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deathwish
21st Dec 2002, 13:55
Flying through Brest airspace yesterday when we heard Easy ?5?6 in an emergency decent to FL100. Obviously his RT was through an Oxygen mask. He got the wx for Nantes and was then handed over to another frequency. It all happened at around 13:35z.

Does anyone know more? I'm surprised no-one else has posted anything.

SAS-A321
21st Dec 2002, 14:21
Most likely a depressurisation of the cabin. They went down to a FL where you can breath the air.

lomapaseo
21st Dec 2002, 14:33
I may be chastized for asking this question here, but I also read about a chinese airliner encountering a similar problem last week (MD82) and descended at such a rate that several people were treated for ear problems, etc.

I always assumed that under the initiating conditions (high altitude) that the masks would drop and then the descent rate would be set to provide a safe margin before blackout (for those that bothered to don their masks).

My question is there a typical rate for descent for this condition?

Orangewing
21st Dec 2002, 14:38
No, there isn't. Just get the thing down.:D

James T. Kirk
21st Dec 2002, 15:23
lomapaseo,

the ear problems would have been caused by the rapid depressurization not the ensuing descent. If the pressurization problem is gradual rather than rapid or explosive then you can descend at or slightly faster than the cabin rate of climb. You have to be pretty sure that the gradual depressurization is not just a precursor to a rapid failure though.

Kirk outů

In trim
21st Dec 2002, 16:45
Cracked windscreen....precautionary diversion, but obviously involving a fairly steep descent simply to get down quick!

Appears to have been well handled. Passengers fed and watered in NTE until a rescue aircraft was sent in a couple of hours later.

JW411
22nd Dec 2002, 20:02
The main and only real reason that commercial aircraft have to make an emergency descent when the cabin pressure is lost is simply because they have passengers in the back!

The drop-out oxygen "should work" and those punters who have actually taken the trouble to listen to the pre-flight safety briefing instead of reading the oil futures in their FT will be able to select a pretty basic piece of breathing equipment from above their heads. This will keep them alive while the crew get them down to 10,000ft in about 3-4 minutes.

Sadly, a small percentage of the masks are likely not to deploy as advertised. If it is a real structural problem then there could also be a certain amount of fog, dust and s**t around the place at which point "well-travelled-and-don't-need-to listen" FT man starts to wish that he had listened and looked during the briefing!

If you have an ear problem then you simply should not go flying. (In fact, the first 1000 feet on the way up is the real indication of a problem).

No crew does an emergency descent for fun! Certainly it would be a considerable embarrassment at 30░W. Not many airlines carry enough fuel to complete such a journey at 10,000 ft with full reserves. (Even at 14,000 ft with the equivalent of single-pack operation it is likely that your relieved punters will spend a fortune in the Duty Free in Shannon instead of "grumbling off" at Heathrow or Manchester).

Happiness is freight - I can stay up there without a single worry for I shall run out of fuel long before I run out of oxygen!

Few Cloudy
22nd Dec 2002, 22:59
Well some questions have been asked and not really answered

- ROD if you start from around FL350, boards out and max
mach/IAS will zero out around 5,000 fpm depending on weight -
higher wing loading types such as the MD-80 would go down
faster still - a wide body generally less quickly

- You might not want to fly at Max speeds, however if you have
structural damage

- Pax oxygen lasts for 15 minutes - crew oxygen much longer

- pax have to be on oxygen >Fl130 - Flight crew > FL100

- FL 100 may be below minimum safe altitude on your route, so
there is a lot to think about

- Ear damage during decompress is rare - the problem is the
descent when the air is trying to push its way back into the
eustachian tubes (nothing to do with Euston Station...)

blueloo
23rd Dec 2002, 03:16
Other day in a 767-200 Sim, descent from FL350 to 10,000 at Mach 0.85/350kts (Limit is 0.86/360kts), ROD was around 7,800fpm.

vertigo
23rd Dec 2002, 08:35
Yet when I ask for a good rate..........:D

Bally Heck
23rd Dec 2002, 11:09
Cracked windscreen? Emergency descent?

A cracked windscreen is to all intents and purposes a non event and indeed it is possible to dispatch with a windscreen cracked subject to some restrictions.

Surely this wasn't the cause of the emergency descent?

Few Cloudy
23rd Dec 2002, 11:11
Vertigo!

You have the right name! These rates are strictly emergency things - not a daily norm - and very uncomfortable for all on board - and, I suspect for ATC too if they don't expect it.

If you really need an emergency rate though and say so, sure you can have it.

Moneyshot
23rd Dec 2002, 14:49
Had a couple of cracked windscreen incidents on the 1-11. In reality, total non-events as the book said to just descend to less than FL250 (to give less differential pressure). One of these was into MRS (charter for world cup 98). After reviewing our procedures and actual degree of damage, the French Stazi were more than happy to allow us to fly back through their airspace for the return leg back to STN.
In the EZY case, if the guy on the radio sounded as though he was on oxygen, it is unlikely that this was a cracked windscreen. I hesitate to speculate until someone with definite knowledge of this incident comes forward.

Mister Geezer
23rd Dec 2002, 20:28
Sounds like just a normal descent profile for any low cost operator! :D

411A
23rd Dec 2002, 20:45
If JW411 thinks that just because he flies a freighter aircraft, cabin pressurisation can be ignored, he is in for a very big surprise.

Supplemental oxygen is there for the flight crew to use IF normal pressurisation is lost or in the event of smoke/fumes and definately NOT to be used for long periods at high altitudes. For that you NEED proper pressure breathing equipment, and crew supplemental oxygen....ain't it.
To think otherwise may well result in a quick trip to the cemetary, never mind the hospital.
Beware...sometimes young guys are misinformed, as in big time:eek: :eek:

JW411
24th Dec 2002, 09:40
Actually dear boy, I probably know more about pressure breathing than you do and I am certainly not a young whippersnapper as you seem to imply.

Perhaps my last sentence was somewhat flippant. What I was trying to impart was that I don't have such a hell-fired need to make an emergency descent and can be somewhat more methodical about it.

Lou Scannon
24th Dec 2002, 11:45
It may be a good idea to remain at altitude in a cargo aircraft when depressurised.
If there is a fire in the hold, getting all the crew onto oxygen then dumping the pressure might be the best way to get it under control.

JW411
24th Dec 2002, 19:00
411A:

Further to my last posting I have had some further thoughts on the subject and would like to make the following comments:

The first time I ever got involved with an oxygen system was more than 40 years ago when I was on advanced flying training in the Royal Air Force flying the DH Vampire. This consisted of a simple constant-flow system with the option of a 100% setting. The oxygen mask was an "H" Type which had a vent plug on the side.

Now then, we used to crawl up to 38,000 feet with this pretty basic apparatus with the purpose of making "high speed runs".
None of us had any difficulty with this and I cannot believe that we were being asked to do something with fatal consequences.

The first pressure demand system that I came across used the American A12A regulator. This was a great improvement over the constant flow system and, incidentally, when fitted to one of my gliders for the purpose of mountain wave flying, at least doubled the endurance of a 750 litre O2 bottle!

I have in front of me Volume 6 of the RAF's AP3456 entitled Aviation Medicine and Survival. In Part 1 Section 1 Chapter 2 which deals with the Physiological Effects of Altitude and at the end of Paragraph 19 it states:

"The oxygen concentration required at an altitude of 34,000 feet in order to maintain an alveolar PO2 (oxygen pressure) of 100 mm Hg is 100%.

20. Ascent to altitudes above 34,000 feet, even whilst breathing 100% oxygen, results in the alveolar PO2 falling below that produced by breathing air at ground level, ie PO2 of 100 mm Hg, breathing 100% oxygen at an altitude of 40,000 feet produces an alveolar PO2 of about 60 mm Hg ie an intensity of hypoxia equivalent to that produced by breathing air at an altitude of 8,000 - 10,000 feet. Ascents to altitudes higher than 40,000 feet breathing 100% oxygen gives rise to significant hypoxia. As indicated by the corresponding alveolar PO2's, the intensity of the hypoxia produced by breathing 100% oxygen at 45,000 feet is slightly more than the hypoxia produced by breathing air at 18,000 feet. The maximum altitude at which it is acceptable to fly an unpressurized aircraft, considering hypoxia alone, when oxygen is breathed at ambient pressure, is 40,000 feet. In the event of decompression of a pressurized aircraft when rapid descent is initiated immediately the cabin pressure falls, breathing 100% oxygen at ambient pressure will provide adequate protection against severe hypoxia at cabin pressures up to 43,000 feet. Severe hypoxia can only be avoided on exposure to altitudes above 40,000 feet by increasing the total pressure of the gasses in the lungs above the pressure of the environment, a technique termed positive pressure breathing- usually abbreviated to "pressure breathing".

As far as I am aware no airliner is equipped for the wearing of pressure breathing equipment by the crew. Most are equipped with a pressure demand system with Normal, 100% and Emergency Flow options.

So if we were (in the interests of flight safety) to summarise the preceding information I think it would be reasonable to assume that most systems are adequate to sustain life at a maximum height of 34,000 feet. Therefore, if you regularly fly above 40,000 feet then you should be very aware that you should get down to at least 34,000 feet pronto.

Personally speaking, I have not been above 40,000 feet for 20 years. In fact, I have not been above 35,000 feet for 15 years.

This takes me back to the last line in my original posting in which I said:

"Happiness is freight - I can stay up there without a single worry for I shall run out of fuel long before I run out of oxygen!". I stick by this statement but I should have added "on the current equipment that I operate".

In any event, there should be no reason on earth for a freighter to have to descend to 10,000 feet for they do not have a rubber jungle in the back and that was my original point!

Lou Scannon has also raised a very interesting and important side issue about the fire suppression issue.

No doubt you will spend your Christmas Day scanning the pages of pprune trying to figure out just who you are going to attack next so let me take this opportunity to wish you a Merry Christmas and a Happy New Year.

PS. We are still waiting to hear how your Oakland chappie managed to try to start all 4 engines on a DC-6 at once when it appears from the DC-6 chaps that this is impossible.

PPS. Was his Chief Pilot Bill K...... by any chance?

PPS. Knowing what a stickler for accuracy that you are the dead centre of town on this side of the Pond is a "cemetery" not a "cemetary".

Semaphore Sam
24th Dec 2002, 20:51
Freight Drivers:
Assume Left Seat, Rt Seat (& F/E, if appropriate) are on oxygen. Most long-haul is augmented or double; there are loadmasters, mechanics, sleeping relief crew on-board. I would get the cockpit safe (on Oxygen), then GET DOWN, as the non-flying guys may be asleep (permanently, if the cockpit guys have attitudes demonstrated in previous posts). Unless you know nobody is in the aircraft except those present in the cockpit, I wouldn't think twice; I'm down! Then check. The sequence is critical.

411A
25th Dec 2002, 01:30
Suspect you are waisting your time Semaphore Sam...some it seems have their collective minds made up.

And...yes JW411, it is possible to turn over all 4 on the DC-6 at one time, at least with the older start panel...but not to start four at the same time. Ignition boost works only on one engine at a time.
Chief Pilot Bill K...? Ah, no actually, was Capt Roy B.... Superb fellow from long ago (1969).

And...a Happy Christmas to you sir!:)

JW411
25th Dec 2002, 09:53
Semaphore Sam:

I don't carry loadmasters, mechanics or sleeping crew members; only operating flight deck crew all with a full oxygen system.

On the very rare occasions that we carry extra guests, we are restricted to F250 for that very reason.

Merry Christmas