Deprussurization Oxygen chart A320

[C.M]

Did you happen to spot where this chart is in the new versions of the A320 FCOM ?

4097

[bbear737]

Surely you should be at FL140 at the 12 minute point (when pax O2 runs out) rather than at FL180 at 12 minutes then descending to FL140?

[Sidestick_n_Rudder]

They hid it pretty well :{

Try Procedures->Special Ops->Flight without pressurization

[C.M]

Indeed they did ! Thank you very much!

[320p]

Could someone please explain as to how this chart is drawn and the calculation behind this profile.

Thank.

[C.M]

I cannot provide at the moment exact answer but just above the table in the FCOM states :
“The capacity of the units is such that the aircraft must descend and remain below the following profile.” Is this a certification of the O2 units based on the worst possible scenario that could exist on earth ? (Emergency descent over the Himalayas ?) just a thought .
Another thing that puzzles me is that since the reaction to produce oxygen for passengers is chemical ,you could expect that it should last a defined period of time , but apparently it doesn’t . Could it be the less ambient oxygen in the cabin the faster the reaction is , thus lasting less ? That could be the case actually , purposely designed like this ....once you descent to a lower altitude the oxygen demand for a living being is less thus the unit can sustain you longer

[nicolai]

There may also be a desire not to expose passengers to low oxygen levels for too long. While the passenger oxygen system will supply sufficient oxygen for survival in the short term, people can develop issues if suddenly raised to, and kept at, a high altitude.

For example if you drive up Mauna Kea in Hawaii, ascending from some 2500ft at the saddle between it and Mauna Loa to the peak at 14000 feet, it is not an altitude that you definitely need oxygen for. However if you don't rest at the half-way station you are quite likely to suffer altitude sickness. Some people suffer altitude sickness at the peak anyway, and certainly their movement, cognition, etc, is affected. This would also be affecting the cabin crew who don't have the long-duration oxygen supply of those in seats 0A and 0K.

Passengers with pre-existing circulatory or breathing problems (including a lifetime of puffing on the evil weed as in many parts of the world) may well not tolerate FL140 indefinitely, or even for a fairly short time. This time at F140 may be a compromise between allowing routing over higher terrain with the 30min@FL140 to escape to lower terrain and a higher chance of long term passenger health effects.