US Air Force pauses flights for over a hundred C-130s over ‘atypical’ cracking | Hacker News Reader

US Air Force pauses flights for over a hundred C-130s over ‘atypical’ cracking

defensenews.com

88 pointsJerry216 comments

Despite the other comments, this is a very serious issue. In fact, it's one of the most serious that can affect an aircraft, and the serial numbers involved are really grounded until inspected (8 hours) or fixed (1-2 months - ie. rebuilt wing.)

Smaller airplanes work around this by having a "massive spar" with no joints that goes entirely through the fuselage.

In the case of larger planes a "center wing box" can be used, like the newer C-130 serial numbers that are not affected.

Source: commercially-rated airplane pilot who's familiar with military jet design.

Yep, it's a serious issue but as I said in my other comment, managing things like this is a relatively routine part of aircraft maintenance. I've been forwarded a preliminary risk assessment that puts the overall risk as "medium". The severity of the problem is obviously catastrophic but the probability of a failure occurring is so low ("extremely remote") that the overall airworthiness risk is not as high as one might think.

Every Hercules has a centre wing box, not just the new ones, and the "rainbow fitting"[0] is the part that attaches the centre wing box to the outer wing boxes. There is a rainbow fitting on the upper and lower surfaces of the box.

It looks like in this case the problem affects aircraft with more than 15000 equivalent baseline hours on their CW rainbow fittings, which is what's being inspected.

Source: am aerospace engineer with Hercules experience

[0] the rainbow fitting is a curved surface designed to transmit loads between two mating parts. It's called out as 99A in this pic: https://ibb.co/tbhcdS9

Here's a picture showing context.

https://media.defense.gov/2017/Jun/19/2001764865/-1/-1/0/170...

This reminds me of a (possibly unrelated) incident involving a C-130A that broke up in flight while serving as a fire-fighter water-bomber. It turns out the original material 7075-T6 wore too quickly and should've been the revised material 7075-T7531. Even C-130B's through C-130E's weren't fully-upgraded with the recommended engineering changes.

http://www.iasa.com.au/folders/Publications/Legal_Issues/Pea...

https://en.wikisource.org/wiki/NTSB_accident_summary_for_N13...

https://aviation-safety.net/database/record.php?id=20020617-...

Here's a structural analysis of the C-130H wing design:

https://fenix.tecnico.ulisboa.pt/downloadFile/395138005046/C...

Ordering inspections such as this is common airworthiness practice - only noteworthy here because of the number of aircraft involved.

It's a bit misleading to say they've been grounded; typically what you'd issue is a special/out-of-sequence inspection to be carried out before next flight, which I suppose to someone outside the industry amounts to the same thing but there's semantic difference.

These aircraft are being inspected to ensure they are airworthy and conform to the approved type design; they're not really being "grounded" which would imply they're not airworthy or not compliant with the type design (which is the case for e.g. the MAX 8).

I'm not sure atypical is the correct word here. This was a problem when I was in the Air Force 13 years ago...

The decision to pause operations and conduct inspections was made after a single C-130 was found with the lower center wing joint cracks, said AMC spokesman Maj. Jonathan Simmons.

One is less than a hundred. Title doesn't explicitly state that all those aircraft had cracking, but still seems a bit misleading in a clickbait sort of way.

Fwiw I interpreted it the way it was intended but I follow aviation stuff a fair amount.

The title seemed clear and I don't follow aviation stuff.

Headline is pretty clear. If one aircraft shows atypical damage, they'll ground all the others just in case they're similarly affected. This probably entails inspections and maybe even pre-emptive fixes (depending on the resolution for the cracked aircraft). So a crack on one of them is just as bad as a crack on all of them.

You’re right. Aviation comes down to being a numbers game. If one aircraft exhibits variances, the problem needs to be understood and if bad fixed before it has a chance to cause a real issue.

Think that this is indicative of the state of the US Air Force as a whole?

I think seeing cracks on ONE plane and deciding to review all of them speaks to a pretty high standard.

"But the risk posed by the issue — that the wing could become dislodged from the aircraft — was so serious that the Air Force decided to move forward with inspections for all planes that could potentially be impacted."

I would think that's a minimum standard, not a pretty high one. Having wings fall off is embarrassing, expensive, deadly, and nobody wants to testify before Congress as to why they let that happen.

One of the mechanics on an aircraft carrier I was on (briefly, I'm not military) said that if they find even one nut on the ground, they'll isolate and ground every single plane they think might be affected.

Playing the numbers game is their job. Logistics win wars.

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