135 Oxygen requirements.

[Humty72]

Ok,

I am looking for some input on the interpretation of FAR 135.157 O2 requirements. I am unable to justify or relate the (b) portion of the regulation to the oxygen duration chart in a King Air B200 (for example). To me the chart does not seem to be able to cover the 2 hour requrement for crewmembers. An example would be for 2 crewmembers and one passenger at about 1500 psi would give you about 50 minutes. I have been unsucessful in my attempts to find a good explanation of this regulation, and I can't seem to figure out that language in section (b)... Any help would be appreciated.. Thanks

 

[soarby007]

Are you talking about 135.157(b)(2) when the cabin pressure exceeds 10,000' MSL & 135.89(a)?

 

[Humty72]

yea.. what is your take on that portion.

 

[soarby007]

I may be wrong, but the way I read it is that if the cabin pressure exceeds 10,000', you have to comply first with 135.89(a) as an unpressurized aircraft and either stay below 10,000' MSL or use oxygen between 10-12,000' if for more than 30 minutes.

If you are going to continue to fly as an unpressurized aircraft above 10,000' msl (135.157(b)(2)(a), and not comply with 135.89(a) then you have to have a two hour supply.

I don't know of anyone who is going to choose that option, nor of an aircraft that I have flown that has the capacity to carry that much oxygen, since normally oxygen use is for emergencies. It seems that they put this 2 hour supply in there to force you to choose to descend between 10-12,000' msl if longer than 30 minutes or below 10,000 msl if longer. A 10,000' cabin pressure is the benchmark chosen when oxygen becomes a concern in the daytime I guess. I've had a couple of cabin pressure failures in the King Air and chose to descend below 10,000' msl.

I don't know if this helps or not.

 

[pilothouston123]

well said soarboy.