Every reason! What do you want to know?
1. They need to be worked on by people that know Aerostars. You don't want mechanics with no experience working on them, as you'll be paying them to learn - and it's a steep curve. Good thing is there's quite a lot of experienced Aerostar shops spread around the country.
2. Airplane is built like tank (nothing structurally really compares). It' like a jet.
3. Plane is not expensive to own if you compare it to 414's ort 421's or turboprops, but can be more than a Baron and certainly Aztec's, Twin Comanches etc. You have two turbos on each side, and they'll need overhauling every 1000hrs on average. Same goes for waste gates. Not terribly expensive, but it adds a little extra compared to simpler twins.
4. The pressurization system won't add much, it's very reliable. The extra costs come from seals - if they have pinhole leak they'll make vacuum pump cycle a lot, which will fail it prematurely. Many do a mod that replaces the door seal with a dedicated electric pump, that saves the vacuum pump.
5. My annuals, were $7K for first (but that was probably pencil-whipped by seller), second was part of engine overhauls so hard to tell, and last one I did was $13K. If you plan on $20K annuals, you'll be in pretty good shape as it will cover a bigger item like a turbo or cylinder that might pop up.
6. They tend to eat MLG tires, so make sure they're tracking straight.
7. My 601P was very reliable overall, but part of that was that I overhauled engines midway. But even on the old ones (300hrs over TBO when I bought her!), she never let me down. In 200hrs I had one vacuum pump fail, a sticking wastegate and one set of MLG tires exchanged - that was it.
8. Fuel economy is great on the 601P (less so on the 700P), because it's so slippery and narrow. I could fly mine for 25gal/hr at 190-200kts up high LOP.
Finally, the reward for all this is the best flying twin in the world with it's push-pull rods. It flies like a dream - tight, like a little fighter jet (not that I've flow that). It's also a very honest plane that will tell you when it's not happy. It was certified without a stall warner just because it gives such ample warning when it's about to stall and buffets like crazy. But you have to fly it by numbers, can't be sloppy or get slow in a base to final turn. Need to stay on the speeds. If you do that, she'll never bite.
I loved my Aerostar. The lure of turbine just got too big, or else I'd still own it. And bang for buck, they're great buys. Just can't get anymore airplane for the money.
Here is the one I owned.
