ADS-B versus S mode
 

Could any qualified ATCs explain how ADS-B versus S Mode works, also how it will effect the day to day work of a controller compared to current systems ?

Some aircraft always appear to be using ADS-B (EI- XXX reg aircraft )whilst others do not. Just curious !

Mode S communicates to our ATC consoles through various commercial VHF or satellite datalinks. Updating us regularly (can be set at various times, practically 5-30 minutes) on the current and projected position of the aircraft. We trust such information on our screens a little more than the spoken word, and can use marginally less restrictive separation standards than full procedural control.

ADS/B sends the position information (without the projection) through the transponder signal direct to recievers maintained by your ANSP. The update rate is measured in seconds rather than minutes, the plan is that it will be equivalent to radar, and radar separation standards will apply.

http://www.airservicesaustralia.com/...sb/default.asp

will tell you more

Mode S (S = Select) provides for downlinked parameters (DAP's) as used in TC currently. Also, its the eventual replacement for Mode A SSR code use. The 4 digit octal SSR code is replaced by a unique 24 bit address. The pilot enters his RT callsign into the FMS - hopefully correctly! DAP's include heading, track, ground speed, 25' altitude updates, selected altitude etc.

Mode S will provide a considerable improvement in redusing RF clutter and garbling. ADS-B (Airborne Dependent Surveillance - Broadcast) relies on GPS data - ok in the wide open spaces but not really accurate enough for European skies - yet. Maybe some applications out there, the middle of oz for instance.

many thanks