TCAS on Emer Descent
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I am not aware of any guideance from Airbus, but some airlines SOPs do call for TA only, and some dont call for any change from TA/RA.
But common sense says you probably should switch to TA only (you dont want to have to make a climb in an emerg des). Switching to TA only will make the other aircraft manoeuvre out of your way, and not vice versa.
But common sense says you probably should switch to TA only (you dont want to have to make a climb in an emerg des). Switching to TA only will make the other aircraft manoeuvre out of your way, and not vice versa.
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Don't forget that where there is an Autopilot Emergency Descent Mode, the first thing that is done is a 90 degree turn off flight plan heading and then the emergency descent with a level off at a preset altitude. This would probably make choice of TCAS mode moot.
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I think that would depend very much on where you are...presumably you are referring to MNPS airspace contingency procedures? The same behaviour in busy continental airspace may not always be the most sensible option.
I would suggest TA as well, and certainly A7700 as a priority - gets ATC on your side v. quickly and may preclude needing TCAS at all
I would suggest TA as well, and certainly A7700 as a priority - gets ATC on your side v. quickly and may preclude needing TCAS at all
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This is just question from a newly qualified TCAS pilot.
I thought that the whole TCAS event takes less than 60seconds from intial traffic traffic to the event finishing.
If your high up and already got the rubber jungle out in the back and the crew are on O2 surely the addition of 60secs isn't going to effect the safety of the decent. In fact if your going down like a bat into hell. I would suspect that you will be given a decent rate TCAS which will still have you going down but just not as fast.
Seems strange that you would turn a quite important peice of safety equipment off, in fact your only one for avoiding collision. When you have another emergency when your attention will be diverted away from maintaining your SA.
As I said this is just my thoughts and please educate me if i have got my head round the TCAS thing the wrong way.
Summary is that my risk assement is that the additional risk of fatal outcome is higher with the TCAS mode downgraded than the additional risk of the emergency decent profile being not the optimal one.
MJ
I thought that the whole TCAS event takes less than 60seconds from intial traffic traffic to the event finishing.
If your high up and already got the rubber jungle out in the back and the crew are on O2 surely the addition of 60secs isn't going to effect the safety of the decent. In fact if your going down like a bat into hell. I would suspect that you will be given a decent rate TCAS which will still have you going down but just not as fast.
Seems strange that you would turn a quite important peice of safety equipment off, in fact your only one for avoiding collision. When you have another emergency when your attention will be diverted away from maintaining your SA.
As I said this is just my thoughts and please educate me if i have got my head round the TCAS thing the wrong way.
Summary is that my risk assement is that the additional risk of fatal outcome is higher with the TCAS mode downgraded than the additional risk of the emergency decent profile being not the optimal one.
MJ
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The TCAS 'TA' mode isn't the same thing as turning it off: while it means that the 'TA' crew would no longer get instructions on traffic avoidance, they still get advisory information. More importantly, all the other TCAS units in the sky know that that particular aircraft won't be manouevring and so can adjust their own response (RA) to compensate
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If you have the time, might I suggest that you select "TA only" unless your company SOP's say otherwise. My reasoning is that if whilst doing this descent, you don't want to be told to start climbing again. Otherwise, what's the point of the descent? In TA only mode, you are still letting other Mode S people "see you" and their aircraft knows that you will not be taking action to avoid.
I was taught that the worst crime in aviation was flying a perfectly serviceable aircraft into the ground.
I was also taught that the second worst crime was to fly a perfectly serviceable aircraft into another aircraft.
Two wonderful pieces of equipment were designed and subsequently incorporated into airliners in an effort to stop pilots from committing these crimes; firstly, the GPWS (and now EPGWS) and secondly, the TCAS.
Now I don’t think any one in their right mind would turn off the GPWS in an emergency descent as they would defeat their last line of protection from flying into the ground.
So I have to agree with mad_jock and ask why anyone in their right mind would turn off the TCAS RA function during an emergency descent thereby disabling their last line of protection against flying into another aircraft?
Strangely enough, if during an emergency descent, the GPWS tells me to climb to avoid flying into the ground, that is exactly what I am going to do. Likewise if during an emergency descent the TCAS tells me to climb to avoid flying into another aircraft, that is exactly what I am going to do.
Passenger Supplementary Oxygen Systems typically last 22 minutes for chemical type oxygen generators and substantially longer for gaseous bottled type systems.
Therefore, what would be the better choice between the following?
1. Flying a textbook emergency descent and having a midair collision during the manouevre and killing all onboard; or
2. Taking about one or two minutes longer to complete the emergency descent due to action taken to follow a TCAS Resolution Advisory on the way.
I was also taught that the second worst crime was to fly a perfectly serviceable aircraft into another aircraft.
Two wonderful pieces of equipment were designed and subsequently incorporated into airliners in an effort to stop pilots from committing these crimes; firstly, the GPWS (and now EPGWS) and secondly, the TCAS.
Now I don’t think any one in their right mind would turn off the GPWS in an emergency descent as they would defeat their last line of protection from flying into the ground.
So I have to agree with mad_jock and ask why anyone in their right mind would turn off the TCAS RA function during an emergency descent thereby disabling their last line of protection against flying into another aircraft?
Strangely enough, if during an emergency descent, the GPWS tells me to climb to avoid flying into the ground, that is exactly what I am going to do. Likewise if during an emergency descent the TCAS tells me to climb to avoid flying into another aircraft, that is exactly what I am going to do.
Passenger Supplementary Oxygen Systems typically last 22 minutes for chemical type oxygen generators and substantially longer for gaseous bottled type systems.
Therefore, what would be the better choice between the following?
1. Flying a textbook emergency descent and having a midair collision during the manouevre and killing all onboard; or
2. Taking about one or two minutes longer to complete the emergency descent due to action taken to follow a TCAS Resolution Advisory on the way.
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And not everything which you might conflict with is fitted with TCAS.
Your just coming in over the north west of scotland inbound to MAN. Just over Lewis you get a cabin pressure failure.
You start your emergency decent all goes well until you have a RA at FL 150 against a Tomcat which is mid exercise on the west coast of Scotland who has just done a pull up from 500ft (opps thats way to low for the yanks say 1500ft) to head off to the fuel bowser. IF your lucky scottish might just see the conflict before the RA but proberly not.
MJ
Your just coming in over the north west of scotland inbound to MAN. Just over Lewis you get a cabin pressure failure.
You start your emergency decent all goes well until you have a RA at FL 150 against a Tomcat which is mid exercise on the west coast of Scotland who has just done a pull up from 500ft (opps thats way to low for the yanks say 1500ft) to head off to the fuel bowser. IF your lucky scottish might just see the conflict before the RA but proberly not.
MJ
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You need to recognise what kind of airpsace you are in, naturally, and tailor your response accordingly.
You might be just as likely to descend into a airliner flown by crews who are not able to use TCAS correctly. What can you do then?
At least a functioning TCAS system on the other aircraft will recognise that you are TA only - it's reponse will be altered acordingly to (possibly) a more aggressive response, but still a safe one for both aircraft.
You might be just as likely to descend into a airliner flown by crews who are not able to use TCAS correctly. What can you do then?
At least a functioning TCAS system on the other aircraft will recognise that you are TA only - it's reponse will be altered acordingly to (possibly) a more aggressive response, but still a safe one for both aircraft.
ECON cruise, LR cruise...
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Let's try a different approach, then...
Let's say that you have left the switch in TA/RA. During your emergency descent, you get an RA.
Now, gents, please raise your hand if you would not follow said RA....
...anyone...???
Good, then - that should wrap it up
I know that TA only will modify the response of the other aircraft - but what would that response be, and would it be any different by you selecting TA only? Bear in mind, you are descending @ 4-5000 fpm on a steep profile (that alone reducing the likelihood of conflict, but lets leave that aside for now). If the other aircraft was climbing, cruising or descending on a normal profile - the easiest way to solve the puzzle would (geometrically speaking) be to issue the other aircraft with a climb command and you with a "Monitor vertical speed".
I'm fully aware that a lot of factors could cause the scenario to play out differently (i.e. you getting a climb command) - but it is a game of statistics in the first place. What if - as stated above - the other crew don't know how to deal with their end of the stick? What if you accidentially in the rush of an emerency descent select ALT on your transponder? What if the other a/c is for some reason or another also in TA ONLY mode? Or what if your SOP says nothing about selecting TA ONLY during an emergency descent?
As long as ICAO have not drafted any policies on the matter @ hand, my airline has not implemented the procedure i our SOP and nobody can find a QRH reference for such a drill - I'd be very tempted to get on with the emergency descend & leave the TCAS alone. You are not gonna die from a decompression - both the F/D & C/C are all on oxygen. Nor is a fire gonna kill you in the 1 minute it takes to resolve an RA (if you reacted quickly enough in the first place & initiated the descent & diversion ASAP i.s.o. waiting to find out that it - God forbid - is uncontrollable).
But hitting the other aircraft IS gonna kill you - no matter what your previous actions & subsequent plans!
Any thoughts? Best reagrds - and a merry Chistmas/Holiday to all
Empty
Let's say that you have left the switch in TA/RA. During your emergency descent, you get an RA.
Now, gents, please raise your hand if you would not follow said RA....
...anyone...???
Good, then - that should wrap it up
I know that TA only will modify the response of the other aircraft - but what would that response be, and would it be any different by you selecting TA only? Bear in mind, you are descending @ 4-5000 fpm on a steep profile (that alone reducing the likelihood of conflict, but lets leave that aside for now). If the other aircraft was climbing, cruising or descending on a normal profile - the easiest way to solve the puzzle would (geometrically speaking) be to issue the other aircraft with a climb command and you with a "Monitor vertical speed".
I'm fully aware that a lot of factors could cause the scenario to play out differently (i.e. you getting a climb command) - but it is a game of statistics in the first place. What if - as stated above - the other crew don't know how to deal with their end of the stick? What if you accidentially in the rush of an emerency descent select ALT on your transponder? What if the other a/c is for some reason or another also in TA ONLY mode? Or what if your SOP says nothing about selecting TA ONLY during an emergency descent?
As long as ICAO have not drafted any policies on the matter @ hand, my airline has not implemented the procedure i our SOP and nobody can find a QRH reference for such a drill - I'd be very tempted to get on with the emergency descend & leave the TCAS alone. You are not gonna die from a decompression - both the F/D & C/C are all on oxygen. Nor is a fire gonna kill you in the 1 minute it takes to resolve an RA (if you reacted quickly enough in the first place & initiated the descent & diversion ASAP i.s.o. waiting to find out that it - God forbid - is uncontrollable).
But hitting the other aircraft IS gonna kill you - no matter what your previous actions & subsequent plans!
Any thoughts? Best reagrds - and a merry Chistmas/Holiday to all
Empty
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I disagree with Empty Cruise. I think that during an emergency descent the chance of triggering an RA is MUCH higher. Your (necessarily) high rate of descent will bring many more targets below you into the "threat zone". TCAS does not know that you are going to level off at a particular level (typically FL100ish), so an awful lot of aeroplanes that would be ignored during your normal 2000fpm descent rate become important at your 5000fpm+ rate of descent.
We set TA only if an engine fails "to prevent climb commands which can exceed single engine performance". So there is a precedent for changing TCAS mode during abnormal operations.
The good thing about setting TA only is that conflicting aircraft will manoeuvre around YOU. You can just carry on unhindered with the emergency procedure you are already carrying out rather than have to start another one.
Who can say that a crew receiving an RA whilst they are carrying out an emergency descent will follow it? At the very least I would suggest that they would pause longer than normal whilst their poor maxed out brains compute the information they are being presented with loud airflow noise/uncancelled alarms/bleeding eardrums* delete as applicable. The last thing we want is crews manoeuvring against an RA, Uberlingen anybody?
Having said all the above, selecting TA only is not part of our emergency descent checklist.
G W-H
We set TA only if an engine fails "to prevent climb commands which can exceed single engine performance". So there is a precedent for changing TCAS mode during abnormal operations.
The good thing about setting TA only is that conflicting aircraft will manoeuvre around YOU. You can just carry on unhindered with the emergency procedure you are already carrying out rather than have to start another one.
Who can say that a crew receiving an RA whilst they are carrying out an emergency descent will follow it? At the very least I would suggest that they would pause longer than normal whilst their poor maxed out brains compute the information they are being presented with loud airflow noise/uncancelled alarms/bleeding eardrums* delete as applicable. The last thing we want is crews manoeuvring against an RA, Uberlingen anybody?
Having said all the above, selecting TA only is not part of our emergency descent checklist.
G W-H
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I'm missing something here. You are doing an "Emergency Descent" because you can't stay for a second longer than where you are. Presumably because something is very, very wrong. And now you set the TCAS to a position whereby you can possibly go back up again! I'm missing something very big here!
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You have to deal wth the most imminent threat 1st......and thats the depress 1st.
I had this recently in the sim and although our company provides no specific guidance (its impossible to legislate for every possible senario) it was quite obvious that we were unable to comply with Climb RAs.
*If we reacted to the "climb" RA we would actually increase our chance of collision as our pull-out from the dive is limited to 2.5g......ie: 3-4,000ft
1. The extra high RoD meant that they were many more 'threats' and consequently RAs. It was disconcerting!!
2. We tended to get an RA "Climb" and then the very next second it changed to an RA "Descend".
I dont know (and cant find) of any software within the TCAS that takes account of aircraft with significantly high RoDs but we certainly noted that the TCAS very quickly changed its mind due to our vertical profile.
I hope someone with specific TCAS knowledge can join this thread.
On you next sim, ask to see this in action. Its well worth it!
I had this recently in the sim and although our company provides no specific guidance (its impossible to legislate for every possible senario) it was quite obvious that we were unable to comply with Climb RAs.
*If we reacted to the "climb" RA we would actually increase our chance of collision as our pull-out from the dive is limited to 2.5g......ie: 3-4,000ft
1. The extra high RoD meant that they were many more 'threats' and consequently RAs. It was disconcerting!!
2. We tended to get an RA "Climb" and then the very next second it changed to an RA "Descend".
I dont know (and cant find) of any software within the TCAS that takes account of aircraft with significantly high RoDs but we certainly noted that the TCAS very quickly changed its mind due to our vertical profile.
I hope someone with specific TCAS knowledge can join this thread.
On you next sim, ask to see this in action. Its well worth it!
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but it is a game of statistics in the first place.
If we were sure everybody else has got a TCAS, it would be better to set TA only.
If we were sure nobody else has got a TCAS, it would be better to leave TA/RA.
The important thing to remember is:
always follow the RA!
This has been covered in other threads, and one can download the Eurocontrol bulletins on this matter.
And in the extremely unlikely case in which you get a CLIMB RA during the descent, follow it!
LEM
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Petitfromage,
V. good points, especially about the change from "Climb" to "Descend, descend now".
This link, specifically p. 35, rh coloumn, second-last paragrpah, indicates that TCAS manouvres are designed around a 0,33 delta-G manoeuvre. Therefore, nothing suggests that a 2,5/-1,0 (or shouldn't it rather be +2,0/-0,0, since flaps may be extended?) G manoeuvre would ever be commanded.
The above link also (in several places) points to TCAS being designed for vertical speeds of up to 10.000 fpm - and therefore that any manoeuvre - even during an emergency descent - will be subject to the same manouvre laws as your "everyday" TCAS.
The word "emergency descent" seems to jumble a few priorities (see above) - how long does your crew oxygen last? Cabin crew? OK, so nobody requred for the safe operation of the aircraft will be incapacitated by interrupting your emergency descent. Even the passengers will not be incapacitated - the emergency descent would be resumed long before their oxygen systems run out (worst case I've heard of is 12 min.)
Trying a bit of math here: -1 min. from the masks drop to start the descent, -3 min. to resolve an RA - that's 8 minutes left to descend from FL410 to FL130 - this requires an average rate of 3500 fpm. Or 3875 fpm to descend all the way to FL 100. Does this sound undoable?
None of the above has altered my argument - a collision will kill everybody - here and now. The lack of oxygen might kill some passengers in a future 10 minutes away. Now - balancing those two scenarios against eachother, I have no doubt in my mind what I'll do. I would do the same if I knew that I would - with absolute certainity - kill 10% of the passengers doing so. Even if I knew it would ultimately kill the flightdeck & cabin crew - but save some of the passengers for now (not talking about how they'd get the thing landed - in that instant, there is a long way to the tollbooth across that bridge) - I would do it.
Statistics - don't you just love them
Empty
V. good points, especially about the change from "Climb" to "Descend, descend now".
This link, specifically p. 35, rh coloumn, second-last paragrpah, indicates that TCAS manouvres are designed around a 0,33 delta-G manoeuvre. Therefore, nothing suggests that a 2,5/-1,0 (or shouldn't it rather be +2,0/-0,0, since flaps may be extended?) G manoeuvre would ever be commanded.
The above link also (in several places) points to TCAS being designed for vertical speeds of up to 10.000 fpm - and therefore that any manoeuvre - even during an emergency descent - will be subject to the same manouvre laws as your "everyday" TCAS.
The word "emergency descent" seems to jumble a few priorities (see above) - how long does your crew oxygen last? Cabin crew? OK, so nobody requred for the safe operation of the aircraft will be incapacitated by interrupting your emergency descent. Even the passengers will not be incapacitated - the emergency descent would be resumed long before their oxygen systems run out (worst case I've heard of is 12 min.)
Trying a bit of math here: -1 min. from the masks drop to start the descent, -3 min. to resolve an RA - that's 8 minutes left to descend from FL410 to FL130 - this requires an average rate of 3500 fpm. Or 3875 fpm to descend all the way to FL 100. Does this sound undoable?
None of the above has altered my argument - a collision will kill everybody - here and now. The lack of oxygen might kill some passengers in a future 10 minutes away. Now - balancing those two scenarios against eachother, I have no doubt in my mind what I'll do. I would do the same if I knew that I would - with absolute certainity - kill 10% of the passengers doing so. Even if I knew it would ultimately kill the flightdeck & cabin crew - but save some of the passengers for now (not talking about how they'd get the thing landed - in that instant, there is a long way to the tollbooth across that bridge) - I would do it.
Statistics - don't you just love them
Empty
Last edited by Empty Cruise; 27th Dec 2005 at 17:44.
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Wrong, Gary Lager, you indeed get TA/RAs from traffic without TCAS, provided it has a transponder with altitude reporting.
Instead of getting coordinated RAs, you will be the only one maneuvering to avoid a collision.
Cheers, LEM
Instead of getting coordinated RAs, you will be the only one maneuvering to avoid a collision.
Cheers, LEM
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1: Initiate emergency descent
2: Squalk 7700
3: Shout Mayday at ATC
I understand that there are lots of other things going on in the cockpit but these are the important things as far as I am concerned. I would say that 3 isn't crucial if 2 is done as I would guess that an emergency descent is in progress with the descent rate, but it would be nice to know whats happenning and that you aren't uncontrollably falling. If there is any traffic below expect avoiding action to be given to all the conflicts (BIG vectors), it would be very rare to ask the emergency a/c to make any turns but there are some senarios that may need this to happen. Hopefully there will be no TCAS RA's if we can get our job done quickly!!
2: Squalk 7700
3: Shout Mayday at ATC
I understand that there are lots of other things going on in the cockpit but these are the important things as far as I am concerned. I would say that 3 isn't crucial if 2 is done as I would guess that an emergency descent is in progress with the descent rate, but it would be nice to know whats happenning and that you aren't uncontrollably falling. If there is any traffic below expect avoiding action to be given to all the conflicts (BIG vectors), it would be very rare to ask the emergency a/c to make any turns but there are some senarios that may need this to happen. Hopefully there will be no TCAS RA's if we can get our job done quickly!!