Question About Service Ceiling

[pilotposer]

Hello,

If an airliner decompresses, the pilots immediately get down to an altitude of 10,000 feet so the passengers can breathe.

Why is it that early aircraft, such as open cockpit planes, have service ceilings above 10,000 feet altitude.

The Boeing Stearman has a service ceiling of 13,200 feet. What exactly does service ceiling mean?

Thank you,

[tiger1962]

The service ceiling for each aircraft is the limit of the airframe and engine(s) safe operation.

All unpressurised aircraft are limited to less than 16,000ft because humans can't breathe at or above that altitude.

[pilotposer]

I understand now, I thought 10,000 feet was the threshold for humans.

Thanks Tim

[lnuss]

For light aircraft the service ceiling is typically the maximum density altitude at which it can still climb 100 feet per minute. Note that the official published figure for a given aircraft is at maximum gross weight, and the altitude is density altitude, which is the actual altitude adjust for temperature, pressure and humidity changes from standard conditions (higher temps and lower humidity mean less dense air). Put another way, the spec is for standard conditions, which are 59º F (15º C), 29.92" Hg (1013 mb) and 0% humidity at sea level, with the temperature dropping 3.5º F (2º C) per 1,000 feet altitude increase. So the temp at 5,000 under standard conditions is 41º F.

 

There are other criteria that can affect such specs, especially for jets or other aircraft that get up to 20K+ feet (roughly).

[pilotposer]

Thanks all, I'll just keep these old birds well below there maximums.

[lnuss]

All unpressurised aircraft are limited to less than 16,000ft because humans can't breathe at or above that altitude.

 

Actually, that's not really accurate, since oxygen masks allow humans to breathe, depending on the design of the oxygen system/mask, to fly at up to 45,000 feet, or so -- above that pressure suits are needed if no pressurization. The Information Manual (IM) for a 1979 Cessna T210N cites a service ceiling of 27,000 feet, for example, and it's not pressurized, but does carry oxygen. The normally aspirated (not turboed) Cessna 206 has a service ceiling of 15,700, but the turbo version has a service ceiling of 27,000 feet. The North American P-51 was not pressurized but routinely operated at altitudes well in excess of 30,000 feet, and at least in some tests could exceed 40,000 feet.

 

I thought 10,000 feet was the threshold for humans.

In unpressurized aircraft, supplemental oxygen is recommended for people flying at and above 10,000, and is required for the crew when at and above 12,500 for 30 minutes or more, and for everyone when at and above 14,000 at any time.

 

There are people in high mountain areas such as the Andes or Himalayas who live most of their lives above 10,000 feet, some a lot higher.

 

Pikes Peak is at 14,110 feet, yet they have lots of people visit there, and even people working in the facilities there, though there legally are time limits for those who work there.

[tgibson_new]

Here is a Northwest Airlines Lockheed Lodestar probably crossing the Rockies with the passengers using supplemental oxygen:

 

https://www.mnopedia.org/sites/default/files/styles/multimedia/public/HE1.5%20p46_oxygen%20masks.jpg?itok=UTqyokcT