10):
Quoting tdscanuck (Reply 9):
Yes, although the screw itself is structurally redundant.

Tom, is it redundant in that it has bi-helical threads so that no single failure lets the nut slip (although it could jam)?

I think it was two separate nuts within the "nut" such that, if any one cracked or stripped the other could take the load. A classic failsafe design. However, it's susceptible to the same problem as all other failsafe designs...if you don't maintain them, they all wear out together.

Quoting larshjort (Reply 17):
I think what some want is another jackscrew so that if one destroys the threads on the nuts, the other one still is in control.

How many levels deep do you want to go? Redundancy is no protection for common mode failures and inadequate maintenance is always headed for a common mode failure.

Tom.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: Roseflyer
Posted 2012-07-08 16:50:37 and read 8928 times.

Quoting NWADTWE16 (Reply 22):
I just want to add, isnt the issue with the MD80 that with one jackscrew (others have one too as stated above) that the issue would be that the MD80 has its tail wings on top of the tail. Does that design make this issue more important to that aircraft or does it have no relavance?

Lubricating the jackscrew and performing the inspections is a bit more challenging due to the vertical stabilizer location, but that doesn't make it any more prone to failure. Compared to a 777 or 747, the 737 has quite a challenging jackscrew to access as well since the area is quite tight. You can do jumping jacks while lubricating the jackscrew on a 747.

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: 737tdi
Posted 2012-07-08 22:54:47 and read 8871 times.

Quoting Roseflyer (Reply 27):
Compared to a 777 or 747, the 737 has quite a challenging jackscrew to access as well since the area is quite tight. You can do jumping jacks while lubricating the jackscrew on a 747.




Now that's funny   . I have had the fortune or misfortune of removing and replacing alot of 737 horiz. stab. jackscrews. Nice little anti-skid covered deck you are kneeling on. Of course they make a hoist for getting it up through the access hole but we don't have it. It's too little guys heaving it up a ladder and through the hole. It's actually not that hard once you have done it a couple of times. If the cables aren't worn, its just a matter of manipulation.

Another topic maybe, but we seem to be having a lot more wear/replacements since the introduction of AeroShell 33. This grease IMO is not nearly as good. It literally leaks itself to death in your grease gun while stored in your storage container. Another thing I noticed is it is terribly clumpy after very few cycles. Have any of you noticed this?

Topic: RE: Are All MD-80 Series Still Flying W Jackscrew Issue?
Username: MD11Engineer
Posted 2012-07-09 02:54:27 and read 8800 times.

Quoting 737tdi (Reply 28):
Another topic maybe, but we seem to be having a lot more wear/replacements since the introduction of AeroShell 33. This grease IMO is not nearly as good. It literally leaks itself to death in your grease gun while stored in your storage container. Another thing I noticed is it is terribly clumpy after very few cycles. Have any of you noticed this?

Actually not. I´m using ten year old Grease 33 for my truck and in it´s tin it just looks like it did when it was new. Grease 7 either dried out or absorbed water from the air.

Jan


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