What is a mode S transponder?

[akafrank07]

Could not find any info on this on google are my flight books

[flyelmoair]

Mode S displays SSR height information from the ac transponder to ATC i'm sure. When working in ATC I heard App Controllers giving instructions to 'Strangle Mode S' .... or was it Mode C? actually got me questioning myself now. I'll ask tomorrow and get back to you.

[Prazum]

Mode S

See also: Air traffic control radar beacon system#Mode S
Another mode called Mode S (Selective) is designed to help avoiding overinterrogation of the transponder (having many radars in busy areas) and to allow automatic collision avoidance. Mode S transponders are compatible with Modes A & C.[2] This is the type of transponder that makes the ACAS II (Airborne Collision Avoidance System) and the ADS-B (Automatic dependent surveillance-broadcast) systems function.

[akafrank07]

Thanks for the replies guys
What is the difference between mode s and c?

[JimNtexas]

Mode S provides more accurate position data to ATC radars than older transponder modes. It can be used to data link data to and from ATC. In the US it is the communications link used by our ADS-B system (http://www.trig-avionics.com/adsb.html). Equipage will be mandatory in a few years.

Of special interest to pilots, it transmits an identification number that uniquely identifies the transmitting aircraft.

More info on Wikipedia (http://en.wikipedia.org/wiki/Air_traffic_control_radar_beacon_system#Mode_S).

Edited to add: Mode C dates back to WWII and is the part of the transponder reply that transmits altitude.

[akafrank07]

Thanks for the link Jim

[paco]

A good way of remembering the difference is that Mode S allows aircraft to text each other :)

[M-ONGO]

Looking at some of your questions on here Frank, do you really have a CPL/IR?

[RTN11]

Mode A: Only transmits the four letter code you set on your transponder

Mode C: Transmits code & your current baro altitude.

Mode S: Transmits the above, along with a plehroa of other information, including callsign/flight number, what you've set in any altitude pre-selector (so ATC can tell you before a level bust occurs), fuel remaining, the list is endless on the more advanced aircraft...

Also, if two aircraft have TCAS and Mode S transponders, they will co-ordinate a resolution advisory so they don't crash, ie one aircraft is commanded to climb, the other to descend.

[Pringle_]

mode S also solves the problem of a lack of SSR codes (4096), the pilot must enter the callsign as submitted on the FPL before getting airborne and ATC can identify the aircraft on radar from the callsign returned in a mode S reply. Each Aircraft is allocated a permanent unique hexadecimal code (useful for identifying infringers ;))

It also improves the effectiveness of TCAS and STCA

[BHK]

additionally to what is listed of the S mode in the threads here, doesn't it automatically detect airborne from ground as well?