Rapid Depressurisation
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From: England
Rapid Depressurisation
Is the current Rapid Depressurisation procedure different from the past (asking as a retiree)? It used to require initiating max rate descent 'without delay', notifying ATC during the descent. Nowadays in busy regions of airspace with aircraft flying random tracks on direct routings would the danger of collision be greater than danger of hypoxia to pax and cabin crew if descent were initiated without ATC clearance? Can TCAS cope with this scenario? How are things done these days?
Apologies if this topic has recently been debated on the Tech Log forum.
Apologies if this topic has recently been debated on the Tech Log forum.
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From: IRS NAV ONLY
No real change, but setting squawk to 7700 and notifying ATC is one of the early steps PM has to make while PF initiates descent, so ATC would be informed pretty quickly.
The only thing that changed recently, is that we no longer turn away from the route, as we don't really fly on airways anymore, but rather random direct routings. We can still use TCAS indications to turn away from any conflicting traffic before ATC is informed, though.
The only thing that changed recently, is that we no longer turn away from the route, as we don't really fly on airways anymore, but rather random direct routings. We can still use TCAS indications to turn away from any conflicting traffic before ATC is informed, though.
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From: Blue sky
Is the current Rapid Depressurisation procedure different from the past (asking as a retiree)? It used to require initiating max rate descent 'without delay', notifying ATC during the descent. Nowadays in busy regions of airspace with aircraft flying random tracks on direct routings would the danger of collision be greater than danger of hypoxia to pax and cabin crew if descent were initiated without ATC clearance? Can TCAS cope with this scenario? How are things done these days?
Apologies if this topic has recently been debated on the Tech Log forum.
Apologies if this topic has recently been debated on the Tech Log forum.
2) there is a PF and there is a PM (presuming you are flying a "big" commercial jet), it's a coordinated action.
3) "without delay" is not the same as "rush into it". You still do the actions without delay, you never rush.
4) random tracks only decrease collision danger. Nobody flies underneath/above apart from maybe 2 seconds crossing. It is more a question of not turning without informing ATC that creates a danger when ATC tries to keep everyone away from you.
4) TCAS will give resolution advisories if necessary, but they are only up/down so it will be nothing more than a change in rate of descent (not really "turning away" ;-)).
Thread Starter
Joined: Jan 1999
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From: England
The band FL300-400 is densely populated in some airspace regions (such as NE and SW USA and NW Europe), as a glance at F24 will confirm. An aircraft initiating max rate descend will drop through these levels in a very short time. Can current TCAS kit cope with such a scenario if ATC has not cleared the descent? A mid-air collision would certainly give rise to more fatalities than hypoxia.
Joined: Apr 2003
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From: Europe
Like many I've wondered why we don't tell ATC any sooner that we are diving down. I'm sure TCAS can cope with traffic, but it will be a confusing scenario, committed to a 7000 feet per minute descent with the speed brakes out, oxygen masks on, adrenaline pumping, semi burst eardrums, and now suddenly you have to reverse course because of TCAS! Watch that speed brake!
Advising ATC used to be a memory item, now it's done after the memory items are safely double checked, fully established in the high rate descent.
Advising ATC used to be a memory item, now it's done after the memory items are safely double checked, fully established in the high rate descent.
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From: germany
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From: Blue sky
Yes it can.
The maneuver itself is called a rapid descent: an idle descent with speedbrakes out. This is a descent that is performed by many pilots daily when they end up too high on profile. If there is turbulence, you have to aim for turbulence penetration speed. If there are thunderstorms you have to avoid them. If there is ice you have to use anti-ice.
If there is another aircraft, I would love to love to take evasive action because I know I'm the cause. TCAS TA aren't aerobatic maneuvers, they are gentle corrections to the pitch. I have that capability and that maneuver is not going to kill me. It would be pretty stupid there would be a collision because one aircraft drove down like a maniac with another just 2000ft below eating his lunch. Also knowing he's forced into a similar emergency descent because you are above him. I wouldn't feel safe diving down like that with TA only. I am the cause, I can avoid as well.
What your company does is company specific, it's not a Boeing procedure (if you fly Boeing).
The maneuver itself is called a rapid descent: an idle descent with speedbrakes out. This is a descent that is performed by many pilots daily when they end up too high on profile. If there is turbulence, you have to aim for turbulence penetration speed. If there are thunderstorms you have to avoid them. If there is ice you have to use anti-ice.
If there is another aircraft, I would love to love to take evasive action because I know I'm the cause. TCAS TA aren't aerobatic maneuvers, they are gentle corrections to the pitch. I have that capability and that maneuver is not going to kill me. It would be pretty stupid there would be a collision because one aircraft drove down like a maniac with another just 2000ft below eating his lunch. Also knowing he's forced into a similar emergency descent because you are above him. I wouldn't feel safe diving down like that with TA only. I am the cause, I can avoid as well.
What your company does is company specific, it's not a Boeing procedure (if you fly Boeing).
Last edited by BraceBrace; 19th March 2026 at 20:55.
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From: Europe
Airbus makes no mention of selecting TA during descent. Neither does Boeing as far as I know.
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From: Tring, UK
Back in the day in the sim, it was all about how quickly you could perform the manoeuvre. Today the training is more focussed on not making things any worse than they are, e.g. coming too close to another aircraft or the ground. Yes, you don’t want to hang about for too long up there but if you have done item one on the checklist: put your oxygen mask on, there is now time to assess the situation. If you know there’s aircraft below you, the MSA is significant and there might be an escape route, these are actually the greatest threats if not taken due account of.
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From: Athens
A320 FCTM
The TCAS mode selector must remain on the TA/RA position. Avoidance of collision has the priority, even if it requires a temporary interruption of the descent maneuver. The TA/RA TCAS mode enables a maximum protection against collision.
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From: Oakland, CA
Good question for retirees watching how procedures evolve. The core principle hasn't changed — immediate descent takes priority over ATC coordination — but how that interplays with modern airspace has been refined a bit.
The key practical update in most modern SOPs: the turn-off-track step has been de-emphasised precisely because RNAV direct routings don't give you the same predictable clear path that airway structures used to provide. TCAS is now the primary tool for avoiding conflicting traffic during the descent, and the immediate squawk 7700 + ATC call gets done in parallel rather than as a prerequisite to the descent.
The time-of-useful-consciousness figures are the same as always — 15-20 seconds at FL350 — so the priority sequence hasn't softened, just the turn geometry guidance.
The key practical update in most modern SOPs: the turn-off-track step has been de-emphasised precisely because RNAV direct routings don't give you the same predictable clear path that airway structures used to provide. TCAS is now the primary tool for avoiding conflicting traffic during the descent, and the immediate squawk 7700 + ATC call gets done in parallel rather than as a prerequisite to the descent.
The time-of-useful-consciousness figures are the same as always — 15-20 seconds at FL350 — so the priority sequence hasn't softened, just the turn geometry guidance.
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From: Oakland, CA
The sequence you're describing makes sense within the rapid decompression framework. One thing worth noting from the systems side: the automated pressure alert thresholds and the crew response window are tighter than many assume.
From an operational perspective, the key variable is whether decompression is explosive (structural failure) or progressive (seal/valve failure). The procedural response diverges significantly between those two scenarios - especially the emergency descent rate and the cabin altitude awareness timing.
Has anyone seen updated guidance from EASA or FAA on the minimum equipment list entries tied to outflow valve monitoring since the 2022 revisions? Would be useful context for this discussion.
From an operational perspective, the key variable is whether decompression is explosive (structural failure) or progressive (seal/valve failure). The procedural response diverges significantly between those two scenarios - especially the emergency descent rate and the cabin altitude awareness timing.
Has anyone seen updated guidance from EASA or FAA on the minimum equipment list entries tied to outflow valve monitoring since the 2022 revisions? Would be useful context for this discussion.
Joined: Dec 1998
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From: UK
Getting a TCAS climb RA on an emergency descent would be an absolute s*** show. A mid air collision catastrophic. Best avoided in my book. Once both we and the pax have oxygen I try to slow the pace down. Over the Atlantic I would initiate a turn off track before initiating the descent. In busy airspace I would have a good look on TCAS before barrelling down - and think in Europe an ATC Mayday call / 7700
would be fairly high on my priority list.
would be fairly high on my priority list.
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Joined: Jan 1999
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From: England
The critical element seems to be the ability of modern TCAS systems to successfully cope with multiple TAs/RAs triggered by a plummeting aircraft (with compromised manoeuvring ability) in congested airspace without some degree of ATC coordination. In the seconds needed for ATCOs to respond to a 7700 squawk the max rate descender will have dropped through several FLs.
Last edited by Discorde; 22nd March 2026 at 09:04. Reason: typo corrected
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From: Tring, UK
Last week I went through an area with a MSA of 26,000’ while cruising in the low/mid 30s. As above, once O2 supplied to pilots and pax, it was going to be a steady and deliberate affair with no rushing, barreling, plummeting or diving as the last thing you need in an emergency descent is a hard GPWS...
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From: USA
The sequence you're describing makes sense within the rapid decompression framework. One thing worth noting from the systems side: the automated pressure alert thresholds and the crew response window are tighter than many assume.
From an operational perspective, the key variable is whether decompression is explosive (structural failure) or progressive (seal/valve failure). The procedural response diverges significantly between those two scenarios - especially the emergency descent rate and the cabin altitude awareness timing.
Has anyone seen updated guidance from EASA or FAA on the minimum equipment list entries tied to outflow valve monitoring since the 2022 revisions? Would be useful context for this discussion.
From an operational perspective, the key variable is whether decompression is explosive (structural failure) or progressive (seal/valve failure). The procedural response diverges significantly between those two scenarios - especially the emergency descent rate and the cabin altitude awareness timing.
Has anyone seen updated guidance from EASA or FAA on the minimum equipment list entries tied to outflow valve monitoring since the 2022 revisions? Would be useful context for this discussion.
The only difference I am aware of is at what speed you choose to descend at: explosive decompression - current speed or less. No structural damage, increase to Vmo.
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From: Blue sky
You give ATC a chance to vector other traffic away from you. However, as correctly mentioned before: terrain is factor as well, so you need a regional QNH from ATC. If you don't have that QNH, you can't completely rely on your charted terrain altitudes because you are probably flying flight levels. Even thought there might only be 500ft difference, it should be on your mind as a pilot when you are preparing an intermediate level off in high terrain.
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From: uk
The terrain shouldn’t be ‘on your mind’, it should be discussed and agreed. “From this point until reporting point Z, MSA is X, so in the event of a depressurisation descent our initial MCP setting will be Y. Once we are on the way down we can then refine that”. Or similar so that whoever gets to initiate the descent has clarity.
It’s an interesting one to watch from the back of the sim as it’s so easy to rush, whereas once the masks are on and you’re talking to each other everything should be done in a measured and steady way. Almost always I ended up with “be slow and however slow you think you are it’s still not slow enough”.
It’s an interesting one to watch from the back of the sim as it’s so easy to rush, whereas once the masks are on and you’re talking to each other everything should be done in a measured and steady way. Almost always I ended up with “be slow and however slow you think you are it’s still not slow enough”.
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From: UK
Agree with all that. It also used to be split so PM did some things such as deploying pax O2 at same time as PF started the descent. Now it’s definitely monitor PM actions then both monitor the descent. I saw someone turn on the emergency exit lights instead of the pax O2 once as they were rushing. If the cabin alt is above about 15000 it should drop automatically but not really the point.
