Turbine Duke cruise altitude and cabin altitude

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Morning guys!

I saw that the turbine duke as a service ceiling altitude of 28,000 but if you climb to that altitude the pressurization system cant keep the cabin altitude below 10,000. It only manages to keep the cabin at 11,000 or so and the aircraft displays a red warning. So what's the point? Why do you have a service ceiling of 28,000 if your pressurization system cant coupe? I guess its worst on the piston duke. Its service ceiling is 30,000 so i guess its cabin altitude must be 12,000 or so.

Do duke pilots climb to 28,000 anyway and ignore the red warning? Or they try to stay below 10,000 cabin altitude? 

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I wonder if auxiliary O2 systems are deployed for flights at those altitudes?

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This is not uncommon. A king air C90a I flew for years would reach 10,000 feet cabin altitude at about 25,000' but was certified to 30,000'. Just meant above 25,000 you were going to put on the O2 mask.


As to why..... possibilities include getting over weather(and possible ice which can be a biggie) and maybe picking up a good tailwind. I've seen 100+knots. I seldom went above 20-22,000'  unless for a good reason as I'm past 60 and didn't want to deal with the increased challenges of an abrupt loss of cabin pressure should it occur - I had one once and it was an eye opener. At 18,000' you have approx 30 minutes, at 28,000 a minute or two and these times are general - smoker/non-smoker, pilot's state of physical fitness weren't factored in. As a non-smoker and in the gym 3-4 times/week then and now I was confident that in the low 20's I'd be fine. That said, opinions are like @ssholes - everybody has one.

Most won't ignore the cabin altitude warning. It's there for a reason. There have been accidents that you can google and read. I got a ride about 30 years ago in a Mooney 252 (unpressurized) that was certified to 28,000 according to the sales rep and he said he used a canula at 28,000' with no problem.


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The Turbine Duke cabin has a maximum pressure differential of 4.7psi, which basically means the maximum possible difference between cabin pressure and outside air pressure is 4.7psi. In practical terms this means the Turbine Duke can maintain a cabin pressure equivalent to sea level while flying at 10,000ft (that is a cabin altitude of 0ft), and at the Turbine Duke’s service ceiling of 30,000ft it can maintain a cabin pressure equivalent to roughly 13,000ft (cabin altitude of 13,000ft)

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I was just reading the FAA rules regarding supplemental oxygen and i found this:

 91.211 Supplemental oxygen.
No person may operate a civil aircraft of U.S. registry t cabin pressure altitudes above 12,500 feet (MSL) up to and including 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration

Does that means it is ok to cruise in the Duke at FL280 without oxygen masks as long as the cabin altitude doesnt reach 12,500? I will stick to FL250 anyway but im curious to know if you can do this legally in a real duke.

@dbw1 how did you feel physically in that king air at that cabin altitude?

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In Canada we can go for a max of 30 minutes between 10 & 13,000' without supplemental O2. Your question as to if that could be applied to a pressurized aircraft with the same "cabin altitude" I can honestly say I don't know. Before retirement I was very knowledgeable out the Air Regs and knew where to find answers for most things but that question never came up.

As to how I felt at altitude without pressurization or O2...... about 20-25 years ago I spent some time in an E110 and after a couple hours at 10k I felt tired, draggy and when we took it to 13k I felt it for sure. Keep in mind I was past 40 and didn't exercise except what i got on the job which was considerable. This was my first fixed wing job after spending the better part of 20 years driving helicopters. Eventually I got into cardio exercise (and other stuff) and that changed my tolerance for altitude amazingly. 10k wasn't an issue then. About half my fixed wing career was in unpressurized aircraft. Exercise and not smoking are the biggest things to aid altitude tolerance....plus add to quality of life.

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Requirements in the US.

14 CFR 135.89 - Pilot requirements: Use of oxygen.

(a)Unpressurized aircraft. Each pilot of an unpressurized aircraft shall use oxygen continuously when flying -

(1) At altitudes above 10,000 feet through 12,000 feet MSL for that part of the flight at those altitudes that is of more than 30 minutes duration; and

(2) Above 12,000 feet MSL.

(b)Pressurized aircraft.

(1) Whenever a pressurized aircraft is operated with the cabin pressure altitude more than 10,000 feet MSL, each pilot shall comply with paragraph (a) of this section.

(2) Whenever a pressurized aircraft is operated at altitudes above 25,000 feet through 35,000 feet MSL, unless each pilot has an approved quick-donning type oxygen mask -

(i) At least one pilot at the controls shall wear, secured and sealed, an oxygen mask that either supplies oxygen at all times or automatically supplies oxygen whenever the cabin pressure altitude exceeds 12,000 feet MSL; and

(ii) During that flight, each other pilot on flight deck duty shall have an oxygen mask, connected to an oxygen supply, located so as to allow immediate placing of the mask on the pilot's face sealed and secured for use.

(3) Whenever a pressurized aircraft is operated at altitudes above 35,000 feet MSL, at least one pilot at the controls shall wear, secured and sealed, an oxygen mask required by paragraph (b)(2)(i) of this section.

(4) If one pilot leaves a pilot duty station of an aircraft when operating at altitudes above 25,000 feet MSL, the remaining pilot at the controls shall put on and use an approved oxygen mask until the other pilot returns to the pilot duty station of the aircraft.

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Are passengers, say in a King Air at FL25,  also equipped with supplemental O2?

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And that above 15,000 feet each occupant of the aircraft must be provided supplemental oxygen.

I believe that includes cabin altitude...


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