INSTRUCTOR AND TRAINEE FLY FOR 25 MINS WITH STUCK MIKE XMITTING THEIR INTERCOM CONVERSATION.

Narrative

THIS WAS TO BE A TRAINING FLT TO PRACTICE INST APCHS IN A RADAR ENVIRONMENT WITH ATC VECTORS. THE FLT ENRTE WAS VFR IN CTLED AIRSPACE BUT NO ATC CONTACT WAS TO BE INITIATED UNTIL CONTACTING SGF APCH. TO FACILITATE INSTRUCTION AND ASSIST STUDENT WITH ATC INSTRUCTIONS; HEADSETS/INTERCOM WERE USED. DURING TAXI; BOTH STUDENT AND I CHKED THE INTERCOM CONNECTIONS/PUSH-TO-TALK SWITCHES AND BOTH XMITTED TO UNICOM; EACH ON A SEPARATE RADIO AND PUSH-TO-TALK. BOTH RECEIVED 'LOUD AND CLR' TO RADIO CHKS. WE PROCEEDED BELIEVING INTERCOM/HEADSETS/PUSH-TO-TALKS WERE OPERATING CORRECTLY. ENRTE; THE STUDENT SELECTED THE APCH FREQ FOR SGF EARLY - - ABOUT 60 NM N. SINCE WE WERE PRACTICING RADIAL TRACKING AND INTERCEPTS; WE HAD THE AUDIO PANEL TO OFF SO WE HEARD NOTHING OVER THE RADIO AND COULD TALK OVER THE INTERCOM WITHOUT DISTRS. WE PROCEEDED TO ABOUT 20-25 NM N OF SGF WHERE THE STUDENT ATTEMPTED TO CONTACT APCH. (WE HAD EARLIER (APPROX 5-10 NM) ATTEMPTED TO LISTEN TO ATIS BUT RECEIVED NOTHING. I (ERRONEOUSLY) ASSUMED THE ATIS WAS BEING UPDATED.) AT FIRST; WE WERE UNSUCCESSFUL IN CONTACTING APCH. I VERIFIED FREQ; AUDIO SWITCH SETTING; ETC. EVERYTHING APPEARED CORRECT. THE STUDENT ATTEMPTED CONTACT ONCE MORE. THIS TIME OUR XMISSION WAS MET WITH THE FOLLOWING RESPONSE. 'YOU HAVE HAD A STUCK MIKE FOR THE PAST 25 MINS' AND THEN THE MOST DERISIVE; CONTEMPTUOUS LAUGHTER I HAVE EVER HAD THE MISFORTUNE TO HEAR. AT THAT POINT (NOT KNOWING WHETHER THIS CAME FROM A CTLR OR OTHER PARTY ON THE FREQ); I DECIDED WE HAD 'ENTERTAINED' SGF LONG ENOUGH. I HAD THE STUDENT TURN THE AIRPLANE NBOUND.