dc10
Posts: 122
Joined: Sun Apr 01, 2007 11:53 pm

Questions About Tcas

Thu May 25, 2000 3:33 pm

Hi! I have 4 questions about TCAS:
1/ Can the Air carrier or the pilot change the settings of the TCAS (ie) the minimum distances/height in which the system will react, or is it the FAA/JAA/DGAC/... business?
2/ How does it work? Does it use a specific radar, or does it use the (weather?) radar in the nose of the aircraft? Or does-it use another system?
3/ When TCAS gives on information (climb, descend...), is it an order to the pilots, (ie) are they obliged to follow it, or is it only a warning? (I guess it depends on company but I'm not sure)
4/ Is this system very reliable, or are there sometimes some "false" warning as sometimes with the GPWS?
Thanks a lot!
DC10
 
richie
Posts: 139
Joined: Wed Dec 22, 1999 10:28 pm

RE: Questions About Tcas

Thu May 25, 2000 5:36 pm

I may not be totally accurate, but you others please correct me if I am wrong...

DC10, here your answers:

1. The pilot has the possibility of changing the 'box' around his airplane up or down. I climb it seems t be more favorable to have more airspace forward and up to be regarded as 'dangerous', and in climb it's the same facing down.

2. TCAS uses the secondary radar system of each airplane (SSR). The box used in the cockpit is the transponder. It does an active scan around the airplane and receives answers form other airplanes around. Out of the responses it calculated trajectories and possible threats. The newest TCAS versions even communicate with each other in case of a threat to determine who sinks and who climbs. As it works via SSR, it is able to track any operating transponder, which makes it see all airtraffic around it (having an active transponder).

3. I believe every company mandates to follow TCAS advisories, unless even greater danger is to be expected. That is like all other safety stuff.

4. As from what I hear, it is well established now and does not trigger off for nothing. In the beginning there were some problems as both TCAS might have recommended escape paths that were still conflicting.

A general comment: what is making me upset is, that the major freight companies do not have to have mandatory TCAS (some of them still installed it for safety reasons. I know of ATLAS and GEMINI). As if it would matter what the payload of airplanes is when they bounce one in another...
 
AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: Questions About Tcas

Fri May 26, 2000 11:56 am

As an operator, not an engineer, I can say the following about the TCAS systems I've used:

1. Pilot can modify display slightly to bias from neutral (normally +/-4000 feet) to "above" (normally +8000/-2000) or "below" (normally +2000/-8000). Software for Traffic Advisory (TA) and Resolution Advisory (RA) is not affected by the display bias. Different systems have different numbers to the above.

2. Uses transponder information, but exactly how I tried to quickly forget. If other aircraft does not have active transponder, you'll see/hear nothing. If other aircraft has transponder, but no mode-S (don't ask I don't want to remember specifics of that) you _may_ see the traffic but will never get an RA.

3. TCAS produces Traffic ADVISORY and Resolution ADVISORY information. There is no _required_ action per FAR, but every company I know about requires following RA unless visual contact is made and/or following RA would possibly endanger the aircraft greater. i.e. descend RA's below 1000'AFL = not good.  

4. Most of the bugs seem to have been worked out, but I still see the occasional phantom target, descend RA at low altitude, etc. Worst problem I think is the system's lack of knowledge of pilot/controller intentions. i.e. contact is climbing rapidly to 10,000' clearance altitude and you're at 11,000' (everyday occurance at DFW).
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
pilot21
Posts: 983
Joined: Sun Oct 24, 1999 8:28 am

RE: Questions About Tcas

Tue May 30, 2000 6:56 pm

As most of your questions have been answered I'm not going to list them all again, expect to throw in my two cents worth.
Firstly, the problems which appear to now be sorted were things like the Dallas Fort Worth hump affect, this apparently was caused by MD80's climbing steeply out of Fort Worth causing the TCAS systems of over flying aircraft to be activated. It now has been sorted. The other problem is that not all TCAS systems are compatable. Remember the Saudia airlines crash in India when an IL-76 hit them climbing out from New Delhi.
Apparently even if the russian aircraft had a TCAS system fitted, because it wouold have been the russian version, it would not have been able to communicate with the american one in the B747???
not sure if this one is sorted yet.
Secondly cargo aircraft, they have to have TCAS installed by 2002 (I think thats the year)
However don't get annoyed at them for escaping safety regulations, they have looked at TCAS and while agreeing with it principle, have sought to bring out a far better system, ADS_B
This was developed by a subsidiary of UPS and is a radar screen for the cockpit. It is still in trials and the FAA haven't accepted it over TCAS, unfortunately, but the system is brillant and basically allows the pilot to see exactly the same information in the cockpit as airtraffic contol sees on the ground.
Visit their website @ www.ADS_B.com
it is a great system
Cheers
Pilot21
Aircraft I've flown: A300/A310/A320/A321/A330/A340/B727/B732/B733/B734/B735/B738/B741/B742/B744/DC10/MD80/IL62/Bae146/AR
 
dc10
Posts: 122
Joined: Sun Apr 01, 2007 11:53 pm

RE: Questions About Tcas

Tue May 30, 2000 7:25 pm

Thanks a lot for your precises answers!
Just another question:
Richie, you spoke about a "secondary radar system of each airplane (SSR)": where is this radar located? In the nose section?
Thanks a lot again!
Regards
DC10
 
AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: Questions About Tcas

Tue May 30, 2000 11:10 pm

>Firstly, the problems which appear to now be sorted were things like
>the Dallas Fort Worth hump affect, this apparently was caused by
>MD80's climbing steeply out of Fort Worth causing the TCAS systems
>of over flying aircraft to be activated. It now has been sorted.

Not "sorted" yet. I still see aircraft climbing rapidly causing TA/RA activation on a daily basis throughout the ATC system. Controllers have simply learned it is easier to advise pilots of overflying aircraft that the climbing aircraft that's about to activate their TCAS is climbing to an altitude below the one the overflying aircraft is already at and that normally will prevent pilots of the overflying aircraft from performing avoidance maneuver. Problem remains.

As to "secondary radar", I suspect what Richie was speaking about was the transponder or "encoded radar signal." Not an actual radar system on the aircraft, but just the reply transmitter portion that replies to ATC (or any other) interrogator signal.

"Primary radar" displays show reflected energy from an object only. "Secondary radar" displays show an enhanced position of that object along with additional encoded information (4 modes or pieces of data).

an ex-hawkeye driver
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
777X
Posts: 850
Joined: Fri Dec 19, 2014 12:44 am

RE: Questions About Tcas

Wed May 31, 2000 7:26 am

Pilot21,

>Apparently even if the russian aircraft had a TCAS >system fitted, because it wouold have been the >russian version, it would not have been able to >communicate with the american one in the B747???
>not sure if this one is sorted yet.

As Richie said, only the latest version of TCAS coordinates with the other a/c, and if it can't (other plane has older TCAS or no TCAS) it will issue it's own RA (as is normal in the older versions of TCAS) so TCAS would have probably saved the day, as it doens't depend on both planes having the system (although it works best when both do)

777x


 
pilot21
Posts: 983
Joined: Sun Oct 24, 1999 8:28 am

RE: Questions About Tcas

Wed May 31, 2000 6:21 pm

Cheers guys

I was actually doing research into ADS_B when I came across the above info. regarding TCAS. The particular article which pointed out TCAS limitations said that the Dallas hump affect had been sorted, guess you can't belive everything you read. Same goes for the article re: Saudia crash, I wondered about the accuracy of the info. as both articles came from reputable sources, but I thought passing on the info. if it wasn't correct, I 'd certainly find out here.
Cheers
Pilot21
Aircraft I've flown: A300/A310/A320/A321/A330/A340/B727/B732/B733/B734/B735/B738/B741/B742/B744/DC10/MD80/IL62/Bae146/AR
 
richie
Posts: 139
Joined: Wed Dec 22, 1999 10:28 pm

RE: Questions About Tcas

Fri Jun 02, 2000 8:15 pm

AAR90, you are exactly right. Most radar environments are working on 2 different systems to present a radar operator with the most accurate airspace picture. The first one is the PSR (primary radar system), the second one is the SSR (Secondary Radar System). While the PSR is independent from any aircraft system (as it is what we usually condider to be the RADAR RAdio Detection And Range), the SSR only functions with the necessary systems in the airplane working (usually referred to as the TRANSPONDER). If you really care about the technical details, open another post. Please.

Now TCAS actually uses the same system, but in an enhanced mode, which allowes to transmit much more information. You could (smiplified!) say that TCAS is a airborne SSR in each airplane.
 
AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: Questions About Tcas

Fri Jun 02, 2000 11:05 pm

>If you really care about the technical details, open another post. Please.

No way dude! I've been zapped by a million watt primary system I flew around for 10 years. Must have absorbed enough of the technical details as it is.  
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
AerospaceFan
Posts: 6990
Joined: Thu Dec 22, 2005 1:43 am

RE: Questions About Tcas

Sat Oct 21, 2006 7:09 pm

I was reading about TCAS in general and came across Table 4 in the following resource (at page 33). Can anyone explain why the aural annunciation changes were made as they were, between "existing annunciations" and the newer ones used for TCAS II, Version 7?

For example, why did "climb, climb, climb" change to "climb, climb"?

Also, are these commands repeated to assure that they are heard?

E.g.: "Climb, climb... climb, climb... climb, climb...."

Thank you in advance for your responses.

Resource mentioned:

http://www.arinc.com/downloads/tcas/tcas.pdf

[Edited 2006-10-21 12:11:10]
What's fair is fair.
 
YYZYYT
Posts: 906
Joined: Tue Apr 05, 2005 12:41 am

RE: Questions About Tcas

Wed Oct 25, 2006 12:37 am

Quoting DC10 (Thread starter):
3/ When TCAS gives on information (climb, descend...), is it an order to the pilots, (ie) are they obliged to follow it, or is it only a warning? (I guess it depends on company but I'm not sure)



Quoting Richie (Reply 1):
3. I believe every company mandates to follow TCAS advisories, unless even greater danger is to be expected. That is like all other safety stuff.



Quoting Pilot21 (Reply 3):
Apparently even if the russian aircraft had a TCAS system fitted, because it wouold have been the russian version, it would not have been able to communicate with the american one in the B747???
not sure if this one is sorted yet.

How about the Überlingen crash: TU154 and 757 collided even though TCAS worked and resolved the issue correctly; the DHL 757 followed TCAS advisory to descend; but the TU154 ignored the TCAS insturctions to climb, but instead followed ATC instructions and also descended.

I recall reading somewhere (probably on a.net) that it is Russian (or maybe Easter European) practice to follow ATC in such situations, but American (or Western European?) practice to follow TCAS instead of ATC...

I also recall that an attempt was being made to standardize the repsonse to TCAS on a world-wide basis, to avoid such conflicting instructions in the future. Anyone have any updates?

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