how safe is 737 NG

[Arydberg]

I happened on this video and think it deserves a look.

Al

https://www.youtube.com/watch?v=vWxxtzBTxGU

[SeenItAll]

Sure. The first place I would turn to to learn completely factual information about complex technical issues related to a highly proven aviation system would be something put together by general news journalists and a personal injury lawyer. Sorry for the sarcasm, but this story is old news.

[KRH270/12]

Well you know these beasts must be hand crafted with big hammers because you got a completely different seating position in those front seats on any one of them...

[Thrust Augmentation]

Can anyone give a right / wrong on the following;

The NG's additional MTOW & service ceiling over the NG were approved on the basis of high accuracy automated production techniques being used for key structural components, which assured finer tolerances?

Ducommun were found to be hand crafting the critical structural parts?

Several hundred NG's had rolled from the production line before Ducommun's practices were highlighted?

[GordonR_Cape]

Can anyone give a right / wrong on the following;

The NG's additional MTOW & service ceiling over the NG were approved on the basis of high accuracy automated production techniques being used for key structural components, which assured finer tolerances?

Ducommun were found to be hand crafting the critical structural parts?

Several hundred NG's had rolled from the production line before Ducommun's practices were highlighted?

Nobody can categorically answer that kind of question, and those who do know, probably don't hang around on this forum, or have signed non-disclosure agreements.

A simplistic answer to your question, is by asking more questions:
How many B737 NGs suffered structural failure and fell out of the sky? None.
How many B737 NGs were flown into the ground by various accidents? Several.

A list of all accidents on Wikipedia provides some context: https://en.wikipedia.org/wiki/List_of_accidents_and_incidents_involving_the_Boeing_737#737 _Next_Generation_(737-600/-700/-800/-900)_aircraft (https://en.wikipedia.org/wiki/List_of_accidents_and_incidents_involving_the_Boeing_737#737 _Next_Generation_(737-600/-700/-800/-900)_aircraft)

For most passengers, structural failure inflight should be the least of their concerns, with takeoff and landings being far more risky. This is nothing like the Comet airliner, where they really did fall out of the sky, due to a design flaw and metal fatigue...

[BARKINGMAD]

[QUOTE=Arydberg;10453267]I happened on this video and think it deserves a look.

Was this what you were after?

https://www.washingtonpost.com/archive/politics/2006/04/17/boeing-parts-and-rules-bent-whistle-blowers-say/5f4e0e7d-9f0a-44b8-afe5-6c90dfd82229/?noredirect=on&utm_term=.e6a1d78c4c55

[Thrust Augmentation]

Thank you GRC;


How many B737 NGs suffered structural failure and fell out of the sky? None.

True, but it's still a pretty fresh aircraft


How many B737 NGs were flown into the ground by various accidents? Several.

Completely not what or why I'm asking.

I'm not trying to suggest for a second that NG's are going to start falling out of the sky, but if approval was granted on the basis of parts tolerances that weren't acheived, I'm puzzled.

[Herod]

True, but it's still a pretty fresh aircraft.
Senility must be setting in. I could have sworn I was flying the NG in 2003. I make that coming up 16 years.

[tdracer]

Sorry to let facts interfere with a good story, but:
Hull loss rate (through 2017).
737NG (-600, -700, -800, -900): 0.17
A320 (A318, A319, A320, A321): 0.21

Fatal Accident rate (again through 2017)
737NG (-600, -700, -800, -900): 0.08
A320 (A318, A319, A320, A321): 0.10

Yep, those 737NGs sure are deathtraps...

BTW, 737NG EIS was 1997 - so not exactly a spring chicken.

[Loose rivets]

I posted on this having picked up the Tube video from another recent poster. I watched it in full and have just read the Washington Post link above. I feel the latter substantiates the old fears.

Not falling out of the sky? Okay, but what about the photo shots of airframes broken into three parts after survivable crashes? They make the point the breaks are reasonably clean around the circumference at the break points.

But be this as it may. If Boeing were setting out to make every part within three thou' tolerance, and hand-building them failed to come close to this, how could the Henry Ford philosophy be so readily abandoned when the parts turn up off-pattern?

What made me take an initial look was the Rosemont vane builds and rebuilds. In short, I'm starting to be spooked on the macro scale.

https://www.pprune.org/archive/index.php/t-616624.html

[slacktide]

What made me take an initial look was the Rosemont vane builds and rebuilds. In short, I'm starting to be spooked on the macro scale.


Well, have a look at the Emergency AD that the FAA issued on April 18 to ground all Cirrus SF50 light jets.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/448c46c035e93a6e862583e0007291d8/$FILE/2019-08-51_Emergency.pdf

Cirrus and Aerosonic (manufacturer of the technical standard order AOA sensor) have identified the probable root cause as an AOA sensor malfunction due to a quality escape in the assembly of the AOA sensor at Aerosonic. Two set screws that secure the potentiometer shaft to the AOA vane shaft may have improper torqueing and no application of thread locker (Loctite) to secure the two set screws. The AOA sensor with this quality escape is labeled with part number 4677-03

Not the first time that a shaft set screw backing off has caused an AoA sensor to fail.

http://www.smartcockpit.com/docs/Boeing_B747-Stick_Shakers_Activation_On_Takeoff.pdf

Examination of the main gear revealed that the set screw that secured it to the shaft was not fully tightened: the overhaul manual specifies an assembly torque of 4.0 - 4.5 inch-pounds for this item. This was established as the reason for the random readings of the resolver outputs with respect to vane displacement, which thus resulted in the right ADC receiving erroneous angle of attack data.

Maybe not the best design choice? I've pretty much never seen a set screw installed in a self-locking threadform, they typically rely on anaerobic sealants to prevent them from loosening. A more permanent type of fastener might be a better choice. (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/448c46c035e93a6e862583e0007291d8/$FILE/2019-08-51_Emergency.pdf)

[NWA SLF]

I've seen analyses by many people with impressive credentials that seem very impressive but amount to, a quote I remember, pseudoscientific sheep dip. tdracer cites the most relevant statistics - fatal accident rates. Even these are skewed but that is nit-picking. Pilot suicides are a hit on the airframe. Airframes lost to bombs are in the statistics. Pilot training - several hull losses have been followed by shutting down an airline due to safety deficiencies.

I've lived the life of engineering through manufacturing to failure analysis and accident investigations. Do out of tolerance parts get used in production? Yes. In fact at one company we engineers needed to analyze parts and determine if they had Critical or Major characteristics, mark those characteristics, and indicate on the part number if it had a Critical or Major characteristic. Referring to W Edward Deming's quality philosophy, I remember him stating in the first of his video series that quality started to go downhill with the hiring of the first inspector. Relying on an inspector to check whether or not you did your job correctly was an insult to workmanship.

In 1974 I had the opportunity to take a course Applied Fracture Analysis by Dr David Hoeppner who had worked for the Skunk Works but wanted to move on to a place where his research could be taught outside the confines of a small part of Lockheed. Our first class would have made those with weak stomachs leave as he brought in failed components that had resulted in fatal crashes. Our class following the crash of TK901 found Dr. Hoeppner bringing in a cargo door latch from a DC-10 and telling us we stupid engineers created this disaster - that was before knowing which part of the design caused the failure. One class, unnerved by his thoughts of engineers, I asked him if he were flying a transcontinental flight and could chose any plane, he selected a Convair 990 (remember, this is 1974). I asked him why not a Boeing? He said in his opinion they got burned early in the company's life and overdesigned everything. Boeing's carry a lot of extra weight due to overdesign. That was back in the days when the 737 was an infant. Dr. Heoppner was upset because he could not get TWA to send their engineers to his class as this was near their overhaul base. One day he entered the classroom particularly elated jumping on top of his desk and dancing. Seems the day before an axle had failed on one of TWA's L1011s. Being a Lockheed product, Dr. Heoppner was asked to investigate and diagnosed stress corrosion cracking. "Those idiots don't know how to identify a simple failure mode and they won't spend the money to send a group of engineers to my class." Unfortunately we engineers learn the most from failures - oh crap, well, I won't do that again." When we reach our peak we retire and let the new people repeat our errors.

[maggot]

It's safe
FFS
sure it's a piece of crap aeroplane but it's safe and cheap

[Dee Vee]

Sorry to let facts interfere with a good story, but:
Hull loss rate (through 2017).
737NG (-600, -700, -800, -900): 0.17
A320 (A318, A319, A320, A321): 0.21

Fatal Accident rate (again through 2017)
737NG (-600, -700, -800, -900): 0.08
A320 (A318, A319, A320, A321): 0.10


Any reason to leave out the 737 MAX statistics and not bring it up to 2019????

[tdracer]

Any reason to leave out the 737 MAX statistics and not bring it up to 2019????
End of 2017 was the latest stats I could find on a quick Google.
As for the MAX, you might want to check the title of the thread :ugh:

BTW - NWA SLF, terrorism and 'acts of war' are normally excluded from the Hull Loss and Fatal Accident rates. I'm not sure about pilot suicide.

[Dee Vee]

As for the MAX, you might want to check the title of the thread :ugh:

Well it was you who included all the A3xx variants, only fair to include all the B737 NG variants.... According to Boeing, they are the same....

[tdracer]

Well it was you who included all the A3xx variants, only fair to include all the B737 NG variants.... According to Boeing, they are the same....

I didn't include the NEO, and I didn't include the MAX. Are you suggesting there is a safety difference between the different models of the A320 family? I'm pretty sure the 737NG has a number of safety features what were not available on a 1960's built 737-200 (when the accident rate was over 10x what it is today).
The thread title asks if the 737NG is safe. That's what I was responding to. There seem to be several other current threads available to you if you want to discuss the MAX.

[FrequentSLF]

Rate based on what? Millions of hours? Hulls? Segments?

[tdracer]

Rate based on what? Millions of hours? Hulls? Segments?

Hull Loss and Fatal Accident rates are per million departures.

[FrequentSLF]

Thanks! Why you do not include in your analysis the 737 400 and 500? I believe they have been in operation alongside the AB 320s... ?

[Bend alot]

It seems that "some" 737 NG have not been built to the required spec.

I do believe that the NG did get a few increases that would increase airframe stress and fatigue - but will that make them unsafe?

There is a chance that the previous versions of the 737 could also operate with the NG increases, but it just removes the error of margin.

History shows that JAL 123 flew very safely for along time after an incorrect repair. In fact they did the calculations on how long the incorrect repair would last before it would fail.

It safely flew something like 20% longer than the calculations determined failure would happen.

So yes 737 NG's have been safe as was JAL 123 after the repair that was not to spec.

Will this none spec construction ever lead to a structural failure earlier - hard to say without doing the actual calculations, but for that exact out of spec conditions would be needed.

As for the break ups of the fuse in those crashes - seen a number similar in non 737 and think even in other 737 types so not sure that is related to the construction specs.

[DaveReidUK]

So yes 737 NG's have been safe as was JAL 123 after the repair that was not to spec.

I hope you have a good lawyer ...

[Bend alot]

I hope you have a good lawyer ...
No need if the NG is built to spec Dave.

But if I need one I shall track one down that represented a JAL 123 survivor/s - they will have some good notes to use.

Boeing were a bit court shy on JAL 123, I doubt that has changed