EMS HELI MISSES TFC CALL DUE TO NON STERILE COCKPIT AND DISTR OF COMPANY FREQ ON LINE.

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I WAS RETURNING TO MY HOSPITAL; FLYING AT 1300 FT MSL (GND ELEVATION IS ABOUT 650 FT MSL). APPROX 3 NM S OF THE ARPT; APCH CTL CALLED ME WITH TFC. I NEVER HEARD THE CALL BECAUSE I AM ALSO REQUIRED TO MONITOR MY COMPANY FREQ AT ALL TIMES. THE SECOND TIME HE CALLED I HEARD HIM. HE GAVE ME TFC AT 12 O'CLOCK AND 1 MI AT 1000 FT MSL; THEN HE TOLD ME TO CLB TO 1500 FT MSL IMMEDIATELY. I DID AND THERE WAS NO OTHER OCCURRENCE. IN FACT I DON'T THINK THERE WAS ANOTHER ACFT IN MY VICINITY; I THINK HE MIGHT HAVE PICKED UP A RADIO CTLED PLANE BECAUSE WHEN I GOT TO 1500 FT MSL HE SAID TFC WAS NO LONGER A PROB. THE REASON I DIDN'T HEAR THE FIRST CALL WAS THAT MY HOSPITAL'S SECOND ACFT WAS OUT ON A FLT AND OUR DISPATCH WAS TALKING TO THEM; THAT NOISE PLUS MY MEDICAL CREW WAS TALKING IN THE BACK CABIN. ALL THAT COMBINED MADE ME MISS THE FIRST CALL. NOW; I INSIST ON A STERILE COCKPIT WHEN IN THE CLASS C; B OR D AIRSPACE. I ALSO INSTRUCT DISPATCH THAT I WILL BE TURNING THEM OFF WHILE I TRANSITION ANY CLASS B; C; OR D AIRSPACE AND WHEN I WILL RE-ESTABLISH RADIO CONTACT WITH THEM.