SMT GIVEN SAFETY ALERT ON UNK TRAFFIC BY APCH CTLR; SMT GIVEN TURN; TRAFFIC NEVER SIGHTED BY SMT.

Narrative

WHILE IN CRUISE AT 4000' HEADED SBND ON V29 APPROX 10 NM N OF THE PTW VOR; PHL APCH ISSUED A TFC ALERT TO US. TFC WAS RPTED AS UNCONFIRMED AT OUR 12 O'CLOCK POS; LESS THAN A MILE CIRCLING AT 3900'. ALONG WITH THE TFC RPT AN IMMEDIATE RIGHT TURN TO 270 DEGS WAS ISSUED AND THE CAPT (PF) IMMEDIATELY ENTERED A 45 DEG BANK TO THE RIGHT. NEITHER THE CAPT NOR THE F/O SAW THE ACFT. ABOUT 2 MINS LATER THE UNCONFIRMED ACFT CALLED PHL APCH FOR TFC ADVISORIES AS HE WAS AN ACFT WITH SKY DIVERS IN A CLBING SPIRAL. HIS ACTUAL ALT AT THE TIME OF OUR TFC ALERT WAS UNCONFIRMED. CONTRIBUTING FACTORS AND CORRECTIVE ACTIONS: SINCE THE START OF THE NEW EAST COAST PLAN; ATC HAS REQUIRED US TO BE AT 3000-4000' ON V29 BTWN ALLENTOWN AND PHILADELPHIA. THIS UNUSUALLY LOW ALT FOR A TURBINE ACFT WHICH CRUISES AT 245 KTS HAS CREATED A DANGEROUS PROB BY MIXING A FAST COMMUTER ACFT WITH SLOWER GA THAT FLY OUT OF THE NUMEROUS ARPTS BTWN ALLENTOWN; POTTSTOWN AND PHILADELPHIA. THE PLTS AND OUR COMPANY MGMNT HAS REQUESTED ATC FOR HIGHER ALTS ALONG THIS ROUTE W/O ANY ALLEVIATION OF THE PROB.