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Safety wire on a 172 oil filter, the twist count nobody checks
New guy on our hangar floor in Tulsa twisted his safety wire so tight the pigtail looked like a braid, and I had to show him why that matters. The spec calls for 6 to 8 twists per inch, and if you overtwist it you work-harden the wire until it snaps under vibration, which is the exact thing it was installed to prevent. I know because I pulled a filter last spring that had a fresh break right at the second twist, and the logbook showed it was done 40 hours earlier by someone in a hurry. We re-did it together with a pair of duckbills and a steady hand, took all of ten minutes. Curious if anyone else has caught a bad safety job on a pre-flight that made you stop and look twice.
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smith.lee5d ago
Question whether one break is really a pattern or just a one-off. I get the physics of work hardening, that part is real, but 6 to 8 twists per inch is for the whole run and a lot of guys count the twist at the pigtail, which is always tighter by nature. Pull one filter with a fresh break and you blame the twist, but you never know if that wire got nicked on the lockwire pliers or rubbed a sharp edge on the housing. Forty hours is nothing on a 172 either, vibration takes way longer than that to chew through good wire. We ran a whole fleet for years with guys eyeballing it and the failures were rare enough that nobody wrote it up. Show the new guy the spec, sure, but making it sound like every overtwisted pigtail is a time bomb is a stretch.
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