AN EMB145 FLT CREW GOES THROUGH 4 APCH CTLRS AND SUFFERS A DELAY OBTAINING AN APCH CLRNC DURING 4 FREQ CHANGES AND LACK OF INFO ON APCHS TO RWYS 9R AND 17 AT PHL.

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WE WERE FLYING FROM BWI TO PHL. WE CHKED ON WITH PHL APCH AND WERE TOLD TO EXPECT RWY 9R. WE WERE BEING VECTORED FOR WHAT LOOKED LIKE A 'DOUBLE' DOWNWIND FOR RWY 9R. WE WERE GIVEN 2 SUBSEQUENT FREQ CHANGES. THE LAST FREQ WAS VERY POOR AND WEAK. WE WERE VECTORED OVER THE TOP OF RWY 9R AND I WAS EXPECTING A L DOWNWIND. AFTER A FEW MORE MI I ASKED WHAT RWY WE WERE EXPECTING; AND WAS TOLD RWY 17. I TOLD THEM WE WERE TOLD RWY 9R BUT COULD ACCEPT THE VISUAL IF WE GOT LOWER. WE WERE TOLD TO EXPECT THAT. RIGHT AFTER THAT; I HEARD OUR PREVIOUS CTLR ON THE FREQ GIVING COMMANDS TO OTHER AIRPLANES. I ASSUMED A CTLR CHANGE. AFTER ABOUT 5-10 MI AND FLYING THROUGH THE RWY 17 APCH COURSE; I ASKED WHAT THEY WANTED. I WAS AGAIN GIVEN ANOTHER FREQ CHANGE. WE WERE VECTORED AROUND FOR A LONG FINAL FOR RWY 17. WE HAD NO FURTHER PROBS. THERE WERE 2 PROBS WE ENCOUNTERED IN THIS SIT. FIRST; TOO MANY FREQ CHANGES WITHOUT PROPER COM BTWN CTLRS AT PHL APCH CTL. SECOND; I BELIEVE THERE IS AN OUTSIDE POSSIBILITY THAT THE RADIO MGMNT UNIT MAY HAVE SWITCHED TO THE STANDBY FREQ WITHOUT INPUT. ALSO THE POSSIBILITY THAT XMITTERS GOT SWITCHED AT APCH CTL. WE MADE NO INPUTS TO EITHER RADIO MGMNT UNITS WHEN WE HEAD THE CTLR 'SWITCH.' I FIND BOTH OF THESE UNLIKELY.