LGT DSNDS BELOW RESTR ALT.

Narrative

VFR; NIGHT ARR INTO LGA. A LDA-ALPHA APCH TO RWY 22 WAS BRIEFED WITH THE ILS TO RWY 22 AS THE BACKUP APCH. LGA APCH CTL VECTORED US E OF THE FIELD AT 3000 FT MSL. ABEAM THE ARPT; APCH ASKED IF WE HAD THE FIELD IN SIGHT. WE RESPONDED POSITIVELY AND WERE GIVEN CLRNC TO DSND TO 2500 FT AND CLRED THE VISUAL APCH TO RWY 22. THE CTLR ADDED A NONSTANDARD RESTR TO NOT DSND BELOW 2500 FT UNTIL ON FINAL OR WHEN GIVEN CLRNC TO DSND BELOW 2500 FT BY THE TWR. THE AUTOPLT WAS DISENGAGED AND DSCNT BEGAN FOR 2500 FT. APCH CTL ISSUED A TA FOR ANOTHER ACFT ON FINAL RWY 22. THE TFC WAS ACQUIRED AND A FREQ CHANGE WAS MADE TO LGA TWR. TWR CONFIRMED A CLRNC FOR THE VISUAL APCH TO RWY 22. WHEN ADEQUATE SEPARATION WITH THE TFC ON FINAL WAS ENSURED; I BEGAN A L BASE AT APPROX 3.5 NM FROM THE APCH END OF RWY 22 AND A CALL WAS MADE TO THE TWR PER PREVIOUS REQUEST. THE ACFT WAS CONFIGURED WITH 2 AND THEN 5 DEG FLAPS. THE CAPT COMMENTED WE LOOKED HIGH AND CLOSE TO THE RWY AND RECOMMENDED EXTENDING THE LNDG GEAR AND EXPEDITING THE DSCNT. I ANGLED THE ACFT SLIGHTLY AWAY FROM THE RWY AND SAID I UNDERSTOOD OUR CLRNC TO BE 2500 FT; UNTIL CLRED LOWER. THE CAPT SAID SINCE WE WERE CLRED FOR THE VISUAL APCH BY THE TWR; THERE WAS NO LONGER AN ALT RESTR. THAT MADE SENSE TO ME; DESPITE MY AWARENESS TO THE PREVIOUS ALT RESTR ISSUED BY APCH CTL. ON BASE AT 1900 FT MSL; THE CTL TWR ASKED IF WE HAD BEEN ISSUED AN ALT RESTR. I ADDED PWR AND STOPPED THE DSCNT RATE OF THE ACFT. THE CAPT ANSWERED; WE HAD BEEN ISSUED A 2500 FT RESTR BUT FELT THE SUBSEQUENT CLRNC FOR THE VISUAL APCH BY THE TWR HAD RESCINDED THAT RESTR. THE TWR RESPONDED THAT IN THE FUTURE; WE MUST MAINTAIN THE 2500 FT RESTR. THE REMAINDER OF THE APCH AND LNDG WERE UNEVENTFUL. THE FOLLOWING FACTORS CONTRIBUTED TO THIS ALTDEV: 1) EXPERIENCE IN FLYING INTO HIGH DENSITY ARPTS SUPPORTS THE CONCEPT OF FLYING VISUAL APCHS TO INCREASE FLOW INTO AND OUT OF THE ARPT. THIS TRANSLATES INTO FLYING A SHORTENED PATTERN; TFC SEPARATION PERMITTING. ONCE CLRED THE VISUAL; I CONDUCTED THE SAFEST APCH; BASED ON MY EXPERIENCE. 2) THE APCH CLRNC; ALTHOUGH ACKNOWLEDGED BY BOTH PLTS; WAS NONSTANDARD AND LET ULTIMATELY TO CONFUSION AS TO THE INTERP OF THE '2500 FT RESTR' AND 'CLRED THE VISUAL APCH' BY THE TWR. 3) AS THE PF; I COULD HAVE COMPENSATED FOR THE 2500 FT ALT RESTR BY PLANNING A LONGER FINAL AT A MINIMUM OF 8 NM FROM THE ARPT TO PROVIDE FOR A STANDARD 300 FT PER NM DSCNT ANGLE. 4) IF RESTRS FOR NOISE ABATEMENT EXIST AT AN AIRFIELD WHERE VISUAL APCHS ARE CONDUCTED; THEY SHOULD BE DEPICTED ON A VISUAL APCH PLATE FOR THE RWY. NONE EXIST FORE RWY 22. THIS ALTDEV COULD HAVE BEEN PREVENTED IF THE PF WOULD HAVE ASKED THE CAPT TO CONFIRM THE ALT RESTR WITH THE TWR WHEN THE QUESTION OF THE ALT RESTR WAS DISCUSSED IN THE COCKPIT ON BASE LEG; RATHER THAN ACCEPTING THE CAPT'S INTERP. SUPPLEMENTAL INFO FROM ACN 292916: LGA APCH ISSUED NONSTANDARD CLRNC FOR A VISUAL APCH TO RWY 22 AS WE FLEW ON DOWNWIND E OF THE FIELD AT 3000 FT MSL. 'CLRED FOR A VISUAL APCH TO RWY 22 -- DO NOT DSND BELOW 2500 FT UNTIL ON FINAL OR WHEN CLRED BY TWR.'