TCAS on Emer Descent
Join Date: Jan 2005
Location: uk
Posts: 1,266
Likes: 0
Received 0 Likes
on
0 Posts
LEM - you are right , of course, misunderstanding on my part.
Again, shouldn't it go back to the decision on the day being based not only on the type of airspace in which you are in (Mid-Atlantic vs. overhead London vs. open FIR) but also the likely occupants of that airspace?
In Class A airspace throughout most of the UK, I would not expect to find much non-TCAS-equipped traffic above FL100, so a decision to select TA may be more useful to others around.
Descending to FL100 directly overhead the CPT VOR with RA selected will probably mean in takes a LONG time to get down, after completing numerous TCAS RAs - that said, prudent decision in that case would be to turn and take the shortest route away from other traffic.
I would never suggest not following an RA - just placing the burden of manouvre on the other aircraft...with emergency descent required we have enough to worry about, for at least the first few thousand feet.
If we are on an unchanging descnet path, no matter what rate, then even if other traffic were on a direct collision course then they only limited manouevring would be required to remove them from that previous unsafe flightpath, hence I'll select TA and let TCAS do the co-ordinating and the other chap do the RA.
Again, shouldn't it go back to the decision on the day being based not only on the type of airspace in which you are in (Mid-Atlantic vs. overhead London vs. open FIR) but also the likely occupants of that airspace?
In Class A airspace throughout most of the UK, I would not expect to find much non-TCAS-equipped traffic above FL100, so a decision to select TA may be more useful to others around.
Descending to FL100 directly overhead the CPT VOR with RA selected will probably mean in takes a LONG time to get down, after completing numerous TCAS RAs - that said, prudent decision in that case would be to turn and take the shortest route away from other traffic.
I would never suggest not following an RA - just placing the burden of manouvre on the other aircraft...with emergency descent required we have enough to worry about, for at least the first few thousand feet.
If we are on an unchanging descnet path, no matter what rate, then even if other traffic were on a direct collision course then they only limited manouevring would be required to remove them from that previous unsafe flightpath, hence I'll select TA and let TCAS do the co-ordinating and the other chap do the RA.
Join Date: Dec 2003
Location: UK
Posts: 214
Likes: 0
Received 0 Likes
on
0 Posts
I'm with Gary Lager on this one. For most of the airspace in which I operate, TA only offers the best solution.
I disagree with LEM that the chance of getting a CLIMB RA during the descent is "extremely unlikely". In fact I would contend that the chances of getting one (or more) are actually fairly high. If you don't believe me, take a trip to your local ATC Centre and have them switch off the filters so that you can see all the transponding traffic.
5milesbaby has a good idea suggesting that we select 7700. Unfortunately, our rule book (supposedly following consultation with ATC) states that we must keep our assigned squawk unless told to squawk 7700. As a result of this, from his list: item 1 will occur fairly briskly, item 2 will probably not occur and item 3 will occur once the situation is under control (ie all the memory items have been completed and the flight profile is stable).
Just my thoughts.
G W-H
I disagree with LEM that the chance of getting a CLIMB RA during the descent is "extremely unlikely". In fact I would contend that the chances of getting one (or more) are actually fairly high. If you don't believe me, take a trip to your local ATC Centre and have them switch off the filters so that you can see all the transponding traffic.
5milesbaby has a good idea suggesting that we select 7700. Unfortunately, our rule book (supposedly following consultation with ATC) states that we must keep our assigned squawk unless told to squawk 7700. As a result of this, from his list: item 1 will occur fairly briskly, item 2 will probably not occur and item 3 will occur once the situation is under control (ie all the memory items have been completed and the flight profile is stable).
Just my thoughts.
G W-H
Join Date: Aug 1999
Location: England
Posts: 1,050
Likes: 0
Received 0 Likes
on
0 Posts
The obvious question to ask here is "how often might this sort of scenario occur".
When we instituted our TCAS training program this scenario was one that seemed in need of consideration.
My thoughts were that TA only was the way to go. After all, if you do that you are (at worst) no worse off than in the pre TCAS era, versus a scenario compelling you to manouevre opposite. General strategy here is that when a scenario occurs that prevents full manouverability, TCAS should go to TA only. The aircraft we flew at that time had "TA only" in several abnormal checklists, e.g. flying control malfunctions.
TA only mode is effectively a 'priority' button (as long as, as others have pointed out, your general operating environment is one of TCAS use by other traffic). I could talk more about this, but it would be mostly repeating others observations so I'll get back to the case in point.
I really felt that we should be pre empting this sort of scenario. In '99, as part of an attempt to quantify the problem I got in touch with the CAA and asked them to do a MOR database search and send me a list, for the previous year, of MORs including the terms "emergency descent" and "RA" or "TA".
We were hoping we might get hit or two and see how things had panned out in real life. It was therefore somewhat sobering to receive back a list of several dozen!
(cautionary note - this was u6.04 days, before u7 's improved horizontal miss distance filtering)
So folks, the bottom line is these scenarios are happening! For real!
- TCAS has been mandated in the UK for what, 6 years now?
- These scenarios are entirely likely and predictable.
- Lack of a clear policy is, frankly, negligent.
If your company doesn't have a policy on this, it should do. Urge your training departments / standards folks / flight safety team to make it happen!
BTW I am available to consult for a very reasonable fee
The former pilot known as Pitbull
When we instituted our TCAS training program this scenario was one that seemed in need of consideration.
My thoughts were that TA only was the way to go. After all, if you do that you are (at worst) no worse off than in the pre TCAS era, versus a scenario compelling you to manouevre opposite. General strategy here is that when a scenario occurs that prevents full manouverability, TCAS should go to TA only. The aircraft we flew at that time had "TA only" in several abnormal checklists, e.g. flying control malfunctions.
TA only mode is effectively a 'priority' button (as long as, as others have pointed out, your general operating environment is one of TCAS use by other traffic). I could talk more about this, but it would be mostly repeating others observations so I'll get back to the case in point.
I really felt that we should be pre empting this sort of scenario. In '99, as part of an attempt to quantify the problem I got in touch with the CAA and asked them to do a MOR database search and send me a list, for the previous year, of MORs including the terms "emergency descent" and "RA" or "TA".
We were hoping we might get hit or two and see how things had panned out in real life. It was therefore somewhat sobering to receive back a list of several dozen!
(cautionary note - this was u6.04 days, before u7 's improved horizontal miss distance filtering)
So folks, the bottom line is these scenarios are happening! For real!
- TCAS has been mandated in the UK for what, 6 years now?
- These scenarios are entirely likely and predictable.
- Lack of a clear policy is, frankly, negligent.
If your company doesn't have a policy on this, it should do. Urge your training departments / standards folks / flight safety team to make it happen!
BTW I am available to consult for a very reasonable fee
The former pilot known as Pitbull
Join Date: May 2003
Location: The Roman Empire
Posts: 831
Likes: 0
Received 0 Likes
on
0 Posts
Hi Giles Wembley-Hogg,
I insist it is extremely unlikely to get a CLIMB RA while descending like a rocket.
Don't get me wrong, I'm not saying it is extremely unlikely to get an RA while doing so, on the contrary, I believe the chances for it increase.
But you definitely won't get a CLIMB RA.
One of the basic principles of TCAS is that it is designed to suggest the smallest correction necessary to the actual flight path.
Can you believe an airplane descending like a rocket getting a CLIMB RA?
Nope!
The rate is so high, that you will get a MONITOR VERTICAL SPEED RA, to reduce it, or maybe even maintain it, as the TCAS will take advantage of this high rate and make the other traffic climb.
But certainly you won't get a CLIMB RA.
A bit of speculation, I know, but if you know the system and some previous incidents, you will come to this conclusion.
Having said that, I'd like to add that in the beginning it was encouraged to selecy TA ONLY in single engine and similar circumstances.
Not anymore.
Now the trend is to ALWAYS leave TA RA selected, as TCAS is perfectly capable of calculating the right maneuvres to be accomplished, even if one of the two airplanes (the one in the emergency descent) does not follow it.
The other one will get a revised RA, but as long as you don't make the worst possible mistake of maneuvering CONTRARY to the RA, everything will be fine.
Remember, if in doubt about the RA, at worst don't do anything..
Still OK if the other one has got a TCAS.
I insist it is extremely unlikely to get a CLIMB RA while descending like a rocket.
Don't get me wrong, I'm not saying it is extremely unlikely to get an RA while doing so, on the contrary, I believe the chances for it increase.
But you definitely won't get a CLIMB RA.
One of the basic principles of TCAS is that it is designed to suggest the smallest correction necessary to the actual flight path.
Can you believe an airplane descending like a rocket getting a CLIMB RA?
Nope!
The rate is so high, that you will get a MONITOR VERTICAL SPEED RA, to reduce it, or maybe even maintain it, as the TCAS will take advantage of this high rate and make the other traffic climb.
But certainly you won't get a CLIMB RA.
A bit of speculation, I know, but if you know the system and some previous incidents, you will come to this conclusion.
Having said that, I'd like to add that in the beginning it was encouraged to selecy TA ONLY in single engine and similar circumstances.
Not anymore.
Now the trend is to ALWAYS leave TA RA selected, as TCAS is perfectly capable of calculating the right maneuvres to be accomplished, even if one of the two airplanes (the one in the emergency descent) does not follow it.
The other one will get a revised RA, but as long as you don't make the worst possible mistake of maneuvering CONTRARY to the RA, everything will be fine.
Remember, if in doubt about the RA, at worst don't do anything..
Still OK if the other one has got a TCAS.
Join Date: Dec 2003
Location: UK
Posts: 214
Likes: 0
Received 0 Likes
on
0 Posts
Re: TCAS on Emer Descent
LEM
Alright, you've won me over to thinking that a CLIMB RA may not be as likely as I first thought. BUT "ADJUST VERTICAL SPEED" is a distinct possibility. It was also the RA that I received last time I tried a very high rate of descent into a piece of airspace that turned out to be busier than it looked! It resulted in me levelling out. Not something I would want to do if I was in the middle of an emergency descent. Would you want to?
The trouble with an RA like this is that you do not have the option to "don't do anything". If you carry on with your emergency descent you are automatically manoeuvring opposite to the RA (ie remaining in the red sector).
It is for this reason that I think your comment that if you are not sure about the RA, then do nothing is possitively dangerous in this situation. Furthermore, all the problems that lead you to make this suggestion could be resolved by selecting TA only.
Surely we want to reduce the workload on the aircraft suffering the emergency?
Incidentally. We still select TA only for single engine operations.
Just my thoughts
G W-H
Alright, you've won me over to thinking that a CLIMB RA may not be as likely as I first thought. BUT "ADJUST VERTICAL SPEED" is a distinct possibility. It was also the RA that I received last time I tried a very high rate of descent into a piece of airspace that turned out to be busier than it looked! It resulted in me levelling out. Not something I would want to do if I was in the middle of an emergency descent. Would you want to?
The trouble with an RA like this is that you do not have the option to "don't do anything". If you carry on with your emergency descent you are automatically manoeuvring opposite to the RA (ie remaining in the red sector).
It is for this reason that I think your comment that if you are not sure about the RA, then do nothing is possitively dangerous in this situation. Furthermore, all the problems that lead you to make this suggestion could be resolved by selecting TA only.
Surely we want to reduce the workload on the aircraft suffering the emergency?
Incidentally. We still select TA only for single engine operations.
Just my thoughts
G W-H
Join Date: May 2003
Location: The Roman Empire
Posts: 831
Likes: 0
Received 0 Likes
on
0 Posts
Re: TCAS on Emer Descent
Hi Giles Wembley-Hogg, as I said in the beginning it would be better to select TA only if we were sure everybody else has got a functioning TCAS.
Unfortunately, for Murphy's law, the day you are going to have a close encounter during an emergency descent, the other guy will have a transponder with NO TCAS
Thus my choice is for always leaving this device fully ON.
If a momentary leveloff will prevent a collision during an emergency descent, so be it.
That's the price to pay, and not a big one I think.
But at least you'll be sure not to hit anybody.
Regarding the "not doing anything", I repeat AT WORST don't do anything.
Don't climb if you have a Descent RA, and don't descent if you have a Climb RA.
Keeping the same path is not considered a maneuver OPPOSITE to the RA, I think.
It's bad, but not catastrophic.
This possibility is accounted for by the TCAS, which will instruct the other guy to increase his maneuver.
At Uberlingen, the system failed because the Russian maneuvered opposite to the RA.
Had he maintained level flight (yes, in the red arc), there would have been no collision.
I would definitely follow the RA even in an emergency descent.
Cheers, LEM
Unfortunately, for Murphy's law, the day you are going to have a close encounter during an emergency descent, the other guy will have a transponder with NO TCAS
Thus my choice is for always leaving this device fully ON.
If a momentary leveloff will prevent a collision during an emergency descent, so be it.
That's the price to pay, and not a big one I think.
But at least you'll be sure not to hit anybody.
Regarding the "not doing anything", I repeat AT WORST don't do anything.
Don't climb if you have a Descent RA, and don't descent if you have a Climb RA.
Keeping the same path is not considered a maneuver OPPOSITE to the RA, I think.
It's bad, but not catastrophic.
This possibility is accounted for by the TCAS, which will instruct the other guy to increase his maneuver.
At Uberlingen, the system failed because the Russian maneuvered opposite to the RA.
Had he maintained level flight (yes, in the red arc), there would have been no collision.
I would definitely follow the RA even in an emergency descent.
Cheers, LEM
Re: TCAS on Emer Descent
At a quick glance, I haven't seen it mentioned here that TCAS will not display traffic descending at more than 10000 ft/min. I know that is an extreme descent rate but my previous old T-tail 4-jet could be persuaded to go there.
Whether that means that non-displayed traffic can still be reacted to by the TCAS kit, with TA or RA, I'm not sure.
Whether that means that non-displayed traffic can still be reacted to by the TCAS kit, with TA or RA, I'm not sure.
Join Date: Jan 2005
Location: uk
Posts: 1,266
Likes: 0
Received 0 Likes
on
0 Posts
Re: TCAS on Emer Descent
LEM - I disagree that we always have to consider 'Murphy's Law' when planning for these sorts of scenarios. As with everything else in Aviation we have to always also consider probabilities, otherwise everything ends up being so over-engineered and doubly- triply-redundant that we can't fly in the first case.
There are some aircraft around without TCAS, though nowadays very few in UK/Central European airspace above FL100 (I have no experience of Oceanic flying so my comments cannot be extended to that arena). Additionally, I would hope that one is able to talk to ATC within the first 30 seconds of beginning an Emergency Descent (when one will have likely descended only 3-4000 from cruising level) who should then be able to provide assistance as well.
Or are we expected to always consider a depressurisation, comms failure AND non-TCAS traffic above FL100/MSA? This is where it seems our respective opinions diverge.
As I have said before, the 'answer' really depends on the personal judgement of the crew on the day, taking into account airspace, traffic levels, ATC service, terrain, and aircraft equipment, amongst other things. I am not brave enough to say ALWAYS do this, or NEVER do that in such circumstances; in certain situations I would probably take your advice (and may not have considered that scenario until you mentioned it here, so thank you), but my advice will remain as it has been, for those of us in busy controller airspace: select TA and let those other black boxes out there know you won't be doing anything except descend!
For info, an ADJUST VERTICAL SPEED can be more than just a level off - this summer over East Germany I was descended to FL270 from FL350 and turned into traffic climbing into me - my 2000fpm descent was eventually transformed by an ADJUST VERTICAL SPEED into a 1800fpm climb (though the scenario was resolved very shortly afterwards).
MrB - you ask an interesting question, I'd like to know the answer to that as well!
There are some aircraft around without TCAS, though nowadays very few in UK/Central European airspace above FL100 (I have no experience of Oceanic flying so my comments cannot be extended to that arena). Additionally, I would hope that one is able to talk to ATC within the first 30 seconds of beginning an Emergency Descent (when one will have likely descended only 3-4000 from cruising level) who should then be able to provide assistance as well.
Or are we expected to always consider a depressurisation, comms failure AND non-TCAS traffic above FL100/MSA? This is where it seems our respective opinions diverge.
As I have said before, the 'answer' really depends on the personal judgement of the crew on the day, taking into account airspace, traffic levels, ATC service, terrain, and aircraft equipment, amongst other things. I am not brave enough to say ALWAYS do this, or NEVER do that in such circumstances; in certain situations I would probably take your advice (and may not have considered that scenario until you mentioned it here, so thank you), but my advice will remain as it has been, for those of us in busy controller airspace: select TA and let those other black boxes out there know you won't be doing anything except descend!
For info, an ADJUST VERTICAL SPEED can be more than just a level off - this summer over East Germany I was descended to FL270 from FL350 and turned into traffic climbing into me - my 2000fpm descent was eventually transformed by an ADJUST VERTICAL SPEED into a 1800fpm climb (though the scenario was resolved very shortly afterwards).
MrB - you ask an interesting question, I'd like to know the answer to that as well!
Join Date: Mar 2004
Location: Scotland
Posts: 147
Likes: 0
Received 0 Likes
on
0 Posts
Re: TCAS on Emer Descent
Dont know if this helps anybody but a while ago I had a airprox with 2 harriers pulling up from low level'ish. I was in crz about 160 they were climbing 7000 fpm plus ( about the same as I would be in ED) TCAS was norm TA/RA but couldn't or didnt resolve the conflict. Just got prox traffic with no brg info, and that only happened after the first one had passed thru my level.
Join Date: Oct 2005
Location: hkg
Posts: 101
Likes: 0
Received 0 Likes
on
0 Posts
Re: TCAS on Emer Descent
Having the wherewithall to squawk 7700 in a Emer Desc probably will not happen.
Interesting thread , but only interesting . This is a double RED failure if you like .
The Mayday call should clear airspace beneath.
And I'm not going to worry about this combination .
vikena
Interesting thread , but only interesting . This is a double RED failure if you like .
The Mayday call should clear airspace beneath.
And I'm not going to worry about this combination .
vikena
Re: TCAS on Emer Descent
It is comforting to know that professional pilots operate their aircraft in accordance with their SOPs.
It is also comforting to reflect that non-professional pilots who think they personally have better ideas on operations than the aircraft manufacturers, avionics equipment manufacturers, civil aviation regulatory authorities, and airline company SOPs, don’t actually fly airliners.
It is also comforting to reflect that non-professional pilots who think they personally have better ideas on operations than the aircraft manufacturers, avionics equipment manufacturers, civil aviation regulatory authorities, and airline company SOPs, don’t actually fly airliners.
Join Date: Jun 2001
Location: Formerly resident of Knoteatingham
Posts: 957
Received 121 Likes
on
61 Posts
Re: TCAS on Emer Descent
I raised this issue quite a few years ago whilst on my 767 command course. No real joy from the trainers so I went to have a chat with the engineers and after several faxes and emails sent bacwards and forwards around the world the "technical" answer was to select TA as other TARA equipped aircraft will issue their own (and if multiple - coordinated) RA(s) based on the assumption that you will maintain your existing vertical profile.
I still haven't seen any formal guidance from any manufacturer though.
Personally, by the time I think of it (in the sim) I am usually at least half way towards 10,000 feet/MSA and I think it would be an extremely sharp mind that would remember to select TA in "anger."
I still haven't seen any formal guidance from any manufacturer though.
Personally, by the time I think of it (in the sim) I am usually at least half way towards 10,000 feet/MSA and I think it would be an extremely sharp mind that would remember to select TA in "anger."
Re: TCAS on Emer Descent
As unlikely as it might seem, I just throw this in as food for thought:
Anyone selecting TA only is always told that other aircraft in the vicinity on TA/RA will do the avoiding. Sure. But what if other aircraft in the vicinity are also on TA only (single-engine; gear-down ferry)? Don't assume that everyone else will, or is 'programmed' to, get out of your way. Again, as unlikely as it is, I throw it in as something to keep at the back of your mind.
Anyone selecting TA only is always told that other aircraft in the vicinity on TA/RA will do the avoiding. Sure. But what if other aircraft in the vicinity are also on TA only (single-engine; gear-down ferry)? Don't assume that everyone else will, or is 'programmed' to, get out of your way. Again, as unlikely as it is, I throw it in as something to keep at the back of your mind.
