Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Tcas - How Does It Work?  
User currently offlineGeoffm From United Kingdom, joined Feb 2004, 2111 posts, RR: 6
Posted (11 years 4 months 2 weeks 2 days 2 hours ago) and read 6679 times:

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.


Geoff M.

6 replies: All unread, jump to last
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 1, posted (11 years 4 months 2 weeks 1 day 23 hours ago) and read 6589 times:

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.

User currently offlineB747FE From Hong Kong, joined Jun 2004, 230 posts, RR: 4
Reply 2, posted (11 years 4 months 2 weeks 1 day 22 hours ago) and read 6569 times:

Try this link:


"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
User currently offlineDeltaGuy From , joined Dec 1969, posts, RR:
Reply 3, posted (11 years 4 months 2 weeks 1 day 20 hours ago) and read 6548 times:

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.


User currently offlineGeoffm From United Kingdom, joined Feb 2004, 2111 posts, RR: 6
Reply 4, posted (11 years 4 months 2 weeks 1 day 2 hours ago) and read 6471 times:

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

Geoff M.

User currently offlineSpencer From United Kingdom, joined Apr 2004, 1642 posts, RR: 15
Reply 5, posted (11 years 4 months 2 weeks 23 hours ago) and read 6452 times:

Does TCAS get affected by level busts? (Please, let's be serious here!)  Laugh out loud

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
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 6, posted (11 years 4 months 2 weeks 22 hours ago) and read 6495 times:

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.

Top Of Page
Forum Index

Reply To This Topic Tcas - How Does It Work?
No username? Sign up now!

Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)

Similar topics:More similar topics...
Beta On Propeller Aircraft...how Does It Work? posted Wed Nov 12 2003 08:59:37 by USAFHummer
Airshow Moving Map -- How Does It Work? posted Mon Jul 1 2002 03:07:43 by ILUV767
INS: How Does It Work? posted Tue Nov 6 2001 16:22:32 by Captjetblast
Llwas - How Does It Work? posted Sat Feb 17 2001 00:36:46 by Foxo
GEnx Bleedless How Does ECS Work? posted Thu Apr 27 2006 01:14:40 by MesaMXORD
Air Tahiti Nui- How Does This Work? posted Tue Oct 11 2005 19:19:27 by Mirrodie
Prop Condensation - How Does It All Start? posted Wed Oct 13 2004 06:43:51 by INNflight
How Does ATC Work In Korea (Inchon ACC)? posted Tue Oct 1 2002 21:31:41 by Ryu2
How Does Papi Work? posted Tue Nov 6 2001 17:54:45 by Coolair
How Does The Tcas Work? posted Mon Feb 2 2004 13:41:31 by Sfilipowicz

Sponsor Message:
Printer friendly format