Plane crashed after 3D-printed part collapsed
20 comments
·December 4, 2025teamonkey
The actual report[1] holds the answer to the question you’re asking.
CF-ABS (or so claimed)
[1] https://www.gov.uk/aaib-reports/aaib-investigation-to-cozy-m...
hatsunearu
Is this a Part 103 Ultralight?
Also it's insane that they used a bolted joint with plastics on a critical place, the plastic will creep under the clamp load and will lose clamp force.
CarVac
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.
brovonov
Lower, according to the report
"Two samples from the air induction elbow were subjected to testing, using a heat-flux differential scanning calorimeter, to determine their glass transition temperature. The measured glass transition temperature for the first sample was 52.8°C, and 54.0°C for the second sample"
Yeah, they might have used ABS-CF filament, but unless they got it from a good brand that uses good resin and proper printing parameters, the actual Tg will be lower, plus the stress from the vibration/load could have made the part fail if it was not for the heat later in flight.
the_mitsuhiko
CF-ABS
> An alternative construction method for the air induction elbow, shown in the Cozy Mk IV plans, is a lamination of four layers of bi-directional glassfibre cloth with epoxy resin. The epoxy resin specified for the laminate has a glass transition temperature of 84°C, after the finished part has been post-cured. The aircraft owner stated that as the glass transition temperature listed for the CF-ABS material was higher than the epoxy resin, he was satisfied the component was fit for use in this application when it was installed
https://assets.publishing.service.gov.uk/media/69297a4e345e3...
buildbot
I think an extended quote shows that this was a really bad call:
“ The aircraft owner stated that as the glass transition temperature listed for the CF-ABS material was higher than the epoxy resin, he was satisfied the component was fit for use in this application when it was installed. A review of the design of the laminated induction elbow in the Cozy Mk IV plans showed that it featured a section of thin-walled aluminium tube at the inlet end of the elbow, where the air filter is attached. The aluminium tube provides a degree of temperature-insensitive structural support for the inlet end of the elbow. The 3D-printed induction elbow on G-BYLZ did not include a similar section of aluminium tube at the inlet end. Tests and research Two samples from the air induction elbow were subjected to testing, using a heat-flux differential scanning calorimeter, to determine their glass transition temperature. The measured glass transition temperature for the first sample was 52.8°C, and 54.0°C for the second sample.“
ohazi
What a misunderstanding -- glass transition temperature means different things for thermoplastics (i.e. anything that comes out of an FDM printer like the CF-ABS in question) and for thermosetting resins like epoxy that actually undergo molecular cross-linking during the curing phase. Thermoplastics will get soft and can deform without limit, while thermosets get rubbery but still more or less hold their formed shape.
MBCook
Given what it was would it have been under actual stress?
Certainly seems questionable to use any 3-D printed plastic material for exhaust. That’s absolutely going to be too hot.
CarVac
It was an intake manifold, so it's continuously under suction. At the temperatures in an engine bay the plastic probably gradually creeped to a point where the restriction increased the suction and suddenly it collapses completely.
bluerooibos
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 system. This system consisted of a fuel controller, high-pressure engine-driven fuel pump, electric auxiliary fuel pump, fuel flow transducer and associated fuel hoses, filters and fittings. Following flight testing, the modified fuel system was approved by the LAA in 2022. The modified fuel injection system had accumulated 37 hours in service when the accident occurred."
So the pilot himself and the LAA were incompetent. LAA is an association for amateur pilots though so I'm not sure what level of rigour they "approve" things with.
Zak
Nearly anything is allowed for experimental amateur-built aircraft like the one in this incident. Unapproved modifications to certified aircraft are forbidden in most parts of the world.
proee
The plane is an experimental class, so I doubt they have to follow a lot of regulations.
null
gostsamo
> The Cozy Mk IV light aircraft was destroyed after its plastic air induction elbow, bought at an air show in North America, collapsed.
o11c
At a glance, that looks like worse than merely the negligence of using a new technology.
The whole point of 3D printing is that the material is moldable when hot but rigid when it cools. And people really should be aware that engines get hot.
cmiles8
This might be Darwin Award eligible!
Actual report: https://aviation-safety.net/wikibase/487013
Material was CF-ABS