I have a question about the “maximum operating altitude” in the POH of the SR22 (17500ft).
What is this altitude? Density is going to significantly impact maximum operating altitude meaning this number can alter depending on environmental conditions. Should this not be a density altitude?
Is maximum operating altitude referring to a legal certification altitude limited by structure/power plant/function/instrument ability? Can you fly above this altitude?
Maximum operating altitude in airliners are limited by three things:
Certified ceiling
buffet margin
thrust margin
Environmental conditions adversely affect all these requirements meaning maximum operating altitude could be lower/higher than stated in POH. This is determined by density.
There are no tables in the POH stating altitude capability charts other than climb rates.
The altitude is exactly what it says it is. It’s the highest altitude to which the airplane was certified during the certification process.
There are different certification requirements for specific operating altitudes and manufacturers will often certify only to one altitude so as to avoid requirements to fly above that altitude
A maximum certificated altitude does not mean the aircraft cannot fo higher, it just means it is a violation of the regulations for it to go higher.
You see the same sort of thing with maximum takeoff weights. Any plane with a MTOW of over 12,500 pounds requires a type rating, so manufacturers will often establish a MTOW of 12,500 pounds to eliminate that requirement even if the plane could easily and safely fly over that TO weight.
Better question is why would you want to go above 17,500’ in a NA? I had a TN for years and even then never went into the flight levels outside of training. The risk/reward just wasn’t there for me.
Note that it does NOT say density or pressure altitude. So, I take it to mean the indicated altitude shown by a properly set altimiter.
Sec. 23.1527 — Maximum operating altitude.
(a) The maximum altitude up to which operation is allowed, as limited by flight, structural, powerplant, functional or equipment characteristics, must be established.
(b) A maximum operating altitude limitation of not more than 25,000 feet must be established for pressurized airplanes unless compliance with §23.775(e) is shown.
Huh? I regularly fly at 13-15K sometimes starting near sea level. Takes around 15 mins to get there for an average of 1000fpm. Plenty of headroom to go higher.
I’ve been to 17500’ multiple times traveling VFR eastbound with a naturally aspirated 2018 G6 SR22. This was usually to take advantage of tailwinds. It’s fun doing 160 kt TAS and 230-240 kt over the ground. No problem.
I’m honestly not sure why 17,500 was chosen for the NA SR22. The SR20 has the same but it will never get there.
The 22 however gets there and has more to spare (at least in my climate)
My C185 doesn’t seem to have a max operating alt and gives performance numbers in the manual for “20,000 ft” and it would easily get there despite being NA.
I’m not privy to the company’s rationale. I would guess that it involves 14 CFR 23.2125 which required “The applicant must determine climb performance at each weight, altitude, and ambient temperature within the operating limitations.” So it might be due to the design of their flight test program. They appear to have picked the highest VFR altitude (17,500 ft MSL) as their target. The highest altitude given in the 3400 lb and 3600 lb SR 22 performance tables is 17,500 ft pressure altitude (found in the time, fuel, and distance to climb chart).
I suspect you are correct. The manufacturer can arbitrarily set a limitation on altitude and there is no need to document anything higher than that altitude.
There are some limits prescribed by the FARs and some equipment requirements, but otherwise, I think the operational limits are set by the manufacturer during the certification process. And that becomes a legal limit for operation of the aircraft.
