FLC ENTERED IMC WHILE ON A VFR FLT PLAN NEAR PHL.

Narrative

I WAS ACTING AS A CREW MEMBER ON A PART 121 FLT FROM BOS TO PHL. WE WERE ON A VFR FLT PLAN. WHEN WE GOT CLOSE TO CLASS B AIRSPACE WE WERE CLRED INTO CLASS B AIRSPACE AND ASSIGNED A HDG AND AN ALT. WE ACCEPTED THIS CLRNC AND PROCEEDED INTO CLASS B AIRSPACE. WHEN WE ACCEPTED THIS CLRNC WE WERE ABLE TO MAINTAIN VMC. THE CTLR WAS VERY BUSY. WITHIN THE NEXT 10 MI THIS HDG WOULD HAVE PUT US IN A BROKEN LAYER OF CLOUDS. WE TOLD THE CTLR WE NEEDED A LOWER ALT OR A DIFFERENT HDG BECAUSE WE WERE NOT GOING TO BE ABLE TO MAINTAIN VFR. THE CTLR SAID UNABLE. THE FREQ WAS SO BUSY WE COULDN'T GET ANOTHER WORD IN. SO WE TURNED TO A NEW HDG WITHOUT CLRNC TO AVOID THE CLOUDS IN FRONT OF US TO MAINTAIN VFR. THE CTLR CAME BACK AND TOLD US TO TURN TO HDG 310 DEGS NOW. THIS WAS TO AVOID CLBING TFC. WHEN WE TURNED TO THIS HDG IT WAS GOING TO PUT US IN THE CLOUDS. WE CLBED 300-400 FT TO AVOID CLOUDS BUT WERE UNABLE TO MAINTAIN VFR. WE ENTERED CLOUDS WITHOUT IFR CLRNC; SO WE DSNDED BACK TO 5500 FT. UPON LNDG; MY CAPT CALLED THE CTLR AND WAS TOLD NO RPT WOULD BE FILED; AND THAT THERE WAS SUFFICIENT SEPARATION BTWN TFC.