Posts: 49
Joined: Wed Oct 17, 2001 6:03 am

Tcas Questions

Tue Jul 09, 2002 3:08 am

If the TCAS system on board an aircraft advises the pilot to take evasive action, is this "order" also transmitted to air traffic control?

Regarding the recent collision over Germany, would the Swiss air traffic controller have received information from the TCAS on both aircraft?
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RE: Tcas Questions

Tue Jul 09, 2002 3:11 am

I was going to ask something similiar in the Tech/Ops forum, but I guess I will just further his question here.....

If two planes get close enough where TCAS has to kick in, is the system somehow linked, for lack of a better word, to the other? What I mean is will both TCAS say climb or will they intentionally differ so they don't just climb (or descend) into each other?
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RE: Tcas Questions

Tue Jul 09, 2002 3:17 am


The TCAS do "talk" to each other, so that they do not give the same order.
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RE: Tcas Questions

Tue Jul 09, 2002 3:19 am

The TCAS, when operating correctly, will coordinate their commands. One TCAS will tell its a/c to climb and the other TCAS will tell its a/c to descend. But they don't always work correctly. I think TCAS is only audible in cockpit and thus would be picked up on the CVR. I don't think a controller would know if a TCAS were to go off.
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RE: Tcas Questions

Tue Jul 09, 2002 3:33 am

TCAS do NOT send information to ATC, only to the pilots.
Sabena ... Never to be forgotten (15 years already , what a shame !! )
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RE: Tcas Questions

Tue Jul 09, 2002 3:35 am

The TCAS system has in its data base the service ceiling of the airplane and its registration number. If neither airplane is near its service ceiling, the system uses the registration number to decide which airplane will receive a climb indication and which one will receive a descend indication. Since the system between airplanes "talk" to each other through the transponders, each "knows" what the other's command is. It appears the system work as it should and the crew followed ATC instructions instead of the TCAS alert. ATC does not receive this information and I don't know what it would take to receive it. One of the problems, in a heavy air traffic zone, is that the screens are so cluttered with data, it makes reading the screens difficult at times.
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RE: Tcas Questions

Tue Jul 09, 2002 3:42 am

TCAS presently does not downlink to ATC. And while the next generation of ATM (enhanced surveillance, etc) is expecting to make greater use of intent data, I don't believe that TCAS orders would be downlinked -- if TCAS is going off there simply isn't the time to let ATC make a decision on evasion. That's why TCAS automatically allocates the climb/descent RA.

IMO the only exception to blindly following TCAS should be in cases where the pilot has visual contact with the conflicting traffic and decides that to follow TCAS would be less safe than to opt for an alternative manoeuvre.

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