To presurize or not to presurize
 

A good friend of mine who is a I.A., was my college professor when I took A&P school and has over a thousand hours in a P337. I think his opinion is for all piston driven pressurized aircraft. He warns me not to get a pressurized 337 because it is so hard to keep the pressurization in good operating condition due to leaks. He makes a good argument with all the stuff that goes through a firewall and has to maintain pressure without leaking not to mention the pressurized magnetos.
Now for those who have p337's what has been your experience with them?
I know they would be great to have even if you didn't use the higher altitudes all the time but might not be worth the headache.
Is the pressure coming off the turbo or another device that I can't remember the name of at the moment.

This is where a test flight really pays off before buying. A leaky airframe will show itself through a lower differential cabin pressure. The max is 3.35 psi. My current P337 achieves it no problem. The previous one did as well. Not so an aircraft I looked at that only went up to 1.7 or so.

The pressurization system is actually pretty simple and mainly maintenance free. I just did a major annual and while there was a lot to do to get the aircraft up to the standard I wanted it at, pressurization was not an issue.

And it is a major plus when going places. It all depends on how you want to use your airplane.

Don't get me wrong I really want a pressurized plane even though I live in flat florida. Is yours getting its pressure from the turbo?

Pressurization comes both the front and rear turbos on the P337. Simply described, on the supply side, the air from the turbos goes through a heat exchanger and then into a plenum where it is distributed to the cabin. On the exhaust side, pressure is controlled by an outflow valve backed up by a pressure relief valve.

The front and rear system air have a slightly different routing. The front system air also passes through the janitrol heater manifold (which is why you can't remove the heater as I have seen discussed. I have yet to use the heater except when checking it).

You can isolate the front or rear systems by pulling the associated dump valve and operate on only one system. So in case of engine failure above high terrain, pressurization is retained although you might see a slight reduction in the differential. (on the Adams A500, pressurization was driven only by the rear turbo so if that system or engine failed, pressurization was lost). So good redundancy on the P337.

Richard

Had a '77 P337 for 3 years and 310 hours. The pressurization was rock solid once we found the hole some idiot put in the pressure vessel to run wiring through. I second the prebuy check of this system. It should make 3.35psi with no problem on either engine alone even at higher altitudes. If it doesn't, something is likely leaking and it will cost to find it, make the seller drop the price accordingly if you are going to buy the plane. FWIW, the P210 uses the same system and I have 3000 hours of P210 time and find that system to be quite reliable. It is the simplest pressurization setup around. The comfort it adds is wonderful and the ability to use higher cooler altitudes without oxygen is just great. Once you own a pressurized plane, you won't go back, trust me. Since you live in Florida, you might look into air conditioning for a P337, or plan to fly with the pressurization set to maintain a cabin altitude of 8000' or so.

+ 1 on the air conditioning. I am in South Florida and it is a game changer. I keep it on until reaching 7 or 8K when it is cool enough outside. It makes a huge difference to the flying experience for passengers too.

I get it now, I always wondered why people couldn't make a few minutes on the ground in non towered airports but never considered the time to reach altitude.

The pressurization system would be the last thing I would worry about on a P model. Very simple system but one must understand the operation. Once you understand it you will be able to troubleshoot most issues as the user. The P model is a special case and there are a lot of complexities that Cessna glued and taped together. Don't get me wrong, the airplane works well when it works right but it's also a mission based aircraft. It's not a Sunday hamburger, look at the scenery type machine. It's heavy, tight inside with limited ventilation and the cowls are packed to the gills with all the components required to "CONVERT" a non-pressurized airplane to a different catagory. The airplane was not "clean sheet designed" to be pressurized, not unlike other birds out there. If you want to go high and long distance then the P model may be the one but if you are looking to fly 200 miles or less a lot then the P model may not be the machine. Don't buy it for that ONE trip per year that you utilize the expensive extra features. The normal aspirated Skymaster will provide 99% of all the needs you may have and lot easier too.

It sounds like you are saying its great but with a lot of strings attached. We got to see on last weekend in panama city and really liked the roominess. It was a 4 seater non pressurized. we set in the back seats and there was plenty of room there too. Is the pressurized smaller on the inside?

Smaller than the original aircraft that were made before the G model, but not enough that it would be a deal breaker for most. All the Skymasters are very comfortable airplanes compared to most small twins and most singles. Obviously much roomier than the Mooney, Bonanza/Baron, close to the 182/210 but not as big as the 310, Saratoga/Seneca. Easier to enter and exit than the low wing aircraft too. Cessna narrowed the cabin a bit when it went to the P model, mainly because of the hull structure.

These Skymasters are complex airplanes compared to a 182, Cherokee 6 and maybe somewhat more complex than the light single retracts like the Arrow and 210. The low purchase price attracts single engine pilots to look and maybe buy. Some find that the upkeep causes finacial burdens and defers maintenance that should be looked at. Compared to a Baron or 310 or Twin Comanche the costs of ownership may be similar. Seems like Beech parts cost more, 310 have bigger engines and TwinCo's have smaller engines. As you increase the complexity with pressurization the cost of ownership can increase some. As with any of these light twins, maintenance needs to be a priority to keep the airplane in correct and complete working order. When shopping be very careful of Skymasters that have not been flown frequently and maintained thoroughly. If the airframe in clean but the plane has been sitting, plan on spending some money to get the plane up to the right airworthiness. A $20,000 annual would not be a surprise depending on the shop you work with. Prebuy is so important but being ready to spend some money is more important. There are some good buys out there but some of them will need some TLC. Not counting the avionics you desire and ascetics inside and out. I can't imagine what these planes would cost new today, I would take a guess at a million dollars would be close. Paying $100k for a good clean P model and then spending $50k to bring it up to specs is still a huge bargin. But it's all relative to what we expect to pay. Just plan some seed money for that first year (20% or more of purchase price) to get it right. Then you can start planning the panel upgrades and ascetics. With all the new approved items out there it's exciting to think of what may be possible in the next year or two.

They are great machines but have to be taken care of.