OceanicPilot

Hey guys/gals,

I'm trying to find the Part 25 certification requirements for turbine powered transport category aircraft in regard to emergency descent requirements. Isn't there a time limit involved in descending to a more favorable altitude where we can all breath? ( I think it's 14k, right? )

The reason I'm asking is because I fly overseas and some of the instructors over here think that to meet the international RVSM requirements for an emergency descent ( turn 30 degress right, fly 20km which is basically a 12nm offset, parallel your original course, and then return to your course when able...where I fly anyway) you must actually fly the 20km at altitude.

I maintain that if I have a decompression requiring air to breath I'm going to direct the pointy end of my jet toward earth and descend while I'm offseting ( as the rvsm procedure allows ) Or am I overreacting? About 2 minutes to offset and then maybe 5 minutes for a high speed descent from max cruise ceiling is within the oxygen limits. Not sure how much longer a descent at failure speed would take in a fuselage damage situation. Haven't done one of those lately.

Anyway, does anyone know what the time limit is for certification?
Anyone,
Anyone,
Bueller??

Any help is greatly appreciated.

HSLD

Is this what you're looking for:

FAR Part 25 Sec. 25.841 effective as of 07/05/1996

rickair7777

What I know of physiology tells me that the 12NM delay might be incapacitating to the occupants in the 40's, and even high thirties due to DCS (the bends) caused by the decompression...even if it was not explosive. If you're a diver a rapid decomp at FL40 would be the same as sitting at 120' for hours (the cruise flight) and then popping straight up to the surface...at that point you need to re-compress real quick. For a diver that means a chamber, for flight crew and pax, that means hustle down to 10K.

100% O2 at 40K cabin pressure provides about sea level O2 partial pressure, assuming that there is enough O2 volume provided and are no leaks around the mask seal.

My guess on the offset would be that they want to minimize (not eliminate) the possible conflict with other traffic on the way down. It would also reduce the closure rate with any head-on traffic.

PW305

look in ICAO DOC 4444 "contingency procedures"... the procedure you're being taught differs substantially, unless the state you operate in has an exemption on file with ICAO. Where are you flying?

OceanicPilot

I saw that when I looked through Part 25 but I thought there was an actual time limit for the descent somewhere. I know that's why there is a limit to the maximum altitude that you can fly with a pack deferred, for instance, so that you can make the descent if you lose the other pack or decompress. It just states that the cabin altitude can't be above 15,000 feet or 25,000 feet for 2 minutes. I fly the Airbus and it has a cabin pressure limiter restricting the cabin altitudes to 14,500 +/-. I suppose that's all the guidance there could be and I was imagining a time limit. Part 25 gives the manufactures the out by saying those design ciriteria only apply to situations "not shown to be extremeley improbable".

We fly with the TCAS in below at cruise altitude so I'd do what I had to do to avoid traffic but I think I'm still not waiting the entire 20 km to descend.

OceanicPilot

I'm flying in China....everything is different over here. It is the most awful excuse for an air traffic system anywhere.