Gazelle on SBS

[rampvan]

I see on another Forum that there was a Gazelle transiting LHR to Northolt which came up on SBS (XZ314) is this just a one off or are the Military helis now starting to carry the equipment needed for SBS id's

[Deleted]

A number of mil choppers carry Mode S so can be seen on the Mode S list but I haven't seen any transmitting ADS-B yet.

[rampvan]

Sorry if I'm being dumb but can you explain the difference between mode S and ADS-B please

[Deleted]

Mode S is function of the radar transponder and transmits details of aircraft speed and other flight parameters. It is mandatory to carry Mode S in certain UK Controlled Airspace at present and will become mandatory for all flights by certain categories of a/c in the near future.

ADS-B is a Mode S facility which transmits aircraft position derived from on-board navigation systems. My understanding is that most Mode S transponders have the ADS-B facility. However, ATC does not require ADS-B because ground radar is far more accurate in determining a/c position. It is therefore not mandatory to transmit ADS-B although many aircraft do perhaps because company regulations require pilots to select the facilty whenever they are flying.

SBS receives and decodes ALL Mode S transmissions and these are displayed on a table on the screen. However, only ADS-B plots on the simulated radar display to show the aircraft position. Information on Mode S flights can include callsign, SSR squawk, registration and various flight parameters -altitude, speed, heading, etc.

Hope this helps.. but shout if you want more info.

[rampvan]

Seems clearer, many thanks