INSTRUCTOR PLT IN A PIPER PA28 INADVERTENTLY ENTERED THE BOUNDARY OF CLASS B AIRSPACE WHILE CONDUCTING A BIENNIAL PVT PLT FLT REVIEW RESULTING IN A CLOSE ENCOUNTER WITH A SAAB 340 COMMUTER. THE RPTING INSTRUCTOR DID NOT KNOW THAT HE HAD COME CLOSE TO THE SAAB ACFT UNTIL BEING ADVISED BY ATC AFTER LNDG.

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I WAS CONDUCTING A BFR FOR A PVT PLT IN THE FRG S PRACTICE AREA; WHICH IS BORDERED BY JFK CLASS B AIRSPACE; ISP CLASS C AIRSPACE; AND FRG CLASS D AIRSPACE. MODERATE TO HVY AIR TFC IN VICINITY TO AND FROM FRG -- MOSTLY SINGLE ENG PLANES BTWN 1000-3000 FT MSL. I WAS IN THE R SEAT. PVT PLT WAS CLBING FROM 1000 FT E; CIRCLING S TO N TO AVOID SINGLE ENG PLANE IN OUR PROX. WE HAD JUST TERMINATED A SIMULATED ENG-OUT EMER PROC. WE WERE BOTH ACTIVELY SCANNING FOR TFC AS REQUIRED. WE RADIOED FRG TWR FOR LNDG INSTRUCTIONS AND CLRNC. UPON CALLING GND CTL FOR AFTER LNDG TAXI CLRNC; CTLR INFORMED US WE HAD COME '...TOO CLOSE TO A SAAB....' WE ASKED WHICH AIRSPACE; AND HE FIRST REPLIED CLASS D; CORRECTED HIMSELF AND REPLIED CLASS A; THEN STATED CLASS B. I ASKED IF WE PENETRATED ANY OF THE ABOVE AIRSPACES AND HE SAID '...YOU JUST CAME TOO CLOSE....' I CALLED THE TWR AND ASKED AGAIN; AND HE SAID '...NOT A PROB....' NO CLARIFICATION WAS GIVEN DESPITE REPEATED REQUESTS. HE WAS CHUCKLING DURING HIS RESPONSE! BOUNDARIES FOR FRG'S PRACTICE AREA CREATE TOO SMALL AN AREA; THAT IS HIGHLY CONGESTED WITH FRG; ISP; JFK MIXED TFC; FOR SAFE AND ADEQUATE TRAINING. PRACTICE/TRAINING AREAS SHOULD BE CLRLY DESIGNATED AND DEPICTED ON SECTIONAL AND VFR TERMINAL CHARTS AND TRANSIENT TFC SHOULD BE DISCOURAGED. ATC ADVISORIES SHOULD BE ROUTINELY AVAILABLE FOR TRAINING ACFT IN THESE AREAS. CTLRS WILL NOT PROVIDE THIS SVC IN THE VICINITY BECAUSE OF HIGH WORKLOAD DEMANDS. FRG IS THE SECOND BUSIEST GA ARPT IN THE COUNTRY!