Emergency descent procedure

[CVividasku]

Hello,

My question or topic of debate tonight is very simple.
The standard procedure if MSA allows, in case of emergency descent, is to descend to FL100
In some countries, for example France, which many airlines in Europe overfly, the majority of airspace at FL100 is class G. You can find ultra lights with no transponder. Gliders with a flarm, light airplanes without altitude report. It's not so common but can happen. Especially on a nice weather weekend.
Above mountains, with MSA above FL100, we would stop at MSA (grid MORA). It's very difficult to know if gliders or small airplanes are likely to climb this high. And over the mountains they may be in E airspace with no radio contact.
Of course, if I think about this, it's because I often fly small airplanes, and sometimes up to and above FL100.

Have you ever considered this a problem ?
Would you stop momentarily at FL120 (which is breathable for most pax) to clarify the absence of trafic, or would you ask ATC in the later part of the descent ?
Or do you fully rely on the TCAS ? Having already encountered other unexpected airplanes while flying at ~100kt, it was sometimes difficult to see them on time. I had a very close call once, in which I saw the conflicting trafic 2-3 seconds before impact only (masked by the cabin ceiling, in descent above me on a colliding course)
I can't imagine how difficult it would be while flying 300kt (250 KIAS) or even faster, while wearing the O2 mask, dealing with ATC, cabin crew, ECAM procedures...

The end of emergency descent procedure is very rarely exercised in the sim..

Cheers

[B2N2]

You need to keep your passengers alive, there is no requirement to keep them conscious.
Time of useful consciousness is not linear.
Oxygen generators work for 15-17(?) minutes.
FL100 is not some magical near space zone of instant death. Without physical activity 16-17000’ is well breathable.

https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/612x650/image_10909025ad63fdd52e64fded907f05795deabbe0.png

Probably a little hypoxia but you’re not asking anyone to do advanced math.
Descend without delay out of high to medium altitudes then adjust descent as required.
By the time you get to little airplane altitudes you’ll be aviating, navigating and talking to ATC.
This is not a panicky ballistic free fall.
It’s a process that has memory items and checklists.

[321XLR]

in all my training, both Flightsafety / Part 91 corporate and Part 121 major US airline, "15,000" was the level we targeted to get down to. Below 15,000 the situation was not life/death urgent immediate.

People in La Paz Bolivia and Juliaca, Peru are making babies at 12,500 feet all day long...

[vilas]

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/1080x693/screenshot_20210520_142121_2_c00b515f2c0da3b1f090c0c5fdd6764 55fb3bc1d.png
This is breakdown of oxygen requirement, should explain it all.

[Smooth Airperator]

As mentioned, the goal here is to keep people alive. FL100 should be good enough to achieve that even for the sick, elderly and babies. Also consider the effects of freezing temperatures at altitude. With the right size hole in the cabin, although people might survive the lack of breathable air, they could freeze to death. Leveling off, to re-assess the traffic situation adds to workload in an already dire situation. The likelihood you'll hit a glider in uncontrolled airspace whilst diving down from high altitude is minuscule. Probably no more likely than hitting a large bird.

[FlyingStone]

Every aircraft with a serviceable transponder must operate it at all times in flight, regardless of airspace - SERA.13001(a) - an t here's very little excuses to operate any aircraft above 10,000ft with no transponder fitted, even for gliders, given the power efficiency of modern transponders.

[FullWings]

“Have you ever considered this as a problem?"

In the broad sense, no, not really. I would suggest that > FL100 much of any traffic you might encounter would be on an IFR plan and/or in contact with ATC and have some kind of EC. In the mountains it’s a different story with GA and recreational flying but you should be stopping the descent some way above the highest terrain in the area.

Also, you need to take into account the chance of an emergency descent into an area with a high unknown traffic density in a band above FL100, then think about random separation, so all of this combined would come out pretty low risk in the overall scheme of things. At a significant number of airports, an EFATO gives a good chance that you will leave controlled airspace at some point on the departure, which objectively would be a higher risk of conflict due to being right in the GA normal height band and the tendency of GA to skirt as close as possible to airspace without going in it.

[Discorde]

From How To Do Well In The Sim (https://www.steemrok.com/howtodowellv4.pdf) (which might now be too out-of-date):

RAPID DEPRESSURISATION

When you call ‘MAYDAY’, if you're in busy airspace and you can get some sort of ATC clearance before you plummet, so much the better. It would be pointless doing the drill perfectly and then slamming into another aircraft beneath you on the way down. It's unlikely your TCAS will call out sensible RAs, nor those of nearby aircraft. The question is: ‘how long do I spend trying to get an emergency descent clearance before hypoxia begins to affect the passengers and cabin crew?’ And of course no-one can give you an answer – you must use your judgement as to when to start down if ATC can’t help.

Have the Rapid Depressurisation and Emergency Descent checklists changed in recent years? When I retired (15 years ago) we were still using the checklists whose first recall items were to don O2 masks and, if the pressurisation could not be restored, start an immediate emergency descent prior to negotiation with ATC. But those checklists originated many decades ago when high altitude civilian air traffic was very much lighter than today's. The chances of collision resulting from an uncoordinated rapid descent in those years were probably deemed to be infinitesimally small, and therefore acceptable. Perhaps that's no longer a valid assumption.

[safetypee]

vilas, the diagram at #4 should be referenced as cabin altitude, that is the dependent parameter for oxygen supply.

B2N2, similar for table at #2

-

The probability of loosing all cabin pressure is low - design requirements (AFAIR Concord was a loss of one window at 50k).
Residual cabin pressure or rate of loss may be alleviated by closure of outflow valves and high air bleed, both usually automatic system reactions.
Air bleed would also counter temperature change.

[CVividasku]

. The likelihood you'll hit a glider in uncontrolled airspace whilst diving down from high altitude is minuscule. Probably no more likely than hitting a large bird.
Exactly my question.

Also, you need to take into account the chance of an emergency descent into an area with a high unknown traffic density in a band above FL100, then think about random separation, so all of this combined would come out pretty low risk in the overall scheme of things. At a significant number of airports, an EFATO gives a good chance that you will leave controlled airspace at some point on the departure, which objectively would be a higher risk of conflict due to being right in the GA normal height band and the tendency of GA to skirt as close as possible to airspace without going in it.
Very good point thanks !

[albatross]

Dumb helicopter pilot question:
Mask, Aviate, memory items, emergency descent, sq 7700, Communicate. Mayday/ PAN - Broadcast Intentions, Checklist, ATC
Would that work?

[CVividasku]

Also, you need to take into account the chance of an emergency descent into an area with a high unknown traffic density in a band above FL100, then think about random separation, so all of this combined would come out pretty low risk in the overall scheme of things. At a significant number of airports, an EFATO gives a good chance that you will leave controlled airspace at some point on the departure, which objectively would be a higher risk of conflict due to being right in the GA normal height band and the tendency of GA to skirt as close as possible to airspace without going in it.
Very good point. Also, even for a normal departure, it can happen in some countries where there is a lot of GA that an inattentive pilot bust the controlled airspace you're flying into. You're climbing very quickly but it can happen. It can also be a drone or anything else..
That's why some of my colleagues insist on a constant visual lookout while in low altitudes.

[EXDAC]

.That's why some of my colleagues insist on a constant visual lookout while in low altitudes.

Only some of them? I hope I never share airspace with the rest of them!

[Amadis of Gaul]

I'd say the odds of one of those guys being underneath you the exact minute you need to do an emergency descent are not real great.

[CVividasku]

Only some of them? I hope I never share airspace with the rest of them!
Yes only some of them haha !
You can't expect everyone to list every threat every time..
Briefings would never end.

[EXDAC]

Yes only some of them haha !
You can't expect everyone to list every threat every time..
Briefings would never end.

Big difference between briefing what should be SOP and correcting a crew member who has their eyes glued to the glass in VMC. I assumed, perhaps incorrectly, that you were commenting on the second case.

[B2N2]

On a previous simulator Proficiency Check for a previous type for a previous employer we had a very creative simulator instructor.
He had come up with a scenario where we had to pull a circuit breaker that removed the power to the fire detection on the remaining engine then subsequently gave us a fire on final.
The chances of this ever happening in life are not zero but statistically insignificant.
Same here.

[Discorde]

Further to post #8: Has a recent assessment been done comparing the risk of the ill effects of hypoxia incurred by occupants of a depressurised aircraft versus the risk of collision during uncoordinated rapid descent? Should the relevant checklists be amended to prioritise clearance from ATC? Here's today's (08 July 23 1410 UTC) airspace activity over the NE US (a significant proportion of which will be operating in the FL300-400 band).

Passengers and cabin crew incurring hypoxia will likely recover when the aircraft has descended to breathable air. The occupants of colliding airliners will likely be less fortunate.

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/989x591/busy_skies_8f97f03f8960d39e6a2b57316238f25d58814f97.jpg

[wiggy]

Discorde

​ Should the relevant checklists be amended to prioritise clearance from ATC? ​​​​​​

I don't have to worry about this stuff any more but from what I recall hypoxia's not the only problem, especially when you get up to the top end of the "FL300-400 band".

I suspect sitting up at FL 400, for any significant length of time, depressurised, waiting for an ATC clearance might not be the smartest move but I'm open to debate.

[safetypee]

Following on from #9;

Cabin Alt alerting is normally at 10,000 ft cab alt. Assuming unnoticed up to that point, and a reasonable leak rate ~1000 ft/min; the crew have 4min during which to protect themselves and passengers (acting as necessary), and negotiate ATM descent as judged being required.

'Show us the data'; failures which frequently come to mind involve lax crew procedures in ensuring that the cabin is pressurised during the climb, not 'explosive' total loss of pressurisation.

Consider the risks; assumed probabilities, likelihood. We are an industry which likes to speculate on the worst case, create new 'procedures' risking corruption of well established ones; to the detriment of current levels of safety.

Aircraft collision … more likely in normal ops; ATM comms, misrouting, incorrect reaction to ACAS.

Don't imaging yourself as a 'hero', instead check that the day job is done correctly; there are many many opportunities to do this vice focus on some obscure situation.

Speculate by all means, but better done with supporting evidence of risk (how many) and a well argued proposition (where, when, why).

[FullWings]

Further to post #8: Has a recent assessment been done comparing the risk of the ill effects of hypoxia incurred by occupants of a depressurised aircraft versus the risk of collision during uncoordinated rapid descent? Should the relevant checklists be amended to prioritise clearance from ATC? Here's today's (08 July 23 1410 UTC) airspace activity over the NE US (a significant proportion of which will be operating in the FL300-400 band).
I think the picture shown is somewhat misleading as the aircraft are not to scale! Yes, there’s a lot about but they are spread through a huge volume, and if you multiply the chance of a full-on rapid descent by that of actually getting close enough to other aircraft to be truly worried, it would come out as a very small number, especially given ATC would be alerted (quickly if 7700 squawk) and most pilots I know keep SA in the cruise on other aircraft above/below them, which helps in these remote circumstances.

I think someone in the UK in the 1960s (?) proved statistically that with the traffic levels then and the measured collision risk, it would be safer in this one respect to get rid of all en-route controlled airspace and assign aircraft random heights and headings than it was to try and have them follow airways and ATC direction.