View Full Version : Mode-S Datalink?

21st Feb 2002, 22:26
Does anybody know what kind of datalink-capability is available in current mode-s transponders? As far as i know two tcas-equipped aircraft can do coordinated RAs, so there must be some kind of a datalink. Unfortunately i don't get more information out of the manuals for the airplane i fly (B733).. .Mode-S should be capable of a lot of information to be transmitted, but do current transponders use that?

21st Feb 2002, 23:54
There most certainly is a datalink in the mode-S transponders... that's what they're there for.

The basis of mode-S is that the radar doesn't require all the transponders in a certain direction to respond, like with mode-A/C, where two transponders may interfere in one direction, but can selectively ask for a response from individual airplanes.

First there is an socalled all-call signal, to which all transponders (A/C/S) will respond, the mode-S transponder then sends his specific adress. Hereafter this target will be selectively interrogated.

For communication there are several communicationprotocols available, which use 112 bit datablocks. 56 bits are used for identification, the other 56 can be used to transfer a message.

There is on top of that the possibility of extended length messages, which use max. 1280 bits, built out of max. 16 segments of 80 bits, via a special burst protocol. These 80-bits segments are embedded in the 112bit datablocks mentioned before.. .These 1280 bits are divided in several phases (annunciation, reservation, msg, close-out).

The mode-S-system has a parity bit to detect errors during transmission.

Offcourse mode-S is used as a data-transfer to exchange information for TCAS.

Several possible future applications of mode-S:. .- flight identification. .- flight information (heading, speed). .- meteorological info (spot wind, spot temp). .- ATC-last minute info (rwy closure)

So mode-S is indeed capable of handling much more than it does now. The only real application at this moment seems to be TCAS. It could be used air-ground but ground-air as well.

. .Not really much, but I hope it helps!

[ 21 February 2002: Message edited by: Pegasus77 ]</p>

22nd Feb 2002, 01:41
Reads like the LFT-Script i had lying around <img src="wink.gif" border="0"> . .I just want to know which of the datalink possibilities are in use right know, what the mode-s transponder we use can do. I know there should be more use of the downlink feature to atc in the future (like MCP-altitude, tas, gs, rates, wind-data etc, identification without squawk) but do the airlines have to buy new boxes or ours capable of doing all that already?

22nd Feb 2002, 01:48
Can't be, did my education at another school, but maybe the teachers exchange stuff :)

Might be interesting to get to know what performance level your transponder has. It depends on that level which capabilities there are for the datalink.

And to be honest, talking about LH... Most data-traffic happens via ACARS; don't really see the need of more data-exchange for companies over mode-S.

[ 21 February 2002: Message edited by: Pegasus77 ]</p>

Dan Winterland
22nd Feb 2002, 02:21
The new and experimental ASMGCS (Advanced Surface Movement Guidance and Control System) at Heathrow uses Mode S to aid ground control. My company is involved with the trial which requires the TCAS to be switched to TA/RA on pushback, and to SBY on approaching th gate. If successful, the system is palnned for Schiplo, Frankfurt, Gatwick and Charles de Gaul.

Wee Weasley Welshman
22nd Feb 2002, 19:00
I participated in a DERA trial last year of a HUD system used on the ground that utilised Mode S transmissions to ensure aircraft seperation in LVP's/Cross Runway Ops etc. It also had features that helped rapid runway exit and taxiway nav/gat finding. It too would require transponders left on until on stand etc. Worked like a dream.

The only issue I see is how to persuade beancounters as to the benefits of paying for the extra functionality.