View Full Version : Emergency Descent over mountain

30th Apr 2004, 10:13
Any one have any tools or tips for emergency descent over mountaneous area like IRAN where grid mora as high as 18000 wide spread? The biggest concern here is the passenger's oxygen available limited to only 10 to 15 mins. Airbus has recommended descent profile but not specific or insufficient explaination. What about Boeing ?


30th Apr 2004, 10:54
It is effecitvely an operator's issue and the relevant oversight agency's. Oh, not to forget, once the inevitable hits the fan, all of the sudden the commander is the responsible party. :yuk:

Very little to do with manufacturers, in fact, I don't think Boeing pilot books mention it at all. :cool:

The relevant guidelines are to be found in the OPS regulations, dunno which one do you use.

The European JAR-OPS1 boils down to this: if you have a limitied pax O2 supply, you need to be at 14000 ft cabin press alt before it runs out. Once depleted, you have 30 mins to get to 10000ft.

Both apply at the same time, i.e. once the masks are deployed, it is the time to 14k ft and the time + 30' to 10k ft. (A/C certified above FL250)

Fly safe,

Silly me, the most important part left out:
If you cannot make the times, speeds, profiles and mountains move to fit, you are not eligible to fly there!

30th Apr 2004, 15:22
Yeah, :ok:

In the airbus special ops, the pictorial descent profile explains as such aircraft must be at or below FL 180 within t +5 mins, and may maintain this level (max) until t +12 (oxy depletes at t + 12++) then descent to FL 140.

why the initial descent must be at or below FL 180 not higher ?
will there be any complication if maintain higher (eg: human factor, oxy on demand).

If no, can I safely say aircraft may maintain as high as possible as long as at the end of t +12 (oxy deplete) aircraft must be at FL 140?:ugh:

30th Apr 2004, 17:04
I believe that BA deliberately had to increase the Pax O2 capacity for 747 flights over Afganistan as the mea was in the 180 region.

In North America fl100 is good east of Calgary-160 to the west(until0 you get the specific Mea.
In the states fl180 west of Denver.

1st May 2004, 06:11
our 777ER has 22mins O2. we regularly fly over iran and we had developed an 'escape route' with the avail O2.


4th May 2004, 15:45
I can't find any other reason, most likely FL180 max. is to minimised the decompression sickness. (nitrogen bubbling etc.) think so ?:}

4th May 2004, 16:18
Sir, I do not know what post or operator do you work for. However, once the FL180 is in your approved manuals I believe it is binding no matter what anyone thinks.

So far you have not told wheter you operate under FAA, ICAO, JAA or other framework. Until then it is complicated to come up with any more relevant ideas.

If you are trying to find grounds for not obeying certain requirements or justify some operation that cuts corners, as a crewman I cannot relate to or take part at that. And no aviation professional will.

Just my thoughts, fly safe.

4th May 2004, 23:04
clickclick - the higher you are, the more oxygen you use, even when breathing it through an (allegedly!) airtight mask. I can't remember the medical explanation behind it all - something about the body "exhaling" oxy through the pores as well as the mouth and nose, so the exhalation rate is higher at altitude due to oxygen's decreased partial pressure - but the short answer to your query is that if you maintain F180 for longer than the book says, then you (or your pax) will run out of oxygen quicker than the book says.

As someone else mentioned above, it is the operator's responsibility, at the flight planning stage, to ensure that the route allows the oxygen descent profile specified by the manufacturer to be met. If it can't be done, then another route must be flown. Often a specific escape route has to be constructed, and the crew should be aware at all times of were they're going to go in the case of depressurisation - that's what they're paid for.

big bus driver
7th May 2004, 20:42
My airline produces tailored pages in the Jeppesen manuals specifying airway MSA's and 'escape routes' (generally lower than Chart 60nm square MSA's) which allow the aircraft to be flown i.a.w with the descent profiles within the FM.

Our Airbus can remain above FL140 for 22 min, Boeings 14min. You can remain between FL140 and FL100 for upto an additional 30 min providing you have supplimentary oxygen for at least 10% of pax (I think).

Without the tailored pages, it would be impossible for us to remain within the JAR rules, yet stay above chart MSA's in the event of a decompression at certain points along the VG81/UL223 accross Turkey and Iran.

8th May 2004, 15:47
In the company I work for we regularly fly over Iran & the company produce escape routes for us, which we insert in the secondary flight plan so it's ready in the case that all hell breaks loose.

13th May 2004, 16:40
It does not matter if either JAA, ICAO or FAA. When comes to human limitation they all should be very similar if not same.

Just wonder why this particular operator (classified), that I discovered through the net, allows emergency descent (due to rapid decompression) to stop descent at FL 250 for some ammount of time before continue descent to 10000 unpressurized.

What about decompression sickness above FL 180.



13th May 2004, 18:45
I recall FL250 being a rule of thumb on the classic over the Atlantic where you stopped descent to ensure you had sufficient fuel to get to an Alternate before descending further. Shouldn't really apply on more modern a/c.

15th May 2004, 22:13
Just a little suggestion in the event that you do have to whistle on down in a hurry over mountainous regions-keep a rough idea of what the SAT should be at prevailing MSA and try,whilst you deal with a thousand and one other thoughts,to keep an eye on actual SAT in descent,looking for that cold weather altimetre error that could take you a little too close to the granite!!!! I dont know how much ISA variation you can expect seasonly at typical MSA altitudes over Iran/Afghanistan but descending over the Alps I usually notice -25deg at around 20,000ft. more often than not.
Route 2 updated with escape route and current diversion approach plates in view seems to pass the time quite nicely.

17th May 2004, 08:26
That is quite another story. What is good for the man and what complies with the regulations. :yuk:

The JAR-OPS1 (Appndx to 1.770) in certain notes speaks of "constatnt rate of descent from the plane's max certificated ops alt to nn nnn ft in mm minutes. Still, I believe it does not in writing preclude an intermediate level-off in order not to hit the ground or for other reason. Wheather it is wise, I do not know.

On the other hand I think it is common sense that if two manual have different limitations on a same issue, both need to be met.

No matter the good will of all involved sometimes a discrepancy will be created and then it is up to the expertise of oversight authority (but they're folks like us anyway) or someone like you who cares enough to notice.


Squawk 8888
20th May 2004, 01:42
As for FL180 recommendation, I vaguely recall reading that somewhere in the range of FL200 even pure oxygen is not enough. IIRC the body requires ~5 inches Hg oxygen pressure in the lungs, so if the atmospheric pressure drops below that the masks for the pax aren't adequate- you need to force the oxygen into the lungs to stay alive.