New to ATC, differences?

[czechwonder]

Hi, what is the difference between things like JFK Tower, JFK approach JFK departure etc?

[KSYR-pjr]

Tower controllers coordinates the sequencing of aircraft within 5 miles of the airport that are landing, as well as those that are just about to take off or have done so.   Tower will also handle very low altitude aircraft that desire to pass within 5 miles or so of the airport, such as helicopter traffic.

Departure control will sequence aircraft who were just switched from the tower frequency away from the airport to their first or second en route fix (or few fixes), as well as begin climbing them out of their airspace and off to the next section of airspace, which could be another approach controller or a center controller.  Center controllers most often controls the higher airspace from 10,000 feet or so up to 60,000 feet.  Center will also handle lower altitude aircraft that are well outside of any towered airports, such as those landing or departing the numerous small, non-towered airports.

Approach control will control arriving aircraft within a ring of typically 30 miles to 5 miles outside the airport by sequencing them towards the airports and in line to land.  Approach control will also handle arriving and departing aircraft that are using nearby, satellite airports.  For example, Buffalo approach, who handles arriving traffic into Buffalo Airport in western NY state, will also handle instrument flight rules (IFR) aircraft that need to land or have just departed nearby untowered Dunkirk airport.

[czechwonder]

what does "ground" do?

[KSYR-pjr]

Ground controllers coordinate the movement of all aircraft and ground-based vehicles within the airport's "movement" areas (taxiways and aprons under ATC control).  No aircraft is allowed to taxi into or through these movement areas without ground ATC's instruction to do so.  There may be an exception to this rule but I am not familiar with any.

At smaller towered airports ground controllers will also provide IFR clearances to IFR flights (instrument flight rules), whereas at larger airports there is yet another frequency called "Clearance Delivery" that delivers IFR and other departing flight clearances to aircraft prior to taxi.

[czechwonder]

Ground controllers coordinate the movement of all aircraft and ground-based vehicles within the airport's "movement" areas (taxiways and aprons under ATC control).  No aircraft is allowed to taxi into or through these movement areas without ground ATC's instruction to do so.  There may be an exception to this rule but I am not familiar with any.

At smaller towered airports ground controllers will also provide IFR clearances to IFR flights (instrument flight rules), whereas at larger airports there is yet another frequency called "Clearance Delivery" that delivers IFR and other departing flight clearances to aircraft prior to taxi.

But when I listen to the JFK Tower feed, aren't they also directing aircraft that are taxiing and clearing for take off?

[KSYR-pjr]

JFK, like most of the largest airports with multiple parallel and intersecting runways, is special in that the tower controllers are giving just enough taxi instructions to get the aircraft clear of all active runways and to a point where they can then "monitor Ground" for the remainder of the taxi. Or, they may instruct a "hold short" at an active runway due to landing or departing aircraft.  Once the runway is clear, tower will then give additional instructions to get the aircraft across the runway to a point to monitor ground.   I suspect that the reason for this multiple role this is so that tower has complete control as to who is crossing active runways.   Once aircraft are clear of the active runways, ground can then safely take over. 

I also believe that tower giving taxi instructions may take the workload off the ground controller, since sometimes the instructions are relatively simple.

[KSYR-pjr]

I should add that often times at the smaller class C and D towered airport, the tower controller is also working the ground frequency (and even clearance delivery at times) so it is easer for the controller and pilot to provide taxi instructions and instruct the the pilot to remain on the the tower frequency for the taxi back to the ramp/gate.