Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural MEL / CDL
General Flight Cancelled / Delayed
Aircraft; MEL; Procedure
While taxiing out of the maintenance ramp we noticed that we were having difficulties connecting [to] ground control. Aircraft had the com 1 MEL'd for being intermittent prior to our departure from ZZZ. Com 1 had a 'Failed 2' on the com 1 screen. Com 2 was giving us difficulties transmitting and receiving while starting our taxi in the Non movement area from maintenance. While trying to contact ground control during our taxi we were concerned enough not to continue movement. After a few minutes stopped by the entrance to [an FBO] we deviate into [the FBO] ramp to assess the communication problems due to no response from ground control. While troubleshooting the problem we followed the checklists to determine if all switches were in the proper orientation (they were). We then unplugged the oxygen masks mics on both the pilot and pilot monitoring sides of the cockpit. Problems with communication ceased. During our troubleshooting the mic on one of the oxygen masks was transmitting through com 1 while the com selection switch was on com 2 and the mic switch was in the normal position on both sides of the cockpit. Tower frequency was on com 1 during our taxi and troubleshooting unknown to us it was transmitting through the oxygen mask mic. Remainder of the flight had no other communication problems. [Cause was a] hot oxygen mask mic.
First Officer reported a hot microphone on an oxygen mask; causing communications to be rendered inoperative.