New ATC Documentary on BBC2
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The pace of change
ICAO needs to ensure that all pilots know to follow TCAS when its instructions are contradicted by ATC, and all ATCOs need to provide turns rather than climb/descent for avoiding action.
1) With some pilots there will always be a shred of doubt when ATC instructions contradict TCAS. And more importantly:
2) There is NOTHING (yet) set down in ATC training to suggest that avoiding action TURNS are best practice when an Airprox is occurring, and pilots are probably reacting to RAs.
In fact, at Swanwick, there must be any number of instructors, even local competency examiners, who suggest that vertical avoiding action is the best way to go. Purely on the basis that 1000ft is easier to achieve than 5 miles, and the good book says that in a loss of separation situation we must "use every means at [our] disposal to obtain the required minimum with the least possible delay". Sounds good, but it's hardly helpful when half the instructors AND the air traffic manual are working AGAINST what is clearly common sense.
TCAS is a brilliant piece of kit. I have seen radar replays of an incident where it managed to keep FOUR aircraft apart, when a Gatwick outbound off 26L was cleared to climb to FL130 towards DET when there were two in the hold at BIG and another coming in from the south to hold at FL110. Left to its own devices, TCAS will keep things apart.
Unfortunately the pace of change in the ATC procedures world is slow, and the pace of common sense is often slower....
LTP
Last edited by LostThePicture; 21st Aug 2003 at 20:39.
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Scott H. Voigt,
Some of the FAA ATC computers are ancient, even now. The ratio of old computers to new computers is improving rapidly, but there are still a large number of very old computers in daily use.
How can I put this gently....
Boeing are not interested in supplying ad-hoc bits of hardware to the FAA.
Boeing want to design, install and operate a national (indeed, world-wide) air traffic management solution that will require a paradigm shift away from the current labor-intensive, inefficient, capacity constrained ATC methods.
As a card-carrying, office bearing member of a trade union that is very publicly campaigning against ATC privatisation, are you really all that surprised that Boeing is a bit reluctant to give away its secrets?
Boeing don’t want to replace the FAA computers – they want to replace the FAA.
I am somewhat familiar with US ATC – and you folks do a fine job and provide an exemplary service. 
In my opinion 99.9% of US air traffic controllers would go the extra mile trying to move traffic in situations where the air traffic controllers in most other countries would just say “too hard” and give up, resulting in airborne holding or slot delays on the ground. It’s that great American can-do attitude at its very best. 
As I am sure you are all too aware, the subject of FAA funding is at the very heart of the privatisation issue.
The current federal budgetary process that allocates funds to the FAA year by year makes planning for medium and longer-term infrastructure investment almost impossible.
Boeing have a big chunk of money and are ready to invest – but they want to own the game, not buy into someone else’s problems.
I couldn’t agree more.
Airlines wont spend a buck unless it’s mandated or they can make their money back within the current financial reporting period.
If it wasn’t mandatory equipment the airliners of today would never have been fitted with EGPWS, TCAS, RVSM, 8.33 kHz radios, fire-resistant furnishings, Mode C transponders etc.
So what’s new? Nothing. Make datalink mandatory – the same as having a transponder is mandatory. No datalink – no fly.
In any case, although the world fleet of 70s and 80s era airliners is enormous, it is diminishing rapidly as these old clunkers are one by one withdrawn from service. They’ve already started parting out 1970s A300s and 1980’s B737-300/400s, for example.
Agreed.
A common solution is what is required. Unfortunately, the current situation is that there are several very expensive development projects running in parallel – and none of them are compatible. To use a 1980s video cassette analogy, one of them will end up being the VHS and one will end up being the Beta.
ChrisN,
I couldn’t agree more.
Actually – you are preaching to the converted.
There is no such thing as absolute safety. The best we can ever hope for (as you quite rightly point out) is an acceptable level of safety.
And as you go on to say later :
I’ve been a big advocate of affordable safety for some time now because I know that there is no other kind.
You are quite right - to be technically correct I should have used the words “deemed to be an acceptable level of risk”, but I went with “perfectly safe” because it has greater impact, is a simpler concept, and because it reads better.
I was referring to the great number of UK based light aircraft (and some UK military aircraft) that are fitted with a transponder but which don’t have an altitude encoder. I wasn’t referring to aircraft that don’t have any kind of transponder.
A you rightly point out – the chance of a non-transponder equipped glider or very light aircraft colliding with an aircraft that is of a class required to carry TCAS is sufficiently remote as to be statistically acceptable. It would seem that the big sky theory, along with a judicious lookout, works very well.
fourthreethree,
I am under no delusion that this is a back-slapping mutual admiration society. I don’t need or seek your approval or respect.
Your words are touching, but unnecessary.
Your clearance might have been “safe”, but the flight path of the aircraft was not safe – and that’s why they got a TCAS RA.
And how can you be so sure that “there was never any danger of an infringement of separation”?
Perhaps you listened carefully for a correct read-back from the flight crew? Great! But how can you know for sure what altitude the flight crew dialled into the autopilot / altitude alerter? How do you know that the autopilot is functioning properly and will correctly and accurately capture the assigned altitude? How can you know that the autopilot is even engaged? There are just too many variables – there is simply no way for you to know for sure that “there was never any danger of an infringement of separation”.
TCAS has no interest in the clearance you have issued. TCAS looks at what the planes are actually doing – not what they have been authorised to do.
There is never any guarantee that a climber or descender will actually level off at its ATC assigned level. If there were a guarantee then there would be no such thing as a level bust.
There was nothing “false” about the RA. The TCAS equipment was in all likelihood functioning correctly and in accordance with its manufacturers specifications and within FAA/CAA approved parameters.
Having said all that, there remains a question as to why these aircraft had such a high closure rate that it generated an RA.
Flight crew of TCAS equipped aircraft should moderate their rate of climb or descent when approaching a cleared level. They are only making work for themselves if they don’t.
Unfortunately, not all crews do. I did hear a brilliant bit of proactive controlling recently :
“[callsign 1] traffic you may see on your TCAS screen is a [aircraft type] in your 12 o’clock, seven miles, cleared to 1,000 feet below your level – he’s got quite a high rate of climb on – about 4,500 feet per minute.”
and then :
“[callsign 2] maintain [level] on reaching - traffic is a [aircraft type] in your 12 o’clock, five miles, maintaining 1,000 feet above your cleared level.”
The controller might as well be saying to the climber : “Hey – reduce your rate of climb, Bozo!” And fair enough too!
I’m not for a moment suggesting that this level of ATC service should be mandatory. Flight crews should already know that they must moderate their rate of climb or descent when approaching a cleared level.
But I did think that this controller exhibited remarkable situational awareness and a proactive but friendly style that quite probably avoided an RA – and that’s got to be a good thing.
Again – the clearance was safe – but the aircraft’s flight path was not.
You (as an air traffic controller working to a man-made set of specifications) have ATC separation minima to respect.
But in the real world (and as some ATCers on these pages have been known to quip) “a miss is as good as five miles”. And indeed it is – it doesn’t matter whether two aircraft miss by 100 feet or by five nautical miles, the outcome is the same – no collision and no calamity.
TCAS certainly will keep the planes apart – but it does it using a different methodology.
Whist ATC minimum separation criteria is specified in terms of 1,000 feet vertically or five nautical miles laterally (sometimes three miles), TCAS TAs and RAs work in terms of the time to (and separation at) the closest point of approach.
For information about TCAS TA and RA criteria refer to this :
Honeywell TCAS Users Manual.
(NB : This document has been around for a while and some of the TCAS traffic display hardware is a bit old fashioned. The current displays are much better.)
From the Honeywell manual :
“TCAS II predicts the time to, and the separation at, the intruders closest point of approach (CPA). Should TCAS II predict that certain safe boundaries may be violated, it will issue a Traffic Advisory (TA)....
If the intruder continues to close, TCAS II will issue a Resolution Advisory (RA) to obtain or maintain safe vertical separation between your aircraft and the intruder....”
And further :
“TRAFFIC ADVISORY (TA) – A symbol change to a filled yellow circle indicates that the intruding aircraft is considered to be potentially hazardous. Depending on your altitude TCAS II will display a TA when the time to CPA [closest point of approach] is between 20 and 48 seconds......Under normal conditions a TA will precede an RA by 10 to 15 seconds.”
and :
“RESOLUTION ADVISORY (RA) – A solid red square indicates that the intruding aircraft is projected to be a collision threat. TCAS II calculates that the intruder has reached the point where a Resolution Advisory is necessary. The time to closest [point of] approach with the intruder is now between 15 and 35 seconds depending on your altitude.”
and :
“TCAS II can track as many as 45 aircraft, display up to 30 of them and can coordinate a resolution advisory for up to three intruders at once. The advisories are always based on the least amount of deviation from the flight path while providing safe vertical separation.”
I’m very happy with the protection TCAS offers.
The net result of two aircraft coming within 100 feet of each other (but missing) is the same as if they were fifty miles apart – there is no collision and no calamity.
I’m not sure how timid you are, but the various TCAS systems that I’ve worked with have more than earned my faith in them.
I disagree.
Flight crews do have a very high level of situational awareness, even without TCAS.
If you instruct me to descend and I see traffic 1,000 feet below me (either on TCAS or out the window, or because I heard it on the radio) then I will question the descent clearance.
If you give me a turn towards nearby traffic at the same level (that I have seen on TCAS or by looking out the window) then I will question the turn.
Sorry – but that’s the way it’s got to be. My self-preservation mechanism won’t allow me to do otherwise.
My comments about the usefulness of a TCAS traffic display as a situational awareness tool (the comments that I addressed to Mr Big, Lon More and others) were mainly in relation to the loss of certain situational awareness cues when datalink is fully implemented and voice instructions are no longer broadcast.
Flight crews don’t currently have flight plan data about other aircraft, and I’m not aware of any proposal for the distribution of this kind of data at any time in the future.
ferris,
Again, really touching but entirely unnecessary. 
Nah – I didn’t. I just love winding you up. 
You wont have to. The process will be automated.
I agree with you about what is technically feasible, and I do agree that it’s a great idea.
But in terms of airspace capacity the rate at which a flight crew can manipulate the autopilot or program the FMC is not yet a limiting factor. It’s not likely to be a limiting factor at any time in the foreseeable future.
In many parts of the world the limiting factor is already the rate at which a human air traffic controller can shout instructions down an unreliable asynchronous VHF voice link. See, for example, the Flight International extract below.
Are you for real or are you just spanking the monkey?
If you are in any way serious then you have a much greater lack of understanding than I’d previously imagined.
This stuff is all in the public domain.
Even older versions of TCAS software will track up to 45 targets and display up to 30 of them. The 30 that are displayed are the ones that are most relevant – ie the ones that have the least time to (and separation at) the closest point of approach. There’s no point in TCAS displaying a target that is four minutes from CPA if there is another target that is 45 seconds from CPA. Unless you manage to miss the 45 seconds target you wont have to worry about the target that is four minutes away. This stuff isn’t rocket science.
Targets that are close but approaching at an acute angle have a much greater time to closest point of approach than targets that are further away but approaching at an obtuse angle. TCAS works in terms of the time to (and separation at) the closest point of approach. It’s simple geometry. There’s no black magic to it.
As earlier, I suggest that there is nothing “false” about these RAs. These RAs result from an unsafe flight path that is brought about by an irresponsibly high rate of climb or descent when approaching a cleared level. Flight crews should know this.
So why are you issuing clearances that you know to be less than optimal?
The 2,000 feet between cleared levels is largely irrelevant to TCAS. TCAS works in terms of the time to (and separation at) the closest point of approach. If your descender gets a 6,000 feet per minute descent going he could still get a TCAS RA – even with 2,000 feet between cleared levels.
I spose we could all be doing something else – like going sailing or playing golf or whatever.
If you’d given the flight crew a simple heads up, like “Descend flight level two-zero-zero, further descent in two-zero miles” or “Descend flight level two-zero-zero, opposite direction traffic climbing to one-thousand feet below” then perhaps they wouldn’t have been in a great rush to get down to FL200 and they wouldn’t have felt the need to give you a nudge. You can either save work for yourself or you can make work for yourself. You choose.
They might be where you are, but that’s simply not the case in many capacity constrained parts of the world which have an abundance of concrete but a shortage of VHF air time. See the Flight International extract below
fourthreethree
You bet your life there is. That’s precisely what TCAS is for.
TCAS has no knowledge of or interest in ATC separation criteria. TCAS will keep the planes apart based on their actual trajectories.
TCAS is largely uninterested in your 2000 feet of separation. TCAS works in terms of the time to (and separation at) the closest point of approach. In short – the closure rate.
It is a controlled situation – it’s just that you are not the one controlling it.
TCAS will simultaneously co-ordinate RAs with up to three intruders (ie four aircraft in total).
TCAS will issue an initial RA that requires the minimum acceptable deviation from the current trajectory.
If your other traffic gets too close then all three aircraft will be issued with a co-ordinated RA.
Oh dear! I can see that this isn’t going to work. 
Lon More,
You have two options. Specify with the initial descent clearance weather they should “Descend now....” or “When ready....”, or else wait for them to call you back and query it. Your choice.
I’m not so sure that it’s ever been an exclusively “American method”. The very sensible practice should by now be universal.
fourthreethree,
Nope – that still isn’t going to work. Your clearance might be “safe” but you have no way of knowing for sure that there is “no chance of a loss of separation” because you don’t know for certain that both aircraft will stop at their assigned levels. And because RAs between airliners are nearly always co-ordinated, what happens if one crew decides to disregard a nuisance RA (based on your traffic information) but the conflicting crew doesn’t? It’s going to be a scenario very similar to Lake Constance.
It’s definitely not a waste of time, as I tried to suggest by including the earlier example of proactive controlling. Flight crews should be aware of the need to moderate their rate of climb or descent when approaching a cleared level. But some flight crews are simply lazy. Reducing the rate of climb on a Boeing airplane requires a pilot to press the “VS” button and rotate a pitch wheel. Some crews are VERY lazy! A timely heads-up from ATC can often convince a lazy flight crew that if they don’t press a button and turn a wheel they are sure to get an RA – and that means that they’ll have to push many buttons and hand fly the airplane. Give them the heads up. I don’t know of too many crews (not even the very laziest of them) who would put themselves in a situation that is sure to generate an RA.
Of course they “reacted”. If they didn’t “react” then they’d deserve to be sacked! Flying an RA isn’t optional.
Whilst it’s technically very easy to modify the RA parameters at the factory, TCAS units are certified in accordance with an approved set of performance criteria. I’m not aware of any TCAS unit that has a user-adjustable RA.
On Honeywell units the time between a TA and CPA varies between 20 and 48 seconds, depending on altitude. The time between an RA and CPA is between 15 to 35 seconds, depending on altitude.
Even if you could adjust the RA parameters – just how close to CPA would you like to leave it?
If there was going to be a nuisance RA due to an irresponsibly high rate of climb or descent then I would expect it to happen when one (or both) aircraft are between 800 feet and 1,500 feet from their cleared levels. Anything greater than about 1,500 feet and you would need an extremely high vertical closure rate (Saturn V ascent profile) to set off an RA. Anything less than about 800 feet and the autopilot has already gone into altitude capture mode, reducing the vertical closure rate.
I note that you say that neither aircraft had a high rate of climb or descent, but I’m almost certain that’s precisely what’s caused the nuisance RA(s). The fact that they were opposite direction (ie high lateral closure rate) would tend to reduce the vertical closure rate RA threshold.
TCAS is aware of the surrounding traffic. TCAS will co-ordinate a four-way RA with surrounding traffic if required.
Although TCAS will make no attempt to achieve or maintain MATS Part 1 minimum separation criteria, it will keep the planes from banging together so long as the crews don’t fly against an RA.
Wedge,
You’re very close – but I think you may be just slightly wide of the mark.
It’s the pilot in command who is in charge of the aeroplane – not the captain.
This is a subtle but important distinction.
Although the captain and the pilot in command are often the same person, there are literally hundreds of flights every day where this is not the case.
Although I am not familiar with the Tu-154 operator’s SOPs, western operators I am familiar with would all designate a check captain performing a check flight and occupying a control seat as pilot in command. The guy in the left seat who is under check is still the captain – but in this situation he’s not the pilot in command.
Although good CRM dictates that all crew members must feel free to speak up when they are not completely happy with a situation or a proposed course of action, and although a good pilot in command should always welcome these contributions and take time to carefully consider them, there are certain time critical situations (like an RA) when the pilot in command has to make a very quick decision and then live with the consequences come what may. And that’s precisely what happened in the TU-154 in Lake Constance.
Check your speed with....
And excellent question for which I think there is no satisfactory answer. The disaster was a team effort.
GroundBound
Thanks for a really excellent post – one that I wholeheartedly agree with.
HugMonster ,
My thoughts exactly.
My understanding is that Peter X was handing (in total) five aircraft.
It is my understanding that the TU-154 and the B757 had both made radio contact with Peter X more than five minutes prior to the collision, but that the TU-154 descent instruction was issued approximately one minute prior to the collision. It’s the prioritisation during the time in between that I can’t figure out.
Was Peter X solely responsible for this disaster? Definitely not.
Was Peter X partly responsible for this disaster? Definitely yes.
eastern wiseguy,
Short answer : YES.
Refer : Honeywell TCAS Users Manual.
(particularly see Adobe pages 34-34 of 83 which are the same as original document pages 31-32)
Slightly longer answer :
(I’ll use the TCAS v7 aurals as examples here. Earlier TCAS software versions are essentially similar.)
The TCAS in the Lake Constance disaster issued a “DESCEND DESCEND” initial RA to the B757 and a “CLIMB CLIMB” initial RA to the TU-154. These RAs were co-ordinated, meaning that before either RA was issued there was an automatic electronic exchange between the two TCAS units and an electronic agreement was reached about which TCAS unit would issue a climb RA and which would issue a descend RA.
After issuing the initial RAs the B757 commenced a descent (in accordance with its RA) and the TU-154 commenced a descent (going against its RA).
Both TCAS units continued to evaluate the traffic situation in real time, looking at the time to (and separation at) the closest point of approach. As you suggest, at this point the TCAS units jointly (because it’s a coordinated manoeuvre) make a decision about whether the initial RAs are working or not.
If they are working then that’s great. If they are not working then a secondary RA will be issued.
TCAS can decide to increase the intensity of the RA in the same direction (eg “INCREASE DESCENT”), or can decide to reverse the direction of the RA (eg change from a “DESCEND DESCEND” to a “CLIMB, CLIMB NOW, CLIMB, CLIMB NOW”).
It is quite likely that in the Lake Constance disaster both aircraft got secondary RAs of increased intensity - the B757 getting an “INCREASE DESCENT, INCREASE DESCENT” RA and the TU-154 getting an “INCREASE CLIMB, INCREASE CLIMB” RA.
If the two TCAS units had decided that it would have been better to swap things around and issue a reversal then the B757 would have got a “CLIMB, CLIMB NOW, CLIMB, CLIMB NOW” RA and the TU-154 would have got a “DESCEND, DESCEND NOW, DESCEND, DESCEND NOW” RA.
Actually – unless you know where to find some very dodgy controllers the best way to see TCAS in action is to rent some simulator time so you can safely explore (and fly) a whole range of TCAS scenarios.
LostThePicture,
Agreed. I’ve never been involved in a 4-way split - that one sounds interesting! Current TCAS systems can co-ordinate RAs with up to three intruders (ie four aircraft in total) – so that 4-way would have been testing the system to its maximum potential! Good job it worked, eh?
Post Script :
In an earlier post on this thread I said that getting the SIDs and STARS right was a pre-requisite for automated terminal ATC via datalink.
One of the great problems with many UK STARs is that they end at a holding fix with no published procedure to get from the holding fix to the ILS. In many other countries the STAR ends at an off airport holding fix that is also one of the initial approach fixes for the ILS. Aircraft don’t have to be subjected to protracted, labor-intensive radar vectoring to get from the holding fix to the ILS - rather, aircraft in or approaching the hold are simply told “cleared ILS”.
Although the following Flight International extract deals with P-RNAV approaches the reason I have included it here is, firstly, because it shows that it is possible to design an ILS approach procedure that starts at an off airport holding fix (such an approach procedure in and of itself does not necessarily require P-RNAV, or even B-RNAV – it could just as easily be designed using existing terrestrial radio navigation aids), and secondly, because a NATS spokesperson has said that in relation to London Heathrow : “In traffic capacity terms, you can be constrained as much by the amount of instruction time on the radio as by the airspace itself.”
It’s worth noting that Boeing FMSs have been capable of P-RNAV approaches for a number of years, but it’s only now that the UK CAA and NATS are finally pulling their finger out to put their stamp of approval on the procedures. Oh well – I guess that change at a glacial pace is better than no change at all!
Flight International 12-18 August 2003 page 12
Hate to say it mate, but you are looking at some OLD data. The FAA doesn't have old computers anymore. We have gotten rid of most of the old stuff. We do indeed have some older software around in the host processing in the new hardware, but our computers don't fail very much anymore. We are also working with new displays and some of the enroute facilities are working with new data systems also. More are to come on line in the next 8 to 12 months.
The Boeing plan does look sexy doesn't it. The problem with it though is when you get into it, it lacks substance and the HOW they are going to do it. We have talked with them about the PLAN... They can never answer the questions of just how they are going to be able to do it, nor can they answer how much is it going to cost and who is going to pay for it...
Boeing are not interested in supplying ad-hoc bits of hardware to the FAA.
Boeing want to design, install and operate a national (indeed, world-wide) air traffic management solution that will require a paradigm shift away from the current labor-intensive, inefficient, capacity constrained ATC methods.
As a card-carrying, office bearing member of a trade union that is very publicly campaigning against ATC privatisation, are you really all that surprised that Boeing is a bit reluctant to give away its secrets?
Boeing don’t want to replace the FAA computers – they want to replace the FAA.
....so that we can move more aircraft. It is something that we like to do here if you aren't too familiar with the US ATC...
In my opinion 99.9% of US air traffic controllers would go the extra mile trying to move traffic in situations where the air traffic controllers in most other countries would just say “too hard” and give up, resulting in airborne holding or slot delays on the ground. It’s that great American can-do attitude at its very best.
Even the more or less minor things that we would like to do we are told that we can't afford it even if we can make it work. So, if it is unaffordable, then it is for now unobtainable.
The current federal budgetary process that allocates funds to the FAA year by year makes planning for medium and longer-term infrastructure investment almost impossible.
Boeing have a big chunk of money and are ready to invest – but they want to own the game, not buy into someone else’s problems.
....many of the things that are going to be needed to improve the through put of aircraft is going to require equipment not just on the ground and in space, but in the cockpit, and as we have found out with datalink. The airlines are not in a position to desire to upgrade their fleets and spend the money. Nor are they in a position to upgrade the nav in the 70’s and 80’s era glass cockpit aircraft that use DME/DME for navigation. This is leaving them out of some of the leading edge nav stuff that we are trying to do to improve efficiencies of getting about in both the terminal and enroute airspace. So it isn’t just the problem of the ATC provider.
Airlines wont spend a buck unless it’s mandated or they can make their money back within the current financial reporting period.
If it wasn’t mandatory equipment the airliners of today would never have been fitted with EGPWS, TCAS, RVSM, 8.33 kHz radios, fire-resistant furnishings, Mode C transponders etc.
So what’s new? Nothing. Make datalink mandatory – the same as having a transponder is mandatory. No datalink – no fly.
In any case, although the world fleet of 70s and 80s era airliners is enormous, it is diminishing rapidly as these old clunkers are one by one withdrawn from service. They’ve already started parting out 1970s A300s and 1980’s B737-300/400s, for example.
While we are speaking of equippage. For us to do our jobs as controllers, we have to have everyone doing things about the same. When we start mixing navigation equipage which in the future may determine separation criteria it makes our jobs a LOT harder. If we want to increase our output, then we have to make the job easier and not harder...
A common solution is what is required. Unfortunately, the current situation is that there are several very expensive development projects running in parallel – and none of them are compatible. To use a 1980s video cassette analogy, one of them will end up being the VHS and one will end up being the Beta.
ChrisN,
....two points seemed to be a generalisation a little too far:
---------------------
"By classifying the AIAAs as class G the UK government is tacitly suggesting that it’s perfectly safe....
---------------------
Perfect safety is unattainable - if the Government/CAA/NATS or whoever has a tacit position, it is that there is an acceptable level of risk, which is around 10 to the -8 or so per flight.
---------------------
"By classifying the AIAAs as class G the UK government is tacitly suggesting that it’s perfectly safe....
---------------------
Perfect safety is unattainable - if the Government/CAA/NATS or whoever has a tacit position, it is that there is an acceptable level of risk, which is around 10 to the -8 or so per flight.
Actually – you are preaching to the converted.
There is no such thing as absolute safety. The best we can ever hope for (as you quite rightly point out) is an acceptable level of safety.
And as you go on to say later :
“....the solutions have to practicable and affordable.”
You are quite right - to be technically correct I should have used the words “deemed to be an acceptable level of risk”, but I went with “perfectly safe” because it has greater impact, is a simpler concept, and because it reads better.
------------------------------------------------
"Which leaves those aircraft without an automatic altitude reporting function. Various flying magazine advertisements show altitude encoding blind altimeters available in the UK, tax paid, for under £150. Is this too much to ask? I think not. "
------------------------------------------------
There is more to it than that. I fly a non-transponder glider....
"Which leaves those aircraft without an automatic altitude reporting function. Various flying magazine advertisements show altitude encoding blind altimeters available in the UK, tax paid, for under £150. Is this too much to ask? I think not. "
------------------------------------------------
There is more to it than that. I fly a non-transponder glider....
A you rightly point out – the chance of a non-transponder equipped glider or very light aircraft colliding with an aircraft that is of a class required to carry TCAS is sufficiently remote as to be statistically acceptable. It would seem that the big sky theory, along with a judicious lookout, works very well.
fourthreethree,
Well well, aint it amazing the responses you get when you turn to reasoned discussion rather than your previous vitriolic garbage. Having read your post I have reassessed my opinion of you. I may not agree with what you say a great deal, but thats the point of a discussion thread. At least now I can respect your view point as one coming from an intelligent human being.
Your words are touching, but unnecessary.
To answer your question, a False RA, or at least my definition of it with regard to my post, is an RA given by TCAS when there was never any danger of an infringement of separation. In my case the action taken by the pilot, which was correct in accordance to airline policy, was to divert from my safe clearance, and climb into opposite traffic, which I had to turn away to avoid a loss of separation.
And how can you be so sure that “there was never any danger of an infringement of separation”?
Perhaps you listened carefully for a correct read-back from the flight crew? Great! But how can you know for sure what altitude the flight crew dialled into the autopilot / altitude alerter? How do you know that the autopilot is functioning properly and will correctly and accurately capture the assigned altitude? How can you know that the autopilot is even engaged? There are just too many variables – there is simply no way for you to know for sure that “there was never any danger of an infringement of separation”.
TCAS has no interest in the clearance you have issued. TCAS looks at what the planes are actually doing – not what they have been authorised to do.
There is never any guarantee that a climber or descender will actually level off at its ATC assigned level. If there were a guarantee then there would be no such thing as a level bust.
There was nothing “false” about the RA. The TCAS equipment was in all likelihood functioning correctly and in accordance with its manufacturers specifications and within FAA/CAA approved parameters.
Having said all that, there remains a question as to why these aircraft had such a high closure rate that it generated an RA.
Flight crew of TCAS equipped aircraft should moderate their rate of climb or descent when approaching a cleared level. They are only making work for themselves if they don’t.
Unfortunately, not all crews do. I did hear a brilliant bit of proactive controlling recently :
“[callsign 1] traffic you may see on your TCAS screen is a [aircraft type] in your 12 o’clock, seven miles, cleared to 1,000 feet below your level – he’s got quite a high rate of climb on – about 4,500 feet per minute.”
and then :
“[callsign 2] maintain [level] on reaching - traffic is a [aircraft type] in your 12 o’clock, five miles, maintaining 1,000 feet above your cleared level.”
The controller might as well be saying to the climber : “Hey – reduce your rate of climb, Bozo!” And fair enough too!
I’m not for a moment suggesting that this level of ATC service should be mandatory. Flight crews should already know that they must moderate their rate of climb or descent when approaching a cleared level.
But I did think that this controller exhibited remarkable situational awareness and a proactive but friendly style that quite probably avoided an RA – and that’s got to be a good thing.
Again – the clearance was safe – but the aircraft’s flight path was not.
As you say, TCAS if left to its own devices will keep a/c apart, but we have separation minima to respect, TCAS will not adhere to that. If you are happy with that scenario then you're a braver man than me.
But in the real world (and as some ATCers on these pages have been known to quip) “a miss is as good as five miles”. And indeed it is – it doesn’t matter whether two aircraft miss by 100 feet or by five nautical miles, the outcome is the same – no collision and no calamity.
TCAS certainly will keep the planes apart – but it does it using a different methodology.
Whist ATC minimum separation criteria is specified in terms of 1,000 feet vertically or five nautical miles laterally (sometimes three miles), TCAS TAs and RAs work in terms of the time to (and separation at) the closest point of approach.
For information about TCAS TA and RA criteria refer to this :
Honeywell TCAS Users Manual.
(NB : This document has been around for a while and some of the TCAS traffic display hardware is a bit old fashioned. The current displays are much better.)
From the Honeywell manual :
“TCAS II predicts the time to, and the separation at, the intruders closest point of approach (CPA). Should TCAS II predict that certain safe boundaries may be violated, it will issue a Traffic Advisory (TA)....
If the intruder continues to close, TCAS II will issue a Resolution Advisory (RA) to obtain or maintain safe vertical separation between your aircraft and the intruder....”
And further :
“TRAFFIC ADVISORY (TA) – A symbol change to a filled yellow circle indicates that the intruding aircraft is considered to be potentially hazardous. Depending on your altitude TCAS II will display a TA when the time to CPA [closest point of approach] is between 20 and 48 seconds......Under normal conditions a TA will precede an RA by 10 to 15 seconds.”
and :
“RESOLUTION ADVISORY (RA) – A solid red square indicates that the intruding aircraft is projected to be a collision threat. TCAS II calculates that the intruder has reached the point where a Resolution Advisory is necessary. The time to closest [point of] approach with the intruder is now between 15 and 35 seconds depending on your altitude.”
and :
“TCAS II can track as many as 45 aircraft, display up to 30 of them and can coordinate a resolution advisory for up to three intruders at once. The advisories are always based on the least amount of deviation from the flight path while providing safe vertical separation.”
I’m very happy with the protection TCAS offers.
The net result of two aircraft coming within 100 feet of each other (but missing) is the same as if they were fifty miles apart – there is no collision and no calamity.
I’m not sure how timid you are, but the various TCAS systems that I’ve worked with have more than earned my faith in them.
....you seem to think that TCAS gives enough situational awareness to know the controllers plan. Enough to question the plan. It doesn't matter how much traffic you can see on TCAS, until you know the flight plan data of every target you see you CANNOT have situational awareness. Doesn't matter how good the user is.
Flight crews do have a very high level of situational awareness, even without TCAS.
If you instruct me to descend and I see traffic 1,000 feet below me (either on TCAS or out the window, or because I heard it on the radio) then I will question the descent clearance.
If you give me a turn towards nearby traffic at the same level (that I have seen on TCAS or by looking out the window) then I will question the turn.
Sorry – but that’s the way it’s got to be. My self-preservation mechanism won’t allow me to do otherwise.
My comments about the usefulness of a TCAS traffic display as a situational awareness tool (the comments that I addressed to Mr Big, Lon More and others) were mainly in relation to the loss of certain situational awareness cues when datalink is fully implemented and voice instructions are no longer broadcast.
Flight crews don’t currently have flight plan data about other aircraft, and I’m not aware of any proposal for the distribution of this kind of data at any time in the future.
ferris,
I'm sure you'll get more respect shown to you after that civil and well-thought out post.
You misunderstood my position about CPDLC and HF.
I estimate I could do 10 times the amount of ATC with VHF voice, than with CPDLC. You certainly couldn't attempt to use CPDLC in high traffic environments.
Until you take the pilots out of the loop....It's not a huge step to have it all talking together to the avionics controls on a/c.
But in terms of airspace capacity the rate at which a flight crew can manipulate the autopilot or program the FMC is not yet a limiting factor. It’s not likely to be a limiting factor at any time in the foreseeable future.
In many parts of the world the limiting factor is already the rate at which a human air traffic controller can shout instructions down an unreliable asynchronous VHF voice link. See, for example, the Flight International extract below.
....your faith in TCAS is a worry. You mention the idea that pilots can have sit[uational] awareness if they use it correctly. Absolute crap.
If you are in any way serious then you have a much greater lack of understanding than I’d previously imagined.
TCAS has limited ability to process targets, and if it gets too many (more than 25??), it just drops them off. Even engineers can't explain to me how or which targets it drops.
Even older versions of TCAS software will track up to 45 targets and display up to 30 of them. The 30 that are displayed are the ones that are most relevant – ie the ones that have the least time to (and separation at) the closest point of approach. There’s no point in TCAS displaying a target that is four minutes from CPA if there is another target that is 45 seconds from CPA. Unless you manage to miss the 45 seconds target you wont have to worry about the target that is four minutes away. This stuff isn’t rocket science.
Frequently, the threat a/c is merging/same direction, and TCAS seems particularly poor at identifying said threats (something to do with rate of change of threat).
....last week I had an arrival stopped at FL200 vs a departure on a different freq (at that time) climbing to FL180 (note to pilot- 2000' sep to stop false RAs - efficient?).
So why are you issuing clearances that you know to be less than optimal?
The 2,000 feet between cleared levels is largely irrelevant to TCAS. TCAS works in terms of the time to (and separation at) the closest point of approach. If your descender gets a 6,000 feet per minute descent going he could still get a TCAS RA – even with 2,000 feet between cleared levels.
The descender thru FL240 queried where his traffic was (it was climbing thru FL110 and crossing) as he couldn't see it on TCAS. That wastes my time when I could be doing something else.
If you’d given the flight crew a simple heads up, like “Descend flight level two-zero-zero, further descent in two-zero miles” or “Descend flight level two-zero-zero, opposite direction traffic climbing to one-thousand feet below” then perhaps they wouldn’t have been in a great rush to get down to FL200 and they wouldn’t have felt the need to give you a nudge. You can either save work for yourself or you can make work for yourself. You choose.
At the end of the day, capacity enhancements are governed more by available airports and runways than anything to do with ATC.
fourthreethree
....there is no solution to aircraft not following and adhering to restrictions.
I would not consider it to be a “false RA” if separation were infringed when the RA was issued....
My problem is when RA's are given when I have a controlled situation and still nearly 2000' separation....
....it is suddenly turned into an uncontrolled situation with less than 1000' separation
TCAS will simultaneously co-ordinate RAs with up to three intruders (ie four aircraft in total).
....forcing me to turn traffic away which was previously not traffic.
If your other traffic gets too close then all three aircraft will be issued with a co-ordinated RA.
....I do believe the criteria for an RA should be changed, and controllers able to override an RA.
Lon More,
“When ready, descend..., cross xxx at FL nnn” For more than 30 years that’s been my normal way of doing things. I've always tried to do it in such a way as to allow plenty of leeway for the pilot i.e. in such time that the average rate need not be more than 2000fpm, Unfortunately, as I stated, many pilots are now automatically questioning the clearance.
I agree entirely with the American method of reducing vertical rate within the last 1000ft....
fourthreethree,
The scenario I am talking about is somewhat different, where there is no chance of loss of separation, I would like the chance to inform pilots of this fact so that when they receive a nuisance RA (agreed, better terminology) they can choose to disregard it.
I can give traffic info to pilots in such a case, indeed I often do, but it seems it is just a waste of time and breath.
....would I be correct in saying that different operators can calibrate their TCAS differently? I only ask because there is one particular operator who, in my limited experience, have more RA's than others. A few weeks ago, I had two of their aircraft, one climbing, one descending, cleared levels separated by 1000 feet, opposite direction. Neither were high roc/d, both had traffic info. At 1800' separation, both had simultaneous RA's and both reacted.
Whilst it’s technically very easy to modify the RA parameters at the factory, TCAS units are certified in accordance with an approved set of performance criteria. I’m not aware of any TCAS unit that has a user-adjustable RA.
On Honeywell units the time between a TA and CPA varies between 20 and 48 seconds, depending on altitude. The time between an RA and CPA is between 15 to 35 seconds, depending on altitude.
Even if you could adjust the RA parameters – just how close to CPA would you like to leave it?
If there was going to be a nuisance RA due to an irresponsibly high rate of climb or descent then I would expect it to happen when one (or both) aircraft are between 800 feet and 1,500 feet from their cleared levels. Anything greater than about 1,500 feet and you would need an extremely high vertical closure rate (Saturn V ascent profile) to set off an RA. Anything less than about 800 feet and the autopilot has already gone into altitude capture mode, reducing the vertical closure rate.
I note that you say that neither aircraft had a high rate of climb or descent, but I’m almost certain that’s precisely what’s caused the nuisance RA(s). The fact that they were opposite direction (ie high lateral closure rate) would tend to reduce the vertical closure rate RA threshold.
....it is against the instinct of any controller to sit back and let a machine which is not aware of the traffic picture carry out your separation for you....
Although TCAS will make no attempt to achieve or maintain MATS Part 1 minimum separation criteria, it will keep the planes from banging together so long as the crews don’t fly against an RA.
Wedge,
One lesson that I think should not be forgotten from this accident is that the Captain should always call the shots whoever is on the flight deck. The apparent argument between him and the more senior check Captain was crucial to the accident, the Captain of the TU knew he was being checked and could not have felt good about contradicting a direct command from a senior pilot. But his reaction to follow the TCAS RA was the correct one. The Captain's decision should never be compromised. Even if all around him think it's the wrong decision – and even if it is the wrong decision.
It’s the pilot in command who is in charge of the aeroplane – not the captain.
This is a subtle but important distinction.
Although the captain and the pilot in command are often the same person, there are literally hundreds of flights every day where this is not the case.
Although I am not familiar with the Tu-154 operator’s SOPs, western operators I am familiar with would all designate a check captain performing a check flight and occupying a control seat as pilot in command. The guy in the left seat who is under check is still the captain – but in this situation he’s not the pilot in command.
Although good CRM dictates that all crew members must feel free to speak up when they are not completely happy with a situation or a proposed course of action, and although a good pilot in command should always welcome these contributions and take time to carefully consider them, there are certain time critical situations (like an RA) when the pilot in command has to make a very quick decision and then live with the consequences come what may. And that’s precisely what happened in the TU-154 in Lake Constance.
Check your speed with....
At the risk of upsetting a lot of people, could those who are blaming the management please explain why they think the management bear more responsibility than the controller and the Russian training captain involved.
GroundBound
Thanks for a really excellent post – one that I wholeheartedly agree with.
HugMonster ,
Incidentally, and given 20/20 hindsight, if the controller wanted to spend some time on the other screen, why would he not give the Tu154 1000' descent immediately he got on his screen - then he knew there could be no conflict.
Instead, he had only two aircraft to play with, and had them at the same level...
Instead, he had only two aircraft to play with, and had them at the same level...
My understanding is that Peter X was handing (in total) five aircraft.
It is my understanding that the TU-154 and the B757 had both made radio contact with Peter X more than five minutes prior to the collision, but that the TU-154 descent instruction was issued approximately one minute prior to the collision. It’s the prioritisation during the time in between that I can’t figure out.
Was Peter X solely responsible for this disaster? Definitely not.
Was Peter X partly responsible for this disaster? Definitely yes.
eastern wiseguy,
As to TCAS....is there a stage in the process where (as it appears on the documentary) the second aircraft is not responding in the manner agreed by the two transponders that one says (electronically) ****** this lets look for another solution and changes its' mind...for example BOTH aircraft now descending TCAS thinks lets try CLIMBING one?
Refer : Honeywell TCAS Users Manual.
(particularly see Adobe pages 34-34 of 83 which are the same as original document pages 31-32)
Slightly longer answer :
(I’ll use the TCAS v7 aurals as examples here. Earlier TCAS software versions are essentially similar.)
The TCAS in the Lake Constance disaster issued a “DESCEND DESCEND” initial RA to the B757 and a “CLIMB CLIMB” initial RA to the TU-154. These RAs were co-ordinated, meaning that before either RA was issued there was an automatic electronic exchange between the two TCAS units and an electronic agreement was reached about which TCAS unit would issue a climb RA and which would issue a descend RA.
After issuing the initial RAs the B757 commenced a descent (in accordance with its RA) and the TU-154 commenced a descent (going against its RA).
Both TCAS units continued to evaluate the traffic situation in real time, looking at the time to (and separation at) the closest point of approach. As you suggest, at this point the TCAS units jointly (because it’s a coordinated manoeuvre) make a decision about whether the initial RAs are working or not.
If they are working then that’s great. If they are not working then a secondary RA will be issued.
TCAS can decide to increase the intensity of the RA in the same direction (eg “INCREASE DESCENT”), or can decide to reverse the direction of the RA (eg change from a “DESCEND DESCEND” to a “CLIMB, CLIMB NOW, CLIMB, CLIMB NOW”).
It is quite likely that in the Lake Constance disaster both aircraft got secondary RAs of increased intensity - the B757 getting an “INCREASE DESCENT, INCREASE DESCENT” RA and the TU-154 getting an “INCREASE CLIMB, INCREASE CLIMB” RA.
If the two TCAS units had decided that it would have been better to swap things around and issue a reversal then the B757 would have got a “CLIMB, CLIMB NOW, CLIMB, CLIMB NOW” RA and the TU-154 would have got a “DESCEND, DESCEND NOW, DESCEND, DESCEND NOW” RA.
Bring back fam flights!!
LostThePicture,
TCAS is a brilliant piece of kit. I have seen radar replays of an incident where it managed to keep FOUR aircraft apart, when a Gatwick outbound off 26L was cleared to climb to FL130 towards DET when there were two in the hold at BIG and another coming in from the south to hold at FL110. Left to its own devices, TCAS will keep things apart.
Post Script :
In an earlier post on this thread I said that getting the SIDs and STARS right was a pre-requisite for automated terminal ATC via datalink.
One of the great problems with many UK STARs is that they end at a holding fix with no published procedure to get from the holding fix to the ILS. In many other countries the STAR ends at an off airport holding fix that is also one of the initial approach fixes for the ILS. Aircraft don’t have to be subjected to protracted, labor-intensive radar vectoring to get from the holding fix to the ILS - rather, aircraft in or approaching the hold are simply told “cleared ILS”.
Although the following Flight International extract deals with P-RNAV approaches the reason I have included it here is, firstly, because it shows that it is possible to design an ILS approach procedure that starts at an off airport holding fix (such an approach procedure in and of itself does not necessarily require P-RNAV, or even B-RNAV – it could just as easily be designed using existing terrestrial radio navigation aids), and secondly, because a NATS spokesperson has said that in relation to London Heathrow : “In traffic capacity terms, you can be constrained as much by the amount of instruction time on the radio as by the airspace itself.”
It’s worth noting that Boeing FMSs have been capable of P-RNAV approaches for a number of years, but it’s only now that the UK CAA and NATS are finally pulling their finger out to put their stamp of approval on the procedures. Oh well – I guess that change at a glacial pace is better than no change at all!
Flight International 12-18 August 2003 page 12
“BA tests precision area navigation at Heathrow”
British Airways has begun trials of high-accuracy, continuous descent approach techniques at London Heathrow airport. Working with the Civil Aviation Authority’s Directorate of Airspace Policy and National Air Traffic Services (NATS), it’s aim is to make approaches quieter, more accurate, simpler in air traffic management terms, and more fuel-efficient.
BA Boeing 747s and 777s....will fly precision area navigation (P-RNAV) flightpaths....
P-RNAV requires lateral accuracy of 1nm compared with existing basic RNAV (B-RNAV) allowance of 5nm.
[etc]
NATS, which is helping to manage the trial, says : “It will reduce the fuel and noise penalty – but also the radio communication workload. In traffic capacity terms, you can be constrained as much by the amount of instruction time on the radio as by the airspace itself.”
The trial will involved BA flights arriving via the Lambourne holding point to the north-east of Heathrow. .... BA says its 747s and 777s are already equipped with flight management systems (FMS) that can carry out the procedure....
BA’s air traffic management project manager for area navigation, Kevin O’Sullivan, says procedures for the P-RNAV approach have been drawn up by the CAA. “These are coded into the normal navigation database as a procedure – like the standard arrivals and standard departures – using the FMS.” [etc]
British Airways has begun trials of high-accuracy, continuous descent approach techniques at London Heathrow airport. Working with the Civil Aviation Authority’s Directorate of Airspace Policy and National Air Traffic Services (NATS), it’s aim is to make approaches quieter, more accurate, simpler in air traffic management terms, and more fuel-efficient.
BA Boeing 747s and 777s....will fly precision area navigation (P-RNAV) flightpaths....
P-RNAV requires lateral accuracy of 1nm compared with existing basic RNAV (B-RNAV) allowance of 5nm.
[etc]
NATS, which is helping to manage the trial, says : “It will reduce the fuel and noise penalty – but also the radio communication workload. In traffic capacity terms, you can be constrained as much by the amount of instruction time on the radio as by the airspace itself.”
The trial will involved BA flights arriving via the Lambourne holding point to the north-east of Heathrow. .... BA says its 747s and 777s are already equipped with flight management systems (FMS) that can carry out the procedure....
BA’s air traffic management project manager for area navigation, Kevin O’Sullivan, says procedures for the P-RNAV approach have been drawn up by the CAA. “These are coded into the normal navigation database as a procedure – like the standard arrivals and standard departures – using the FMS.” [etc]
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Actually – unless you know where to find some very dodgy controllers the best way to see TCAS in action is to rent some simulator time so you can safely explore (and fly) a whole range of TCAS scenarios
.There will soon be a generation of ATC's who will have seen a total of ZERO aircraft up close and personal,their whole experience being derived from a few hours of PPL training and a course at Cranebank(I believe!).The aerodrome side of training for all is being removed and I believe this is to the detriment of OUR(i.e. you AND me) business as a whole.As to renting simulator time...do the bean counters see a cost benefit? If they don't it won't happen...not holding MY breath.I saw the TCAS in operation in a sim at Cranebank....how many more experienced Atco's will?
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Bik
Another cogent post as we're coming to expect, but let's put all this into perspective.
TCAS is great - no question, I think that all pilots have come to find it to be one of the most important pieces of kit at their disposal. However, from the view of a safety regulatory point of view (and I'm only playing Devil's Advocate here), a 4 way RA does not, at the outset of conflict resolution in the planning phase, have any degree of inherent, built in separation. I'm not saying that it is not safe, as I think we have established TCAS IS safe, but it cannot form the basis of a separation mechanism on it's own because you cannot show, AT THE MOMENT, any pro active, pre planned separation, only a tactical phase resolution. The TCAS separation is purely reactive. I'm sure this bothers safety regualtors and operators alike.
But there are projects in place to investigate the use of Mode S information to couple with TCAS that could eventually mean that it WILL be integrated into actual input in separation. Mode S can provide information on the data block on the radar to show selected level, selected rate of climb/descent and, perhaps, TCAS RA and it's order of direction.
Now, remeber when we were talking about ATCOs becoming system managers Bik, a couple of weeks ago? Well, let's extrapolate that idea.
On the flight deck, pilots get the ATC cleared level, select the relevant level and relative rate of climb descent. The controller/monitor bod is watching all this info via Mod S, can see an incorrect level selection and correct it, can spot a potentially excessive RoD/C and rectify (not necessarly instruct to change but point out that it may be excessive, fter all you fly the planes!)and in the event of TCAS RA, and I believe that this one should be implemented ASAP to stop a rerun of Lake Constance, a controller will be able to observe the RAs given to each aircraft and leave well alone unitl the Mode S shows the event to be over. Most imnportantly, there will never be the need for a controller to give contradictory avoiding action in the event of TCAS RAs ever again because the whole scenario will be displayed on their screen.
These are huge leaps forward in technology led safety and form an interesting future. And for all those out there who say "What if the cleaner knocks the plug out?", then we revert to the system we have now, same as if someone pulls the plug now we go
procedural etc. Today's best practice is tomorrow's back up plan.
P7
Post Script
The P-RNAV arrival at Heathrow is being developed so that British airlines can prove the system works in practise, then devise their own procedured into airfields with poor ATC service and/or poor or unserviceable nav aids. It will also provide quieter CDAs so that night quotas can rise but the public can be shown that they're not getting a raw deal. Maybe.
Another cogent post as we're coming to expect, but let's put all this into perspective.
TCAS is great - no question, I think that all pilots have come to find it to be one of the most important pieces of kit at their disposal. However, from the view of a safety regulatory point of view (and I'm only playing Devil's Advocate here), a 4 way RA does not, at the outset of conflict resolution in the planning phase, have any degree of inherent, built in separation. I'm not saying that it is not safe, as I think we have established TCAS IS safe, but it cannot form the basis of a separation mechanism on it's own because you cannot show, AT THE MOMENT, any pro active, pre planned separation, only a tactical phase resolution. The TCAS separation is purely reactive. I'm sure this bothers safety regualtors and operators alike.
But there are projects in place to investigate the use of Mode S information to couple with TCAS that could eventually mean that it WILL be integrated into actual input in separation. Mode S can provide information on the data block on the radar to show selected level, selected rate of climb/descent and, perhaps, TCAS RA and it's order of direction.
Now, remeber when we were talking about ATCOs becoming system managers Bik, a couple of weeks ago? Well, let's extrapolate that idea.
On the flight deck, pilots get the ATC cleared level, select the relevant level and relative rate of climb descent. The controller/monitor bod is watching all this info via Mod S, can see an incorrect level selection and correct it, can spot a potentially excessive RoD/C and rectify (not necessarly instruct to change but point out that it may be excessive, fter all you fly the planes!)and in the event of TCAS RA, and I believe that this one should be implemented ASAP to stop a rerun of Lake Constance, a controller will be able to observe the RAs given to each aircraft and leave well alone unitl the Mode S shows the event to be over. Most imnportantly, there will never be the need for a controller to give contradictory avoiding action in the event of TCAS RAs ever again because the whole scenario will be displayed on their screen.
These are huge leaps forward in technology led safety and form an interesting future. And for all those out there who say "What if the cleaner knocks the plug out?", then we revert to the system we have now, same as if someone pulls the plug now we go
procedural etc. Today's best practice is tomorrow's back up plan.
P7
Post Script
The P-RNAV arrival at Heathrow is being developed so that British airlines can prove the system works in practise, then devise their own procedured into airfields with poor ATC service and/or poor or unserviceable nav aids. It will also provide quieter CDAs so that night quotas can rise but the public can be shown that they're not getting a raw deal. Maybe.
