AN EC135 PLT HAS AN NMAC WITH ANOTHER ACFT JUST AFTER HAVING RADIO TROUBLES.

Narrative

DEPARTED ELMIRA; NY; ON A VFR FLT DIRECT TO HERSHEY; PA. STROBE LIGHTS WERE ON. AFTER DEPARTING ELMIRA; CONTACT WAS MADE WITH ELMIRA DEP CTL FOR FLT FOLLOWING AND TA'S. A XPONDER CODE WAS RECEIVED AND A CLB WAS MADE TO 3500 FT MSL. THE COMPANY OPS WERE CALLED AND THE FLT PLAN ACTIVATION WAS CONFIRMED. SOMETIME DURING THE FLT; THE #2 RADIO PIN SWITCH GOT BUMPED TO THE 'OFF' POS. I DIDN'T HEAR ANY RADIO CALLS TO APCH; BUT THIS IS NOT UNUSUAL AT TIMES DUE TO THE LOW VOLUME OF TFC. DURING THE FLT; THE VISIBILITY WAS BTWN 6-10 MI WITH HAZE. N OF WILLIAMSPORT; PA; CONTACT WAS ATTEMPTED WITH ELMIRA APCH; BUT NO CONTACT WAS MADE. REALIZING THAT THE RADIO PIN SWITCH HAD BEEN TURNED DOWN; A CALL WAS MADE TO WILLIAMSPORT RADIO TO SEE IF THEY WOULD CONTACT ELMIRA APCH TO EXPLAIN THE SIT. CONTACT COULD NOT BE MADE. THE FREQ WAS CHANGED TO WILLIAMSPORT TWR AND THEY MADE CONTACT WITH ELMIRA APCH AND A FREQ FOR ZNY WAS RECEIVED. BTWN FREQ CHANGES; THE SCAN FOR TFC WAS CONTINUED. AS I LOOKED UP TO CONTINUE MY SCAN AND TO CONTACT ZNY; THE PAX IN THE L SEAT SAID THAT THERE WAS AN ACFT TO THE R. IMMEDIATELY TURNING TO THE R; A WHITE ACFT PASSED ABOUT 100 FT BELOW US UNDER THE CTR OF THE ACFT. CONTACT WAS MADE WITH ZNY. THE FLT WAS CONTINUED WITHOUT ANY OTHER INCIDENTS.