LR-60 WITH N90; EXPERIENCED TCAS RA WITH VFR TRAFFIC. REPORTER INDICATING AIRSPACE STRUCTURE; COUPLED WITH ATC PRACTICES; CONTRIBUTED TO THE EVENT.

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WHILE AT 3000 FT APPROX 20 MI N OF TEB; WE RECEIVED AND COMPLIED WITH A TCAS RA. AT 3000 FT; ATC TURNED US TO A 110 DEG HDG WHERE WE SPOTTED TFC AT 2 O'CLOCK POS; 5 MI; 100 FT BELOW MOVING R TO L. MOMENTS LATER; (THE PNF SITTING R SEAT) VISUALLY ACQUIRED THE TFC SIMULTANEOUSLY ACKNOWLEDGING TO ATC THAT TFC WAS IN SIGHT. TCAS PRODUCED AN AURAL TA AND WE CONTINUED TO MONITOR THE TFC. APPROX 30 SECONDS LATER; I OBSERVED THE TFC TURN SLIGHTLY TOWARDS US AND DSND TO 200 FT BELOW OUR LEVEL. WE PREPARED OURSELVES FOR AN RA AND SECONDS LATER THE TFC CLBED TO WITHIN 100 FT OF OUR ALT; LESS THAN 1 MI AWAY; AND TAS GENERATED AN RA CLB. WE CLBED TO 3700 FT; CLRED TFC; AND THEN SLOWLY RETURNED TO ASSIGNED ALT OF 3000 FT. WE DID NOT HAVE TO CONTACT ATC UNTIL OUR DSCNT BACK TO ALT WHERE I STATED WE WERE TCAS CLB. CTLR CAUTIONED US OF TFC ABOVE AT 5000 FT AND TO RETURN TO 3000 FT. NO FURTHER DISCUSSION WAS MADE BTWN US AND ATC. NYC APCH CAN HAVE US FLY AT THE BOTTOM OF THEIR CTLED AIRSPACE OF 3000 FT WHILE UNCTLED TFC CAN FLY AS HIGH AS 2999 FT IN THE SAME AREA. CASE OF WRONG PLACE AT THE WRONG TIME.