Explosive decomp
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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.
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.
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5miles,
you're right, I often forget this part of aerodynamics : cash-flow around the airframe.
Denti,
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 ?
you're right, I often forget this part of aerodynamics : cash-flow around the airframe.
Denti,
The automatic squawk sounds good at first. However, it can make people jittery for completely the wrong reason.
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 ?
...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 ?
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 ?
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.
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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."
"Qantas's mechanical woes continue, with an aircraft flying from Adelaide to Melbourne forced into rapid descent after its cabin depressurised."
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Or, instead of an automated system, why not just put 7700 way up high(er) in the checklists?
) 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
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.
Question: roughly, how many degrees do you need to drop the nose?
Stu_h's idea of an automated 7700 when the cabin climbs too fast seems great.
Maybe we could extend that to include a failed engine whilst airborne?
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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 
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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.
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Maybe we could extend that to include a failed engine whilst airborne?
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.
