P-ceiling vs. T-ceiling

[skystudent]

I'm new to the group. I've done some searching on this subject, but haven't found the answer. Sorry if I missed it:

The P337 is certified to 20000 and the earlier T337's to 31000. In the following aritcle,

http://www.superskyrocket.com/pages/.../history_2.htm

"The later T337 and P337 models are only certified to 20,000 feet, whereas the earlier turbo models have no such limitation, a quirk of changes in the certification standards that took place in the 1970s."

Questions:

Is the "low" ceiling for the P337 indeed a certification "quirk." Is it a real performance limitation (i.e. convergence of Vx and Vy)? Is it due to pressure-differential limitations on the fusilage?

Is it legal to fly a P337 above 20000?

If it is legal, any experiences you can relate?

What's the skinny, please?

Thanks in advance. This seems to be a knowledgable and friendly forum and a great find.

[kevin]

A P337 is not certified about 20,000, so it is not "legal" to fly it up there.

Depending on outside air temperature and power setting, the P337 will frequently not maintain full cabin pressurization very much above 20,000. The rear turbocharger on this aircraft is the controlling factor.

According to the best information I have, the P337 will fly above 20,000 if you running a high power setting, and does fine up there. Above 25,000 is probably not practical.

To answer the next question that frequently comes up, no, there is no way to "turn off" the pressurization and use the turbo output just for the engines.

The T337 turbochargers are not the same units as the P337 (and it's not the same airframe, a different airplane really). The T337 turbochargers serve only the engines, and in that airplane, you can get a higher service ceiling assuming you have the right oxygen equipment (pressure demand mask above 25,000' if I recall correctly). Remember that 31,000 on the turbo is a true service ceiling - rate of climb less that either 50 or 100 fpm, I can't remember, and you are probably getting 55% power or something like that. The actual operating ceiling that one might really use is lower, perhaps in the mid to high twenties.

Kevin

[Paul Sharp]

My 1967 T337B has factory O2 and is certified to 33K feet. I don't think that a demand diluter system is actually required above 25K feet, but it is highly recommended.

I think the most limiting factor these days for the T models is the 25K ceiling more or less implemented by the new RVSM regs.

[Ken MacLean]

Originally Posted by kevin

A P337 is not certified about 20,000, so it is not "legal" to fly it up there.

Depending on outside air temperature and power setting, the P337 will frequently not maintain full cabin pressurization very much above 20,000. The rear turbocharger on this aircraft is the controlling factor.

According to the best information I have, the P337 will fly above 20,000 if you running a high power setting, and does fine up there. Above 25,000 is probably not practical.

To answer the next question that frequently comes up, no, there is no way to "turn off" the pressurization and use the turbo output just for the engines.

The T337 turbochargers are not the same units as the P337 (and it's not the same airframe, a different airplane really). The T337 turbochargers serve only the engines, and in that airplane, you can get a higher service ceiling assuming you have the right oxygen equipment (pressure demand mask above 25,000' if I recall correctly). Remember that 31,000 on the turbo is a true service ceiling - rate of climb less that either 50 or 100 fpm, I can't remember, and you are probably getting 55% power or something like that. The actual operating ceiling that one might really use is lower, perhaps in the mid to high twenties.

Kevin

Do you know what creates the 20,000 certified ceiling for the P337? Is it pressure differential about that altitude? Can the outflow valve be opened to maintain the approved differential and breathe oxygen instead? In other words, is there a legal way to fly a P337 above FL200?

Thanks.

Ken MacLean

[JeffAxel]

Ken,
The FL200 limit is an operating limitation, so it is not approved or legal to fly higher. The cabin altitude in a P337 is 10,000ft at FL200. I am not sure why they limited the P337 this way. The P210N has the same pressurization setup, but can fly to FL230 where the cabin altitude is 12,100ft or so. The R model P210 is approved to FL250, but you must wear oxygen above FL230. It also shares the same 3.35psi pressurization setup.

[Ken MacLean]

Thanks for the info. I presently have 3 airplanes for 3 different missions and a P337 would replace all 3 if it could legally go to FL250. That would save a lot in insurance, hangaring, maintenance, etc. (I already know about 337 maintenance with my T337C.)

Is FL200 in the limitations section of the POH? Also, I haven't seen anywhere an FAA definition of "certified ceiling". Where is that found?

Thanks.

Ken

[JeffAxel]

Ken, the limitation is in the Limitations Section of the POH.

[Red Air Rambo]

I've seen 210 with no problem.

[Sapper]

Originally Posted by Paul Sharp

My 1967 T337B has factory O2 and is certified to 33K feet. I don't think that a demand diluter system is actually required above 25K feet, but it is highly recommended.

I think the most limiting factor these days for the T models is the 25K ceiling more or less implemented by the new RVSM regs.

RVSM is FL290 - FL410, so you could go up to FL280.

[jchronic]

As someone whose normal Skymaster flying never takes them much above 1000 feet, this discussion is somewhat academic to me. But thought I'd throw out something for you high-flyers to keep in the back of your mind: getting down from up there in the event of an emergency.

Short sea story from my airline days: Had a rapid decompression in a DC9 at FL350 and as we configured the airplane for a rapid descent, it began a violent buffeting. Natural assumption was some kind of structural failure/damage so we elected to descend at 230-240 KIAS instead of M.8/350KIAS. It was about the longest 15 minutes of my career, thinking the airplane might be coming unglued.

Certainly not a reason not to fly high if the mission calls for it, but remember that it will take some time to get down from up there.

Joe

[Red Air Rambo]

Originally Posted by jchronic

As someone whose normal Skymaster flying never takes them much above 1000 feet, this discussion is somewhat academic to me. But thought I'd throw out something for you high-flyers to keep in the back of your mind: getting down from up there in the event of an emergency.

Short sea story from my airline days: Had a rapid decompression in a DC9 at FL350 and as we configured the airplane for a rapid descent, it began a violent buffeting. Natural assumption was some kind of structural failure/damage so we elected to descend at 230-240 KIAS instead of M.8/350KIAS. It was about the longest 15 minutes of my career, thinking the airplane might be coming unglued.

Certainly not a reason not to fly high if the mission calls for it, but remember that it will take some time to get down from up there.

Joe

+1 , however from my 7 trips to the altitude chamber during 22 years of military service I can tell you that time of useful consciousness at 35,000-37,000 is around 5 minutes at best. 18,0000-20,0000 is 30+ for most (we never spent more than 30 minutes at 18,000 before climbling up and no one went out). With the warning systems on the aircraft, gear down and spoiler's out (if so equipped) you can acheive 2000 fpm and be below 12,500 in 3-5 minutes. If you need more time use mask's.....at least for the pilot, if oxygen equipped (and u should be if venturing into the flight levels). Having been part of the squadron that intercepted Payne Stewart's plane I know about altitude's effect all too well. That said I love the tail winds in winter when flying east and I like the weather below me!

[wybenga]

The P is not certified above 20,000 because it does not have an emergency exit and it operated on a waiver for supplemental oxygen which was not standard on the airplane as certified