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Rolf Diederichs
Director,
NDT.net, Germany, Joined Nov 1998, 604

Rolf Diederichs

Director,
NDT.net,
Germany,
Joined Nov 1998
604
01:04 Feb-17-2000
Alaska Airlines Boeing MD-83 Accident on 31 January 2000

A McDonnell Douglas Model DC-9-83 (MD-83) airplane crashed on Jan. 31, killing all 88 aboard.

The FAA has participated in the subsequent accident investigation to determine possible causes of the accident. One area of interest in the investigation has been the jackscrew assembly of the horizontal stabilizer.

A Safety Board metallurgist has been examining the jackscrew recovered from the accident aircraft. The shreds of metal seen attached to that jackscrew are of the same material as the threads of the gimbel nut that would normally be attached to that jackscrew. That nut has not been recovered. There is no determination at this point when those metal transfers occurred.


At February 11, 2000 the FAA released an Emergency Airworthiness Directive:
http://www.faa.gov/apa/AFFAIRS/md80ad.htm

"Perform a general visual inspection of the lubricating grease on the jackscrew assembly and the area directly below the jackscrew and surrounding areas for the presence of metal shavings and flakes."

"Perform a general visual inspection of the jackscrew assembly to detect the presence of corrosion, pitting, or distress. .... If any corrosion, pitting, or distress is detected, prior to further flight, replace the jackscrew assembly with a new or serviceable assembly, in accordance with the applicable alert service bulletin."

I was told that this visual inspection isn't a very easy procedure, nor a completely reliable.

Does anybody has more information or any opinion.

Rolf Diederichs



    
 
 
Dianne Wood
Dianne Wood
07:34 Feb-17-2000
Re: Alaska Airlines Boeing MD-83 Accident on 31 January 2000
: A McDonnell Douglas Model DC-9-83 (MD-83) airplane crashed on Jan. 31, killing all 88 aboard.

: The FAA has participated in the subsequent accident investigation to determine possible causes of the accident. One area of interest in the investigation has been the jackscrew assembly of the horizontal stabilizer.

: A Safety Board metallurgist has been examining the jackscrew recovered from the accident aircraft. The shreds of metal seen attached to that jackscrew are of the same material as the threads of the gimbel nut that would normally be attached to that jackscrew. That nut has not been recovered. There is no determination at this point when those metal transfers occurred.

:
: At February 11, 2000 the FAA released an Emergency Airworthiness Directive:
: http://www.faa.gov/apa/AFFAIRS/md80ad.htm

: "Perform a general visual inspection of the lubricating grease on the jackscrew assembly and the area directly below the jackscrew and surrounding areas for the presence of metal shavings and flakes."

: "Perform a general visual inspection of the jackscrew assembly to detect the presence of corrosion, pitting, or distress. .... If any corrosion, pitting, or distress is detected, prior to further flight, replace the jackscrew assembly with a new or serviceable assembly, in accordance with the applicable alert service bulletin."

: I was told that this visual inspection isn't a very easy procedure, nor a completely reliable.

: Does anybody has more information or any opinion.

: Rolf Diederichs


*The threads of the jackscrew, when installed on the plane, are greased to facilitate smoothe operation. In manufacture of the MD-80/83, after the installation is visually inspected and approved (the mechanics involved are meticulous about their work), there is further work being done in this area and above the jackscrew assembly. Some of it involves drilling operations, and where drilling is carried out, there are always metal shavings produced. If all the shavings are not cleaned out with pressurized air or with vacuums, then they will obviously 'drift' downward over whatever is below, in this instance the greased jackscrew assembly. This alarms me.

Inspections are done with mirror and flashlight only in some of the more difficult-to-see areas. Is a more careful inspection not being carried out because it is so difficult to have to remove the 'banana' fairing in order to see completely the jscrew assembly.

Could these shavings affect the jackscrew operation...eventually? Your opinion?

The photographs of the recovered affected parts show some very long shreds clinging to the screw. It could be from wear, defective nut, tightness, or corrosion (possible, but maybe not too likely). What bothers me the most is that it might have been caused by metal debris caught on greased threads causing grinding and shredding. I believe in normal maintenance the jackscrew is re-greased - at least, it seems to me that should be something that needs to be done periodically. Couldn't metal flakes and shavings be detected at that time?

Has it been concluded that the metal shreds prevented the normal operation of the horizontal stabilizer, keeping the pilot from recovering from that dive? Were the shreds pre or post?

Since the gimbal nut has been recovered, there should be some more findings soon, if in fact we don't have them already.

Dianne Wood


    
 
 
Todd Torrence
Todd Torrence
04:24 Feb-18-2000
Re: Alaska Airlines Boeing MD-83 Accident on 31 January 2000
I am a college student earning a degree in nondestructive testing, so im not an expert in the field. However, when i saw this story on the news they said the metal shaveings were sticking to the jack screw. Just from the statement I was frist thinking maybe the part was not demagnetized properly, if, in fact it was magnetic partical tested. But after thinking about it I figured they wouldn't let something like that happen. My next thought was about the heat treat condition of the screw. Ive heard of cases where the material would be case hardned but not fully heat treated. I imagine this would have some effect on the operation of the screw. Also, if the metal shaveings were persent this would put even more stress on the jack screw. These are just ideas. I was just wondering what other people thought.


    
 
 
Rolf Diederichs
Director,
NDT.net, Germany, Joined Nov 1998, 604

Rolf Diederichs

Director,
NDT.net,
Germany,
Joined Nov 1998
604
00:39 Feb-18-2000
Re: Alaska Airlines Boeing MD-83 Accident on 31 January 2000
The e-mail format did not show the following link to
further information and images of the
Gimbal nut and jackscrew from horizontal stabilizer.

http://www.ntsb.gov/Events/2000/Aka261/


    
 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1236

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1236
04:32 Feb-18-2000
Re: Alaska Airlines Boeing MD-83 Accident on 31 January 2000
It would seem that in ANY complicated item such as an aircraft there are many things that COULD 'be' or 'become' defective.
This discussion group is interested in this incident (I think) because much of the responsibility for the safe operation of aircraft is based on NDT findings.
To point to NDT inspections as the ONLY options for the continued safe operation of aircraft may be pushing expectations of NDT a bit far. But, apart from scheduled replacement of SOME parts, what other options are there for in-service checks.
From the reports to date, the Alaska Airlines accident has a probable cause based on a specific part malfunctioning (the jack-screw).
Dianne Wood has pointed out some of the "observations" made of the recovered materials which indicate that some sort of visual concerns were merited. Were these reported on the last inspection or was it so common that they were not noted?

A recent news report on the inspection of all similar aircraft suggested that a significant number of these components were "suspect" (defective??). So this was not a new problem identified by the crash, but merely a problems highlighted as a POSSIBLE cause.
Perhaps there are several aspects to consider from an NDT perspective:
1. What constitutes a visual observation worthy of noting?
2. What action is taken to address an observation prior to putting the component back in service?
3. When a component failure COULD have drastic consequences is visual inspection adequate?
4. What early warning systems can be installed to assist the operator (pilots) of potential problems (torque sensors, vibration analysis??)

My point #2 seems to be addressed by the Feb 11 FAA directive where they issued an instruction (obligation??) that " .... If any corrosion, pitting, or distress is detected, prior to further flight, replace the jackscrew assembly with a new or serviceable assembly, in accordance with the applicable alert service bulletin."
Will this be carried out in all inspections? It seems expensive to "replace the component" and with the way industry everywhere is so worried about costs, what will constitute observable 'corrosion, pitting or distress' (I would think that the "distress" item would be difficult to qualify).
Perhaps a bit more grease will make the component "serviceable" thereby meeting the FAA directive and save the cost of disassembly and replacement.

Ed





    
 
 
Lee Bird
Lee Bird
09:29 Feb-18-2000
Re: Alaska Airlines Boeing MD-83 Accident on 31 January 2000
Just curious,
Can this assembly be better inspected using a fiber optic video scope
instead of flash light and mirror?



    
 
 
bagiartqwe
bagiartqwe
03:52 Jan-31-2007
Ooops! She did it again... Disgrace for Britney Spears!
Disgrace for Britney Spears! Ooops! She did it again...
http://bagiart.info/?p=30


    
 
 

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