Having fun helping a new owner with this 421. The problem is they are all getting old. Troubleshooting weird electrical problem with post lights and finally traced it to a broken collar on the firewall connector and over the years people had over tightened the post light connectors to the point it was pushing the center pins to contact the outer threaded portion sometimes and popping the transistors. But not all the time and random lights would cause it on different circuits.

Then when you get in there you find radio harnesses long abandoned with others in their place and poorly made/installed by repair stations. Only solution is to pull it all out and start over.

The airframe has held up well. This one was a med flight airplane in Denver for most of its life.
Logs show engines making TBO. I used to fly another B and took the engines to TBO without ever pulling a cylinder.

I think the accessories will be the weak point more than large airframe components. Working Pressurization controller parts, valves, pumps, deice timers etc. Starter adapter dampeners. Quill shafts and some other unique parts. bushings, some bolts in the gear and little things like fuel cap parts. eBay and scrap yards have been a good source of "working when removed" for now to try or have as cores.

It is about in the same position Beech 18s were 15-20 years ago. Less and less working for a living. A few become pets and parts are out there but services for the components are starting to dry up.

So few people understand what the spring is for on post light connectors and why you don't overtighten.

The old airframe issue is one very good reason to consider MU-2s. There are three factory service centers, and Mitsubishi still actively supports the plane which is amazing since they made the last one in 1986! Mitsubishi has resumed putting on a safety conference for MU-2 operators every two years and there are representatives from the company in attendance to answer questions. They still put out service bulletins and parts are available, maybe expensive, but available. I recently fried the cabin input heat sensor (my fault, I miss set the cabin heat control in the dark) and the fault was diagnosed and fixed in a few hours at Intercontinental Jet in Tulsa. They had the part in stock! Mitsubishi is consistently rated among the best manufacturers for aircraft support. The plane isn't made anymore, but it certainly isn't an orphan either. The safety culture around the plane since recurrent training became a requirement in 2009 is a big plus as well and the MU2 is now among the safer twin turboprops operating.

Jeff Axel
N54PC

Thread drift here but can you elaborate on that? My Baron panel is lit by post lights - I use a 1/4 open end wrench to tighten the connector but only until it felt slightly snug. Is that too tight?

Hah, just been deal'n with same issues on a 310R - I just pulled all the post lights and put in a LED strip, much easier to deal with .

Thread drift here but can you elaborate on that? My Baron panel is lit by post lights - I use a 1/4 open end wrench to tighten the connector but only until it felt slightly snug. Is that too tight?