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2018; ATC induced loss of separation between 2 FR aircraft

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  • Registered Users Posts: 1,399 ✭✭✭Beersmith


    TCAS did its job as you say, we just read of the issues with two controllers giving the same descent commands. We have also know about one pilot following TCAS and other the controller in other cases.

    I've always wondered, as it always seems to be a descent or climb command, would a turn right 90 degrees not work for every situation like this instead? Or something similar? Then both aircrafts would do the exact same thing and be guaranteed to miss each other?!


  • Registered Users Posts: 550 ✭✭✭AnRothar


    Beersmith wrote: »
    We have also know about one pilot following TCAS and other the controller in other cases.
    Historically the rules regarding TCAS actually vairied from state to state.
    This resulted in an unfortunate incident.
    ICAO recognising that this lack of standardisation was undesirable standardised the rules mandating pilot to follow TCAS.

    I've always wondered, as it always seems to be a descent or climb command, would a turn right 90 degrees not work for every situation like this instead? Or something similar? Then both aircrafts would do the exact same thing and be guaranteed to miss each other?!
    Both aircraft will do the same thing, they will follow TCAS.
    Keep things simple, one goes up the other goes down.

    Bear in mind that when TCAS reports "clear of conflict" standard ATC separation may not yet exist.

    There are trials of an updated version of TCAS which can reverse the decision regarding who is to change in which direction.
    They discovered it's wasn't as easy as they thought.


  • Posts: 0 [Deleted User]


    I've seen on AvHerald where commercial pilots apparently have had some criticisms of ATC at Barcelona.


  • Registered Users Posts: 4,160 ✭✭✭goingnowhere


    Rules are you do what the TCAS tells you, ignore the controller

    TCAS negotiates with the other aircraft to build the escape and is smart


  • Banned (with Prison Access) Posts: 1,306 ✭✭✭bobbyy gee


    it was in 2018


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  • Registered Users Posts: 874 ✭✭✭HTCOne


    ACAS which incorporates turn commands is under development (might be actually in service by now).

    It is a very complicated system, it doesn't just have to resolve conflicts between the initial 2 aircraft that have lost separation, it also has to negotiate with all other aircraft in the vicinity to ensure deconflicting aircraft A & B doesn't cause a mid air with aircraft C, D, E etc. With the absolute accuracy of modern nav equipment, multiple aircraft are often directly above / below each other on airways / tracks for a significant period of time. I remember reading a post incident report years ago on the North Atlantic where an A340 go hit by an updraft which brought them up a couple of thousand feet, setting off a TCAS Resolution Advisory in the 747 above them, which then set off an RA in another 747 a further 1000 feet above.

    Some modern aircraft deconflict themselves, ie autopilot follows TCAS instructions. I know the A350 does this at least.


  • Registered Users Posts: 1,348 ✭✭✭basill


    HTCOne wrote: »
    Some modern aircraft deconflict themselves, ie autopilot follows TCAS instructions. I know the A350 does this at least.


    Our 321neos and newer A330s have it as standard.


  • Registered Users Posts: 1,399 ✭✭✭Beersmith


    Would a 90 degree turn work though?


  • Registered Users Posts: 874 ✭✭✭HTCOne


    Beersmith wrote: »
    Would a 90 degree turn work though?

    Depends on the traffic situation I would say.


  • Moderators, Motoring & Transport Moderators, Technology & Internet Moderators Posts: 22,622 Mod ✭✭✭✭bk


    Beersmith wrote: »
    Would a 90 degree turn work though?

    If you look at the picture in the article of the flight paths, you can see why both going 90 degree right wouldn't work:

    https://static.independent.co.uk/2020/09/20/23/NearMiss.png?width=990

    Imagine if the aircraft 1-Pal turned right at 14:57, but aircraft 2-Zgz didn't turn right at the point, 1-Pal would fly right into it (or at least very close).

    Even if 2-Zgz also turned right at the same time, 1-Pal would now be chasing right behind it.

    Now if they coordinate, and 1-Pal turn 90 degree left, while 2-Zgz went 90 degree right, that could work.

    However they went with altitude for TCAS, because each aircraft transmits it's altitude via transponder. So that information is easily gotten, as is range via measuring the round trip time of the request. Basically TCAS 2 can tell how far away another aircraft is and it's altitude, but not how far left or right it is.

    It can give guidance on the vertical, but not the horizontal.

    So that makes it impossible to coordinate turns like this. Much easier and safer to arrange changes in altitude.

    As HTCOne points out, ACAS X is under development to offer far more options and involving more aircraft close to crowded airspace. And there is ADS-B to offer more positional data.


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  • Registered Users Posts: 10,095 ✭✭✭✭smurfjed


    We have also know about one pilot following TCAS and other the controller in other cases.
    wasn’t this the reason TCAS 7.1 was implemented ? It gives the ability to reverse reactions.


  • Registered Users Posts: 6,920 ✭✭✭billy few mates


    TCAS uses highly accurate transponder altitude and interrogation response times to coordinate the RA between conflicting aircraft, the current generation of TCAS can only generate vertical commands for resolution advisory.
    The reason it can't generate turning or lateral commands is because of limitations in the accuracy of the directional antennas which would be needed to coordinate a RA with turning aircraft.


  • Registered Users Posts: 2,979 ✭✭✭Stovepipe


    The downside is that when you jam a lot of aircraft into a small piece of airspace, courtesy of RVSM, you increase the chances of aircraft colliding, even if they are taking avoiding action.


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