Unexpected cracking found on critical Boeing 737 Next Generation part

https://komonews.com/news/local/exclusive-unexpected-cracking-found-on-critical-boeing-737ng-equipment

by erentz • 7 years ago

221 114 7 years ago

alan5• 7 years ago

Engineers design pickle forks to last the lifetime of the plane, more than 90,000 landings and takeoffs, a term known as "flight cycles" in the aviation industry, without developing cracks.

That number made me do a double take. Seems planes never stay on the ground for very long.

godzillabrennus• 7 years ago

Time is money.

Hopefully autonomous vehicles used on demand see many more hours on the road than our personal vehicles.

ReptileMan2• 7 years ago

They literally stay only the turn around time in commercial aviation in busy operations. At least that is the goal. And of course maintenence and repair.

And an airframe is used over decades. Add some serious safety factor and you are up there at 90000.

But since the 737 max grounding, NGs have seen more usage. So bad news for Boeing. And heaven forbid another grounding - there will literally be not enough physical planes to fly in the skies.

quickthrower2• 7 years ago

there will literally be not enough physical planes to fly in the skies.

It'd be interesting - flight prices go up and people realise they didn't need to fly as much as they thought they did?

tus88• 7 years ago

One flight a day for 90,000 flights is 246 years. You are right.

phire2• 7 years ago

Sometimes they fly routes that are only 30min long. With a 30min turnaround, that could mean a flight every hour.

If they kept one plane flying round trips all day, they might fit 16 flights into a day and theoretically burn through the 90,000 cycles in under 16 years.

axaxs3• 7 years ago

Not an aerospace engineer, but this seems like a weird way to measure airplane life. A transpacific plane could have 1/10 the cycles but equal airtime, and one would think that the stresses of flight are worth considering. Wonder why it's not measured in hours, like say, tractors, or miles flown. Do we measure any other engined vehicle this way?

Obi_Juan_Kenobi• 7 years ago

A cycle involves pressurizing the cabin relative to the atmosphere approaching flight altitude, and then depressurizing during the descent.

The pressure differential may not seem like much, 6-10 psi in most cases, but the cabins are quite large, so these forces become substantial. Advanced airframes like the composite 787 use that extra strength, in large part, to lower cabin altitude (i.e. keep higher pressure) because it has such a substantial effect on passenger comfort.

Cycles is absolutely the best way to consider airliner lifespan because that is the most significant stress on the airframe.

agurk• 7 years ago

There are a variety of ways that age of something can be measured with two common examples in everyday life being people and cars commonly measured in years and kms/miles respectively. The metric chosen is one that adds value for understanding the impact.

Aeroplanes and their components do have a lot of different ways of having their ages measured, depending upon what one cares about. Engines are a good example of something where the hours spent running is usually the most salient.

For fusalages, as we're talking about here, pressurisation cycles is actually very important in pressurised airframes. This is because it is the main source of material fatigue which is a major cause of issues - usually in the form of cracks. This was discovered the hard way with the de Havilland Comet[0].

Smaller non-pressurised planes are normally measured in total flight hours, but the effect of repeatedly pressuring and depressuring is so great that it's the biggest factor that will affect the life of the bigger airframes.

[0] https://en.wikipedia.org/wiki/De_Havilland_Comet#Accidents_a...

flexer2• 7 years ago

Planes are extremely expensive pieces of machinery and you don't make money if you're not flying passengers with them. I'd be more surprised if they weren't in the air as many hours as possible.

9nGQluzmnq3M• 7 years ago

For context, the 737 NG is previous iteration of the 737 (before the MAX) and among the most popular aircraft ever built, with over 7000 in service. Grounding this would absolutely cripple the airline industry.

However, the NG also has an excellent safety record, and 35000 cycles is equivalent to 5 flights (takeoff & landing) every day for 10 years. So while this may lead to extra checks on older aircraft, it's highly unlikely to cause a MAX-style global grounding.

samstave3• 7 years ago

What is the actual safety record of the B-52, which i subjectively consider to be the safest machine in history.

How would the B-52 match up against modern commercial airliners? (Does anyone, other than boeing, even track this stat?)

The calc would be something along the lines of;

Date-of-design -> completion, testing, commissioning, hours in flight - accidents, crashes,pilot error, time in service, fuselage age, etc...

I am subjectively of the opinion that the B-52 is the greatest aircraft ever made.

ethagknight• 7 years ago

Tell me more of this b-53 safety record

ceejayoz2• 7 years ago

http://www.airsafe.com/events/models/rate_mod.htm indicates 79 fatal 737 incidents with about a quarter billion flights under their belt.

https://www.globalsecurity.org/wmd/systems/b-52-safety.htm indicates 76 B-52s destroyed in accidents across 7.5 million flight hours.

They're not perfectly comparable sets of numbers, but the B-52s look substantially riskier on a per-hour basis.

brians• 7 years ago

That’s not subjective; you just made it up.

For one thing, B-52s seem to have substantial safety externalities for nearby cities.

Pfhreak• 7 years ago

The part was found damaged at 35,000 cycles. That means it took less than or equal to 35,000 cycles. It's not clear whether it cracked earlier, how many such failures would be needed to down the plane, etc.

mieseratte• 7 years ago

Assuming a proper maintenance schedule, we can reasonably reduce that time window.

tobib• 7 years ago

A lot of text providing very little information.

kjar• 7 years ago

I’m not flying anymore. Between the GHG annual personal emissions and the stunning staggering massively deadly failures of rushed Boeing product launches. Finally I will note the whole damn process is dehumanizing and terrible.

heavyset_go• 7 years ago

The worst part of these revelations is that the aviation industry is exalted as the standard other industries should look up to when it comes to safety.

If Boeing can't escape the perverse incentives that tempt every company, then what company can and why are we relying on this economic model to drive such a high stakes industry?

SomeOldThrow2• 7 years ago

Relying on profit-motivated companies to consistently provide value at safety critical levels seems short sighted.

txcwpalpha• 7 years ago

The worst part of these revelations is that the aviation industry is exalted as the standard other industries should look up to when it comes to safety.

I don't see why that's "the worst part". Flying is the safest mode of travel, and among airliners the 737NG is one of the safest planes in aviation history. The fact that cracks have been discovered doesn't change that, and the routine inspections which have discovered these cracks and will lead to them being fixed is precisely the reason why these aircraft, and the aviation industry as a whole, are so incredibly safe.

kube-system3• 7 years ago

They are the standard. Commercial airline safety issues are uncommon enough to be newsworthy.

Boeing's customers care a lot more than most automaker's customers. 1 in 4 cars on US roads have known unresolved safety recalls.

hef19898• 7 years ago

Cracks are not necessarily something critical. As long as they are identified early enough the affected parts are simply added to the relevant checks (C, D, whatever) and after a predefined number of cycles or hours. Also ad-hoc checks might be required.

Aviation is the standard exactly because defects are identified and handled the way they are, they also tend to be remedied quickly. If not all affected aircraft are grounded, like the 737MAX.

These 737NG cracks can by no means be compared to the 737MAX clusterfuck. The former is pretty normal while the latter is a safety and certification issue of enormous dimensions.

amelius• 7 years ago

The worst part of these revelations is that the aviation industry is exalted as the standard other industries should look up to when it comes to safety.

If airplanes were like computers ...

albertgoeswoof• 7 years ago

It’s still a very safe method of transport, relatively speaking.

But your other points are 100% correct.

tfha• 7 years ago

I don't think anyone needs to be concerned about the safety of flying, even with all the news flying is still statistically extremely safe.

I will agree though that the TSA has made things pretty dehumanizing.

arkitaip• 7 years ago

It's crazy how much the flight experience varies between countries. I recently traveled between Sweden and Germany and the entire experience from online check-in to reaching my destination was painless and very convenient. There was very little queuing and the longest one was on the tax free when I bought water... Didn't even have to show my passport during the flights and I was never checked by security.

Xcelerate• 7 years ago

It's weird. I never used to be afraid of flying at all, but the 737 MAX crashes sort of "triggered" the fear for me. I still fly frequently but I find the experience terrifying now.

As a data scientist, I know the odds of something going wrong are extremely low, but unfortunately I'm not able to rationally control my emotions during flight; the fear is involuntary and difficult to suppress. It also doesn't help that I work at a large tech company and see how many bugs are in the codebase (even with some of the best software engineers in the world), and the fact that airplanes are increasingly run by software makes me feel kind of queasy.

r00fus• 7 years ago

Maybe if you watch more terrifying accidents involving other modes of travel? Car travel is statistically much more dangerous.

Seriously I see the 737 Max debacle as an exception that proves the rule.

But the dehumanizing part can be fixed. We may in the future look on the TSA security theatre as an era of incredible FUD.

elif3• 7 years ago

As for direct GHG emissions, the most efficient mode of travel depends on many factors involving the models, occupancy, and route, but generally speaking, planes can become more efficient than trains for distances >= 700 miles.

Transfinity• 7 years ago

Source: https://www.ucsusa.org/clean-vehicles/getting-there-greener

Turns out motor coaches (e.g. Greyhound busses) are the most efficient at pretty much any distance.

hansthehorse• 7 years ago

There is a 9 year old documentary on two Boing whistleblowers describing cracking probability on the 737ng. It's an hour long: https://www.youtube.com/watch?v=IaWdEtANi-0

alexis_fr2• 7 years ago

Extremely interesting. Especially, around 19-21 minutes, we find the same problem as on 737 Max: Boeing has the delegated authority from the FAA to certify their own processes and parts.

I’m never flying Boeing again. They were hammering crucial parts to fit, provoking crackling; redrilling holes when the hole was 3 inches apart, endangering the whole structural integrity; painting it all green and sending that to production.

The documentary is about the circles of the airframe structure, not about the wing forks of today’s article, so that makes one new type of botched work from Boeing.

peteretep2• 7 years ago

I’m never flying Boeing again

I suspect you were intending this to be obvious hyperbole, but also this will be very difficult if you’re flying at all regularly. While you can have a look at the equipment the airline thinks it’ll be flying at booking time, there’s no guarantees about which plane will actually show up, and the airline isn’t going to refund your ticket because they decided to swap out their A350 for their 787 for operational reasons.

newnewpdro• 7 years ago

If a part's made of aluminum and undergoes cyclic stress, even staying within its instantaneous modulus of elasticity, it will eventually crack.

Note the aluminum curve in the graph here [0], it never levels off horizontally.

My understanding is this effectively means the modulus of elasticity for aluminum parts is forever diminishing. Aluminum is a metal that's "work hardened", it's basically becoming increasingly brittle the more cyclic stress it experiences.

I'd been told in the past that commercial planes are regularly X-rayed for cracks as part of their maintenance, because of their extensive use of aluminum.

None of this should be a surprise except that it's supposedly "unexpected" in the pickle fork. These vehicles have always been high maintenance machines, in order for them to be safe all the structural aluminum must be regularly inspected for cracks, the cracks should be expected and parts replaced as needed.

[0] https://en.wikipedia.org/wiki/Fatigue_limit

Edit:

Out of curiosity I did some digging for photos of this part and more information, this thread delivers some insightful links and citations:

https://www.pprune.org/rumours-news/625886-737ngs-have-crack...

dredmorbius3• 7 years ago

AFAIU, ultrasound is far more typically used than x-rays, as the acoustic properties of fractured castings are more distinctive than their xradiographs.

Apparently induction testing is also used (likely on a similar basis to ultrasound: properties deviate sharply from norm/spec).

corbani• 7 years ago

The modulus of elasticity of aluminum does not change with cycling (or basically with anything else but big temperature differences).

Fatigue is a damage accumulation process, that does not show in the most obvious properties, like modulus or strength.

The aviation regulations changed a long time ago from requiring to avoid cracks to requiring to have structures that can operate with cracks long enough to for them to be detected, as is exactly the case here. Of course nobody design planes to crack, but the regulations reflect the realization that completely avoiding cracks is impossible ...

m0zg2• 7 years ago

> We're told this is very much an ongoing investigation, and that it's unclear whether or not this is a widespread issue.

TL;DR: a crack in a critical part was found in one plane during a routine inspection. But you wouldn't know that unless you read all the way to the middle of the article. This is a non-story engineered to create outrage and clicks.

kube-system3• 7 years ago

Another source tells us Boeing quickly reported the issue with the single plane to the FAA last week, and now more planes with similar cracking have been found.

m0zg2• 7 years ago

How many? Could be as few as 2. Out of thousands.

oplav• 7 years ago

> Another source tells us Boeing quickly reported the issue with the single plane to the FAA last week, and now more planes with similar cracking have been found.

Looks to be more than just one plane.

anon91831837• 7 years ago

Unsurprising given the 2010 Al Jazeera revelations of the Boeing-Ducommun conspiracy and cover-up: critical structural elements that were supposed to be CNC machined by Ducommun were crudely made by hand and Boeing managers ordered them installed into 737 NG (-600, -700, -800, -900) anyhow. And then when a blue-ribbon panel of Boeing employees went to find out what happened, their findings were buried and no corrective action was taken. 737 NG's are flying around with substandard critical structural components like spars and the areas around doors, leading to several fuselage breakups on hard landings and runway overruns, which has killed at least several passengers to date. In past similar incidents, aircraft fuselages survived intact. There's a very real possibility that one or more 737 NG's may breakup in heavy turbulence, hard landings and runway overruns at any time, and Boeing knows about it, but has done nothing to remedy it.

https://youtu.be/IaWdEtANi-0

dehrmann• 7 years ago

leading to several fuselage breakups

[citation needed]. It's what AJ is positing, but it's presented like a correlation, I don't think investigators called that out an a cause of the breakups, and it's been 10 years since that was made and this doesn't seem to be a major problem. One thing I read suggested that the fuselage is strongest at the wing, so the break happens away from that section. That, and hard landing is an understatement; One landed short of the runway, another overshot it, and one dropped onto it.

https://commons.wikimedia.org/w/index.php?title=File%3AAnima... (4:55)

v8engine• 7 years ago

For those curious about how this part looks, Boeing Pickle Fork graphic illustration:

https://www.pprune.org/rumours-news/625886-737ngs-have-crack...

basicplus2• 7 years ago

See link for pictures of design

http://newsinflight.com/2019/09/28/boeing-workers-found-new-...

Unexpected cracking found on critical Boeing 737 Next Generation part

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