A B757 PIC RPT ON THE DIFFICULTY OF ADHERING TO THE STABILIZED APCH CONCEPT WHEN FLYING THE RWY 13 RIVER VISUAL APCH DURING A NIGHT OP AT LGA; NY.

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ON THE KORRY 2 ARR INTO LGA THE ATIS STATED THE ILS TO RWY 22 WAS THE APCH IN USE. WINDS ON ATIS WERE STATED AT 220 DEGS AT 8 KTS. APPROX 30 SECONDS BEFORE WE GOT TO KORRY; APCH CTL TOLD US TO EXPECT A RIVER VISUAL TO RWY 13. I NEVER HAD FLOWN THE RIVER VISUAL TO RWY 13 PRIOR TO LAST NIGHT. THE INSTRUCTIONS WE WERE GIVEN WERE; 'MAINTAIN 3000 FT UNTIL ABEAM THE EMPIRE STATE BUILDING' 'DO NOT DSND BELOW 2000 FT UNTIL ESTABLISHED ON FINAL' AND 'CLRED FOR THE VISUAL APCH.' IF YOU LOOK AT THE ILS APCH TO RWY 13 AT LGA; YOU WILL FIND THAT THE GS INTERCEPT POINT IS W OF THE HUDSON RIVER AND AT AN ALT OF 1900 FT. THE RIVER VISUAL APCH CALLS FOR FLYING OVER THE HUDSON RIVER ROUGHLY PERPENDICULAR TO THE ILS RWY 13 APCH COURSE. FLYING OVER THE HUDSON RIVER POS YOU'RE E OF THE GS INTERCEPT POINT AND 100 FT ABOVE IT (CLOSER TO THE ARPT). ADDITIONALLY; AT NIGHT; IT IS DIFFICULT TO DEFINITIVELY DETERMINE EXACTLY WHERE CENTRAL PARK IS LOCATED. BASED ON THE CLRNC TO MAINTAIN 2000 FT UNTIL ESTABLISHED ON FINAL; THE FACT THAT THE TURN TO FINAL IS INITIATED INSIDE THE GS INTERCEPT ALT AND 100 FT ABOVE THE GS INTERCEPT ALT -- IT IS VIRTUALLY IMPOSSIBLE TO FLY WHAT WOULD NORMALLY BE CONSIDERED A STABILIZED APCH.