Is it possible to de-rate a pressurized aircraft?

[YankeeClipper]

I've read plenty about the benefits and costs of pressurized cabins. I'd love to cruise 10k with nary the pop of an ear (truly--I have terrible issues with my ears and pressure changes), but the costs of a P-model are just beyond the budget for my mission. But if I could take the quiet and weather resistance of the P, and lose the maintenance and insurance costs, it would seem ideal. Nice thing is, it is not unreversible, unlike, for example, welding up gear for similar objectives.

[YankeeClipper]

To clarify, I'm wondering if it is possible to remove--for lack of a better word--the pressurized rating of the aircraft, so as to remove the constraints and obligations associated with that (insurance, oxygen, etc). Naturally, I would also be flying it as a non-pressurized aircraft at that point.

[klpilot]

Originally Posted by YankeeClipper

Naturally, I would also be flying it as a non-pressurized aircraft at that point.

Why not save the hassle and buy a non-pressurized airplane in the first place then?

[YankeeClipper]

As I mentioned in the original post, the pressurized hull has several perks over the non (along with some disadvantages too, of course).

[YankeeClipper]

Wanted to post a follow up for posterity.

According to a local IA, you cannot de-rate, however, you don't have to fly with the pressurization working. In other words, you can decline to fix issues with the pressurization system, as long as the IA believes it doesn't pose a threat to safety or proper operation (beyond pressurization itself).

Alas, those issues are, according the same source, but a fraction of the costs associated with 'P' models. The obstruction of the additional systems accounts for much of the additional costs. The extra boost of the 225 turbo, unless faithfully reigned in by a determined pilot, burns up components a little more quickly than the 210 turbos, and much faster than the NAs. This, not from my own experience.

[rrolland]

Your IA is correct. You can choose to opt to fly with the pressurization inop. Just like you can choose to fly with it turned off (there is an on/off switch).

You cannot remove the system in however -which I think you mean as de-rating- as the pressurization system is linked and a part of other systems such as heating (combustion heater) and ventilation. By opting to fly with the pressurization inop, you end up carrying the weight of the system for no benefit.


As mentioned somewhere else though, the pressurization system has proven reliable for me. As have the turbos.

[hharney]

The pressurization system on the P model is probably the simplest systems in the aircraft. Other than leaks in the pressure vessel, there is really nothing else that is a concern. It works well but is only a 10,000 ft cabin at 20,000 ft. When comparing pressurized planes that's not much differential. There is a purpose for the P model so don't make it what it isn't. The added weight to the P model is substantial so why would you buy one and then not have a use for the very purpose of the model? I could never understand when folks wanted to make the 337 a fixed gear airplane. But I am sure someone could come up with a reasonable reason.

What's the mission, as you have described in other threads, buy the model that fits the mission. One thing to consider is the environmental system (cabin heat) for the Turbo and the P model is a Janitrol gas heater. With the normal aspirated models the heat is directly off the mufflers. The Janitrol can be a finicky item and expensive. Maybe you are familiar with them, have you had a gas heated aircraft? I have always thought simple is better but in some cases the mission requires the gas heater.

With your mission being 1-3 hours twice a month in the North East it may be that a normal aspirated Skymaster will do a really good job for you. These flights may be easily accomplished with the standard NA airplane. If weather dictates ICE there is NO Skymaster model that can launch into Known Ice. So if weather keeps you from going and you have to be there then you are looking at the wrong airplane. If you can say leave a day earlier or stay a day later for the weather to pass then the Skymaster will do the job. Even the P model at Flt Lvl 160 or 180 won't get you over most summer weather. It may provide a better ride but you will still be deviating for build ups. You didn't mention how many seats are required. If most flights are 1 -2 people then a heavy plane with work but if you need 4 seats for adults then the P model can be restrictive. Fuel loads for 1-3 hours are pretty simple in any of the models. The occasional long trip every year will require a fuel stop but once a year is reasonable. If you can afford the P model price and upkeep then it's a great tool for what it does but there are a lot of Skymasters sitting because someone bought them and can't keep them in the air. Fuel cost and maintenance grounds them because the low purchase price attracts a buyer that can't maintain the airplane. Therefore it makes for a difficult quest to find a good, well maintained Skymaster aircraft. The good ones just aren't listed for sale because the market won't justify selling the aircraft for the money they are worth. Owners keep them because they love them and can't really justify something else.

Bottom line, find a 337 that has been taken care of, that fits your mission or be prepared to spend some money to bring the airplane up to standards. The best Skymaster to buy won't be listed on all the usual sites. It is being flown regularly, maintained and you will have to sweet talk the owner in selling the plane.

[YankeeClipper]

Some great additions to the library, Herb. Much appreciated.

I've already approached the only skymaster owner I know of in this area about selling. He's not even remotely interested, even in time sharing. So I guess I'm in for a fixer upper. Either that, or someone who just lost a medical

My mission, as you have correctly sussed, is to be able to make some relatively short trips around the east. Anything from Prince Edward Island down to the Outer Banks (out of CT). Those look to me to be somewhere between 2 to 3 hours depending on the model you fly. As my other thread pointed out, I just wasn't sure which model actually fits the mission, considering that I don't know which if any model will get me over these 15000 foot tops that we've been seeing a lot lately. But you've pointed out now that the pressurized isn't likely to fulfill that. So that kind of settles that. From what I read the turbo is able to go considerably higher perhaps because of its lighter weight, I'm not sure. Or, perhaps it's that the pressurization has an all too sudden failure beyond a critical point.

The potential for the turbo to climb higher over that weather, or faster out of sudden icing conditions, is what allures me to forced induction in general. So then there's the cost justification you alluded to. You may recall that Ed had posted very detailed numbers on his normally aspirated, which came out to about 12 thousand a year in maintenance over the course of nine years. But then one of the recent posts on my other thread suggested that that was a high number for a normally aspirated and perhaps more in line with a turbo model. If the latter is true, then I'm definitely good with the cost of ownership on a T. But if Ed's numbers on a normally aspirated are correct and to be expected of a reasonably well maintained aircraft, and a turbo really will run about one-and-a-half to two times that cost, then ownership of a T starts to become less justifiable for me, even if I can swing it.

By the way, your comment in video about getting butterflies before a flight, even for an experienced pilot, was reassuring. For starters it means I'm not just chicken. But it also means that a critical appreciation for the gravity of what it is you're undertaking can stay with you after all those years. Those butterflies are there to keep you alive. Hope they travel with me always, personally.

.

[edasmus]

"if Ed's numbers on a normally aspirated are correct"....

These words, quoting your last post, is a tricky statement. Maintenance expense isn't really a matter of "correct" or not. There are so many variables that go into what maintenance will cost that accurately forecasting it's numbers is like forecasting the weather. You can study the forecast until your blue in the face but in the end what ya see is what ya get. Now that's not to say we shouldn't make a good faith effort to make sound decisions based on we think will happen or is likely to happen, but in the end, when it comes to owning a Skymaster or any other airplane for that matter, if unplanned maintenance expense is going to break the bank, then do not own an airplane. They are always more expensive then you plan for them to be.

BTW, I just reread the post you referenced regarding my maintenance expense and though I am not looking at the actual numbers for the time that has passed since I wrote that, the continuing expense of the airplane to this date has been in line with that post. My annual in February of 2018 ran around $8000.00 going on memory.

Ed

[YankeeClipper]

Thanks for the update, Ed. Was curious about that.

It's not about breaking the bank, so much as justifying it. I'm only going to be flying about 72 hours or so, in other words 6 hours a month. So I'm trying to figure out if it's really worth carrying something like a pressurized model if they really are 2 times the cost of Maintenance compared to yours. For those hours it may not make sense to be spending 16 or 18 thousand in maintenance alone on a normal basis.

[hharney]

Just my opinion, but I think Ed's maintenance costs are on the high side of average. I have only really owned one Skymaster but dad had an original 67 model before this model that I have now. Saying that I have been maintaining this C model I have since 1994. I have been through both engines, I used factory remans, 20 years apart from each install.

I have used a handful of maintenance facilities over the years. Some have been what I call normal and some have been overpriced and overrated. My normal aspirated bird over the last 25 years has probably averaged $2500 to $3000 for annuals. There are always the known and unknown items that come up on some annuals so that number goes up but my average means that I have had a lot of annuals in the $1500 to $1800 range. I can remember a couple not more than $1200. There are shops out there that are just more expensive and I think that is where Ed is at. Is the maintenance better? In some cases yes but not always. I had a couple shops that got me for numbers that Ed is quoting. I didn't go back. I think it's good for a different set of eyes to look at the plane at times but remember every time you go to a new shop you are paying to educate the shop about your plane. I get very comfortable with shops that I frequent so I think it's best to have a second opinion, or at least I used to. I been doing my own annuals for the last 10 years. Really ever since I did my restoration on my plane in 2008 I have done 80% of the annuals including an engine exchange. That's where you really save some money. Not everyone can take the time to do this I understand but I have grown to really know my plane. Most of my annuals now are very routine. I tend to be doing more proactive items than reactive items because stuff is all good.

I don't know where the idea that a pressurized model is 2 times the maintenance cost? I don't believe it and probably is less than 1 1/2 times if the aircraft is kept up. You have to fix stuff that breaks because it will lead to more issues. It's the first annual after buying the plane that can be a shocker as it's normally a shop that has never seen the plane and will want to really go over the plane in fine detail. If the plane was purchased at a discounted price then it may have not been flown and not been properly maintained. That will cost you some money the first couple years. I think we can all agree that this has been discussed across this board many times.

Find the right plane that fits the mission and prepare to spend some money the first couple years. But there is no guarantee that you may need an engine too. There is just always that risk buying someone else's problem. So do your homework, as you are doing, and really find the right plane or save some money to make the right bird fit your mission. But saying that just because it's a P model you have 2 times the maintenance is not correct. Not even close. A non-pressurized turbo model can be even less than the P model. And in some cases the turbo model will be very similar to the normal aspirated. The only diff is turbos, which really don't require much and the gas heater.

Just my thoughts, and not trying to dis Ed's expenses just trying to compare with whats out there.

[edasmus]

No “dis” taken Herb. 😊

You’re likely correct in your opinion. I pay for convenience of a home airport shop at a relatively large Chicago corporate type airport. I figure only a handful of cities across the country would match our high prices. BTW, standard T-hangers here go for between $400 and $500 per month. This may aid in giving some reference comparing costs as well.

[YankeeClipper]

Ah! I wish! Six hundred here in the NYC tri-state area, IF you can find one open.