Mr Spaceman
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A Question About Tcas?

Tue Jan 07, 2003 7:20 am

Hi guys.

(unfortunately it's been a while).

I've got a neat little receiver that I use to listen to ATC when visiting airports around Toronto (it's an ICOM IC-R2). When I'm at home I can still hear pilots communicating with Toronto Intl's approach controllers, all the way from when they first check in, untill they're handed off to Toronto's tower. Unfortunately, I can only hear the pilots side of the radio work (I live 12 nm from Toronto Intl), however, it's pretty easy to fill in the blanks about what the controllers are requesting, etc.

Over the past few days I've heard a couple of pilots ask for additional information that they were not recieving on their TCAS.

The first pilot stated to the approach controller that his TCAS was showing an "amber target" and asked the controller if he could let him know what altitude the other aircraft was at?

The second piloted stated to the approach controller that he had a TCAS target and wanted to know if the other aircraft was below him or beside him?

My question is...Does a TCAS not show the altitude of other aircraft that are flying close by? Or could it be that these particular airliner's TCAS's were not functioning properly?

I've read articles in the past about TCAS, but I've forgoten what all their capabilities are. I also did a search, but the posted info (which was great) didn't answer my question....unless I missed it.

Chris  Smile





"Just a minute while I re-invent myself"
 
avt007
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RE: A Question About Tcas?

Tue Jan 07, 2003 9:20 am

If the target a/c doesn't have altitude reporting (mode C) which is unlikely, or if it isn't working, then the TCAS system can't display relative altitude, only position. As such ,it won't generate warnings. I'm not sure it would even give an amber display. The first level of display is white, then amber for close traffic, then red for real danger. There are a lot of parameters, distances and times involved, but I don't feel like digging for the books Big grin Also, the pilots might be looking for confirmation of what their TCAS is telling them. TCAS displays altitude relative to yours, for example an a/c 1500 feet below you and climbing would have a white symbol with "-15" beside it, and an arrow pointing upwards. And finally, if the a/c is quite close, depending on the size of display used, the symbols are crowded an not easy to read. Hope this helps Smile
 
airplay
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RE: A Question About Tcas?

Tue Jan 07, 2003 10:02 am

TCAS equipped aircraft have a top and bottom TCAS antenna. Preferably, these antennas are directional. In other words, they can detect the direction of the transmission.

Many aircraft equipped with TCAS do not have directional antennas on the bottom. This is optional, and an omnidirectional antenna can be used. Therefore it is possible for traffic below the aircraft to lack bearing information. This is known as "no bearing" traffic. It is usually represented by a "NO BEARING" annunciation, a relative altitude (if available) and distance to the target.

If no altitude information isn't available from the target, either because the aircraft isn't equipped with an encoder, the transponder ALT mode is not selected or the unit is unserviceable, then the TCAS assumes that the target relative altitude is +/- 1200 feet.

The colors (and shapes) of the symbols of the traffic display are purely dependant on the distance to the target and the altitude of the airplane. For example, RAs are inhibited at a certain altitude above the ground (different depending on MOPS).

Blue or white diamonds are proximate or other traffic. Yellow circles are traffic advisories. Red Squares are resolution advisories.
 
FredT
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RE: A Question About Tcas?

Wed Jan 08, 2003 1:26 am

Just one addition: The classification of targets in TCAS depends on target distance divided by rate of closure between subsequent interrogations. This value (time until impact in the worst-case scenario) is called a tau value and the tau limits for TAs (Traffic Advisories) and RAs (Resolution Alerts) change with altitude.

To those unaware of it, it might also be of interest that the aircraft will coordinate their RAs over the mode S datalink (if mode S equipped).

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Mr Spaceman
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RE: A Question About Tcas?

Thu Jan 09, 2003 1:40 am

Hello gentlemen.

Thank You for your replies. Your info was great.

>Avt007, you mentioned that "the pilots might be looking for confirmation of what their TCAS is telling them". That thought also entered my mind as a possibility. Perhaps both of these aircraft's pilots were simply checking their TCAS's against the approach controller's radar.

>Airplay, when you mentioned the "shapes" of the symbols, you reminded me that the second pilot first stated that he had a "small" aircraft on his TCAS, then he asked approach if his TCAS target was below him or beside him.

How did he know the target was a small aircraft? Do the TCAS symbols indicate this info after interrogating the target aircraft's transponder?

>FredT, it was interesting to learn from you that some aircraft have the ability to coordinate RAs over the mode S datalink (if mode S equipped). That sounds like a great way to ensure the crew has been alerted to a possible traffic conflict.

Chris  Smile

"Just a minute while I re-invent myself"
 
Minuteman
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RE: A Question About Tcas?

Thu Jan 09, 2003 5:09 am

This might not be completely Tech/Ops, but I think this is one of the coolest things to come along for GA in a while.

Its a Mode-S capable transponder from Garmin that will also offer traffic advisories if you have one of their moving map units as well.

http://www.garmin.com/products/gtx330/
 
FBU 4EVER!
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RE: A Question About Tcas?

Thu Jan 09, 2003 9:05 am

Hello,Mr. Spaceman;
Telling a "target" as being a "small" plane is really not possible,but is a term normally used for targets without Mode "S" capability,which generally encompasses most light aircraft.Light a/c=small planes,hence the term.
Flying an MD-80/90 out of London /Heathrow,I usually get some info on my TCAS of planes without any altitude indication.My concentration will always be attracted by the aural annunciation "TRAFFIC!" and an amber indication on my TCAS screen but no alt. indication.This is because most of the light planes around don't have Mode "S" Transponders.Hence the Captain's query about this light traffic's whereabouts.
"Luck and superstition wins all the time"!
 
FredT
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RE: A Question About Tcas?

Thu Jan 09, 2003 5:46 pm

"it was interesting to learn from you that some aircraft have the ability to coordinate RAs over the mode S datalink (if mode S equipped). That sounds like a great way to ensure the crew has been alerted to a possible traffic conflict."

Not as much a way of making sure they're alerted - they will be when the TCAS goes off - as a way of making sure that the two RAs won't cause another conflict. I e, if one aircraft tells the crew to climb the other shouldn't.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Mr Spaceman
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RE: A Question About Tcas?

Fri Jan 10, 2003 4:13 am

Hi guys.

Thanks for that information.

>FBU 4EVER!, now it's very clear to me as to why the pilots of and airliner would assume that a TCAS target is likely a small aircraft.

>FredT, OK, I understand what you mean about how having a mode S datalink onboard will help make sure that the two aircraft's RAs won't cause another conflict.

>Minuteman, Thanks for that link. I'm constantly reading about new avionics that are becoming available for GA aircraft in the aviation magazines that I read, however, I wasn't aware of this mode-S cabable transponder from Garmin. I guess I'm falling behind in my reading.

Chris  Smile





"Just a minute while I re-invent myself"
 
bio15
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RE: A Question About Tcas?

Wed Jan 15, 2003 12:04 am

>>>My concentration will always be attracted by the aural annunciation "TRAFFIC!" and an amber indication on my TCAS screen

FBU (and the rest):
I've been searching previous posts to understand where the pilots find TCAS information, but with no success. Where is this 'screen' you refer to located? Are the TCAS units a standard on commercial aircraft?

I was wondering if on the 767/757 the display is linked with the HSI just as the weather display


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Thanks in advance
-Alfredo

 
Bjones
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RE: A Question About Tcas?

Wed Jan 15, 2003 1:15 pm

TCAS information can be displayed in different places depending on the aircraft and the desires of the crew. I fly the KC-135 and it is always displayed on our VVI and can be displayed on a center MFD and on the pilot or copilot's MFD depending on what mode the MFD is in. We usually display it in the center and do not bring it up on the individual sides (aside from the VVI).

The lack of altitude information is not an indication of lack of mode S, but rather lack of mode C. A target without an altitude can result in a traffic advisory (TA) but not a resolution advisory (RA). A target with only altitude and range but not bearing can give either an RA or TA but it will be aural and textual not graphic.
 
bio15
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RE: A Question About Tcas?

Thu Jan 16, 2003 7:10 am

Thanks Bjones, I sort of get the idea. But what is the VVI?
 
FredT
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RE: A Question About Tcas?

Thu Jan 16, 2003 7:19 pm

Vertical Velocity Indicator, or VSI.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
FDXmech
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RE: A Question About Tcas?

Fri Jan 17, 2003 12:15 am

My first encounter with TCAS (CO), the TCAS shared the same display with the weather radar. If memory serves me, you could choose either weather or TCAS to display. But if weather was selected but TCAS sensed an RA or an intruder, the display would automatically switch over to TCAS.

Most newer aircraft superimpose TCAS onto the ND (Nav Display) whereas the aircraft picked up via TCAS are imposed on the ND's moving map display.

And as stated above, the VSI.

You're only as good as your last departure.
 
Rick767
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RE: A Question About Tcas?

Fri Jan 17, 2003 12:25 am

Our older aircraft have the TCAS displayed on the electronic VSI display (these a/c were newly fitted with the TCAS system post-delivery). The VSI also highlights red around the "danger regions" in traffic conflicts (avoid specific climb / descent rates).

The newer aircraft including all of the 767-300s have the TCAS targets imposed on the ND with traffic avoidance "danger regions" highlighted red in regions of the ADI (avoid specific pitch attitudes). These newer jets came with TCAS built in from the factory.

In both cases putting pitching the aircraft into the green zone is the general idea.
I used to love the smell of Jet-A in the morning...
 
bio15
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RE: A Question About Tcas?

Fri Jan 17, 2003 9:08 am

Thank you all, I got it now.

Rick: I didn't know the 767-300 had a biult in factory TCAS unit. I assume the 747-400, 717 and 777s have them incorporated as well, am I right?

-Alfredo
 
Mr Spaceman
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RE: A Question About Tcas?

Wed Jan 22, 2003 5:40 am

Hi guys.

In the 737 cockpit photo below, is the VSI (which looks electronic - located below the Altimeter), that you can see, the type that TCAS info can be shown on?

If the answer is yes, is the display on the VSI similar to the one that's shown on the Garmin link posted above by minute man? (like a small radar type of view). That 737's VSI instrument looks to small for that type of display....or is it? I suspect an electronic VSI's TCAS display might be in the form of only numbers, colours and arrows (nothing to fancy).


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Chris  Smile
"Just a minute while I re-invent myself"
 
FredT
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RE: A Question About Tcas?

Wed Jan 22, 2003 6:46 am

That's the kind. Says "TCAS" in the lower left corner, that's a hint.  Big grin You'll see segments of the VSI go green and red depending on the RA you receive. TCAS targets will be on the ND, unless I'm completely mistaken - not exactly the same displays as those I've been fooling around with.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Mr Spaceman
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RE: A Question About Tcas?

Thu Jan 23, 2003 7:37 am

Hello FredT.

Thanks for pointing out to me that "TCAS" is marked right on that VSI instrument itself.

I didn't even notice it. I understand that RAs (Resolution Alerts) will appear on the VSI, and the aircraft target itself will be on the ND (Navigation Display)....in some airliner types.

Chris  Smile
"Just a minute while I re-invent myself"
 
Bjones
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RE: A Question About Tcas?

Thu Jan 23, 2003 1:50 pm

The VVI in the 737 shown would provide a red arc and a green arc along the outside of the display indicating that any area in the green will provide a climb or descent rate sufficient to avoid a collision. This arc will only appear during an RA. The center of the VVI will show any TCAS targets that are within the range it is set to. Any aircraft in the range but not expected to become a conflict will be a white outline of a diamond. An aircaft that may become a potential conflict will be a solid white diamond. An aircraft that becomes a TA (traffic alert, higher probablity that it will become a conflict) will be a solid yellow diamond and the TCAS will announce "traffic". A RA will be a solid red square and the arc will appear along the edge with aural commands from the TCAS such as "climb", "climb now", "monitor vertical speed", etc. When the conflict is over it will announce "clear of conflict". Each target regardless of type will show an altitude relative to yours such +10 (=1000 ft above you) and an arrow pointing up or down if the other aircraft is in a climb or descent at 500 feet per minute or greater.

The 737 shown most likely also has the capability to display TCAS information on the pilot or copilot lower CRT (MFD).
 
Mr Spaceman
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RE: A Question About Tcas?

Fri Jan 24, 2003 6:05 am

Hello Bjones.

Thank You, for explaining what is displayed on the VVI when the TCAS receives a Traffic Alert or when a Resolution Advisory occurs.

I've heard the "A" in the acronym for a TA or RA refered to as both an Alert and an Advisory. Does it really matter what a pilot calls it?

I suspect that a TCAS's "TA" is a Traffic Alert, and an RA is a Resolution Advisory...which uses aural comands when a potential conflict is becoming more dangerous.

Chris  Smile
"Just a minute while I re-invent myself"
 
FredT
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RE: A Question About Tcas?

Fri Jan 24, 2003 5:46 pm

Traffic Alert/Resolution Advisory. And yes, it does matter. Aviation is not the right place to get things mixed up I’m afraid.

A RA is accompanied by aural instructions: “Descend”, “Don’t sink” and so on. A TA is accompanied by an aural alert: “Traffic, traffic”.

Rumor has it LH had to replace the “don’t sink” command...  Big grin (Hint: read it out loud... and pretend you’re talking with a thick German accent).

BTW, (vain attempt to avoid flak from all the germans  Smile) I’m Swedish and we’re just as bad with some of these pronounciation issues - don’t be surprised if you hear a Swede tell you there’s a chip down below in the ocean...

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Mr Spaceman
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RE: A Question About Tcas?

Sat Jan 25, 2003 5:01 am

Hello FredT.

Thanks for your reply.

OK, Thank You for clearing up for me/us what the correct expression is for a TA and an RA.

PS, that's pretty funny about how Lufthansa had to replace it's TCAS's "dont sink" command. hehehe Big grin

I've noticed that some Swedes on A.Net also type out their words as they would say them. Their accents must be pretty strong I guess. You've never done that.

Chris  Smile
"Just a minute while I re-invent myself"
 
Bjones
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RE: A Question About Tcas?

Mon Jan 27, 2003 5:29 am

Actually "don't sink" or "don't think" as we always thought it was saying is not a TCAS aural advisory. It is a GPWS advisory that is triggered by a descent shortly after takeoff (before reaching 1500AGL).
 
Rick767
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RE: A Question About Tcas?

Mon Jan 27, 2003 6:12 am

"Rick: I didn't know the 767-300 had a biult in factory TCAS unit. I assume the 747-400, 717 and 777s have them incorporated as well, am I right?"

No idea to be honest. I don't even know that all 763s feature built-in TCAS with targets on the HSI? Ours do, that's all.

To clarify, on our older aircraft the TCAS system is ONLY on the VSI. The symbols and RA Green / Red display only appear on the VSI.

On newer aircraft (including all 763s) the aircraft symbols appear on the HSI display, with RA commands in red on the ADI.
I used to love the smell of Jet-A in the morning...
 
FredT
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RE: A Question About Tcas?

Mon Jan 27, 2003 5:33 pm

Bjones,
my bad. Just had to get that joke in.  Big grin Thanks for setting things straight.

Some of the nitty gritty tech details and a list of the aural alerts.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.

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