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  #1  
Unread 01-20-10, 03:08 PM
Flyer22 Flyer22 is offline
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To P or not to P, that is the question

I am looking into the various costs of owning and operating a 337. I am currently in a toss up between a P337 and unpressurized, T337.

The pros of pressurization are obvious, while the advantages of unpressurized aircraft, other than costs, seem to be in the higher certified service ceiling, ability to seat 6, and possibly more interior space. Can anyone verify?

Can anyone quantify the additional costs of operating a pressurized Skymaster such as maintenance, training, and insurance?

Thanks
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  #2  
Unread 01-20-10, 05:18 PM
Dave Underwood Dave Underwood is offline
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I have operated a P337 now for 10 years now. Yes, you are limited to 5 seats, but as anyone will tell you, the 337 is really a four seater carrying a tonne of luggage. The rear seats are very small and not easy to get into. Kiddi seats at best. I have never installed the 5th seat and save on the insurance.

As for maintenance, not much real difference in equipment from a T. You have a pair of dump valves on the rear fire wall and an altitude controller. As there were smokers in my plane at one point, I had to have the dump valves overhauled early in my ownership. You also do have a door seal which can be an issue. Replacements are expensive. I have considered an inflatable seal, but the beer budget always gets spent on something else.

If the aircraft does not pressurize, you are in for a bit of an voyage of discovery to find all the leaks. Once done, everything remains stable. Finding the leaks and fixing them all may take a bit of time. If you can find a place with the right equipment and experience, the challenge is reduced. We have used a leaf blower with much success. You can hear most leaks.

One thing as it is a pressure hull is that any holes, for say a new antenna or GPS require a DER approval with hoop stresses being a concern. That means a doubler plate and enough rivets of the right strength. There are many DER's, but you might want to search for references on this site for Ray Torres of RT Aerospace.

Some of the systems are slightly different, but not a major deal.

Flying is no different from other 337's I have flown. That said, it is very nice to be in cruise at say 18 k, above all the traffic and weather, but not wearing a nose bag. ATC also treat you differently in the high altitude sectors, the exception being they might think you are a turbine, but you're not.

The one consideration is to always be thinking about the decent profile. At 1000 fpm from 18 k to say sea level is 18 minutes and if you are doing 180 kts plus on the decent you need to start a long way back - 3x18 nm. If you take slow rate, even further out.

There are a few training considerations. Emergency decent being one, but it is all pretty well spelt out in the POH. You don't need a high altitude endorcement, but as you are approaching the danger zone above 18k, it might not be a bad idea, though not required until you are flying over 25k.

They are a great IFR machine when equiped.

Hope that helps. Let me know if you have any other questions.

Regards - Dave
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  #3  
Unread 01-21-10, 10:44 AM
Flyer22 Flyer22 is offline
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Thanks for the reply. I flew cargo and pax over the Rockies for a 135 operation in some (unpressurized) Navajo's, so I am familiar with trying to go down and slow down without shock cooling, as well as operating with oxygen.

I am also hoping to find a 337 w/ Gami injectors and run LOP. It seems like I should be able to fly 1000nm in the high teenes with a bit of tailwind if I have an aircraft w/ the long range fuel option.

I am sold on inline thrust and turbocharging for my family missions out of Denver, and yes, the 5th seat is for future kid.

Do you think that you have higher insurance rates with the pressurization than without?

Are there any required annual recurrent training requirements that you don't see with an unpressurized 337?

Thanks
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  #4  
Unread 01-21-10, 05:14 PM
Dave Underwood Dave Underwood is offline
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I run GAMI's and although it does help to lower consumption a bit when LOP, I still use a range limitation of about 800 to 850 nm. My age I guess. I also like to always have at least an hour in the tanks or more when I land. Age again.

On cooling, I always try for no faster than 2 " a minute on decent, but you have had that experience with the Navajo. I think it is all about decent planning and telling ATC what you want and when you want it by.

On insurance, you would have to check with your supplier. Here in the UK it does not seem to make any difference. I'm paying about the same as a T337 based on discussion. Again insurance is different here. I suggest you shop around. There is one broker who specialises in 337's who's rate were ok in the past and also offered pretty good service, but also try Avemco as well.

There was another thread on insurance costs - suggest you search.

On training, I would suggest you spend some time flying with someone familar with flight in the high teens. It is different and you do need to be thinking about how to quickly loose 6 to 8 thousand feet with out bending the plane but staying awake at the same time. I am ok up to about 15 k feet as a non-smoker who would claim to be fit (ok I am big build) and have skied that high with out problems after the second day.

Recurrent training in my experience does not cover pressurised flight, more standard procedures on the 337. I did RTC for my initial training and they were pretty good as John had a 337 at the time.

As I suggested earlier, although not required, get a high altitude endorsement and I woudl think the insurance folks would be happy. It also gives you the knowledge & understanding of both the flight and human issues.

I view having a P the same as having A/C in my car 20 years ago. As soon as I had experienced it I would find it very hard to buy a car with out it. That said, I also occasionally fly non-pressurised aircraft and it is no big deal either way.

On long legs, I always find higher has less turbulence and less traffic, more directs and you are above most weather.

I would suggest if you are looking for a P to get one with de-ice as it does make the decent through ice layers a little more comfortable. That said, the plane will still fly with a lot of ice, but then again, you are a test pilot with no control over the conditions.

Hope that assists.

Blue Skies - Dave
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  #5  
Unread 01-21-10, 05:19 PM
Dave Underwood Dave Underwood is offline
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In the above post, please translate all occurances of "decent" as "descent".

OK, all decent descents are great. Too late and too tired..

Dave
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  #6  
Unread 01-21-10, 07:34 PM
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hharney hharney is offline
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I just have to pipe in on this discussion too. I think this topic deserves more input around the camping environment at Sun N' Fun. You should plan to come out and actually kick the tires of all these models. SOAPA is counting on having at least one of each for those interested parties to be able to stroke these birds in person. Just a suggestion.

As for me on this topic, I always say "what is the mission"? If it is high altitude MEA's and longer distance flights then the P model might be warranted. I flew in the mountains for the first 20 years of my piloting hobby. Only had the privilege of turbos (C320) with one of 4 aircraft that I had some time in. The Skymaster's were all normal and typically flying in the low to mid teens for most cross country flights. I flew very little IFR then so MEA's were usually not in the picture. But if a person was flying IFR, in the west, over the mountains, the P model might make better sense. Now a resident of the mid west flat lands, a P model really doesn't compute for me. I typically always file for cross country now but the MEA's are below 10K. From 8-10K is the normal Skymaster's best friend. I can say that turbos and pressurization would be nice but there has only been maybe a handful of times that I really needed it. When comes to maintenance I am really glad I have the normal. My IA is too. He works on both and the normal does make life a lot easier. Skymaster is a great airplane, whether it's a P model or just the normal depends on the type of mission you are going to use it for. Most of my flying is just recreational and maybe a half dozen long flights a year. I really like the performance that I have with the lighter weight for the type of flying that I do. I enjoy unimproved strips, back country and weekend warrior flying.

Coming to Sun N' Fun this April will give a great opportunity to see aircraft and talk to the pilots. A huge advantage before you buy. Be careful out there because the Skymaster has been known to have a fair share of ramp queens. A good thorough pre-buy is a must. Make sure you select the inspector that is familiar with Skymasters but not the specific plane you are inspecting. You probably know this routine, good luck and hope to see you in Lakeland.
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  #7  
Unread 01-21-10, 09:04 PM
djarrett djarrett is offline
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Smile

flyer22
That is a great Idea for you to go to sun and fun your see all kinds get lots of ideas.
I fly p337 back and forth across the country at least once or twice a year and into the bahamas and the other islands. I fly at 16k one way and 17k the other and it works great. only diferance would be if the winds are crazy and Then I go down and get below the teens. I fly out of Montana and the p337 is the ticket to get out of the mountains and go down the the road. The p337 is also great for low alt and sight seeing. There is no problem of getting down, is just and matter of droping the gear and one notch of flaps great speed breaks. See you at sun and fun N268 Yvonne and DAve
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  #8  
Unread 01-22-10, 05:33 PM
aldoradave aldoradave is offline
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I have had my 73 P337 for just a year but really like the plane. MOst of my flying is out west and VFR through the mountains, but spending a lot of time where traffic might be a problem.

I just hate to reply to ATC with "no joy" and that is one of the important benefits of my P model. Normally I climb quickly to 13.500 or 14,500 and my cabin pressure doesn't get much over 9,000 ft. At those altitudes you just don't find a lot of traffic as the turbine boys are way above and the NA ones are well below.

Having the 5th seat works out OK for me as I have three small kids. However I have ordered the cargo pod from RT Aerospace for a more comfortable cabin.


Dave Dillehay
N84E
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  #9  
Unread 01-25-10, 03:30 PM
Flyer22 Flyer22 is offline
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Thanks for the great replies.

I think a trip to SnF would be a must before I buy, although I probably will not get out there this year.

My typical mission is Denver to Atlanta, just about 1000nm on the dot, and I would like to make it eastbound non-stop. That means high altitudes for both fuel efficiency and tailwinds, as well as LOP operation. Other missions include the Bahamas and some westbound travel from Denver, as well as "flightseeing".

As Denver residents we are acclimatized to 5000ft, and frequently drive/hike/bike/ski above 10,000 ft with no ill effects, which is not the case for people who reside at sea level. Therefore, we are a little more capable of hanging out at high altitudes, be that 12k w/o pressurization, or 20k w/ cabin pressurized to 10k as would be the case with a P337.

I guess I am just trying to figure out the maintenance and insurance hits. So far, from your inputs, they don't seem to be showstoppers.
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  #10  
Unread 01-25-10, 10:08 PM
djarrett djarrett is offline
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good luck on 1000 mile legs I have140 gal plus and I plan on 190Knts . I thinks if you have a little wind or or if you use less than 30 gal per hr. you won't get the speed. you figure it out. If you can plan on 1000 per leg you will land short. I plan on three to three and one half hour flight are just fine with me and then I have lots of fuel to if things go sideways.
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  #11  
Unread 02-03-10, 11:10 AM
Shalimar Shalimar is offline
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To "P" or not to "P", that is the question

Very interesting thread, to all that's been said; as the owner of P337H, N64N I would add the following: It's an ideal aircraft for the mission that you describe but I do agree that thousand mile legs will put you at the limit of range. Certainly beyond my comfort level, but that's an age thing as someone commented.
Except for anything requiring penetrating the pressure hull, the pressurization adds little in terms of maintenance. The systems are small and I have found them to be very reliable. If you need to penetrate the hull, that's a whole new challenge, both to reseal if you are going through an existing opening or to go through the DER process if you are adding something like an antenna.
That said, I have found maintenance on the P's to be substantially more complicated than on a normally aspirated 337. I am an A&P/IA and do my own work and the engine compartments are crowded, almost nothing can be accomplished without removing other components and systems which, of course need to be reinstalled, but wait, while its out let's inspect and repair. A friend once remarked that the P337 has all the systems of a King Air without the room to work. It helps to be a watchmaker with the arms of a Chimpanzee to get in there and do stuff.
The pressurization system makes the aircraft very warm, hot in fact. You are sealed in this capsule and the compressed air from the pressurization is hot until you get to altitude. May not be a big problem in Denver, but it is in Phoenix where I fly. Once you are at altitude, it can get cold so a properly working heater is a must. The Janitrol heaters are another system that requires maintenance and is subject to an AD. No big deal but just one more system that requires maintenance and takes up front engine compartment space.
Insurance is a giant pain in the butt. Insurance companies must think that this is some kind of mini-airliner because they insist on recurrent training and the premiums are very costly, much more so than a non-"P". There is another thread that talks about this.
All that said, the P Skymaster is a fantastic aircraft. Great performance in a small package, relatively economical to own and fly. My recommendation is to find an A&P/IA who knows the plane to do a thorough pre-buy and to do your maintenance. Also consider attending a CPA 337 systems and procedures course, very valuable.
Best to you
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  #12  
Unread 02-03-10, 08:17 PM
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Frank Benvin Frank Benvin is offline
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The first P models had 128 gal and the newer ones 146gal Correct me if I am wrong. We had a 73P Flew form Vancouver Island to Reno / Reno to Pheonix We had to really watch fuel on the first leg with a head wind. If you are planning longer trips I would go for the larger tanks.
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  #13  
Unread 08-15-12, 12:06 PM
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I'm resurrecting this thread because it's the exact question I have. I'm a potential P337 buyer, but probably not until later next year. The reason I'm asking now is that I can make it to Groton, but if I decide not to get a P337 there are a few other unpressurized planes that I might choose over the 337 and attending this year becomes less of a priority.

Some of the reasons I think I need a P337:
I frequently visit short strips (2200' paved with no obstructions, 2500' paved with trees one end, 2900' grass w/ no trees - all less than 1000'MSL elevation.) The bulk of my flying is north of 40deg latitude. I have a 4x/year route that goes south around/thru JFK/LGA, PHL, BWI and DCA and the deviations I get are horrendous. From what I've heard if I can get to 15K or higher I'll get much straighter routing. I've been routed over 150nm off course in a single flight. I won't go out over the water in my single and it does poorly above 12,000'. I'm also sick of picking my way through local summer weather at 9,000-11,000 ft. My wife gets headaches if not on O2 above 10-12K and neither of us are fans of the nosebag.

So onto my specific questions. I have searched the site and read 100's of messages, but I still have an unanswered question or two:

1) Re: Cabin temp with pressurization. Can you turn off the pressurization until you're at altitude to keep incoming fresh air temps down? Can you bypass the pressurization intake and get direct fresh air? If so, is there any problem with turning pressurization on suddenly at altitude? If not, how much above outside air temp do you see the cabin temps during climbout?

2) How much do the intercoolers help with incoming cabin air temps? If you can estimate an actual temperature diff in degrees F that would be great.

3) If you have a P337, what's your actual empty weight? What have you added that bumped it up significantly? What's the lowest empty weight I'm going to realistically find on a P337 without AC?

4) What are the differences between the 73-77 T337G (I think this is the official Cessna code for the early pressurized aircraft) and the 78-80 P337H? For some reason this is tough to find. It's often listed as "minor changes." I have found differences by manufacturing year (seat rails, tanks) but not by model letter.

So, please - talk me out of a pressurized plane!

Thanks for your help,

Jim C

Last edited by JimC : 08-15-12 at 12:09 PM.
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  #14  
Unread 08-25-12, 07:28 AM
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No replies? Was it too many questions?

Let's just try one line of questioning:

How much does your Turbo or Pressurized 337 actually weigh empty? What's the gross? What's your year & model?

I can find the book figures; I'm interested in real-world answers. I have yet to fly a plane from any manufacturer that's actually as light as the factory numbers.
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  #15  
Unread 08-25-12, 08:03 AM
Dave Underwood Dave Underwood is offline
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A reply

I will be back in my office in the next day or two and will pull my latest wt & bal and have a look at my various manuals to try and answer some of your questions.

D
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