PLT OF AN EMS AEROSPATIALE; AS 350 ASTAR ECUREUIL HELI; PENETRATED CLASS C AIRSPACE DURING DSCNT FOR LNDG DUE TO NOT BEING ABLE TO CONTACT APCH CTL ON NORMAL FREQ. ATC ADVISED THAT THEY HAD BEEN EXPERIENCING PROBS RECEIVING ON THE 'GIVEN' FREQ SO PROVIDED ANOTHER FREQ WHICH SUBSEQUENTLY WORKED SATISFACTORILY.

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I WAS APCHING ZZZ ON AN EMS FLT WITH 1 SERIOUS PATIENT ON BOARD. I WAS ON COMPANY VFR FLT PLAN WITH FLT FOLLOWING BEING DONE ON COMPANY EMS FREQ. I INITIATED ATTEMPT TO ESTABLISH RADIO CONTACT WITH APCH OVER XXX AT 9500 FT MSL ON FREQ 126.3 MHZ WITHOUT SUCCESS. I CONTINUED TO ATTEMPT CONTACT APPROX EVERY 1-2 MINS. WHEN APPROX 7-10 MI N OF THE RPTING POINT; I INITIATED A DSCNT. MY DEST WAS THE HOSPITAL; WHICH IS ABOUT 2 MI WNW OF ZZZ. I CONTINUED TO ATTEMPT CONTACT WITH ZZZ APCH. I BELIEVE I ENTERED CLASS C AIRSPACE; BUT WAS STILL UNABLE TO CONTACT ZZZ APCH. I DID; HOWEVER; HEAR APCH TALKING TO OTHER ACFT; BUT HEARD ONLY 1 SIDE OF THE CONVERSATIONS. I ALSO CHANGED VHF COM RADIOS WHICH USE SEPARATE ANTENNAS; RECEIVER; XMITTER; BUT THIS DID NOT HELP. WHEN I REACHED A POS APPROX 6-7 MI W OF THE ZZZ ARPT; I HEARD APCH CTL ADVISE SOMETHING TO THE EFFECT 'HELI CALLING ON FREQ 126.3 CONTACT APCH ON FREQ 120.8.' I SWITCHED FREQS AND APCH RESPONDED; STAY OUTSIDE CLASS C AIRSPACE. I ADVISED 'UNABLE' AND WAS TOLD TO 'HOLD POS.' APCH THEN GAVE ME A XPONDER CODE AND TOLD ME TO PROCEED TOWARDS THE HOSPITAL. THEN APCH SAID 'RADAR CONTACT 5 MI W OF ZZZ ARPT; CONTACT THE TWR.' I CONTACTED THE ZZZ TWR AND ADVISED MY INTENTIONS AND WAS TOLD RPT LNDG ASSURED. I EXPLAINED TO THE TWR THAT I HAD BEEN UNABLE TO CONTACT APCH CTL AND THE LCL CTLR EXPLAINED THAT THERE HAVE BEEN RECEIVING PROBS ON FREQ 126.3. I ATTEMPTED NO FEWER THAN 10 RADIO CALLS TO APCH. AS I WAS TRANSPORTING A SERIOUS PATIENT; I CONTINUED INBOUND AS I WAS HEARING APCH; BUT THEY WERE NOT HEARING ME. I WAS ALSO ESSENTIALLY LOW LEVEL IN VERY RUGGED TERRAIN WHICH ATTENUATES RADIO COMS. I MOST LIKELY DSNDED THROUGH THE CORNER OF THEIR CLASS C AIRSPACE AROUND ZZZ WHILE ATTEMPTING TO POS THE HELI BELOW THE CLASS C FLOOR WHILE INBOUND TO THE HOSPITAL. THERE IS A PROC TO LAND AT A TWR CTLED ARPT WHEN RADIO CONTACT IS LOST; BUT NO PROC FOR CLASS C AIRSPACE (IE; NO LIGHT SIGNALS). I DID NOT INTENTIONALLY ENTER CLASS C AIRSPACE; MY INTENTIONS WERE TO CONTACT ZZZ TWR UPON REACHING THE CLASS D SURFACE AREA; BUT ULTIMATELY WAS ABLE TO CONTACT ZZZ APCH PRIOR TO THAT POINT.