ATC and TCAS ????
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Fly one mile right, I says. With GPS Nav etc we fly under each other's bellies. But then doing just that over GAFA country(as non standard level flying was preverlent), got ticked off by my company for this smart arse proceedure, after ATC lodged a complain. So now I remain a dumb arse until the next mid air crash and that becomes the norm. 
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ATC Watcher
Nearly. I'd be happier if you moved the capitals and said this instead:
"Always follow the RA and NEVER EVER MANOEUVRE AGAINST IT"
I'd be even happier with:
"Follow the RA if you possibly can. If you can't, fly as close to it as you can. Whatever happens NEVER EVER MANOEUVRE AGAINST IT".
To reiterate a point I make every time this accident topic comes up, failing to follow RAs is nowhere near as dangerous as manouevering opposite.
I'm not saying it is a good idea to ignore RAs. It is easily possible to imagine circumstances when fully complying with the RA might be impossible.
In such circumstances it is vital that people retain the 'never manouevre opposite' as the one overriding rule not to be broken.
I always get a little concerned that zooming in on the 'Follow the RA' aspect means that folks miss out on the 'never manoeuvre opposite' message.
My concern then is that when placed in a position where full compliance with an RA is not possible, that a crew are suddenly dumped in a SOP breaking position. Once an SOP is broken, how do you get back into the groove? Very awkward psychologically I would think.
If that makes any kind of sense.
Others,
On the whole traffic display (TD) useage thing. Very briefly: in a collision scenario the best thing to do with it is use it as a tool help you get a visual spot. Once you can see the other aircraft you maybe will have some options for a lateral manouevre. So whilst TCAS attempts to solve the vertical, the back up plan is for a lateral solution by visual spotting or an ATC vector; but NEVER a turn based SOLELY on the TD.
CPB
ALWAYS FOLLOW THE RA and never ever manoeuvre against it !
"Always follow the RA and NEVER EVER MANOEUVRE AGAINST IT"
I'd be even happier with:
"Follow the RA if you possibly can. If you can't, fly as close to it as you can. Whatever happens NEVER EVER MANOEUVRE AGAINST IT".
To reiterate a point I make every time this accident topic comes up, failing to follow RAs is nowhere near as dangerous as manouevering opposite.
I'm not saying it is a good idea to ignore RAs. It is easily possible to imagine circumstances when fully complying with the RA might be impossible.
In such circumstances it is vital that people retain the 'never manouevre opposite' as the one overriding rule not to be broken.
I always get a little concerned that zooming in on the 'Follow the RA' aspect means that folks miss out on the 'never manoeuvre opposite' message.
My concern then is that when placed in a position where full compliance with an RA is not possible, that a crew are suddenly dumped in a SOP breaking position. Once an SOP is broken, how do you get back into the groove? Very awkward psychologically I would think.
If that makes any kind of sense.
Others,
On the whole traffic display (TD) useage thing. Very briefly: in a collision scenario the best thing to do with it is use it as a tool help you get a visual spot. Once you can see the other aircraft you maybe will have some options for a lateral manouevre. So whilst TCAS attempts to solve the vertical, the back up plan is for a lateral solution by visual spotting or an ATC vector; but NEVER a turn based SOLELY on the TD.
CPB
Pegase Driver
Capt Pit Bull ( hope this is not a CRM nickname 
)
You are absolutely right. Your remarks make a lot of sense and indeed the emphasis should be on not to manoeuvre against a RA. Good point .
Now how do we get this idea to progress further ?
On your second remark , about visual aquisition, I can support your comment but cannot forget the fact we discovered while examining the TU154 FDR : the a/c turned towards the 757 and was still doing 1900 ft/min when it collided.
The awsome fact , in that collision, is that if the TU154 crew did not see the 757 , it possibly had stayed on course, and had passed well ahead of the 757, ( but this is speculation ) but more importantly, it would most probably have levelled off at FL350 , therefore would have reduced its rate prior to that, passing definitively above the 757.
Depending on how you look at the geometry, had the TU 154 been between 2 and 4m higher they would have missed each other.
It is not easy to find a procedure covering 100% of cases.
) You are absolutely right. Your remarks make a lot of sense and indeed the emphasis should be on not to manoeuvre against a RA. Good point .
Now how do we get this idea to progress further ?
On your second remark , about visual aquisition, I can support your comment but cannot forget the fact we discovered while examining the TU154 FDR : the a/c turned towards the 757 and was still doing 1900 ft/min when it collided.
The awsome fact , in that collision, is that if the TU154 crew did not see the 757 , it possibly had stayed on course, and had passed well ahead of the 757, ( but this is speculation ) but more importantly, it would most probably have levelled off at FL350 , therefore would have reduced its rate prior to that, passing definitively above the 757.
Depending on how you look at the geometry, had the TU 154 been between 2 and 4m higher they would have missed each other.
It is not easy to find a procedure covering 100% of cases.
Last edited by ATC Watcher; 3rd Jul 2004 at 19:26.
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And yet we never learn.....
Here we are debating whether or not the aviation community has come to grips with the wonders of TCAs technology and yet....
....we still have not agreed to an international form of units of measurement !!!!!!!!!!!!!!
Yes that's right we still have countries measuring height in meters, pressure in inches or Hpa, speed in Km/h or knots and the list goes on.
When giving our QNH to a particular charter group (US owned/operated) operating here for a major Middle Eastern airline recently who are used to using inches, QNH 997 was read back 3, yes 3 times, as 2997. Now please remember that the fancy dan TCAS is an altimeter and pressure based setting etc. therefore the whole thing is a complete crock if you have 400+ feet of difference in settings between FIR boundary's or poorly set altimeters.
Can we pleeeeeeese agree on one form of measurement in the aviation community, or at least run with the majority which would see the end of INCHES, METERS (I think the Cathay gang now about that little bun fight between their FIR's!), and KM/H !!!!!! It would have saved the passengers and crews of the worlds worst mid air collision in India which was a direct result of the lack of standardization in the industry!
....we still have not agreed to an international form of units of measurement !!!!!!!!!!!!!!
Yes that's right we still have countries measuring height in meters, pressure in inches or Hpa, speed in Km/h or knots and the list goes on.
When giving our QNH to a particular charter group (US owned/operated) operating here for a major Middle Eastern airline recently who are used to using inches, QNH 997 was read back 3, yes 3 times, as 2997. Now please remember that the fancy dan TCAS is an altimeter and pressure based setting etc. therefore the whole thing is a complete crock if you have 400+ feet of difference in settings between FIR boundary's or poorly set altimeters.
Can we pleeeeeeese agree on one form of measurement in the aviation community, or at least run with the majority which would see the end of INCHES, METERS (I think the Cathay gang now about that little bun fight between their FIR's!), and KM/H !!!!!! It would have saved the passengers and crews of the worlds worst mid air collision in India which was a direct result of the lack of standardization in the industry!
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Now please remember that the fancy dan TCAS is an altimeter and pressure based setting etc. therefore the whole thing is a complete crock if you have 400+ feet of difference in settings between FIR boundary's or poorly set altimeters.
Only half a speed-brake
D.D.: My call exactly. It is the feature of surveillance displays to compensate for pressure setting thus you'll see aircraft on proper altitudes. That's for transponders in general.
However the 997hPa/2997in sound like it could be a beginning to a very scary story.
FD.
However the 997hPa/2997in sound like it could be a beginning to a very scary story.
FD.
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DD
So you can can confirm that below the transition layer when an aircraft has his/her altimeter set at an innacurate QNH (which we see on the radar) that the interigating transponders won't see the same information???? If that is the case it would negate ATC verifying levels would it not?
Only half a speed-brake
F3S
I've seen screen that did not compensate for QNH difference.
If altimeter readings would be transmitted, you would see me jump up and down as I change the altimeter. QFE fields like Sofia (LBSF, elev. 1700'+) come to mind immediately. You'd see a mulititude of RA in stack if someone spu nthe baro knob.
How yould you feel about providing separation to someone with incorrectly set altimeter???
No way. Mode A is strictly QNE information and this provides for some major benefits. It is alco ATCO's responsibility to ensure terrain clearance under radar vectors, right?
If altimeter readings would be transmitted, you would see me jump up and down as I change the altimeter. QFE fields like Sofia (LBSF, elev. 1700'+) come to mind immediately. You'd see a mulititude of RA in stack if someone spu nthe baro knob.
How yould you feel about providing separation to someone with incorrectly set altimeter???
No way. Mode A is strictly QNE information and this provides for some major benefits. It is alco ATCO's responsibility to ensure terrain clearance under radar vectors, right?
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FD
"If altimeter readings would be transmitted, you would see me jump up and down as I change the altimeter"
We do see your altitudes jump up and down on the radar when wrong QNH is set on your altimeter and the QNH is subsequently changed, thats why we challenge the levels for separation.
Example...
An example in this FIR with our adjacent FIR Tehran. An inbound acft was at FL120, our transition layer is FL140. At the same exit/entry point an outbound is on QNH flying at A110, inbound the aircraft at FL120 on 1013. Our QNH was 997, the difference of 16Hpa which had the inbound aircraft at A116 which A. on radar would be a loss of separation, B.I f the aircraft were on conflicting courses/climbs descents etc. it should give a TCAS alert????
We do see your altitudes jump up and down on the radar when wrong QNH is set on your altimeter and the QNH is subsequently changed, thats why we challenge the levels for separation.
Example...
An example in this FIR with our adjacent FIR Tehran. An inbound acft was at FL120, our transition layer is FL140. At the same exit/entry point an outbound is on QNH flying at A110, inbound the aircraft at FL120 on 1013. Our QNH was 997, the difference of 16Hpa which had the inbound aircraft at A116 which A. on radar would be a loss of separation, B.I f the aircraft were on conflicting courses/climbs descents etc. it should give a TCAS alert????
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Sigh.....Lawyers again, looking for a deep pocket
Even when the stuff works right, you still get sued in the good old USA (S. G.)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Russian Families Sue US Companies for Plane Crash
TCAS gives pilots correct instructions, controller does not,
but lawyer says TCAS at fault... sound familiar?
The families of six Russians who perished as a result of a
mid-air collision over Germany have decided to sue Honeywell and
other aviation equipment manufacturers in the US, blaming the TCAS
systems on both aircraft for the crash that killed 71 people in
2002. This, even though all investigations have pointed to an error
on the part of the Swiss controller -- had the pilots both followed
the TCAS commands, there would have been no accident.
A total of thirty Russian families have filed suit
against Honeywell and four other companies. The six lawsuits, filed
Thursday in Miami, allege that the companies failed to provide
adequate procedures, instructions and training.
The Bashkirian
Airlines Tu-154 collided with a DHL
International cargo aircraft on July 1, 2002 less than
a minute after receiving a radio transmission from the
one and only controller on duty at the Zurich ATC center. The
Russian jet was transporting 45 students and their families to
Barcelona, Spain.
The lawsuit claims that the collision warning system told the
Russian jet to climb while the Swiss controller told it to
descend. Instead of following the correct command from the TCAS
collision avoidance system, the Russian pilot followed the
controller's instructions and descended. At the same time, the DHL
pilot was correctly commanded twice by the TCAS system to
descend. Obviously, had both pilots followed the commands of the
TCAS systems, there would not have been a mid-air
collision.
Nevertheless, Gustavo Fuentes, a Miami attorney representing the
families behind the six lawsuits, claims that "the Russian pilots
did not have sufficiently clear instructions as to what to do when
this alarm system started to give them instructions at the same
time that the air traffic controller was giving them conflicting
instructions."
Honeywell International has released a statement where it said it had not seen the lawsuit and could not comment on it. However, the company has reiterated that the investigation into the crash concluded that the TCAS equipment functioned properly, and that the only reasonable explanation was that the accident was the pilots' fault for failing to follow the system's
commands.
According to Fuentes, more lawsuits were to be filed in
California, New York, New Jersey, and Washington.
The controller on duty in 2002 was Peter Nielsen -- he was
fatally stabbed outside his home on Feb. 24. Swiss police arrested
a Russian architect whose wife, son and daughter died in the
crash.
Even when the stuff works right, you still get sued in the good old USA (S. G.)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Russian Families Sue US Companies for Plane Crash
TCAS gives pilots correct instructions, controller does not,
but lawyer says TCAS at fault... sound familiar?
The families of six Russians who perished as a result of a
mid-air collision over Germany have decided to sue Honeywell and
other aviation equipment manufacturers in the US, blaming the TCAS
systems on both aircraft for the crash that killed 71 people in
2002. This, even though all investigations have pointed to an error
on the part of the Swiss controller -- had the pilots both followed
the TCAS commands, there would have been no accident.
A total of thirty Russian families have filed suit
against Honeywell and four other companies. The six lawsuits, filed
Thursday in Miami, allege that the companies failed to provide
adequate procedures, instructions and training.
The Bashkirian
Airlines Tu-154 collided with a DHL
International cargo aircraft on July 1, 2002 less than
a minute after receiving a radio transmission from the
one and only controller on duty at the Zurich ATC center. The
Russian jet was transporting 45 students and their families to
Barcelona, Spain.
The lawsuit claims that the collision warning system told the
Russian jet to climb while the Swiss controller told it to
descend. Instead of following the correct command from the TCAS
collision avoidance system, the Russian pilot followed the
controller's instructions and descended. At the same time, the DHL
pilot was correctly commanded twice by the TCAS system to
descend. Obviously, had both pilots followed the commands of the
TCAS systems, there would not have been a mid-air
collision.
Nevertheless, Gustavo Fuentes, a Miami attorney representing the
families behind the six lawsuits, claims that "the Russian pilots
did not have sufficiently clear instructions as to what to do when
this alarm system started to give them instructions at the same
time that the air traffic controller was giving them conflicting
instructions."
Honeywell International has released a statement where it said it had not seen the lawsuit and could not comment on it. However, the company has reiterated that the investigation into the crash concluded that the TCAS equipment functioned properly, and that the only reasonable explanation was that the accident was the pilots' fault for failing to follow the system's
commands.
According to Fuentes, more lawsuits were to be filed in
California, New York, New Jersey, and Washington.
The controller on duty in 2002 was Peter Nielsen -- he was
fatally stabbed outside his home on Feb. 24. Swiss police arrested
a Russian architect whose wife, son and daughter died in the
crash.
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Fox3snapshot:
You said:
I think what you are seeing is the aircraft being flown to the correct level after the altimeter setting gets changed. I can't imagine the crew correcting the altimeter setting but then remaining at the original incorrect altitude/FL with all the cockpit indications now showing them off their assigned level.
Have a look at AvWeb - Transponder Basics under the heading Altitude reporting (it's a long way down the page).
I can see from your point of view you give a QNH change and see a change in altitude readout. However, I contend that it is not a direct cause and effect and a few other factors get into the act.
[PS. I always looked forward to entering your airspace when in your part of the world. A bit like coming home!]
Maasalaama.
DD
You said:
We do see your altitudes jump up and down on the radar when wrong QNH is set on your altimeter and the QNH is subsequently changed, thats why we challenge the levels for separation.
Have a look at AvWeb - Transponder Basics under the heading Altitude reporting (it's a long way down the page).
.....your transponder transmits your aircraft's PRESSURE ALTITUDE (rounded off to the nearest 100 feet) whenever it receives a Mode C interrogation and is switched to ALT mode. <snip> Because the transponder reports pressure altitude, the altimeter setting that you dial into your altimeter's Kollsman window has absolutely no effect on your Mode C altitude reports
[PS. I always looked forward to entering your airspace when in your part of the world. A bit like coming home!]
Maasalaama.
DD
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I think it is worth mentioning that TCAS can be surprisingly accurate in azimuth (a wx radar return off an aircraft will often coincide with the TCAS position and tie in with the position determined by the Mark 1 eye-ball). However, NEVER, EVER use TCAS alone to manoeuvre laterally - that is not how it is designed to be used.
I think it is worth acknowleging the often high azimuth accuracy, because if people are told it is not accurate, yet see it working well every day they might consider (as Glueball suggested) using it. DO NOT!
When it comes to the RA - manoeuvre as little as possible ie just outside the red zone (whether it is on the VSI or the ADI). More separation is not necessarily better separation.
G W-H
I think it is worth acknowleging the often high azimuth accuracy, because if people are told it is not accurate, yet see it working well every day they might consider (as Glueball suggested) using it. DO NOT!
When it comes to the RA - manoeuvre as little as possible ie just outside the red zone (whether it is on the VSI or the ADI). More separation is not necessarily better separation.
G W-H
Ground instructor
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Thanks for that coment on how azimuth can be accurate, I will highlight that in my teachings in ground school.
To get back to the 1st post, it was Tragic what happened to your friend and the bottom line is... rules have changed because of it and I believe the following additional guidelines were issued by ICAO?
1. When changing flight level to avoid nuisance RA's it is good practice to reduce your VS to 1000 fpm when within 1000ft of your required Flight Level, this should stop most "I'm climbing, your descending to within 1000ft of each other vertically" RA's.
2. If during an RA another aircraft is seen, the pilot should not assume that it is the aircraft generating the TCAS RA, so it should be ignored. Easy for them to say, but it makes sense as TCAS should be aware of all aircraft in the vicinity and will issue the RA for up to 3 conflicting aircraft at one time.
Once again my sympathy to you. Pray God we learn.
To get back to the 1st post, it was Tragic what happened to your friend and the bottom line is... rules have changed because of it and I believe the following additional guidelines were issued by ICAO?
1. When changing flight level to avoid nuisance RA's it is good practice to reduce your VS to 1000 fpm when within 1000ft of your required Flight Level, this should stop most "I'm climbing, your descending to within 1000ft of each other vertically" RA's.
2. If during an RA another aircraft is seen, the pilot should not assume that it is the aircraft generating the TCAS RA, so it should be ignored. Easy for them to say, but it makes sense as TCAS should be aware of all aircraft in the vicinity and will issue the RA for up to 3 conflicting aircraft at one time.
Once again my sympathy to you. Pray God we learn.
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Regarding the Flight Level vs. Altitude readout for ATC’s;
The transition altitude is usually configured into the Radar Display Software (RDS).
The ATC sets the local QNH into the RDS.
The RDS displays all Pressure Altitudes above the Transition as they are received (1013.25Hpa), in Flight Levels.
The RDS converts all Pressure Levels that are below the (configured) Transition, to Altitudes.
Because the RDS and the Aircraft convert based on QNH setting, they both see the same value (if they are set to the same QNH).
ATC’s can test this by setting a “very” different QNH into the RDS and observing that only aircraft below transition will show the variation. (Do not do this at an operational position, or without warning other sectors on the same RDS).
Invictus
The transition altitude is usually configured into the Radar Display Software (RDS).
The ATC sets the local QNH into the RDS.
The RDS displays all Pressure Altitudes above the Transition as they are received (1013.25Hpa), in Flight Levels.
The RDS converts all Pressure Levels that are below the (configured) Transition, to Altitudes.
Because the RDS and the Aircraft convert based on QNH setting, they both see the same value (if they are set to the same QNH).
ATC’s can test this by setting a “very” different QNH into the RDS and observing that only aircraft below transition will show the variation. (Do not do this at an operational position, or without warning other sectors on the same RDS).
Invictus
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Desert Dingo
It all makes sense now, thanks for your valuable input to what has turned out to be an interesting topic of discussion within the fraternity here. The link you posted was provided a top explanation.
My next question though is what altitude information is displayed on your TCAS display on the adjacent traffic as this once again could differ to what the ATC radars would be displaying if it is derived from the transponder/tcas equipment only based on 1013.
Shukran, hope to see you back through this patch again someday.
My next question though is what altitude information is displayed on your TCAS display on the adjacent traffic as this once again could differ to what the ATC radars would be displaying if it is derived from the transponder/tcas equipment only based on 1013.
Shukran, hope to see you back through this patch again someday.
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A lot of good info and you lot have obviously thought about this issue in depth. I would suggest that if the readers and writers here are on the recieving end of a TCAS event, the outcome will be an incident report and nothing worse (maybe a few red faces depending on the dynamics that caused the kit to activate).
But do I have to read PPrune or the Ueberlingen and JAL accident reports before I start flying round in a TCAS equiped aircraft? No. I get a pilots license, read the company and aircraft manuals, do the training and launch.
Yes - we are very aware of the subject at the moment - some more aware than others. But how wide spread is the awareness? And what is the impact of time as it all fades in our memory? Where is the lasting reminder that TCAS is an interdependant system requiring everyone to sing from the same hymn book?
Lets see ICAO step up to the batter's box.
ICAO needs to conduct a thorough review and rewrite of all the TCAS material. Weight needs to be given to the important elements of the system, and the information needs to be distributed in the most relevant documents.
ICAO needs to take the lead in developing internationally accepted training. This must strictly reflect the standards and procedures they have written. There are well developed training packages out there, but where is the accepted "master" TCAS training guide to measure them against?
ICAO then needs to ensure all national authorities mandate compliance with its SARPs and training requirements. This means everyone in the industry - airlines, training organisations, ATC, manufactures (aircraft and equipment) - everyone. There is no room for deviation or misinterpretation. And beware the poor translation. Get this wrong and nothing is improved.
ICAO should follow all this up by auditing everything with the letters TCAS linked to it. They don't have to do it all themselves, there are other organisations out there that can give them a hand. But once they have the SARPs agreed upon, everyone must abide by them.
I know the BFU made recommendations down these lines (I have read the whole report), but ICAO must read between the lines and realise they have to overhaul all their writings.
Was it Spike Milligan that said - "We have learnt from our mistakes and can repeat them almost perfectly".
I am sure that we will learn the hard lessons from this tragic accident, and that steps will be taken to sharpen up many areas of the industry.
Skyhawk1 - I too, will always remember what happened that night, and feel the loss that is shared by many. I know what has been learnt can be used not only to prevent a similar accident but also improve many areas of aviation safety.
But do I have to read PPrune or the Ueberlingen and JAL accident reports before I start flying round in a TCAS equiped aircraft? No. I get a pilots license, read the company and aircraft manuals, do the training and launch.
Yes - we are very aware of the subject at the moment - some more aware than others. But how wide spread is the awareness? And what is the impact of time as it all fades in our memory? Where is the lasting reminder that TCAS is an interdependant system requiring everyone to sing from the same hymn book?
Lets see ICAO step up to the batter's box.
ICAO needs to conduct a thorough review and rewrite of all the TCAS material. Weight needs to be given to the important elements of the system, and the information needs to be distributed in the most relevant documents.
ICAO needs to take the lead in developing internationally accepted training. This must strictly reflect the standards and procedures they have written. There are well developed training packages out there, but where is the accepted "master" TCAS training guide to measure them against?
ICAO then needs to ensure all national authorities mandate compliance with its SARPs and training requirements. This means everyone in the industry - airlines, training organisations, ATC, manufactures (aircraft and equipment) - everyone. There is no room for deviation or misinterpretation. And beware the poor translation. Get this wrong and nothing is improved.
ICAO should follow all this up by auditing everything with the letters TCAS linked to it. They don't have to do it all themselves, there are other organisations out there that can give them a hand. But once they have the SARPs agreed upon, everyone must abide by them.
I know the BFU made recommendations down these lines (I have read the whole report), but ICAO must read between the lines and realise they have to overhaul all their writings.
Was it Spike Milligan that said - "We have learnt from our mistakes and can repeat them almost perfectly".
I am sure that we will learn the hard lessons from this tragic accident, and that steps will be taken to sharpen up many areas of the industry.
Skyhawk1 - I too, will always remember what happened that night, and feel the loss that is shared by many. I know what has been learnt can be used not only to prevent a similar accident but also improve many areas of aviation safety.
Pegase Driver
BOPralph : I see what you are trying to say, but you are shooting at the wrong target.
ICAO is not a superpower , it is an assembly of States representatives ( sometimes with different agendas up their sleeves.)
ICAO is us, collectively.
For your info . ( and very briefly, as I could write for hours on this )
TCAS is not an ICAO invention, it is a pure made in USA thing , and which was introduced by a US Presidential order against ICAO recommendation at the time. An ICAO group was working ( too slowly I agree) on a universal ACAS. But with TCAS out there , with no guidance material outside the US airspace, and pressure from other States to do something , ICAO had to backtrack and modify its work to accomodate part of TCAS.
The initial ICAO ACAS training manual came AFTER the US documentation was out. . Those US docs did not mention the absolute need to follow RAs on nearly all cases , especially if conflicting with ATC, for the typical US legal reasons. Therefore the term " Advisory " came about.
ICAO wanted more time to study implications before mandating such a system. The US denied them that and went ahead unilaterally. The rest of the world had to follow ( Sounds familiar eh ? ).
TCAS was hastily introduced and many of the shortcomings and flaws were tested in life traffic. ( and to some extend still are today ) This is the sad truth.
ICAO is not a superpower , it is an assembly of States representatives ( sometimes with different agendas up their sleeves.)
ICAO is us, collectively.
For your info . ( and very briefly, as I could write for hours on this )
TCAS is not an ICAO invention, it is a pure made in USA thing , and which was introduced by a US Presidential order against ICAO recommendation at the time. An ICAO group was working ( too slowly I agree) on a universal ACAS. But with TCAS out there , with no guidance material outside the US airspace, and pressure from other States to do something , ICAO had to backtrack and modify its work to accomodate part of TCAS.
The initial ICAO ACAS training manual came AFTER the US documentation was out. . Those US docs did not mention the absolute need to follow RAs on nearly all cases , especially if conflicting with ATC, for the typical US legal reasons. Therefore the term " Advisory " came about.
ICAO wanted more time to study implications before mandating such a system. The US denied them that and went ahead unilaterally. The rest of the world had to follow ( Sounds familiar eh ? ).
TCAS was hastily introduced and many of the shortcomings and flaws were tested in life traffic. ( and to some extend still are today ) This is the sad truth.
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Fox3snapshot:
The only altitude information TCAS ever displays is that relative to the other traffic. The traffic symbol can have a 4 character tag; A plus/minus sign and 2 digits for altitude difference in hundreds of feet and an up or down arrow if it is climbing or descending more than 500 feet per minute. Once again, like the transponder, this is all based on a hardwired standard pressure altitude setting, so the pilots cannot stuff it up with an incorrect altimeter setting. If the aicraft are separated by by only (say) 100 feet, then that is what both aircraft will see in relative terms (100 ft) and you will see in absolute terms (eg. FL 249 and FL 250)
More info at
TCAS Symbols
and some good pictures of a typical display during RAs down towards the end of
TCAS Displays
DD
My next question though is what altitude information is displayed on your TCAS display on the adjacent traffic as this once again could differ to what the ATC radars would be displaying if it is derived from the transponder/tcas equipment only based on 1013.
More info at
TCAS Symbols
and some good pictures of a typical display during RAs down towards the end of
TCAS Displays
DD
Last edited by Desert Dingo; 6th Jul 2004 at 00:52.
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The only altitude information TCAS ever displays is that relative to the other traffic. The traffic symbol can have a 4 character tag; A plus/minus sign and 2 digits for altitude difference in hundreds of feet and an up or down arrow if it is climbing or descending more than 500 feet per minute. Once again, like the transponder, this is all based on a hardwired standard pressure altitude setting, so the pilots cannot stuff it up with an incorrect altimeter setting.
If an RA, a red square above which in red would be, +01 with a downward pointing arrow. This can be switched to display flight levels, as per DD's explanation.