Back in March, a small aircraft in the UK lost engine power while coming in for a landing and crashed. The aircraft was a total loss, but thankfully, the pilot suffered only minor injuries. According to the recently released report by the Air Accidents Investigation Branch, we now know a failed 3D printed part is to blame.
The part in question is a plastic air induction elbow — a curved duct that forms part of the engine’s air intake system. The collapsed part you see in the image above had an air filter attached to its front (towards the left in the image), which had detached and fallen off. Heat from the engine caused the part to soften and collapse, which in turn greatly reduced intake airflow, and therefore available power.
While the cause of the incident is evident enough, there are still some unknowns regarding the part itself. The fact that it was 3D printed isn’t an issue. Additive manufacturing is used effectively in the aviation industry all the time, and it seems the owner of the aircraft purchased the part at an airshow in the USA with no reason to believe anything was awry. So what happened?
The part in question is normally made from laminated fiberglass and epoxy, with a glass transition of 84° C. Glass transition is the temperature at which a material begins to soften, and is usually far below the material’s actual melting point.
When a part is heated at or beyond its glass transition, it doesn’t melt but is no longer “solid” in the normal sense, and may not even be able to support its own weight. It’s the reason some folks pack parts in powdered salt to support them before annealing.
The printed part the owner purchased and installed was understood to be made from CF-ABS, or ABS with carbon fiber. ABS has a glass transition of around 100° C, which should have been plenty for this application. However, the investigation tested two samples taken from the failed part and measured the glass temperature at 52.8°C and 54.0°C, respectively. That’s a far cry from what was expected, and led to part failure from the heat of the engine.
The actual composition of the part in question has not been confirmed, but it sure seems likely that whatever it was made from, it wasn’t ABS. The Light Aircraft Association (LAA) plans to circulate an alert to inspectors regarding 3D printed parts, and the possibility they aren’t made from what they claim to be.
That’s crazy honestly
I’m going to err on the side that the seller was just an enthusiast who designed and printed it themselves but they live in a cold place so the problem never manifested during their own use? Or they’re just not very familiar with material properties of 3D printable plastics?
Glad no one was injured too badly
Smart enough to create a very complex 3D model of that, but stupid enough to use PLA in a high heat environment? A 3D model somehow available on the net then printed by an idiot? The report gives no details other than it was purchased at an airshow in the US and Grok despite extensive searching produces nothing more than found is in the accident report.
That glass transition temperature indicates PLA, not ABS with its much higher temperature.
From 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°C.”
CF-PLA filament does exist, but who would have the capability to 3D print such a complex part so professionally based upon its external finish and be stupid enough use PLA in an engine compartment unless it was a mis-marked filament spool?
On second thought about a mismarked filament spool , to successfully print the part with PLA and not ABS, the printer would need to be set for PLA since the print head (hotend) temperature for ABS is much higher than PLA and using PLA at ABS settings would create a mess. So, someone intentionally used PLA.
Maybe they used a printer with NFC tags on the filament spool, causing the printer to use the correct settings for the material? Maybe the part was printed from PLA as a test, and either unknowingly sold as ABS, or the owner of the plane bought this one cheap, knowing it was PLA, but not understanding the implications, or thinking it would be fine because there is a constant flow of cold air through it?
That would prevent the part from overheating, until the throttle is set to idle while the engine compartment is hot.
It could be the sellers fault, the owners fault, or a genuine mistake.
This is quite crazy, I love 3d printing and being “cheapo” but this is the extreme combination of smart and dumb. It reminds me the guy that died making his own rocket to see how the earth was flat.
Read this a few days ago, I’m wondering if the part was designed and sent with bad specs to some commercial 3D print service or the service cheaped out on material