Explosive decomp

[alwaysdirect]

We just had an explosive decomp in Sweden, would you as a pilot divide from your clearance? As in turning right? When would turn on 77? When would you alert me?


Just had my annual exam and I couldn't explain, because I think it's a company checklist where Pilots have more than enough to do than alert me as an ATCO.

What should I do as an ATCO?

[Tarq57]

So what happened?
Aircraft type and level? Anyone injured? A link to the story, perhaps?

[orgASMic]

Damn right he is going to deviate from his clearance. He needs to descend very quickly to the aircraft get into more oxygen and to relieve the strain on the structure in case anything else gives way.
If you are lucky he will have sufficient situational awareness to turn off track and descend into clear airspace but his office is now a howling maelstrom of paper cups and flight publications, so dont count on it.
I would definitely expect him to remember to squawk emergency and I would definitely remind him if I did not see it. If all I get is one shout of 'mayday' I will tag it and get busy trying to make some room.
I would then be telling my watch Supervisor/Sector Chief/anybody to spread the word for everyone to get the hell out of the way and to offload the rest of my traffic cos the emergency aircraft is now the only show in town.

[Crazy Voyager]

We did? True I don't work in aviation (at least not yet) but I haven't heard a word about an explosive decompression over Sweden, when was it?

[HEATHROW DIRECTOR]

orgASMic..... great stuff. Sounds like Airplane!! I don't recall major emergencies being that exciting. Couple of phone calls... tell the Boss... sit and watch and separate from other traffic. Leave the crew alone as much as possible. Oh yes... speak at half your normal speed. Next please...

[Don't Tell Him Pike]

I don't recall major emergencies being that exciting.

Decompression's not that big a deal Min stack and below though, is it?:ok:

[eyeinthesky]

UK guidance is DON'T turn off track as it is likely to put you in conflict with more traffic. Squawk 7700, shove the nose down and continue straight ahead. We will try to clear the sky beneath you. When you are able, tell us your issues and intentions.

The only exception to the 'do not turn' would be if TCAS indicates conflicting traffic beneath you...!

[OutsideCAS]

And of course, all the above assumes that barotrauma hasn't incapacitated the crew completely (subject to altitude and rate of explosive decompression).

[novation]

I beleive there is an Icao instruction which suggests pilots may turn in the descent. However in the UK most atco's would prefer the a/c to continue straight. I personally operate an expect the unexpected mentally and will keep all a/c away from one in an emergency descent as far as possible.

[HEATHROW DIRECTOR]

novation.... Wise words..

[Denti]

To be honest i rarely see guys squawking 7700 in the simulator during that exercise and it is, together with an ATC call, pretty low on the list. Most pilots still work according to the old rule aviate -> navigate -> communicate, in that order. I do agree though that squawking 7700 as early as possible is probably a very good idea, especially in busy areas like most of europe or some parts of the US.

[Escape Path]

would you as a pilot divide from your clearance?

We must if we are above a breathable altitude.

When would turn on 77? When would you alert me?

Honestly, that would be the first thing I would do...after being well established in the descent.

Quoting Denti (my respects to you sir, btw :ok:)
Most pilots still work according to the old rule aviate -> navigate -> communicate

Pretty much. A briefed and rushed example of what we are supposed to do in such a case (depress.) is don our masks, ask the F/A if they see any structural damage and then do the specific procedure which itself can take some 10 or 15 seconds (in my experience at least, DHC-8). So don't expect the crew to inform you they are declaring an emergency just as they descend from their level. And please oh please do not call the crew every 5 seconds if they haven't called you; if they are still conscious they will call you when everything is sorted out in there. We will remember that we have to talk to you guys too :ok:

[grounded27]

Rapid decent is best done in a spiral to prevent from overspeeding the A/C.

[SNS3Guppy]

Rapid decent is best done in a spiral to prevent from overspeeding the A/C.

Only in light piston airplanes during primary training.

I experienced an explosive depressurization the year before last, involving a windscreen failure. The left side windscreen blew out, taking some of the cockpit interior with it, as well as the top of the isntrument panel and glareshield, and as luck would have it, the checklist and emergency checklist (which was on the glareshield, at the time).

After taking immediate action to ensure crew safety, the next step was to sit on our hands and evaluate. I wasn't aware of how much more damage was done. The cockpit interior panels were fractured, and the initial appearance was that perhaps structural damage was present beyond the windscreen. We had aerodynamic buffeting and noise, because much of the glareshield was outside the airplane, still attached, and disrupting airflow. I wasn't in a big hurry to do anything until I had a better idea of what was wrong. I certainly didn't want to make changes, including airspeed changes, until I knew the effect.

Generally with a rapid depressurization, after one has put on oxygen and established communications, one's next priority is to descend. Whether one departs one's "track" or not really depends where one is, and what's available. If one is on an oceanic track, one is expected to depart the track with a 90 degree turn off course. If one is flying on a domestic leg, one might make a turn to an appropriate field, one might turn back to the departure point, or one might be best to press on ahead.

The general order of priorities is always, in order: Aviate (fly the airplane), Navigate (direct the airplane), Communicate (talk).

In the case of my depressurization, I did communicate with ATC, but not until I had addressed the problem and had an initial plan in mind. At that point, I advised ATC what I had, told ATC what I would do, and made a request to have assistance standing by when we landed.

Talking with ATC and squawking 7700 both fall under communicating; important, but not the top priority in an emergency.

[BrATCO]

I know a place (around RESMI, for those who know it), where an explosive decomp at FL370 and the subsequent emergency descent to FL100 would let the traffic cross 26 levels, a dozen flows, 4 sectors, 2 ACCs and CDG approach in 2 minutes.
In this case, the biggest problem for us is to co-ordinate with lower sectors.
When one starts the descent, we get the information 4 seconds later. If we're not dealing with something else, we'll see it straight away. Expect then ONE message (that you won't hear) to confirm your clearance.
4 more seconds later, when we see that you've lost 1000', the emergency descent becomes obvious and we begin the co-ordinations with lower sectors.

Sqwak 7700
We've got automated systems to show a traffic performing an emergency descent to sectors who wouldn't see it in normal situation (filters to avoid overflow of useless informations), sqwaking 7700 as soon as possible forces the system and the traffic will immediately show in orange on every sector at once, which can make us save precious seconds.

Turn
In normal situations, when we vector a traffic, we anticipate the new trajectory. As we don't know your intentions, when you turn, we've got the information about the new trajectory only 10-15 seconds (5000' ?) after the end of the turn (because of the caculations, averages, smoothenings included in the radar system). If you turn too often, "cleaning" your way in lower levels becomes much more difficult.

[stu_h]

Just curious.

Given the advancement of onboard FMS systems, would it not be possible to create a system whereby certain flight conditions would automatically cause the selection of 7700 on the transponder?

Understandably, the first task of the crew is to fly the aircraft, so if a way could be found to automatically alert ATC to an emergency descent which possibly also includes a turn off track - in a busy traffic environment, that cannot be a bad thing?

[DFC]

The issue about turning is long established and is only in part related to traffic avoidance.

If you want to descend in an expeditious manner do you;

a) shove the control column forward and change the loading by the maximum negative amount until the desired attitude is reached; or

b) roll the aircraft which will then all by itself lower the nose while maintaining 1g, trim as you go and smoothly level the wings in the new nose low attitude.?

Basic flying which is more gentle on the aircraft.

The argument about traffic below and going straight or turning has little relevance in domestic airspace since there is little point avoiding the parallel traffic simply to survive long enough to spear a crosser. Or cause a break-up by bunting the aircraft unnecessarily as per UK procedure.

With no pax on board and FL350 or less (depending on type) then as SNS3Guppy says once on oxygen and stable whats the point in rushing. There is as they quite also correctly point out 2 situations - with suspected structural damage and the alternative - system failure causing rapidly increasing cabin alt. Each requiring very different process.

With pax on board then pay heed to the fact that FL250 is the max for the rubber jungle being used for an entended period but - also no point in them being concious and breathing passing 10,000 if you have broken the aircraft entering the descent.

My opinion;

Crew Oxygen,

Internal communications,

Passenger Oxygen,

Descent - using the smallest change in g possible i.e. in most cases a gentle roll and allow the nose to drop. Situational awareness - Alps etc don't go for 10,000 in the alt sel. South China etc go for escape route.

7700 - it is in the checklist and as said above everyone in range gets an alarm and/or filter breakthrough.

Our job is to ensure the safety of our aircraft. I don't at that stage worry about anyone that is no on board our aircraft.

Mayday call when it is the next priority.

[ferris]

Our job is to ensure the safety of our aircraft. I don't at that stage worry about anyone that is no on board our aircraft. I would've thought that people not on board your aircraft may pose a grave threat to the safety of your aircraft- if they hit it at 900 knots.

Out of interest- what guidance do companies provide in the event that you get an RA whilst in the descent? It's no so far-fetched anymore.

[DFC]

I would've thought that people not on board your aircraft may pose a grave threat to the safety of your aircraft- if they hit it at 900 knots.




Agree 100%.

If they don't get out of my way then I will have to do something so that I survive long enough to write the complaint. :O

Other aircraft have their own crews to look out for themselves. I am busy enough with my own at that stage.

[BrATCO]

Ferris wrote :

in the event that you get an RA whilst in the descent?

I know TCAS and STCA don't work the same way, but I've got 2 questions :
- Would a RA trigger with this kind of a rate ?
- Would a RA be of any use anyway ?

STCA in my system would blink once here, once there, but the computer stops the alarm when it "thinks" it's already too late.
Hence the need for us to anticipate because the automated helps we benefit in normal conditions can be ineffective in such a case.
No STCA doesn't always mean there's no very short term conflict.


DFC,
If they don't get out of my way then I will have to do something so that I survive long enough to write the complaint.

That's the point !
If you want them to go out of your way, maybe a little help from ATC could help...
But as long as we don't know where you're going, we can't do much.

I perfectly understand your technical need for a turn. And I agree with you : straight ahead, right or left, there's a traffic.
If a turn lets you keep the remains of your plane around you, why not ?
Question : roughly, how many degrees do you need to drop the nose ?

Would this turn become SOP in every AO, then we would be able to anticipate only 2 possibilities : right or left turn. We would know how many degrees. Much easier than now, when anything can happen with no advice.

Stu_h's idea of an automated 7700 when the cabin climbs too fast seems great.

We immediately know you've got a problem, we know you're descending. And thanks to this new (hypothetical) worlwide SOP, we know you're turning X degrees.
After less than 8 seconds, we know if this is a right or a left turn.

Now that we know your intentsions, why not just fly the plane down to FL100, we take care of the surrounding traffic, military activities, et al... except maybe during the 10 first seconds.
See ? We've won almost 20 sec. And no need to talk.

Once the plane is fly-able again at FL100, contact us, say "MAYDAY", "diversion", "it's cold up here" or whatever you want.
We've got now plenty of time to navigate together (if you need help), file the papers (Mayday, new FPL to new destination, talk to supervisors, operations, the Pope...) and argue about descending without prior clearance. :)

Worlwide "SOP" has been implemented for TCAS-RA, why not for explosive decomp/emergency descent ?

[5milesbaby]

One word - money.

[Denti]

The automatic squawk sounds good at first. However, it can make people jittery for completely the wrong reason. We had a rapid decompression lately in our company. A pressure controller failed and the outflow valve opened completely, causing the cabin to climb with more than 4000fpm. Crew actions were done, the mask dropped, however it was possible to regain manual control of the cabin again and there was no special need for an emergency descent. Therefore only a normal descent was done and requested. Now in case of that automatic squawk every ATC around would start asking questions as it is apparently not an emergency descent.

In our experience real explosive decompressions are exceedingly rare, slow or rapid ones happen quite a lot more often. They often do not require an emergency descent.

About the turn, as far as i know it is only a fix procedure in very few airspaces, like over the north atlantic, in my country ATC told us that straight ahead is ok since there are a lot of planes in every direction anyway. We wouldn't reduce the riskt to hit someone by turning away. Straight ahead does not need a negative g manouver at all, in fact flying it smoothly or even better using normal autopilot modes (level change for example) is a lot better than adding injured passengers and cabin crew to the list of problems.

[BrATCO]

5miles,
you're right, I often forget this part of aerodynamics : cash-flow around the airframe. :O

Denti,
The automatic squawk sounds good at first. However, it can make people jittery for completely the wrong reason.
Don't forget we're paid to worry anyway...
What wrong would there be if a plane squawks 7700 and the pilot calls a few seconds later to say "Disregard the emergency, we just need to descent FL250, then we'll call you back with our intentions" ?

The situation you discribe is just a "lazy" valve. 4000' per minute means almost 3 minutes before the cabin reaches FL250. That's more than enough for pilots to express their needs and for the controller to organise a fast descent which will be considered as a priority, not an emergency.
2 way communication is established... Almost a normal situation : I had 2 or 3 "fast" descents in 2010.
Seems to be the kind of "Emergency" descent they had tonight in Australia.(check "spectator's balcony")

The situations SNS3Guppy and DFC describe are a bit different : parts of the plane making their own way through the blue sky, cold wind in the cockpit, possiblity of damaged structure, pilots unable to communicate with ATC, ATC unable to anticipate...thus asking questions...
Why not take the worst possibility into account first and be reassured (or not, but at least we're ready) when the pilot can call ?

stu_h's idea of an automated 7700 would save almost 30 secs for ATC to prepare the traffic. That would be 6 messages/readbacks whith no hurry, we could put up to 4 miles more between the conflicting traffics than now. Lower sectors and military control would see it come too, even before co-ordination.

A squawk 7700 and no contact from the pilot would mean a predictable X degrees turn and descent FL100.
ATC turns the traffic, waiting to witness the turn/descent, or the pilot calls and we get back to normal.
The traffic that would have been turned X degrees (just in case) for 30 seconds or less wouldn't have lost much time and the situation would be much more "under control", even though no contact at all with the emergency.

Why not automatically trigger 7700 when the masks fall ?
Or, instead of an automated system, why not just put 7700 way up high(er) in the checklists ?
Wouldn't cost much, would it ?

[Tarq57]

...The situations SNS3Guppy and DFC describe are a bit different : parts of the plane making their own way through the blue sky, cold wind in the cockpit, possiblity of damaged structure, pilots unable to communicate with ATC, ATC unable to anticipate...thus asking questions...
Why not take the worst possibility into account first and be reassured (or not, but at least we're ready) when the pilot can call ?
Maybe it's not considered a priority to provide an automatic SSR response to this sort of event because it simply isn't very common.

I think some kind of datalink, or automatic squawk change to notify ATC when an a/c is carrying out a TCAS RA would be more pertinent.

Explosive decompressions are rare. I note that the OP hasn't come back to report on what took place over Sweden. I'm thinking he was probably asking "what if" rather than saying "this happened". Or maybe it happened on a SIM.

[rennaps]

It seems not so rare after all, it happened yesterday

"Qantas's mechanical woes continue, with an aircraft flying from Adelaide to Melbourne forced into rapid descent after its cabin depressurised."

[Tarq57]

"it" happened yesterday, being (apparently) not an explosive decompression, which is the type of situation I am referring to.

[Escape Path]

Or, instead of an automated system, why not just put 7700 way up high(er) in the checklists?


That's the point we all have been talking about; it has been taught to us pilots for ages that you need to fly before doing anything else, ergo "Aviate, Navigate, Communicate". We need to make sure our aircraft is under control and that whatever problem has occurred, we are addressing the most critical bits of it so that then (while being still alive :E ) we can call you chaps and ask for your much appreciated help. Squawking 7700 requires being concious :)

Take this video for example: YouTube - ThomsonFly 757 bird strike & flames captured on video (http://www.youtube.com/watch?v=9KhZwsYtNDE)

Engine failure at rotation and you don't hear from the crew after roughly 10 seconds. The same principle applies to all emergencies that are critical for aircraft handling/performance/structural integrity.

I think some kind of datalink, or automatic squawk change to notify ATC when an a/c is carrying out a TCAS RA would be more pertinent.


Why? You can fly and talk at the same time. But there could be some sort of SOP stating that in the event of a TCAS RA manoeuvre, PF executes it and PM calls ATC while pushing the IDENT button on the transponder; might help a bit

Question: roughly, how many degrees do you need to drop the nose?

Do you mean "how many degrees do we need to turn off course?". If so, I was taught 45° off course. Anyone else?

Stu_h's idea of an automated 7700 when the cabin climbs too fast seems great.

+1

Maybe we could extend that to include a failed engine whilst airborne?

[5milesbaby]

When it came out that airlines were teaching to turn off track, NATS consulted them and simulated a 30 degree turn for controllers to learn and practice technique. It didn't take many simulations to realise this wasn't the best practice in the UK :}

[Denti]

I think some kind of datalink, or automatic squawk change to notify ATC when an a/c is carrying out a TCAS RA would be more pertinent.

That is part of the system design from the very beginning. Since coordinated TCAS RAs depend on Mode S datalink there always was and still is an automatic RA flag on the Mode S signal, however most ATC systems are not able to use it.

[SNS3Guppy]

Maybe we could extend that to include a failed engine whilst airborne?

Why? A failed engine isn't necessarily an emergency; it's usually an abnormal situation, and not one in which a rush to do anything needs to be made.

We really don't need aircraft to begin squawking 7700 for us and automatically making decisions or taking action that's the responsibility of the crew.