Can someone explain me the TCAS in relation to Transponders mode A, C and S? What will give alerts and advisories?
The more I try reading about it, the more it confuses me.. The plane I fly now don't have TCAS but has a Mode S XPonder...
Max
XPonder mode A/C/S vs TCAS
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fougapilot
- Rank 7
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Max,
Xpnder mode A only replis a "ping" to ATC so they have a 2D position,
Xpnder mode C adds an altitude readout from your encoder corrected to 29.92. Thus allowing ATC to read your altitude and has a 3D position.
Xponder mode S also sends info like A/C registration, TAS and eventually GPS position.
Right now, you need a Mode S to fly in Europe above FL280.
Your airplane most likely has an IFF (identification friend or foe) which is a Xpnder mode C that sends 2 different codes. One you set in the airplane at ATC's request, the other that is permanently set so the NATO guys don't fire at you. Or at least that was the case when I was there.
TCAS needs a mode C to work. It received the info from other transponders and depict the aircraft position on the screen. Should the airplane become too close, it will issue an TA (traffic advisory) should the airplanes come so close that there is a collision risk, it will issue a RA (resolution advisory). Before issuing an RA, the TCAS will communicate with the TCAS in the other airplane and they will decide whom climbs and whom descend (TCAS only provides you with vertical resolutions). Pilots MUST follow the RA and not ATC. THe mid air collision (between 2 airliners) over Europe a few years back was caused (amongst other factors) because one of the pilot followed ATC instruction and not TCAS. ALWAYS FOLLOW TCAS!
Should the other airplane not have mode C, your TCAS will not be able to provide an altitude readout nor a valid RA.
Hope this helps,
F
Xpnder mode A only replis a "ping" to ATC so they have a 2D position,
Xpnder mode C adds an altitude readout from your encoder corrected to 29.92. Thus allowing ATC to read your altitude and has a 3D position.
Xponder mode S also sends info like A/C registration, TAS and eventually GPS position.
Right now, you need a Mode S to fly in Europe above FL280.
Your airplane most likely has an IFF (identification friend or foe) which is a Xpnder mode C that sends 2 different codes. One you set in the airplane at ATC's request, the other that is permanently set so the NATO guys don't fire at you. Or at least that was the case when I was there.
TCAS needs a mode C to work. It received the info from other transponders and depict the aircraft position on the screen. Should the airplane become too close, it will issue an TA (traffic advisory) should the airplanes come so close that there is a collision risk, it will issue a RA (resolution advisory). Before issuing an RA, the TCAS will communicate with the TCAS in the other airplane and they will decide whom climbs and whom descend (TCAS only provides you with vertical resolutions). Pilots MUST follow the RA and not ATC. THe mid air collision (between 2 airliners) over Europe a few years back was caused (amongst other factors) because one of the pilot followed ATC instruction and not TCAS. ALWAYS FOLLOW TCAS!
Should the other airplane not have mode C, your TCAS will not be able to provide an altitude readout nor a valid RA.
Hope this helps,
F
The Harvard doesn't have IFF (it barely has UHF, only 1 UHF radio) and doesn't have TACAN.fougapilot wrote:Max,
Xpnder mode A only replis a "ping" to ATC so they have a 2D position,
Xpnder mode C adds an altitude readout from your encoder corrected to 29.92. Thus allowing ATC to read your altitude and has a 3D position.
Xponder mode S also sends info like A/C registration, TAS and eventually GPS position.
Right now, you need a Mode S to fly in Europe above FL280.
Your airplane most likely has an IFF (identification friend or foe) which is a Xpnder mode C that sends 2 different codes. One you set in the airplane at ATC's request, the other that is permanently set so the NATO guys don't fire at you. Or at least that was the case when I was there.
TCAS needs a mode C to work. It received the info from other transponders and depict the aircraft position on the screen. Should the airplane become too close, it will issue an TA (traffic advisory) should the airplanes come so close that there is a collision risk, it will issue a RA (resolution advisory). Before issuing an RA, the TCAS will communicate with the TCAS in the other airplane and they will decide whom climbs and whom descend (TCAS only provides you with vertical resolutions). Pilots MUST follow the RA and not ATC. THe mid air collision (between 2 airliners) over Europe a few years back was caused (amongst other factors) because one of the pilot followed ATC instruction and not TCAS. ALWAYS FOLLOW TCAS!
Should the other airplane not have mode C, your TCAS will not be able to provide an altitude readout nor a valid RA.
Hope this helps,
F
I was just confused with what TCAS receives from A C or S. So, it doesn't receive anything from a A (not even the bearing info?). And when it gives a RA with a C, will the RA be different than if it was from a mode S or a TCAS equipped aircraft? I'm just curious about it.
Thanks again f,
Max
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fougapilot
- Rank 7
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- Joined: Fri Oct 08, 2004 4:49 am
Max,
TCAS will receive only bearing info from mode A. When we are overflying a "bug smasher" with mode A only, our TCAS shows a "gost". Basically just a target without any altitude read out. The traffic could be a few hundred feet or many thousands feet, no way for us to know.
The TCAS can look either ABOVA, BELOW or A/B (above and below). Normally we will set it to ABOVE for climb and BELOW for cruise and descent. When set to Above, it will look at traffic from 3000ft below to 10 000ft above the airplane. The reverse is also true when Below is selected. It will depict all targets within this altitude range (within the selected range NM) If A/B is selected, it looks at both above and below but with a smaller range (5000ft comes to mind, but I am not sure). If only mode A is received, it displays the gost because it does not know its altitude. Although I suspect it knows better then displaying gosts when we are at higher altitude simply because mode A aircrafts cannot fly above 12 500ft. I have never seen a gost when above FL250.
To have a valid RA, the target must have a mode C. Since TCAS is only capable of providing vertical resolutions, it needs to know the target's altitude to work. Without a mode C equipped target, you will not get a resolution. Only an Advisory.
If 2 airplane are on a collision course and only you have a TCAS but the other airplane has mode C, your TCAS will provide you with vertical flight path instruction to avoid the other airplane.
If 2 TCAS equipped airplane are on a collision course, both TCAS will communicate and decide the best course of action. One will instruct the crew to climb, the other to descent. Its the only safe way to go. If the TCAS didn't talk both crew could receive climb instruction and the problem would get worst.
When you receive an RA, YOU MUST FOLLOW TCAS AND NOT ATC. Normally an RA will not require a climb ar descent ogreater then 1500ft per minute. Such a manoeuver requires only a small pitch adjustment and should nearly be invisible to the pax. That is if you react immediatly. If you waste time searching for the traffic, you may need an abrupt manoeuver to avoid a collision.
Currently, mode S only helps ATC. In the near future, with the help of the included GPS position, it will help TCAS determine if 2 airplane are on a colision course sooner and wil be able to provide lateral resolution (turn to XXX heading...) and even perhaps 3 dimension resolution (slow down to MachXX)
Cheers,
F
TCAS will receive only bearing info from mode A. When we are overflying a "bug smasher" with mode A only, our TCAS shows a "gost". Basically just a target without any altitude read out. The traffic could be a few hundred feet or many thousands feet, no way for us to know.
The TCAS can look either ABOVA, BELOW or A/B (above and below). Normally we will set it to ABOVE for climb and BELOW for cruise and descent. When set to Above, it will look at traffic from 3000ft below to 10 000ft above the airplane. The reverse is also true when Below is selected. It will depict all targets within this altitude range (within the selected range NM) If A/B is selected, it looks at both above and below but with a smaller range (5000ft comes to mind, but I am not sure). If only mode A is received, it displays the gost because it does not know its altitude. Although I suspect it knows better then displaying gosts when we are at higher altitude simply because mode A aircrafts cannot fly above 12 500ft. I have never seen a gost when above FL250.
To have a valid RA, the target must have a mode C. Since TCAS is only capable of providing vertical resolutions, it needs to know the target's altitude to work. Without a mode C equipped target, you will not get a resolution. Only an Advisory.
If 2 airplane are on a collision course and only you have a TCAS but the other airplane has mode C, your TCAS will provide you with vertical flight path instruction to avoid the other airplane.
If 2 TCAS equipped airplane are on a collision course, both TCAS will communicate and decide the best course of action. One will instruct the crew to climb, the other to descent. Its the only safe way to go. If the TCAS didn't talk both crew could receive climb instruction and the problem would get worst.
When you receive an RA, YOU MUST FOLLOW TCAS AND NOT ATC. Normally an RA will not require a climb ar descent ogreater then 1500ft per minute. Such a manoeuver requires only a small pitch adjustment and should nearly be invisible to the pax. That is if you react immediatly. If you waste time searching for the traffic, you may need an abrupt manoeuver to avoid a collision.
Currently, mode S only helps ATC. In the near future, with the help of the included GPS position, it will help TCAS determine if 2 airplane are on a colision course sooner and wil be able to provide lateral resolution (turn to XXX heading...) and even perhaps 3 dimension resolution (slow down to MachXX)
Cheers,
F
