jumbojet
Posts: 1038
Joined: Mon Dec 29, 2003 3:01 am

Tcas Question

Wed Apr 28, 2004 10:52 pm

In looking at this photo, I am sure the airplanes aren't as close as the image appears, but it brings up a point. What does the pilot of each of those planes see on his/her TCAS screen? Is the TCAS system giving verbal directions to the pilots that another aircraft is near? If the pilot has a visual, does he/she ignore the TCAS all together?
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InnocuousFox
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RE: Tcas Question

Thu Apr 29, 2004 12:29 am

I would contend that they are not necessarily close in that picture. However, most TCAS stuff is just positions of the aircraft around you. Only in a potential conflict situation does it actually give instructions.
Dave Mark - Intrinsic Algorithm - Reducing the world to mathematical equations!
 
INNflight
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RE: Tcas Question

Thu Apr 29, 2004 12:32 am

TCAS does also stand for

Tyrolean Civil Aviation Spotters  Smile

TCAS only gives you an alert if two aircraft are about to crash! Not if they can fly by each other..


regads,
Florian - Member of TCAS  Smile
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flymia
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RE: Tcas Question

Thu Apr 29, 2004 5:50 am

On a screen I think it shows all the other aircraft and if a collision is possible it will tell you. If the two TCAS of the two planes interact and know a collision is going to happen then it will give instructions.
"It was just four of us on the flight deck, trying to do our job" (Captain Al Haynes)
 
BritPilot777
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RE: Tcas Question

Thu Apr 29, 2004 7:16 am

On the TCAS Screen (Traffic Collision Avoidance System) the flight crew can see other planes in their vicinity shown as dots, next to which they can see how far the other aircraft are from them and how much higher, or lower they are than themselves.

Only if a collision is imminent, will the TCAS give instructions. However there are problems with this, I believe it was a DHL 757 and a Russian jet in a mid air crash not to long ago in Europe, near Switzerland I think, (Please correct if I am wrong).
The TCAS system gave instructions as well as the Controller on the ground. This fatal mistake claimed many lives.

Now who do you listen to? The Computer, or the Controller?
Forever Flight
 
N6376M
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RE: Tcas Question

Thu Apr 29, 2004 7:54 am

as a result of the DHL crash, I believe the "rules" have now been clarified to provide that TCAS instructions superceed any other.
 
fly727
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RE: Tcas Question

Thu Apr 29, 2004 8:04 am

as a result of the DHL crash, I believe the "rules" have now been clarified to provide that TCAS instructions superceed any other.

That is still in the air. Not definitely stated yet.

Only if a collision is imminent, will the TCAS give instructions. However there are problems with this, I believe it was a DHL 757 and a Russian jet in a mid air crash not to long ago in Europe, near Switzerland I think, (Please correct if I am wrong).

The TCAS that provide Resolution Advisories is called TCAS II and unfortunately is not used by all aircraft yet. TCAS I is the one most commonly used and provides only Traffic Advisories.

TCAS III is under development and will give resolutions in both a horizontal and vertical axis.

This should be better explained in Tech/Ops (and already have been).

RM  Smile
There are no stupid questions... just stupid people!
 
S12PPL
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RE: Tcas Question

Thu Apr 29, 2004 8:11 am

TCAS, as said above only gives warnings when a collision is about to happen. It will shout instructions such as "Decend now! Decent now!" or "Climb now! Climb now!", etc. to the pilots.
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tristar2000
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RE: Tcas Question

Thu Apr 29, 2004 9:49 am

Fly727 has the best description.

But remember the principle behind the TCAS system is that the a/c equipped with a TCAS interrogates the other a/c in the sky (like an ATC radar would), and analyses the reply. Now the altitude of the other a/c will be given by its encoding altimeter (ADC on bigger airplanes).

Given that, a TCAS equipped a/c won't "see" the other plane if that plane's transponder is turned off, or if the mode c (altitude reporting) is not working correctly. If the encoding is wrong, then the TCAS won't "see" the correct altitude.

A/C equipped with TCAS II systems have at least one mode-S xpder with the 24-bit binary code specific to the a/c. (For example, if 2 planes with TCAS II systems come face to face, since the code is different, one will get instructions to go up, the other to go down) The pilot will know how much he needs to climb or descend because a green stripe will appear on his VSI (Resolution Advisory (RA)) to show him where to go, the remainder will usually be in red (meaning don't go this way or you could collide).

The deadline for TCAS II installation for many airplanes here in North America is early 2005 (turbine powered and more than 12 500 pounds I believe). There are many older business jets to be upgraded, which usually have a TCAS I, that is when they have a TCAS installed at all.

People sometimes confuse TCAS (Traffic Collision Avoidance System) with the GPWS (Ground Proximity Warning System). The latter will for example tell you to "WHOOP WHOOP PULL UP!!!" when you're about to crash in the ground.

Then you have the EGPWS and TAWS, but like mentioned above, that's more Tech/Ops stuff.

Hope this helps,
Steven  Smile
 
Rick767
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RE: Tcas Question

Thu Apr 29, 2004 10:12 pm

"as a result of the DHL crash, I believe the "rules" have now been clarified to provide that TCAS instructions superceed any other."

"That is still in the air. Not definitely stated yet."


It is not still in the air and it never was. The rules were reiterated after the incident as it became apparent many crews did not know what to do in this situation.

ICAO PANS-OPS, Doc 8168 was amended after this accident to strengthen the provisions on pilot responses to resolution advisories, the procedure itself has never changed:

"If flight crews receive simultaneously an instruction to manoeuvre from
ATC and an RA, and they conflict, the advice given by ACAS should be
followed."


And in the newly updated Doc 8168 again strengthens the position which has always been in force:

"In the event of an RA, pilots shall:

....

  • follow the RA even if there is a conflict between the RA and an air traffic control (ATC) instruction to manoeuvre;


  • not manoeuvre in the opposite sense to an RA;


  • ....
    I used to love the smell of Jet-A in the morning...