Live data from Hacker News

A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

bbc.com

201–210 of 223 posts

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#201

Earlier quoted context omitted.

There’s a massive difference between the thermal properties of the materials you listed.

Yes, that's why I listed them. And even then: none of those first three are (safely) usable for this application. PEEK or ULTEM or something better than that.

I absolutely agree. At the same time, I’m just flabbergasted that someone really thought they’d pass off PLA crap for such a purpose, it literally loses shape in sunlight. PETG isn’t going to cut it and I wouldn’t want to be on a plane with PETG in a heat-sensitive part, but that would still have been less ridiculous given that a) it’s significantly better than PLA in this regard, and b) unlike PEI and PEEK, it can be printed with ease on just about any FDM.

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#202
post #2

I wonder what material it was printed with. edit: It was ABS-CF, which shouldn't be used under stress long-term in higher temperatures than maybe 65-70°C, or lower depending on the blend.

I wonder who installed it. Was the pilot home 3D printing mods for their plane? And is that even allowed? Super concerning if there was a company behind the installation. I'd think any semi competent engineer would know better. Edit: from the report - "A modification application was made to the LAA in 2019, by the aircraft owner2 , to replace the engine’s throttle body fuel injector with a mechanical fuel injection s…

The LAA classified the proposed modification pf the overall fuel system as minor based on the owner’s description of it, and approved it on that basis. But the owner lied and did not disclose the fact that the induction elbow was modified at all or that it was 3D printed. The report does not discuss any required inspection by a person authorized by the LAA prior to returning the aircraft to service. So it seems like the LAA modification process is a trust-don’t-verify policy.

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#205
This last line is concerning:

>The Light Aircraft Association (LAA) said it now intends to take safety actions in response to the accident, including a "LAA Alert" regarding the use of 3D-printed parts that will be sent to inspectors.

Does this mean that anybody using any 3d printed part in an aircraft will be subjected to this scrutiny? If I use the proper materials with a suitable printer (eg, printing PEEK with a properly specced printer), how much convincing will it take to get these governing bodies off my back?

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#206
post #57

This is the mechanical equivalent of vibe coding. 3D printing itself isn't exactly to blame but the negligence of the company that created and sold this part and omitted it's use from an inspection. Just because a part has the shape of an engineered part does not make it compatible, strong, safe, and fit for purpose. This part could have likely been fine if it used a different material such as Ultem.

In what way is this like vibe-coding -- or do you just mean both are bad? According to the report: > The aircraft owner who installed the modified fuel system stated that the 3D-printed induction elbow was purchased in the USA at an airshow, and he understood from the vendor that it was printed from CF-ABS (carbon fibre – acrylonitrile butadiene styrene) filament material, with a glass transition temperature3 of 105°…

I mean it in a very particular way.

The vendor selling the 3D-printed part at an airshow probably didn't think: "I'll deceive pilots." They likely thought: "I can 3D-print this part to spec, it looks right, it fits, and pilots will be happy." The capability to create professional-looking outputs outpaced the discipline required to validate them.

Same with vibe coding: the LLM isn't lying. It's producing code that passes basic inspection. But both technologies have collapsed the cost of creating something that looks production-ready while preserving all the ways something can fail in actual use.

Before 3D printing and LLMs, there were natural friction points that forced validation:

• Manufacturing a metal aircraft part required industrial equipment, precision tooling, material selection expertise. The process itself embedded quality gates.

• Writing professional software required years of training, code review practices, deployment infrastructure. The difficulty forced rigor.

Now, both technologies let anyone produce outputs that visually and functionally resemble professionally engineered work without any of the underlying validation:

• A 3D printer can output a part that looks dimensionally correct, has proper tolerances, fits perfectly—but the material choice was never stress-tested against thermal cycling.

• An LLM can generate code that compiles, runs, produces correct output for test cases—but has no error handling, SQL injection vulnerabilities, or memory leaks that only appear at scale.

This is a relatively new failure mode where professional appearance becomes decoupled from professional rigor. And customers can't easily tell the difference until something breaks.

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#207
post #57

This is the mechanical equivalent of vibe coding. 3D printing itself isn't exactly to blame but the negligence of the company that created and sold this part and omitted it's use from an inspection. Just because a part has the shape of an engineered part does not make it compatible, strong, safe, and fit for purpose. This part could have likely been fine if it used a different material such as Ultem.

In what way is this like vibe-coding -- or do you just mean both are bad? According to the report: > The aircraft owner who installed the modified fuel system stated that the 3D-printed induction elbow was purchased in the USA at an airshow, and he understood from the vendor that it was printed from CF-ABS (carbon fibre – acrylonitrile butadiene styrene) filament material, with a glass transition temperature3 of 105°…

This is an experimental homebuilt aircraft, so the regulations on manufacture and replacement parts are much less stringent than commercially sold aircraft.

Also, the part it was replacing was a fiberglass part in an epoxy resin, with a glass transition temperature of 84°C. So the 105°C glass transition temperature of the replacement part should have been better than the original.

However, the original had an aluminum tube supporting the inlet, which provided extra structural support beyond fiberglass epoxy resin. And upon testing, the actual glass transition temperature of the 3D printed part was 52.8°C for one sample and 54.0°C for another, so much lower than expected.

Now, because the regulations are much less strict for experimental homebuilt aircraft, there may not be the traceability to figure out where in the chain the issue came up. Was it a bad batch of filament? Did the person making the part use the wrong kind of filament? Who should have tested the glass transition temperature of a coupon of the same material as the replacement part? Did the 3d printed material glass transition temperature change over time, possibly due to something like fuel or exhaust fumes?

The recommendation from this report is to disallow 3d printed replacements for this part, but it should be possible to do with the right material and proper testing and analysis (as well as leaving in the aluminum tube for additional support), as this is an air intake and it should be possible to find a 3d printed material that can withstand the kind of temperatures an air intake is subjected to, given that the original part is a fiberglass with epoxy resin.

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#208
post #103

It's important to note the plane is a Cozy Mk IV, which is an experimental light aircraft that is built at home out of foam and fiberglass by following instructions you get online. The design is very good, and hundreds have been flown over the last ~35 years, but Cozy pilots are the aviation equivalent of people who run Arch Linux as their daily driver; many of them are tweaking their aircraft with some frequency. Th…

Do we know whether the part was made out of spec, or whether the spec specified inappropriate materials?

It sounds like it was something like PLA when it was supposed to be ABS.

According to https://assets.publishing.service.gov.uk/media/69297a4e345e3...

> The aircraft owner [...] understood from the vendor that it was printed from CF-ABS (carbon fibre – acrylonitrile butadiene styrene) filament material, with a glass transition temperature of 105°C [...] he was satisfied the component was fit for use in this application when it was installed.

> [...] Two samples from the air induction elbow were subjected to testing, [...] The measured glass transition temperature for the first sample was 52.8°C, and 54.0°C for the second sample.

I've known 3D printing folks who run off a throwaway prototype in a cheap, easy-to-print material to check for fit before printing in more difficult, expensive materials. Easy to imagine a careless manufacturer getting the PLA prototype mixed in with the ABS production parts, and selling it by mistake.

Of course, the aviation industry usually steers clear of careless manufactures....

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#209

Earlier quoted context omitted.

Manufacturers who use 3D printing use specialized 3D printers, not the same thing that hobbyists use. They also handle all of the testing of parts to ensure they meet the design spec and they have the equipment to validate each printed part to ensure it doesn't have any major defects.

You can see the layer lines in the part. WTF? I don’t build aircraft parts. But I sure as hell wont use thermoplastics in this situation. I don’t even 3D print parts for mildly hot environments where failure is just annoyance. Whoever built this should be charged.

I've printed and used intake manifolds for (automotive) engines in the past, without issue. Obviously that's not the same stakes as an aircraft, but I don't see why it wouldn't be possible to do safely.

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#210
post #103

Earlier quoted context omitted.

Do we know whether the part was made out of spec, or whether the spec specified inappropriate materials?

It sounds like it was something like PLA when it was supposed to be ABS. According to https://assets.publishing.service.gov.uk/media/69297a4e345e3... > The aircraft owner [...] understood from the vendor that it was printed from CF-ABS (carbon fibre – acrylonitrile butadiene styrene) filament material, with a glass transition temperature of 105°C [...] he was satisfied the component was fit for use in this applicatio…

That's... absurd. ABS is a terrible choice for anything in an engine bay - ABS breaks down over time when in contact with oils.

I've used PA6-CF for similar purposes in the past. Obviously not for aircraft, though.

Post reply on HN