>It’s the rear spar pickle forks which crack
The cracks form in the outer chord of the rear pickle forks (Figure 1) and the behind lying safety straps, just where they pass from the rear spar of the center wingbox to the fuselage side of the aircraft, Figure 2.
>This is also the area where the fuselage side has a cutout to let the main landing gear strut fold in with its attached wheel.
>The combination of a wing center-wingbox pushing wing and landing gear forces into the fuselage in an area where the fuselage has a large cutout for the folded main landing gear makes this area complex regarding forces and how these work the parts during flights.
>The stress spectrum in the area can also have been affected by the later fitting of winglets on the NG, not foreseen in the original design of this area.
>Winglets change the pressure distribution of the wing to a distribution spreading further outboard, by it increasing the wing root bending moment.
I don't think that's the case, and I don't think that's what the link you provided says. 5% of the pickle forks are showing cracks, after a minimum of 20k flights.
It's probably an incorrect analysis (maybe the didn't account for enough cycles in fatigue/failure testing given the extra load from the winglets, maybe the extra load is not well understood and they had bad assumptions). I am very harsh on Boening on how they handled the MAX development and crashes. The pickle fork situation is unfortunate but seems like it is likely an honest error that was caught in the right way and is being dealt with in the right way. I fly 737s frequently, too.
Not excusing anything about MCAS, but the "cracks in an aluminum airframe" thing is a VERY normal and established cycle/process. Well known and a normal thing. This news piece is just journalistic piling on to hot news.
Not excusing anything about MCAS, but the "cracks in an aluminum airframe" thing is a VERY normal and established cycle/process.
Cracks can be a normal and expected thing. These parts were designed to last the lifetime of the airframe (around 90,000 cycles) and are failing in under 30,000 cycles.
This raises eyebrows for two specific reasons: 1.) Boeing was already installing subpar parts (edit: not pickle forks) from Ducommon in the 737 NG 2.) The wings fall off if the pickle forks fail completely.
This news piece is just journalistic piling on to hot news.
MCAS isn't the only fire Boeing is fighting right now (they're also battling poor quality control with their KC-46 and 787 lines among other things). Some guy on PPRuNe is claiming that the pickle fork problem was just improper manufacturing[1], which when put in context would make it appear as if Boeing has some major structural problems with its organization.
Yes, but it's very long cycle failures at low frequency, and people suspect it's because of additional stress caused by winglets. Winglets reduce drag and save fuel, it's an important change. It may have been very difficult to predict and test this failure. And most importantly, the FAA and Boeing are handling it properly.
Yes, but it's very long cycle failures at low frequency, and people suspect it's because of additional stress caused by winglets. Winglets reduce drag and save fuel, it's an important change. It may have been very difficult to predict and test this failure. And most importantly, the FAA and Boeing are handling it properly.
Cracks have been found in NGs both with and without winglets, so that is almost certainly not the issue at hand.
That's because when they merged with McDonnell Douglas, MD executives got the top spots in Boeing, so their shitty culture transferred over to the new company.
The long-standing joke is that MD took over Boeing with Boeing's money
> These parts were designed to last the lifetime of the airframe
Can these be replaced? If they have the expected lifetime of the airframe they might not be serviceable. Out of curiosity: can these cracks be repaired other than replacing the part?
Metal fatigue is a reasonably well understood phenomenon, that is managed by the aircraft inspection cycle.
The actual crack appearance rate diverging from the modelled appearance rate at design time is a potential worry and indicates an issue somewhere along the line. How bad that issue actually is requires more investigation. It's a complex situation because metal fatigue is a statistical process, so you don't know if the cracks you've found are the best case or worst case.
Or perhaps it's news that's just missing a few details.
Cracking and wear and tear on the structure might be normal, but it sounds like the issue here is that the 737NG airframes are showing signs of wear and tear much faster than expected.
You are assuming they are relatively normal hairline cracks. They are grounding planes, so the cracks reported here might be different from that. There does not seem to be enough information to conclude sensationalist news.
Airlines with many more 737's handled it correctly. Not saying it isn't a crisis. Just saying it's an airline specific crisis, not a Boeing crisis. That's the piling on bit.
Airlines with many more 737's handled it correctly. Not saying it isn't a crisis. Just saying it's an airline specific crisis, not a Boeing crisis. That's the piling on bit.
The AD sets forth two distinct priorities: high cycle and low cycle airframes. Those with higher cycles required near immediate inspection because they are presumably more at risk for these cracks, in airlines with larger fleets inspections of younger frames may not be complete yet.
Southwest (owner of the largest 737 fleet in the world) grounded their (two, IIRC) NGs that required inspection sooner and failed that inspection. I don't believe Southwest has finished inspecting the other 600 or so planes in their fleet. Qantas (an airline with an enviable safety record) found cracks in much younger planes than expected (even after the expectations had been lowered from these parts lasting a lifetime to maybe lasting 1/3 that). Qantas took appropriate action, and were another airline to experience these cracks with such young airframes I'd hope they'd ground their NGs too.
I'd hope that the Southwest and Qantas findings would cause other airlines to ground their NGs too if their cycle count is similar. Why assume that your aircraft are different?
Fwiw, all MAX are already grounded. As I alluded, the "normal" process works pretty well for cracks. If the MAX fleet needs "crack" attention, it will happen.
Sure, and the established process will fix it. This is not an MCAS level newsworthy event.
Cracked pickle forks are absolutely noteworthy. Qantas flies its 737s in relatively mild weather, has a reputation for technically skilled pilots and excellent maintenance staff. If there were any fleet where you'd expect to find no cracks it would be Qantas. Instead Qantas has found a third NG with cracked pickle forks (out of a total of 33 NGs that required inspection).
Just to add, here’s a forum discussion from 5 years about about aircraft cracks in general. People are saying they are common in all aircraft even during manufacturing.
The issue here isn’t about airframe cracking in general, which is fairly normal and expected in the lifetime of the plane, but cracking in the “pickle fork” in particular— which is abnormal, as these are not normally expected to crack during the plane’s lifetime according to Boeing’s own modelling and expectations — engineers had rated these at 90,000 cycles, the effective lifetime of the craft.
This appears to indicate (yet another) QC and manufacturing deficiency (Boeing already is dealing with other such issues with the 787 and KC-46).
The claim by OP that this is normal because aluminum cracking is normal is really wide of the facts. This part was engineered to withstand the forces it experiences for a certain timespan, and the fact that some now appear to be failing in less than one-third of the lifespan the materials engineers expected it to calls into question whether Boeing or a subcontractor is failing to engineer these components to spec.
Except this is not about cracks in the airframe but in a component that is certified for significantly more cycles than when the cracks are being found. If these were benign FAA wouldn’t have released an AD to inspect and repair them.
> I believe it was 27,000 vs the 30,000 Boeing stated. How long is 3,000 landings in days/years?
Boeing's originally stated lifetime was 90,000.
After the initial discovery of the unexpected cracking, the FAA ordered an inspection of all pickle forks with more than 30,000 cycles within 7 days -- this is probably the source of your confusion. The "youngest" cracked pickle forks discovered so far was on a plane with 27,000 cycles, which is to say 63,000 cycles early (not 3,000 early) with respect to what Boeing rated it for.
Yes and I am sure all these airlines know this too and yet they are grounding them even though it costs them real money. It seems these airlines are less comfortable with the kind of cracks they noticed or the speed of their growth, but maybe you have a first hand knowledge why they are just wrong.
No. An individual airline or two didn't handle things right. Boeing didn't screw up, and it's completely unrelated to the whole MAX thing. Similar issues exist for Airbus. Aluminum cracks.
Yes, metal cracks and Boeing provides service intervals to inspect various pieces of the airframe. These cracks are appearing sooner than expected. The pickle fork is a critical piece of airframe - if it cracks badly, the wings come off. Grounding the planes is the correct action in this situation.
No one is relating this article or what they are talking about to MAX/MCAS, you're the only one bringing it up. The article even mentions "The new problem is distinct from Boeing's ongoing crisis over its 737 Max planes"
I have to wonder how seriously Southwest and Alaska Air are reconsidering their relationship with the Boeing and the 737. Rumor is that SWA might be considering a switch to Airbus.
I just want to let you know that there are concerns with Airbus also. Article in the Oct/19 issue of Flight International Magazine the following:
It is worthwhile mentioning that the Airbus A320 wing was
designed 35 years ago for a 70t platform, and has remained the same
on all versions, from the A318 through to the A321.
While unchanged, the wing has seen a steady loading
increase: to 83t on the first A321, then 89t and 93.5t, and is
finally expected to go up to 101t on the A321XLR.
This increased wing loading has meant higher take-off
speeds, reaching close to the maximum tyre speed limits, and
a lower safety margin at altitude – in other words, a tighter
“coffin corner”, and lower stability protection.
Where and when would the civil aviation authorities stop
manufacturers from creeping ever so closer to the performance
limits of a product?
> Where and when would the civil aviation authorities stop manufacturers from creeping ever so closer to the performance limits of a product?
You hit the nail on the head. These manufacturers and the airlines are compromising safety for dollars: trying to put more people on a plane than it was designed for.
You are saying that Airbus is close to the limits. It is immensely different than Boeing being the certifier of its own planes, and having two major failures already on record with hundreds dead (the Duncommon airframes and the MAX).
Part of Southwest's competitive advantage has been that the vast majority of their aircraft use the same platform which simplifies training of crew and maintenance of aircraft.
Switching to Airbus would necessitate complete retraining of thousands of people and would increase costs at least in the short term substantially.
Luckily, they can look at AS post VX merger as a good example of how to integrate A320s into an all 737 fleet. So while they will absolutely have costs, they may be able to bring in folks who've done it before.
>This is also the area where the fuselage side has a cutout to let the main landing gear strut fold in with its attached wheel.
>The combination of a wing center-wingbox pushing wing and landing gear forces into the fuselage in an area where the fuselage has a large cutout for the folded main landing gear makes this area complex regarding forces and how these work the parts during flights.
>The stress spectrum in the area can also have been affected by the later fitting of winglets on the NG, not foreseen in the original design of this area.
>Winglets change the pressure distribution of the wing to a distribution spreading further outboard, by it increasing the wing root bending moment.
https://leehamnews.com/2019/10/08/boeings-737-in-another-pic...
So Boeing also made changes from the 737 to the 737 NG without complete reanalysis of how the changes affected all the parts?