There is one major feature a 340 has over a 421.

You can fly the 340 under BasicMed.

Not so with the 421.

Something to consider...

Mike C.

Some plusses for the 421C:
+Seldom mentioned: you can fuel it while standing on the ground, no ladder or step- stool needed. Minor convenience, but kinda nice for sure.
+I understand that if you load all six seats in a 340, you will want to watch the aft cg. That’s not an issue in the C421 when seating six adult passengers.
+Approx 8” space between seats in the 421, which is comfortable to pass thru. Somewhat closer in the 340.
++ Either one can be a very nice bird, just choose one that has been well-maintained.

Gary S

I've operated my 340 for 2 years and its been a great machine, but requires a good bit of maintenance. There is always something to fix, but it is rarely more than something small, like an egt probe.
If I had a need to ever carry more than 4 people on a regular basis, the 421 would be my choice. I see no reason why the 421 would cost any more to operate, aside from the geared engines being a bit more expensive, and using more fuel. I actually think the simpler fuel system in the 421C might make it a bit cheaper, seeing that there quite a few more fuel pumps in the 340.
The 340 will be able to operate off of shorter runways, but rarely will that be a factor for most people. The 421 will be significantly quieter, and will have a greater differential pressure which will allow it to operate a bit higher if needed.
If my runway length would allow it, I would be flying a 421 now.

If I was considering a 421, I'd get a King Air 90 instead. I am extremely happy with my 340 but these birds are not for the faint of heart when it comes to maintenance. (Essentially trading engine expense for airframe items like Phase inspections and calendar items). You have to be able to withstand a bad year or two, and still be able to fly a lot. Engines are expensive, and 421 engines More so.

The reason I stopped looking at 414s and 421s was the nearly double acquisition cost compared to the 340 (as it happens I ended up paying more for the 340 but that's because it had a ton more electronics).

As said many times, the actual bird you find is more important than the model- they are now so old that individual maintenance pedigree is the single most important factor in acquisition.

My 421C was easy to maintain. The engines ran cool and were reliable. I lost a turbo during my ownership and thats about it. It was as fast as a C90 and I often flew under weather they were stuck in. I could even fly at FL270.

You have to pay up front for a good example. Noobs think they are getting a deal buying at a low price, and then knock the type when maintenance eats them up. Experienced buyers pay for the top examples, which is why they still bring what they do. Those buyers spend far less in the end overall. I learned the hard way on the PBaron. I owned several big twins after that and never looked back.

Get the 421C.

I have to ask, can a 421 be flown with lower operating costs than a King Air model with similar capacity and performance?

From what I’ve seen 414/421 charter for $750/hr range. C90 are similar speed and substantially more expensive. Calendar items will especially kill a low utilization private owner on a KA

I think so.

The King Air is slow and expensive. I think the 421 cost per mile will be less, say about 60% the cost of a King Air 90.

There are turbine options that approach the cost of a 421, but the King Air isn't one of them.

Mike C.

I have 1700 hours of operating expenses for my 421C. A 421C in “good” condition is about 60% of the operating cost of a C90.

With GW under 6000, the 340 could be flown under Basic Med.

With limitations on altitude...

BasicMed also restricts pilots to operating no faster than 250 KIAS and no higher than 18,000 feet MSL per § 61.113(i)(2). However, these restrictions do not relate to the operating limitations of the aircraft. It is permissible to fly an aircraft under BasicMed that is capable of flying faster and/or higher than those limits as long as the aircraft can be safely flown within them, and as long as the flight is conducted according to the regulations.

although the 340 can be flown like that, I would think of it as "less than optimal."
the airplane really shines above 18k; I try to get to low 20s every flight where it's practical.

The 340 has the same pressure differntial (4.2) as my Aerostar (4.25)
I usually fly between 16 and 18K

At 22K everything is a bit hotter, its not much faster and the difference in cabin altitude makes for a more tiring day.

22K -> 9200ft cabin.
17500 ->6200 ft cabin.

If the weather is good, VFR at 17,500 is pretty awesome, you can go over all the class B's, C's, many of the tiny ground based restricted areas etc... almost no traffic at that altitude too high for most of the pistons and too low for the turboprops...

You are also high enough that you clear all terrain and can go straight as an arrow direct...

In Socal I can usually save 15 minutes of random vectoring by going VFR...
Now if the weather is not perfect, its a different story...

Paul

It is 600 vs 700 vs 800 dollars per hour.

Otherwise not much of a difference.

I doubt you'll see $1/hour difference in the 340/414 as they are virtually the same systems on slightly different fuselages.

Having operated a 340, 414 and a 421C, I doubt you would see a noticeable difference in them either. There is a 400 hour AD on the 421 starter adapters that will cost a couple dollars to comply with, but is offset by the lower cost of cylinder issues. All of the wet wing Cessna's have a fuel valve AD, but the cost is relatively insignificant.

I wouldn't pick one or the other based on cost per hour.... The 421 is the nicest of the fleet, and would be my first choice of ownership as it's much quieter, and the engines run significantly cooler...

Jason