A B727 CAPT AND FO SUBMITTED RPTS DESCRIBING THEIR DEP ON THE JFK 7 WHICH IS BASED ON AN NDB RATHER THAN ON A VOR. THEY RPTED THAT NDB'S ARE NOT SENSITIVE ENOUGH TO MAKE A SMOOTH TRANSITION.

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DEPARTED JFK RWY 31L FOR JFK 7 DEP; BRIDGE CLB. CAPT MAKING TKOF RADIO SETUP WAS AS FOLLOWS: CAPT HAD CANARSIE VOR; 039 DEG RADIAL SET IN HSI. ADF TUNED TO BRIDGE; 414. COPLT HAD JFK VOR; 253 DEG RADIAL SET. SID CALLED FOR A L TURN ASAP DIRECT TO BRIDGE; CROSS JFK 253 DEG RADIAL AT OR ABOVE 2500 FT AND DO NOT FLY W OF CANARSIE 039 DEG RADIAL. PRIOR TO TKOF; I NOTICED VOR/ADF BEARING NEEDLE FLUCTUATING IN ADF MODE. COPLT CHKED IDENT AND IT WAS GOOD. TOOK OFF AND STARTED L TURN DIRECT TO ADF. ADF BEARING APPEARED TO BE TAKING US RIGHT OF WHERE WE THOUGHT ADF WAS LOCATED. AT THE TIME; THE CAPT COULD NOT MONITOR CANARSIE BEARING BECAUSE BEARING NEEDLE WAS IN ADF MODE. STARTED TO INFORM ATC; BUT THEY GAVE US A L TURN TO INTERCEPT JFK 156 DEG RADIAL. WHILE TURNING; NOTICED CANARSIE 039 DEG RADIAL STARTING TO MOVE ON HSI. FLEW SLIGHTLY W OF RADIAL. I DO NOT THINK THAT THIS SID SHOULD BE BASED ON THE BRIDGE NDB. NDB'S ARE NOT AS RELIABLE AS VOR'S. IN THIS CASE; WITH ALL THE NAVAIDS THAT WE HAD TO MONITOR AT THE SAME TIME; THERE WAS VERY LITTLE TIME TO STRAIGHTEN OUT THE PROB. HAD WE FLOWN THE BREEZY POINT CLB OF THE JFK 7 USING ONLY THE CANARSIE VOR; WE WOULD HAVE HAD A MORE RELIABLE NAVAID AND THERE WOULD HAVE BEEN NO PROB.