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MD83FO
29th Jan 2012, 16:46
Wandering if there is another reason besides terrain to maintain FL 180/7min
FL140/30 min. For 13 min oxy sys.
Is it recommended (terrain permitting) to descend straight to FL100 ?
Someone suggested its recommended to fly the profile to let the body adjust.

Thanks many.

aviatorhi
29th Jan 2012, 21:51
Wandering if there is another reason besides terrain to maintain FL 180/7min
FL140/30 min. For 13 min oxy sys.

Is someone telling you to stop your descent prior to the MEA and/or 10,000 feet?

Is it recommended (terrain permitting) to descend straight to FL100?

If you have a rapid decompression, almost always (I'd stop for traffic if I absolutely had to, but just until it's no longer a factor).

Someone suggested its recommended to fly the profile to let the body adjust.

Adjust to what? A significantly higher altitude than you're leveling off at? "The body" just got a surprise ride to 30+k feet from between 4k to 6k, since you want it to be at no more than 10k, why would helping it "adjust" to 180 or 140 be desirable?

While there is a possibility of decompression sickness for any altitude change, the possibilities of it occurring from an RD are extremely low. It's a lot more common in underwater activity, where 33 feet of water come down on you with a pressure of the entire atmosphere above water (in laymans terms, the body of someone diving who goes from about 30 feet to about 10 feet is rough;y equivalent to an RD).

misd-agin
29th Jan 2012, 22:55
10,000', or less, for depressurization.

The 17,000', 25,000' etc restrictions are for terrain restricted areas.

I-2021
30th Jan 2012, 10:11
It gets quite cold during a rapid decompression and it is a very very stressing environment. Your life as well as cabin crew and passengers one is attached to that oxygen mask, so you will be really looking forward to go to lower levels, where you can breath in a probable hyperventilation status (you'll be quite stressed) and where the temperature is more user friendly.

Cheers

mustafagander
1st Feb 2012, 08:16
Where is it written, in what FCTM, that you don't descend to A100 as soon as possible provided that there is no terrain problem?

The punters are under great stress, get them to a benign environment NOW.

wiggy
1st Feb 2012, 10:06
Surely this whole debate is moot until we have the type the OP is asking about ( maybe his/her handle is a clue).


10,000', or less, for depressurization.

The 17,000', 25,000' etc restrictions are for terrain restricted areas.

That doesn't apply to all aircraft, some have an initial descent to FL150 (terrain allowing) and only a subsequent descent to FL100 when fuel vs. range to alternate allow (think overwater mid-ocean,ETOPS .... and yes it's in at least one aircraft's FCTM/FCOM).


While there is a possibility of decompression sickness for any altitude change, the possibilities of it occurring from an RD are extremely low

Maybe, but you can certainly start getting the intial symptons ( joint/ache tingles)... in any event I've never ever heard of perfroming a stepped descent simply to allow passengers to adjust...and you're going the wrong way, so to speak, to need for decompression/safety stops.....:ooh:


As always I'm sure it's all in the relevant FCOM.......

aterpster
1st Feb 2012, 14:10
mustafagander:

Where is it written, in what FCTM, that you don't descend to A100 as soon as possible provided that there is no terrain problem?
The punters are under great stress, get them to a benign environment NOW.

It is written loud and clear for those who fly in western South American.

MrHorgy
1st Feb 2012, 15:59
Forgive my ignorance, but why, in non terrain critical situations, do we not descend to FL100? I'm speaking more in Europe as the US has the TL at 180, but surely if the MSA/MEA is around 5000, it makes ATC separation a lot easier?

In a real situation over London, I think i'd want to descend to either 090 or 080 (depending on direction) as it means I won't smash into something else! Or am I missing something here..

wiggy
1st Feb 2012, 16:31
Forgive my ignorance, but why, in non terrain critical situations, do we not descend to FL100

Because not all aircraft are the same, not all FCOMs ( Flying manuals in old money) are the same, and not all flights are fuel planned in the same way. ( and jet aircraft burn more fuel per mile the lower they fly)

One example - Mid-Atlantic on some aircraft on some routes, if you unthinkingly blast straight down to FL100 it is quite conceivable you will then have insufficient fuel to reach any of your nominated alternates....in fact on a bad day you might not have enough fuel to make any land at all...that's why some airlines/some manufacturers FCOM's state that in the absence of significant terrain always halt the decent at an intermediate level, in our case FL150, (the level used for the planning of a decompressed diversion), and only continue down to FL 100 when landing is assured. You're not going to kill passengers at a cabin alt of 15000, seeing as they're seated and not required to perform any exacting mental tasks then the majority will OK. As a result the cabin crew can begin selectively taking passengers off the masks, saving the gas for the minority who may need it


In a real situation over London, I think i'd want to descend to either 090 or 080 (depending on direction) as it means I won't smash into something else! Or am I missing something here..

:uhoh: :uhoh:

Yep, I think you have. If you do descend to FL80 or FL90 you'd better hope you miss all the traffic in the OCK/BNN/LAM and BIG holds, all FL 70 and upwards, plus the stuff heading into the holds and all the stuff climbing out of the various London Airports.

Personally in a "real situation" over London ( in fact just about anywhere these days, even the ocean) there's so much metal flying around I might take at least a few seconds, having got crew and passengers onto Oxygen, to coordinate and/or at least declare a Mayday before initiating any descent at all.

thermostat
4th Feb 2012, 02:19
First, I would descend at the Vb speed (turb penetration). Keep the aircraft in tact. Who wants to loose the tail or a wing? Don't "Red line" it.
Next, atmospheric pressure is 50% at 18,000 ft.
The emergency is from 40,000 ft to 18,000 ft. Thats where you need to get down in a hurry.
Below 18,000 ft there is no longer an "emergency". You still need to descend but it's not that critical any more. They will live at 18,000 and below.
We are still following procedures that were put in place just after the war and it's time to upgrade them.
Don't be a puppet. Start thinking.

misd-agin
4th Feb 2012, 04:01
My checklist -
O2 on,
establish crew comm.,
if cabin uncontrollable - pax O2 on,
"WITHOUT DELAY: Emergency descent accomplish"

ATC coordination comes later. Aviate first.


It does not say to descend at turbulence penetration speed. They want you getting down UNLESS there is concern about structural integrity.

Denti
4th Feb 2012, 06:31
Yup, on my type it is a descent to lowest safe altitude or 10.000ft whichever is higher at a target speed of Mmo/Vmo with speed brake extended. At normal cruising levels one could extend the gear as well which would enable a Mmo descend but not Vmo anymore (320kts instead of 340). Only if structural integrity is in doubt we have to limit our speed.

wiggy
4th Feb 2012, 07:15
"WITHOUT DELAY: Emergency descent accomplish"

ATC coordination comes later. Aviate first.


Don't know where you aviate but certainly on the North Atlantic Tracks, even using Strategic Offset you can end up with lots of traffic below you, all same way, same day and in very close proximity.

I'd say that's one instance where "Aviating first" might mean well mean delaying the decent for a few seconds to turn off track before initiating descent.

fireflybob
4th Feb 2012, 07:16
Slightly off the thread topic but Boeing say "consider structural integrity" before increasing speed.

If I have been settled nicely in the cruise at FL380 and there's a sudden loss of cabin pressure I would say it is highly likely that the structural integrity is in doubt. Obviously follow the prescribed sops but sheer self survival is going to say go down! You're going to feel pretty damn cold apart from anything else! As has been said it's important to get out of the high levels asap just for survival.

One example - Mid-Atlantic on some aircraft on some routes, if you unthinkingly blast straight down to FL100 it is quite conceivable you will then have insufficient fuel to reach any of your nominated alternates....in fact on a bad day you might not have enough fuel to make any land at all...that's why some airlines/some manufacturers FCOM's state that in the absence of significant terrain always halt the decent at an intermediate level, in our case FL150, (the level used for the planning of a decompressed diversion), and only continue down to FL 100 when landing is assured. You're not going to kill passengers at a cabin alt of 15000, seeing as they're seated and not required to perform any exacting mental tasks then the majority will OK. As a result the cabin crew can begin selectively taking passengers off the masks, saving the gas for the minority who may need it

wiggy, I thought there was a statutory requirement to provide oxygen to pax when above FL100 (although 30 mins without when above FL100 but below FL130 certainly used to be in the regs)?

dwshimoda
4th Feb 2012, 07:29
Do you fly four engine? I might be missing the point, and apologise if I am, but our ETOPS says that for critical fuel planning we take the worst of these three cases:

1. Depressurisation, diversion @ FL100 (or MORA) at LRC,
2. Simultaneous engine failure, depressurisation and diversion at
single engine cruise with APU running,
3. Engine failure, diversion at optimum FL or MSA with APU running.

So case 1 ensures we do have enough fuel for the divert. Plus, as you say, I would establish the off track turn before hitting FLCH.

thermostat: not sure what type you fly, but ours is very clear - descend at MMO / VMO, including full speed brake unless structural integrity is in question. 0.78 /290kts would not cut the mustard.

Firefly: again, don't know about type, but ours are approx 12 mins when tugged by the pax - no point trying to "save the gas" as once they're pulled, they go. It's not a bottle system.

DW.

fireflybob
4th Feb 2012, 08:14
Firefly: again, don't know about type, but ours are approx 12 mins when tugged by the pax - no point trying to "save the gas" as once they're pulled, they go. It's not a bottle system.

dwshimoda, yes same here!

misd-agin
4th Feb 2012, 14:57
wiggy - I've been NATS qual'd since 1990. There's always the chance for exceptions, which is why we have human beings instead of silicon chips running the show.

Had a developing slow speed incident at altitude due to temperature spike to +29C at FL380(!!!!). VHF has unuseable due to static. Immediately selected 'lower' on TCAS to sort traffic if we had to do a comm out emergency descent. Luckily we flew out of the hot air bubble prior to having to descend.

Thirty minutes later another flight was not as lucky and had to descend 4,000' as they reached minimum cruise speed due to the temperature spike.

Meikleour
4th Feb 2012, 15:47
misd-agin: are you sure you really encountered a true +29C at FL380 rather than an iced up TAT probe giving an incorrect temp.?

wiggy
5th Feb 2012, 03:58
I've been NATS qual'd since 1990. There's always the chance for exceptions, which is why we have human beings instead of silicon chips running the show.

Well we've been NAT'ing for about the same length of time then. Just to be clear I have absolutely no argument with that or you. The worry is this those who can't see that despite their QRH ultimately the golden rule in aviation is "don't crash"....(or at very least least don't hit me on the way down)

Rgds...may all your problems be small ones...

wiggy

bubbers44
5th Feb 2012, 04:37
23,000 hrs and no emergency descents so don't dwell on it much but once in a lifetime if it happened I wouldn't wait, just turn right off track and get down with no delay. With GPS nav you are now going away from opposite and same direction traffic with little chance of conflict. Keep it simple, just turn and dive. I know, somebody might be using offtrack 1 mile nav but usually you can see out the window while you are doing this, if not you gave it your best shot and it is not your day.

misd-agin
5th Feb 2012, 14:03
Meikleour - 100% sure? No. But minimal moisture content. Also, a second a/c was unable to maintain altitude in the same area, so I believe our systems were operating normally.

Meikleour
5th Feb 2012, 17:12
misd-agin (http://www.pprune.org/members/128797-misd-agin): the reason I asked was because on several occasions, in the tropics, cruising in Cirrus I have seen transient spurious TAT readings and had the FADECs affected. The clue is when you see the Thrust Lever blue circles moving back on their own. This is because the probes are getting temporarily iced up and are giving spurious high readings to the FADEC and it tries to restrict the maximum thrust available. One occasion was a genuine failure of the FADEC probe heating but the others were just transient and caused by shortterm ice build up on the probes. I have never seen this in temperate lattitudes though.

misd-agin
6th Feb 2012, 15:00
ISA +29C. -28C at FL380.


Meikleour - thanks.