TCAS query

[aaaabbbbcccc1111]

If the pilot is responsible for his own separation during an RA, and we should give Traffic information to other a/c regarding the RA a/c. We are still responsible for the separation of all other a/c, if the RA a/c was starting to erode the separation of another 3rd party a/c, but the other a/c was not getting an RA, would you give avoiding action, or even a tweak left etc, even though you were not fully aware of the RA a/c intentions.

[rab-k]

What a nice picture your scenario conjurs up. :eek:

ATC is not aware of any TCAS resolution until a pilot tells us. Therefore we must attempt to maintain and regain separation on the basis that you don't know if someone is TCAS equipped, or if indeed they are so, whether it is servicable. To throw your hands up, close your eyes and cross your fingers is not an means of separating that we're encouraged to adopt. A defence of "I thought he had TCAS and would sort it himself, Your Honour" would not really help you out.

Until such time as a crew state they are complying with a TCAS RA, it is the job of ATC to separate all the traffic. Once informed of the RA and having replied in the standard 'Roger', should 'traffic' be in the face of, for example, an aircraft climbing in response to an RA, I'd probably go for issuing "Avoiding Action" to the 'traffic', consisting of radical heading change. This would mean that any RA the 'traffic' may subsequently receive after my heading instruction could also (hopefully) be complied with, or if it does not have a functioning TCAS then at least you have taken positive action to maintain or regain the separation between the 'traffic' and the aircraft with the RA.

Of course, if you have had time to pass traffic info and the aircraft concerned are both VMC and in visual contact, you may be told by a crew that they are happy to see themselves clear of the traffic and they may decline to take a ninety degree turn to the left, for example, but on their heads be it.

Really it is impossible to judge on the basis of a scenario like this what you may or may not do in the real world, but doing nothing is not an option.

[Say Again, Over!]

I agree with rab-k,

Until I'm told to butt-out (by reporting RA action), I'll be fighting like mad to keep them from touching.

The current version of TCAS doesn't provide for lateral avoidance. So even during an RA, if I thought a turn might help, I'd suggest it. If I'm still in charge, then I'll go with everything I can think of.

...God forbid...


LX

[Radarspod]

Would an indication by the display system of an RA taking place help out at all? Mode S radars downlink the RA information automatically from an aircraft reporting one. If that could be used to flash a warning up, would it help?
Of course, I am assuming that plenty of nuisance and false RA alerts happen....could be quite annoying:eek:

[rab-k]

If that could be used to flash a warning up, would it help?

In a word - YES!

Of course, I am assuming that plenty of nuisance and false RA alerts happen....could be quite annoying:eek:

Not sure if any "nuisance and false" RAs exist really. Sure you'd get lots of TAs so they could be filtered out so as not to become a nuisance, but I think an RA is an RA - if you want to live - you obey it, then worry about whether or not it was genuine after the event.

[foghorn]

I agree with rab-k,
The current version of TCAS doesn't provide for lateral avoidance. So even during an RA, if I thought a turn might help, I'd suggest it. If I'm still in charge, then I'll go with everything I can think of.
Not the way it's supposed to be done over here. "Roger" is the only correct response to being told an aircraft is following a TCAS RA, no lateral conflict resolution should be given: cockpit workload is high and it could be a distraction; throwing in a turn as well as the TCAS vertical manoeuvre could confuse a crew as to which to follow (c.f. Uberlingen); if performance is marginal a turn won't help a climbing a/c. Best to let them follow TCAS and sort things out once they've finished.

[BDiONU]

Would an indication by the display system of an RA taking place help out at all? Mode S radars downlink the RA information automatically from an aircraft reporting one. If that could be used to flash a warning up, would it help?
Of course, I am assuming that plenty of nuisance and false RA alerts happen....could be quite annoying:eek:
Looked at this and didn't think it was really much help. For one thing the time between the event and it displaying to the controller is quite long (think radar sweep intervals). The time lag means you're always going to be quite a long way behind the actual event.

BD

[PPRuNe Radar]

Not sure if any "nuisance and false" RAs exist really.

They do. Usually caused by inappropriate descent or climb rates when approaching the safe cleared level, which of course TCAS is unaware of.

Probably not too often in Oceanic airspace though I agree :)

[Jerricho]

"Roger" is the only correct response to being told an aircraft is following a TCAS RA, no lateral conflict resolution should be given:

I'm also led to believe some company ops stipulate that during an RA event in a turn, there is a maximum turn rate laid down of not very much, to allow for a "wings level" attitude to try and visually acquire the traffic.

[tired-flyboy]

5.2 On being informed that an aircraft is manoeuvring in accordance with a TCAS RA, a controller must not issue control instructions to that aircraft. Once an aircraft departs from an ATC clearance in response to an RA, the controller ceases to be responsible for providing standard separation between that aircraft and other aircraft affected as a direct consequence of that RA manoeuvre. However, controllers should continue to provide traffic information to aircraft affected by the manoeuvre. taken from MATS pt1

And then

5.3 The controller’s responsibility for providing standard separation for all aircraft resumes
when the following conditions have been met to the satisfaction of the controller:
a) The flight crew informs the controller that the TCAS manoeuvre has been
completed, and either
b) i) The controller acknowledges the report from the flight crew of the aircraft that
reported the RA that the aircraft is returning, or has returned, to its assigned
clearance, or
ii) The controller issues an alternative clearance to the aircraft that reported the RA
and this has been acknowledged by the flight crew.

Surely this answers the original Q.

So would I, yes or no depending on the situation.

[rab-k]

They do. Usually caused by inappropriate descent or climb rates when approaching the safe cleared level, which of course TCAS is unaware of.

Probably not too often in Oceanic airspace though I agree :)


:E Damn, I've been rumbled!

Genuine question - if the TCAS issues an RA will the crew not respond irrespective of whether it is due to an "inappropriate descent or climb rate", with the resulting effect on ATC being the same whether genuine or RA or otherwise?

I'd have though if the mechanical voice in the cockpit booms "Traffic! Traffic! Climb! Climb! Adjust Vertical Speed!" the crew would do so on the basis that it is better to comply now and consider later, than waste critical seconds trying to interpret information on what could be a fairly cluttered display. (Never having read a manual on TCAS I know not of such procedures :O )

[aaaabbbbcccc1111]

the controller ceases to be responsible for providing standard separation between that aircraft and other aircraft affected as a direct consequence of that RA manoeuvre.
Yes that is what I was trying to ask badly. In the text above, it states we are not responsible for providing separation between the RA a/c and other a/c affected by the original a/c RA manoeuvre. I agree that we cant control the RA a/c, but if the 3rd party a/c has not had an RA itself, then we must be responsible for the 3rd party a/c, even though it states above we are not.
I agree with comments that we should and would do something.

[Tarq57]

Originally Posted by Radarspod View Post
If that could be used to flash a warning up, would it help?
In a word - YES!

Fairly strongly inclined to agree. Technically I would have thought this wouldn't be too difficult to implement, even at a basic level of functionality, say for example, if an RA was to cause the transponder to immediately change code to something in the 7000 range, then there would within a very few seconds be an indication to the controller that (1) an RA had occurred, (2) which a/c were involved.
This is a fairly important knowledge to have, and relying solely on the crews' being able to get an RT message in, on a possibly busy frequency,at a time of high workload, is a shonky procedure at best.
Unfortunately, it's what we've got.

Read a very well penned article in "The Controller" (IFATCA magazine) following Uberlingen. (Wish I'd copied it.)
One of the recommendations, for personal operating practice, in the situation where a controller is aware there is about to be a loss of separation, is, as well as taking the immediate steps to restore the safe spacing, (which is usually a vertical movement, that being the quickest option), throw in a turn. (This, of course, doesn't apply following recognition of an RA, but could be suggested.) A turn isn't normally used in these situations, coz it takes longer to achieve your 3 (or 5) mile spacing, than a 1000ft climb/descent. But if it is added to the instruction, at least the aircraft won't hit, even if separation is lost. (Provided, of course, the aircraft were "dead ringers" laterally prior to the instruction.)
Since TCAS only provides it's safety net in the vertical sense, this makes perfect sense to me. Might have a loss of separation; far preferable to the alternative.
Personally, I'd be providing traffic/suggesting turns/ as appropriate right through the event, regardless of what MATS says my responsibilities are.

[PPRuNe Radar]

I'd have though if the mechanical voice in the cockpit booms "Traffic! Traffic! Climb! Climb! Adjust Vertical Speed!"

It won't ... at least not in the same breath ;)

When a new RA is computed, one of the following aural annunciations may be triggered:

• If a target is approaching at the same altitude:
“Climb, climb, climb!” -- or --
“Descend, descend, descend!”

• If a target is approaching from above or below and will cross your altitude:
“Climb, crossing climb! Climb, crossing climb!” -- or --
“Descend, crossing descend! Descend, crossing descend!”

• If targets are approaching above and below your own flight path and the present vertical speed should be maintained:
“Monitor vertical speed! Monitor vertical speed!”

When a pitch change to an existing RA is required, one of the following aural annunciations may be triggered:

• If the existing vertical speed is not sufficient anymore:
“Increase climb! Increase climb!” -- or --
“Increase descent! Increase descent.”

• If the previous pitch command is cancelled and a direction change is now required:
“Climb, climb now! Climb, climb now!” -- or --
“Descend, descend now! Descend, descend now!”

The respective visual pitch commands are displayed on the Attitude Indicator. Some airlines may also have an additional red band on the Vertical Speed Indicator. No matter which instrument, the pilot’s job simply is to get out of the red zone. Normally, TCAS commands a vertical target speed of 1500 to 2000 fpm.

When the traffic separation is increasing, the pitch command is removed from the PFD accompanied by the aural annunciation “clear of conflict”.

Ask someone on your unit to show you the RITA programme if you aren't sure about TCAS. It gives some good examples along with the visual and aural cues.

[West Coast]

I find myself in agreement with the poster about not wanting a turn as well. If I'm low energy when I receive a RA, I don't want to further lessen my performance by dividing my lift componants. I imagine a pilot response to a turn right or you die transmission would be do roll fairly aggressive into it. Let the TCAS do its thing at that point and hope for the best.

[Quokka]

ADS-B transmissions occur every second and sometimes every half-second. Radar sweeps or screen updates are commonly every 5 seconds depending on the system & radar, so whilst there would be a delay in the controller receiving a warning of the TCAS R/A via SSR, a future enhancement to ADS-B software could quite feasibly allow for an instantaneous transmission to the controller that a TCAS R/A was in progress. Thats assuming widespread adoption of ADS-B coverage and assuming continental ADS-B coverage (great idea that won't happen in my lifetime :rolleyes: ...it'll never happen :ugh: ).

However, beyond VHF range in oceanic airspace, such an idea for a TCAS R/A warning to Air Traffic Control via an ADS-C transmission could take an hour or more to get to the controller due to the unreliability of international messaging via satellite. Trust me, I've seen a 40 minute delay in a Flight Level excursion message via ADS-C that confused the hell out of my system when it arrived after the aircraft had appeared in MSSR coverage maintaining a different level.

[millerman]

Eurocontrol are already looking into an RA downlink system and I have personally been involved in trials and preliminary FHA/PSSA meetings.
Personally I believe it is a good thing - the more the controller knows about what the pilot should be doing - the better:)
The downlink time is not a problem in a multi radar mode S environment. Worst case scenario is 10 seconds (from what I can remember) which is a lot quicker than the verbal confirmation we normally receive (depending on cockpit workload)
The problems start when the pilot doesn't respond correctly or even goes against the TCAS RA - I know this shouldn't happen but we all know it does:eek: But is this situation any worse than todays confusion?
Also the rules of seperation provision would have to change, eg. a pilot receives an RA and acts properly in accordance with the RA, the controller sees the RA downlink and also sees that the pilot is complying with the downlink but until the pilot confirms this verbally the controller is still responsible for seperation:ugh: But at least with downlink the controller shouldn't issue instructions that go against the RA:ok:
It is early days but some system should be available in the future (I don't know of the present progress of the Eurocontrol project). There are also issues with the HMI and how much information the controller actually needs

[BDiONU]

Technically I would have thought this wouldn't be too difficult to implement, even at a basic level of functionality, say for example, if an RA was to cause the transponder to immediately change code to something in the 7000 range, then there would within a very few seconds be an indication to the controller that (1) an RA had occurred, (2) which a/c were involved.
Depends on the rotation rate of the radar head. Lets say its a standard ATC radar rotating at 6 times a minute, 10 seconds per rotation. If you just miss a sweep it could be 19 seconds until it was picked up and then displayed on the ATCO's screen. Then the ATCO has to recognise it for what it is etc. etc. Even going down the route of providing a specific alarm function you still trip up over the time lag difficulty.

BD

[BDiONU]

Eurocontrol are already looking into an RA downlink system and I have personally been involved in trials and preliminary FHA/PSSA meetings.
<snip>It is early days but some system should be available in the future (I don't know of the present progress of the Eurocontrol project). There are also issues with the HMI and how much information the controller actually needs
Stalled.

BD

[millerman]

BDiONU
Now there is a surprise...not;)
Another Eurocontrol project that they spend thousands on that doesn't make it to fruition:(
At least it keeps people in a job in the ivory towers:E ...or am I just being cynical?

[Radarspod]

Depends on the rotation rate of the radar head. Lets say its a standard ATC radar rotating at 6 times a minute, 10 seconds per rotation. If you just miss a sweep it could be 19 seconds until it was picked up and then displayed on the ATCO's screen. Then the ATCO has to recognise it for what it is etc. etc. Even going down the route of providing a specific alarm function you still trip up over the time lag difficulty.
BD

Agree that the downlink time could prevent it from being useful immeidately, but as mentioned above, a multiradar environment could speed things up. However, even if the controller did not get immediate indication, it may be useful to have an indication as to why an aircraft is doing something unexpected and you can't raise them. I'm only asking out of interest, as at the moment the info is junked on receipt and it seems a waste of bandwidth :}

P.S. Being picky, the slowest enroute NATS radar turns at 7.5RPM, / 8 sec rotation, with many at 10RPM / 6 second. :=

[BDiONU]

BDiONU
Now there is a surprise...not;)
Another Eurocontrol project that they spend thousands on that doesn't make it to fruition:(
At least it keeps people in a job in the ivory towers:E ...or am I just being cynical?
If things like this were not subject to R&D then we'd never know what did work and what didn't. Yes its unfortunate that somes things sound very promising but practical investigation shows that they don't provide the hoped for benefits.

BD

[BDiONU]

Agree that the downlink time could prevent it from being useful immeidately, but as mentioned above, a multiradar environment could speed things up. However, even if the controller did not get immediate indication, it may be useful to have an indication as to why an aircraft is doing something unexpected and you can't raise them. I'm only asking out of interest, as at the moment the info is junked on receipt and it seems a waste of bandwidth :}
P.S. Being picky, the slowest enroute NATS radar turns at 7.5RPM, / 8 sec rotation, with many at 10RPM / 6 second. :=
Mode S radars mean only one radar interogates the SSR, thats a function of how it works.

BD

[Radarspod]

Mode S radars mean only one radar interogates the SSR, thats a function of how it works.
BD

Sorry. lost me........:confused:

If you mean only one radar interrogates the transponder of that aircraft, I think you are refering to a function called clustering or Surveillance Coordination Network (SCN), of which the possibility of having a network of radars where only one radar interrogates the aircraft at any one time. Only 3 SCNs (if i remember correctly) have been deployed so far in Europe, and for those deployments, none have been deployed in that fashion - all of the radars within the clusters still interrogate the aircraft in cover regardless of what the others are doing. At the moment and certainly for the near-medium future, every Mode S radar will see any aircraft in its cover (subject to IC allocations and surveillance responsibilities allocated).

So each radar detecting an aircraft in its cover would downlink the TCAS RA, allowing possibilty of quick indication if using Multiradar tracking in the RDP / display.

[BDiONU]

Sorry. lost me........:confused:
If you mean only one radar interrogates the transponder of that aircraft, I think you are refering to a function called clustering or Surveillance Coordination Network (SCN), of which the possibility of having a network of radars where only one radar interrogates the aircraft at any one time. Only 3 SCNs (if i remember correctly) have been deployed so far in Europe, and for those deployments, none have been deployed in that fashion - all of the radars within the clusters still interrogate the aircraft in cover regardless of what the others are doing. At the moment and certainly for the near-medium future, every Mode S radar will see any aircraft in its cover (subject to IC allocations and surveillance responsibilities allocated).
So each radar detecting an aircraft in its cover would downlink the TCAS RA, allowing possibilty of quick indication if using Multiradar tracking in the RDP / display.
Trying to get my head around it as well :\ I'm thinking of the Interrogator Codes, only 15 available, and the interrogator doing an All-Call to acquire 'new' transponders entering its coverage. Then (as I understand it) the interrogator locks out the transponder from responding to any new All-Call requests. With only 15 IC's throughout Europe it makes things tricky where your coverage overlaps.
I see from your profile that you're an expert on mode 'S' so any help or pointers you can give to a simple explanation would be greatly appreciated!

BD

[BDiONU]

P.S. Being picky, the slowest enroute NATS radar turns at 7.5RPM, / 8 sec rotation, with many at 10RPM / 6 second. :=
Just looked it up (my figures were quite olde ones) and you're quite correct, so you could still conceivable 'miss' a sweep and have no update for 15 seconds :}
GDF - 7.5
Clee - 7.25
CLX - 7.6
Bur - 7.5
Heathrow - 15!

BD