Hi

Simple question I hope, but what do the + and _ figures signify below the symbol when other aircraft appear on the radar ?

Thanks Paul

the + is traffic above you and the - is traffic below you.

Thanks Bryan, what do the numbers signify ?

I think +10 is 1000f above -11 is 1100f below etc etc.

Thanks Julian

Yup, + indicates traffic that is above your current altitude, something to note is the numbers that follow it is a representation of the total altitude it is above you, not it's AGL, or MSL Altitude.

Vice versa for the '-' sign.

Reference image linked from wiki.flightgear.org

TCAS, its acually the transponders in the a/craft talking to each other, that provides that info, it gives ATC the same infomation

jeff

TCAS, its acually the transponders in the a/craft talking to each other, that provides that info, it gives ATC the same infomation

jeff

 

Yes, TCAS will send out standard interrogation pulses causing any transponder-equipped aircraft to reply, just as they do when interrogated by a ground ATC radar. It uses the mode C altitude data from those transponders, combined with directional antennas to determine range, direction and altitude of other aircraft.

 

The really interesting part occurs when two aircraft which both have TCAS-equipment are converging in such a way that the possibility of a collision begins to become increasingly likely, requiring an RA (resolution advisory) be generated visually on the cockpit TCAS display, and aurally on the speaker or pilot headset.

 

In this case, the two TCAS computers in the respective aircraft will begin communicating directly with each other, using the Mode S transponders as communication data links.... in effect, working out between them which aircraft is going to climb, and which is going to descend. This all takes place behind the scenes at high speed.

 

When the actual RA is generated, the TCAS box which instructs its pilot to cimb, does so because it knows that the other aircraft's TCAS is simultaneously instructing ITS flight crew to descend...

 

Of course, if the conflicting aircraft has only a standard mode A/C transponder, and no TCAS, none of this negotiation can take place.

Thanks guys, could not find any of this great info. on google. Much appreciated.

Paul