Avoiding action
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Avoiding action
Just a quick question, I was given avoiding action yesterday, to prevent a loss of separation more than a collision I think. The instruction was " avoiding action ,descend now 3000' ". This was followed by a TCAS TA "traffic traffic" as we started to descend, and we saw the other a/c pass down our left side at least 3 miles away. No problem, but I just wondered if you guys have been given any new instructions about giving avoiding action as a climb or descent, rather than a heading or turn, since the Swiss midair?
I am obviously referring to the potential for a conflict between a TCAS RA and an ATC instruction. I am in no way criticising the ATCO in my case.
I am obviously referring to the potential for a conflict between a TCAS RA and an ATC instruction. I am in no way criticising the ATCO in my case.
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This little chestnut was discussed quite a bit on the last two pages of this thread. There are many, many ATCOs (including members of the training staff) who would maintain that vertical avoiding action is the way to go, because it's the quickest way to restore lost separation. I would disagree with this course of action, purely because of the confusion that could be caused if you are getting into a TCAS encounter (as is likely, if avoiding action is being given!). Turns are the way to go.
LTP
LTP
Ohcirrej
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I agree with LTP. Especially in a busy terminal environment, where several SID's can interact with each other (or in a hold), "level" avoiding action can have a major knock on effect.
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Squeaker,
Avoding action instructions are determined by what action will best resolve the situation, safest and quickest (based upon non TCAS aircraft). This could be an immediate descent, an immediate climb, or a combination with turns. It doesn't do anyone any good to give you an immediate instruction that resolves one confliction to only put you into another situation.
When you factor in TCAS, it gets more complicated because we don't know what instruction that your TCAS is going to tell you to do. There have been many documented cases of TCAS giving instructions that resolves the initial confliction to only put the pilot in a worse situation with another aircraft.
I've had pilots receive TCAS resolutions (on traffic that did not exist or was not a factor) that had they followed the instructions of TCAS they would had flown into the ground or into other traffic.
I support TCAS and I think that it is a great safety aid, but it scares me to have a pilot take an action that can potentially make the situation a whole lot worse.
Mike
NATCA FWA
Avoding action instructions are determined by what action will best resolve the situation, safest and quickest (based upon non TCAS aircraft). This could be an immediate descent, an immediate climb, or a combination with turns. It doesn't do anyone any good to give you an immediate instruction that resolves one confliction to only put you into another situation.
When you factor in TCAS, it gets more complicated because we don't know what instruction that your TCAS is going to tell you to do. There have been many documented cases of TCAS giving instructions that resolves the initial confliction to only put the pilot in a worse situation with another aircraft.
I've had pilots receive TCAS resolutions (on traffic that did not exist or was not a factor) that had they followed the instructions of TCAS they would had flown into the ground or into other traffic.
I support TCAS and I think that it is a great safety aid, but it scares me to have a pilot take an action that can potentially make the situation a whole lot worse.
Mike
NATCA FWA
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I support TCAS and I think that it is a great safety aid, but it scares me to have a pilot take an action that can potentially make the situation a whole lot worse.
From reading various publications (don't ask me what they are) that we are going along the lines of lateral avoiding action being the preferred course of action. A lateral turn does not conflict with the vertical instructions given by TCAS and so should be less confusing for a pilot in what is a high stress situation.
Mike
A GPWS alert takes precedence over a RA. If they responded to a RA that sent them down, the subsequent GPWS would have them climbing again. I had a RA a few years ago in Reno. It had us climbing twords VFR traffic that also gave us a RA. Simply leveled out for a second. No big deal.
A GPWS alert takes precedence over a RA. If they responded to a RA that sent them down, the subsequent GPWS would have them climbing again. I had a RA a few years ago in Reno. It had us climbing twords VFR traffic that also gave us a RA. Simply leveled out for a second. No big deal.
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Yes, an interesting document. There is a case for parts of it (the bits about vertical avoidance instructions possibly conflicting with TCAS RAs) to be included in the MATS Part 1, either as part of the TCAS Supplementary Instruction, or elsewhere.
Not a flawless document however. I had to gasp when I saw example 5.5. "Consider increasing the descent rate of the descending aircraft - inertia may be such that an attempt to level off could make things worse." What about the TCAS?! Conflicting vertical instructions can make things worse - recent history has shown that. And the diagram in the example is hardly complementary to the caveat stated in section 2.3; "This can result in the aircraft's position presented to the controller on the radar display being three quarters of a mile out of date immediately prior to the next update."
And the stuff trotted out from the Rules of the Air is meaningless as well. Totally inapplicable to a radar control environment. Common sense, together with an appreciation of the prevailing traffic situation, is what is required.
I find it shocking that, fifteen months after the Lake Constance mid-air, there are still no formal guidelines set out for British controllers on the use of avoiding action in conjunction with TCAS. The MATS 1 is updated every three months, so there have been at least four opportunities to have made the necessary amendments. Unfortunately, until the amendment occurs, there will still be a great number of controllers (and OJTIs) who will continue to issue (and teach their students to issue) potentially unsafe avoiding action.
LTP
Not a flawless document however. I had to gasp when I saw example 5.5. "Consider increasing the descent rate of the descending aircraft - inertia may be such that an attempt to level off could make things worse." What about the TCAS?! Conflicting vertical instructions can make things worse - recent history has shown that. And the diagram in the example is hardly complementary to the caveat stated in section 2.3; "This can result in the aircraft's position presented to the controller on the radar display being three quarters of a mile out of date immediately prior to the next update."
And the stuff trotted out from the Rules of the Air is meaningless as well. Totally inapplicable to a radar control environment. Common sense, together with an appreciation of the prevailing traffic situation, is what is required.
I find it shocking that, fifteen months after the Lake Constance mid-air, there are still no formal guidelines set out for British controllers on the use of avoiding action in conjunction with TCAS. The MATS 1 is updated every three months, so there have been at least four opportunities to have made the necessary amendments. Unfortunately, until the amendment occurs, there will still be a great number of controllers (and OJTIs) who will continue to issue (and teach their students to issue) potentially unsafe avoiding action.
LTP
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It would be nice to be working for a unit where TCAS resolution and ATC instructions are formally briefed and trained for.....sadly this is not the case at many units and the Swiss contol situation will be repeated....trust me!
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Thanks for the replies, and a good link to the CAA doc.
I would say that our training tends towards "follow TCAS", and I'm pretty sure that the more we practice flying RAs on our base checks/LPCs, the more we will become conditioned into doing that automatically. Obviously, we also practice the call to ATC of "TCAS climb/descent", but I wonder how often this results in a crossed transmission i.e. the aircraft calling at the same time ATC is trying to give avoiding action instructions. Would it be possible to incorporate a system whereby the transponder automatically indicates to the ATC controller that an RA is in progress, and which aircraft are involved in the TCAS contract? I'm thinking along the lines of a similar display to ident, or maybe a colour change.
I would say that our training tends towards "follow TCAS", and I'm pretty sure that the more we practice flying RAs on our base checks/LPCs, the more we will become conditioned into doing that automatically. Obviously, we also practice the call to ATC of "TCAS climb/descent", but I wonder how often this results in a crossed transmission i.e. the aircraft calling at the same time ATC is trying to give avoiding action instructions. Would it be possible to incorporate a system whereby the transponder automatically indicates to the ATC controller that an RA is in progress, and which aircraft are involved in the TCAS contract? I'm thinking along the lines of a similar display to ident, or maybe a colour change.
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I'm sure in the not to distant future with the advent of Mode S and data-link, controllers will be able to see a vertical profile of jets, that may indicate a TCAS manoeuver. Or even highlight by flashing (kind of like our STCA) an aircraft receiving a TA or RA? I'm sure some of our Mode S guru-types (like Scott) would be able to shed more light on this.
But Sqeaker, you're right, sod's law dictates that while you're making your "TCAS climb/descent" call, the controller may be crossing with you with avoiding action. There has been a change to the phraseology for avoiding action, requiring the use of the callsign twice at the start of the transmission. The rationale I guess is to lessen the chance of the callsign being trod on.
But Sqeaker, you're right, sod's law dictates that while you're making your "TCAS climb/descent" call, the controller may be crossing with you with avoiding action. There has been a change to the phraseology for avoiding action, requiring the use of the callsign twice at the start of the transmission. The rationale I guess is to lessen the chance of the callsign being trod on.
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As metioned in previous posts, turns are normally the best way to resolve the confliction in a TCAS environment. This, however, should not preclude the ATCO from using their judgement in initiating a climb/descent instruction to help the situation.
We all understand that if an a/c is responding to a TCAS RA then there is nowt we can do in the vertical plain. If you resolve the confliction before TCAS kicks in then using vertical is a useful tool.
We all understand that if an a/c is responding to a TCAS RA then there is nowt we can do in the vertical plain. If you resolve the confliction before TCAS kicks in then using vertical is a useful tool.
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West Coast,
Don't forget that when you are responding to an RA, I am NOT allowed to issue you any control instructions that could be considered as contrary to what the TCAS RA is telling you do do.
As a controller my only option to when you respond to an RA is to issue traffic, and hope that you don't wack another aircraft.
Mike
NATCA FWA
Don't forget that when you are responding to an RA, I am NOT allowed to issue you any control instructions that could be considered as contrary to what the TCAS RA is telling you do do.
As a controller my only option to when you respond to an RA is to issue traffic, and hope that you don't wack another aircraft.
Mike
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Sqeaker,
If you are responding to an RA, I'm not supposed to issue any turns, climbs, or descents. My only option is to issue traffic, then sort out what happened.
Another interesting issue with TCAS is when I issue traffic on non-transponder equiped traffic using the phraselogy, "traffic two o'clock 3 miles, north bound, altitude unknown." The pilots will sometimes say they see the traffic on TCAS (which is impossible since the traffic doesn't have a transponder), and quit looking for the traffic.
Mike
If you are responding to an RA, I'm not supposed to issue any turns, climbs, or descents. My only option is to issue traffic, then sort out what happened.
Another interesting issue with TCAS is when I issue traffic on non-transponder equiped traffic using the phraselogy, "traffic two o'clock 3 miles, north bound, altitude unknown." The pilots will sometimes say they see the traffic on TCAS (which is impossible since the traffic doesn't have a transponder), and quit looking for the traffic.
Mike
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Squeeker;
One problem with issuing a vector that close in is one, the vector probably isn't going to work if you are close enough to get a TCAS RA. Two, you don't know which way to really go for the fastest escape manuever, radar is NOT that accurate in the enroute environement thus the reason that we need five miles of separation. We could give you a turn to the right and actually be taking you closer to the aircraft instead of further away in the final few seconds. Altitude is a VERY good thing. You don't need much of it and you can get it VERY quickly up or down.
regards
Scott
One problem with issuing a vector that close in is one, the vector probably isn't going to work if you are close enough to get a TCAS RA. Two, you don't know which way to really go for the fastest escape manuever, radar is NOT that accurate in the enroute environement thus the reason that we need five miles of separation. We could give you a turn to the right and actually be taking you closer to the aircraft instead of further away in the final few seconds. Altitude is a VERY good thing. You don't need much of it and you can get it VERY quickly up or down.
regards
Scott
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When providing avoiding action to a military fast jet it is often better to go for height separation rather than a turn as anyone who has seen a GR4 trying to turn at high speed will testify to. Getting at least 3000ft is sometimes far quicker than getting 5nm. Equally, providing avoiding action within a known traffic environment indicates that something has gone wrong with the system already. Outside of CAS avoiding action is aimed at, where possible, achieving 3000ft or 5nm from unknown ac. These ac may or may not have TCAS, which may or may not agree a safe course of action based on predicted profiles of both ac. Additionally, the conflicting ac may or may not have SSR at all. Furthermore, TCAS and radar separation are based on two entirely different principles, an ATCO may give avoiding action at 10nm knowing the turn or climb will achieve 3000ft or 5nm, TCAS however will only kick in based on time to collision and profile, this may or may not be at the same point the controller issues the instruction. I personally see no conflict between the two systems when TCAS it is used as a last ditch effort to prevent a collision. However, TCAS does fall down when RA's are generated between ac that are climbing and descending to cleared levels, which provide separation, but due to the ac's conflicting profiles and the systems inability to grasp this simple ATC concept, false or spurious RA's are generated. These RA’s may place the ac in question into far greater danger; the machine may be good but as with everything, people are involved as well.
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Considering the lag factor on our radar information (ie. the altitude we have displayed is usually a few hundred feet behind what the aircraft is really at if they are on a fast descent or climb) we could quite easily make the situation worse by issuing a vertical avoiding instruction. So I agree with the guys who said a hard turn to both aircraft is all we can do (and cross our fingers and toes). Although have to admit that not having been in that situation I really don't know what I would do until it happened (and I sincerely hope it never does). It would be easy to throw everything at it, ie. climb/descend/turn left/turn right/ traffic is etc etc etc.
Mike
I accept that you are being taken out of the loop for a matter of time as I respond to a RA. The limitations of radar make me believe the current policy of non intervention and traffic calls as the best response to an iffy situation
I accept that you are being taken out of the loop for a matter of time as I respond to a RA. The limitations of radar make me believe the current policy of non intervention and traffic calls as the best response to an iffy situation