geoffm
Posts: 2082
Joined: Fri Feb 27, 2004 5:58 am

Tcas - How Does It Work?

Sat Jan 15, 2005 8:25 pm

I know what it does, but how does it do it? Just a summary, I don't want the full gory details. For example, how do the transponders talk to each other - VHF for example? Do they transmit their position/direction information or is this done by radar? What sort of range do they have?

I've read this thread: http://www.airliners.net/discussions/tech_ops/read.main/79059/ but it doesn't really answer the questions.

Thanks

Geoff M.
 
air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: Tcas - How Does It Work?

Sat Jan 15, 2005 10:40 pm

In real basic terms from the A300 AMM:

A. The TCAS computer transmits interrogation messages at 1030 MHZ to ATC transponders of nearby aircraft and receives reply messages at 1090 MHZ.

B. The Mode-S transponders generate squitter messages once per second. The squitter message contains that aircraft's unique identification code (address). When a squitter message is received from a nearby Mode-S transponder, TCAS sends a Mode-S interrogation to the address contained in the message. The reply is used to determine range, altitude and bearing of the intruding aircraft.

Basically, the 2 transponders determine postion relative to each other based on the information exchanged.

From a quick read through our AMM it apperas the indicator range selectable between 6nm and 12nm, so 12 nm is the range of the indicator.
 
B747FE
Posts: 217
Joined: Mon Jun 21, 2004 11:09 pm

RE: Tcas - How Does It Work?

Sun Jan 16, 2005 12:15 am

"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
 
DeltaGuy
Posts: 3965
Joined: Wed Sep 12, 2001 5:25 am

RE: Tcas - How Does It Work?

Sun Jan 16, 2005 1:41 am

Most analog-guage aircraft have their TCAS displays built into their VSI, therefore called an EVSI. It still performs the VS function, but it will have a small aircraft symbol, and display the traffic in symbols around your own symbol. When an approaching aircraft gets too close, it will turn into a square, then a red square. The CAWS (cockpit aural warning system) will sound out a TA, or Traffic Advisory, such as "Traffic, Traffic"....if it gets to the point of the traffic becoming a red square, you will get a TR, or Traffic Resolution, such as "Descend, Descend, Descend"....at this point, the VSI will come alive with arcs on the commanded FPM....the computer will decide if you should climb at 2,000 FPM, or descend like a banshee at 5,000 FPM, etc etc. A green arc will denote where the needle should be...a red arc tells you where you should not be flying to..i.e. into the traffic. If you were to give too shallow of a climb, CAWS would tell you "Monitor vertical speed", until you corrected with sufficient climb.

The other aircraft's TCAS computer, of course, would have it coordinated so that you both weren't descending  Smile/happy/getting dizzy Kind of a crash course description (no pun intended), but there ya go.

DeltaGuy
"The cockpit, what is it?" "It's the little room in the front of the plane where the pilot sits, but that's not importan
 
geoffm
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Joined: Fri Feb 27, 2004 5:58 am

RE: Tcas - How Does It Work?

Sun Jan 16, 2005 7:38 pm

That's the sort of summary I wanted - thanks!

Geoff M.
 
spencer
Posts: 1518
Joined: Sun Apr 25, 2004 8:30 pm

RE: Tcas - How Does It Work?

Sun Jan 16, 2005 11:13 pm

Does TCAS get affected by level busts? (Please, let's be serious here!)  Laugh out loud
Spencer.
EOS1D4, 7D, 30D, 100-400/4.5-5.6 L IS USM, 70-200/2.8 L IS2 USM, 17-40 f4 L USM, 24-105 f4 L IS USM, 85 f1.8 USM
 
air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: Tcas - How Does It Work?

Sun Jan 16, 2005 11:37 pm

I'm not sure what you mean. TCAS simply interogates other aircraft for range and speed. If the other aircraft enters the parameter gates in the software, TCAS will activate the appropiate warning. Therefore, assigned aircraft levels don't matter. TCAS doesn't care what your assignment is (that's the altitude alerter's job), all TCAS cares about is how close and your closure rate to other aircraft.

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