Not sure where you got that idea. You're not even close. The Marquise interior is almost TWICE the size of a C421.

https://www.globalair.com/aircraft-for- ... specid=476
https://www.globalair.com/aircraft-for- ... specid=362

When I sold my C340 and bought a Marquise of the same vintage, my maintenance costs decreased and my dispatch rate increased.

Not sure where you got that idea. You're not even close. The Marquise interior is almost TWICE the size of a C421.

There is definitely some sketchy info online. I think you're comparing the instrument panel to rear bulkhead distance in the 421 to the cabin size of the MU2. I've spent significant time in both aircraft and owned a Marquise for 4 years and can guarantee they are NOT about the same size inside.

The Marquise cabin is slightly larger than the Conquest II and about 10% smaller than a B200.

421 doesn't meet that criteria.

Broken nose gear link puts the plane on the nose, gear repair, fuselage repair, two props, and two engines. Ask Robert Johnson who had that happen.

There's nothing wrong with a 421. Best airplane burning avgas. If you have one you like, keep it and lavish it with care and new engines. Fantastic.

But the fear of turbine engines is misguided. I had it too and was "this close" to buying a 421 instead. But I've put 1300 hours on my turbines and have changed the oil once and cleaned nozzles 5 times. That is the totality of my engine work. You won't find such a short list for that length of time on a GTSIO-520. No mags, no plugs, no exhaust, no valves, no fuel injectors, no turbo, no wastegate, and so on. You literally do nothing to the engines during routine inspections.

The other fallacy is that when something goes wrong, it's always major bucks. Not so. The vast majority of cases are fixed with relatively low cost, and are detected by analysis well before it becomes severe. For example, oil analysis said a bearing in the torque sensor was going out for someone I know, the analysis is so sensitive they identified the exact bearing. $12K later, fixed before it even failed. Even burning up a first stage wheel will very likely be less than $75K.

The other fear is that one nanosecond of pilot inattention cooks the engine into a useless heap. Not really so. It is relatively hard to cook the engines and it would take a really clumsy pilot to do it, the same kind of pilot who would go full throttle on the GTSIO-520 with the mixture lean, a perfectly analogous kind of thing.

GTSIO-520 is $75K OH and it runs for 1600 hours, $47/hour.

TPE331-10 is $225K OH and it runs for 5000 hours, $45/hour.

That hour of the TPE331 is way more miles.

The last thing is that the King Air is among the most expensive turboprops to maintain. Since they are so numerous, that tends to be what people think of as general turboprop maintenance. That isn't the case for a lot of turboprops. That would be like saying you would never buy a 421C because a Duke costs so much to maintain.

My message is simple: turboprops are more affordable than most people think.

Mike C.

Gear up or gear collapse landing.

You are way over $75K.


That is HIGHLY unlikely, an engine that is totally destroyed, which is rare among already rare failures.

Things to consider:

You can buy used engines, for way less than $250K. This is common in the turboprop world, not so much in pistons. This can get you back flying for an exceptional event.

You can get an engine program. You pay $/hr and they take care of HSI, OH, and unscheduled events. You never face a big bill, just money all the time per hour. Very common in jets, not as much in turboprops but available, and unheard of in pistons as no vendor would take that risk.

FOD is perhaps the largest realistic "big" risk, but that is included in many turbine insurance policies. My policy covers FOD with a $25K deductible. If a rock gets thrown into my engine, and takes out the entire high speed group, then I'm out $25K, insurance pays the rest. Your piston insurance has nothing like that.


I have yet to hear of a $110K event in a TPE331. I'd think the engine would have to literally fall off the airframe to cost that much.

Worst case I ever saw was an MU2 K model with TPE331-6 engines where the prior owner had burned those engines to a crisp by repeatedly flying it well past temp limits from total lack of understanding. Yet the plane was still flying. A borescope revealed half the first stage wheel was gone. They did a hot section, $75K per side, new first wheel, new first stator, put everything right. This is the worst event I know of.

Mike C.

Insurance....

There is definitely some sketchy info online. I think you're comparing the instrument panel to rear bulkhead distance in the 421 to the cabin size of the MU2. I've spent significant time in both aircraft and owned a Marquise for 4 years and can guarantee they are NOT about the same size inside.

The Marquise cabin is slightly larger than the Conquest II and about 10% smaller than a B200.

>Gear up or gear collapse landing.
Gear up covered by insurance.

Are you saying that Gear Collapse on a turbine is not way more expensive than a pistion?

Mike I agree with a lot of what you say. One correction is the new GTISO520’s have a 2,000 hour TBO. If a Turbine has a nose gear collapse it can also be very expensive. Maybe not on some high wing planes.

I only talk to ATC when it’s required ,you have to talk to them all the time.
Most of my trips are 300nm or less and one or two people.
I have depreciated my plane to zero and can deduct new engines and Avionic’s.
I only have about 5 years left to fly at my age and do not want the hassle of learning how to fly a Turbo Prop or Jet that I don’t need even though I “could” afford one.

My 421C works perfectly for the type of flying and places I will going for the Next five years.

Mike, what does the 2500hr hot section inspection on a -10 engine go for? Just a point for the perspective TPE331-10 owner to keep in mind...….HSIs on -6 and -1 engines are at 1800 hours, with a 5400 hr TBO and there are some gear box inspections in there as well as I recall......just stuff to be considering when looking at turboprop ownership. Seems like there are more than a few turboprops with hot section inspections in their immediate future for sale.....

They can be anything from $20K to maybe $100K, worst case scenario. I would say the average is around $50-70K. Not a trivial sum, but I've calculated that you'd almost save that on not having to do oil changes every 25hrs, and mess with plugs. It adds up. The Aerostar was easily $500 per change with labour.

News to me, thanks. What change allowed this?

Now, how often do you get there? Without a top?

Apparently, this change has not made it into the TCM SIL98-9 OH docs.

It shows all GTSIO-520 engines at 1600 hours or less. I've attached the latest SIL98-9 that I can find, dated 2015. You got a newer one?


Mostly correct. I can, and do, fly VFR sometimes, but it is rare.

If you want to do the majority of your flying VFR, then a 421 is a better fit.

I find VFR flying far more work than IFR, I have to do everything including airspace and traffic avoidance. Guess it is just what you are used to.


Cool. Have fun with it!

Mike C.

Typically about $35K. The -10 engines are FAR better at HSI than the -5, -6 engines.


For the -1, -5, -6 engines, 1800 first HSI, 3600 second HSI and "TBO extension", which is really a gear box inspection (sometimes called GBI). Then OH at 5400 hours.

Typical HSI for -1, -5, -6 engines is $60-70K. GBI is ~$20K. So they do cost more for mid cycle work, so their per hour cost is a bit higher than -10, about $70/hour instead of around $55/hour.

The funny part is that my gearbox is a -6 gearbox since my engines are -6 converted to -10AV. Yet, by some magic, Honeywell says my gears can go 5000 hours with no GBI. But, a -6 engine, with the same gears, can only go 3600 hours. Yeah, don't make sense.

Further, depending on the burner can setup, my engine could be eligible for 3500 HSI and 7000 OH, no gear box inspection. So my gears can now go 7000 hours.

Sometimes these intervals make no logical sense, but the takeaway is that the engines last a REALLY LONG TIME, and they routinely get there without trouble.

Mike C.

Like Mike I now prefer to fly IFR as I just find the workload easier. But one of the good things about having an older TP is that they're actually ideally suited for the 15000ft-18000ft range and VFR. Mine really isn't well suited for much above FL220. Climbs slow and the smaller wing makes the AOA higher, so it actually flies slower up there. Its an ideal high alt VFR machine, actually. 17500ft is perfect for it.

Not trying to convince you at all, just a point of view on older TP's. You seem to have the ideal plane for your mission w. the 421.

One last insight:

The FAA recently clarified that overhauls are not mandatory for part 91. This has always been true, but the FAA letter really makes it clear and official.

What that means is when I reach the supposed overhaul time of 5000 hours, I can elect to do the HSI, since inspections are required, and then fly another 2500 hours to 7500 SMOH. We already know the gear box is good for that based on what Honeywell allows.

At my current rate of flying, ~150 hours/year, this is ~40 years from now. My plane would be over 80 years old.

Translation: my engines will likely never be overhauled, they are "lifetime" engines. The next 6000 hours, if the airframe makes it that far (and it certainly can), will cost me two HSI ($35K/each) and that's all I need to do. Including the 1000 hours or so I have already achieved, that works out to $10/hour for engines for ~7000 hours of use.

The kicker is that my engines will go to 7500 hours no problem. Some airline operators and ag operators take the TPE331 to 9000 hours.

And if, by some miracle, the engines reach 7500 hours and are running fine, then do another HSI and go to 10,000 hours!

Going past TBO in a GTSIO-520 is clearly possible as well, but not nearly to that extent. The intervals in turbines are just so large as to be effectively infinite for the owner operator.

Mike C.