posted on Oct, 11 2018 @ 02:41 PM
originally posted by: network dude
a reply to: The GUT
But it is proposed to happen in the Stratosphere, which is well above regular flight levels.
That is not necessarily true. The stratosphere begins just above the tropopause, which can be as low as 23,000 feet near the poles. It is usually at
about 33,000 at mid latitudes and 66,000 feet near the equator. Because (primarily) of airframe pressurization limits (think Comet) older airliners
usually cruise at the low to mid 30s. The certified service ceiling for all 737s, except the 737-max, is 37,000 feet. On the Max, it is 41,000 feet.
On the 757, it is 42,000 and on the 767 it's 43,000. I fly a 747-400 and we're certified to 45,000 feet (with pressure demand oxygen delivery masks.
However when we're hauling passengers instead of freight, we don't like to go that high. At 45000 feet, the partial pressure of ambient oxygen is only
about 24mmHg. Since alveolar oxygen partial pressure is 104 mmHg, if cabin pressure is lost, your lungs try to pressurize the cabin instead of the
other way around. Since the passenger emergency oxygen system is a demand re-breather type and not a pressure system, they are only effective for a
short time. So if the cabin is lost, it's time to (very) quickly turn ignitors on, pull all thrust levers (throttles) closed, throw the speed brakes
out, kill the autopilot, and shove the nose over to dive at .88 Mach or Vmo and head for 14000 feet or lower (unless you are over the Rockies, Alps,
Himalayas or other granite clouds.
edit on 11-10-2018 by F4guy because: forgot about passenger safety