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Questions About Tcas  
User currently offlineDC10 From Canada, joined Apr 2007, 0 posts, RR: 0
Posted (14 years 7 months 1 week 3 days 14 hours ago) and read 2754 times:

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

11 replies: All unread, jump to last
 
User currently offlineRichie From Switzerland, joined Dec 1999, 143 posts, RR: 0
Reply 1, posted (14 years 7 months 1 week 3 days 12 hours ago) and read 2579 times:

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...


User currently offlineAAR90 From United States of America, joined Jan 2000, 3498 posts, RR: 46
Reply 2, posted (14 years 7 months 1 week 2 days 18 hours ago) and read 2535 times:

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!
User currently offlinePilot21 From Ireland, joined Oct 1999, 1386 posts, RR: 2
Reply 3, posted (14 years 7 months 5 days 11 hours ago) and read 2491 times:

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
User currently offlineDC10 From Canada, joined Apr 2007, 0 posts, RR: 0
Reply 4, posted (14 years 7 months 5 days 10 hours ago) and read 2487 times:

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


User currently offlineAAR90 From United States of America, joined Jan 2000, 3498 posts, RR: 46
Reply 5, posted (14 years 7 months 5 days 7 hours ago) and read 2479 times:

>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!
User currently offline777x From United States of America, joined Dec 2014, 20 posts, RR: 0
Reply 6, posted (14 years 7 months 4 days 22 hours ago) and read 2459 times:

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




User currently offlinePilot21 From Ireland, joined Oct 1999, 1386 posts, RR: 2
Reply 7, posted (14 years 7 months 4 days 12 hours ago) and read 2444 times:

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
User currently offlineRichie From Switzerland, joined Dec 1999, 143 posts, RR: 0
Reply 8, posted (14 years 7 months 2 days 10 hours ago) and read 2426 times:

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.


User currently offlineAAR90 From United States of America, joined Jan 2000, 3498 posts, RR: 46
Reply 9, posted (14 years 7 months 2 days 7 hours ago) and read 2420 times:

>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!
User currently offlineAerospaceFan From , joined Dec 1969, posts, RR:
Reply 10, posted (8 years 2 months 1 week 3 days 11 hours ago) and read 2340 times:

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]

User currently offlineYYZYYT From Canada, joined Apr 2005, 999 posts, RR: 0
Reply 11, posted (8 years 2 months 1 week 5 hours ago) and read 2273 times:

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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