Narrative:

We departed on this flight and all communications were initially normal. At cruise altitude while on ZFW frequency; we started to have communication problems. At first we had a difficult time checking in. Tried a different radio and we were able to reestablish communications for a short while. Then the problems restarted. We had intermittent communications with ATC. The controller said he could hear us; but that we appeared to have a hot microphone and were blocking his frequency. Needless to say; the controller was irritated and that is understandable. We then switched frequencys and had a difficult time checking in. After having difficulties on the second frequency; it appeared fairly obvious that the problem was with us and that switching radios did not solve the problem. We troubleshot the communication system and unplugged various mikes; etc; made sure no buttons were pushed on the observer's panel and thought we had the problem isolated to the first officer's audio panel. At that point we switched roles; with the first officer taking the remainder of the leg and I as captain took over radio communications as my panel seemed to work just fine. We notified maintenance who met the aircraft and determined that the problem actually appeared to involve a stuck microphone on the observer's oxygen mask microphone. The problem was internal to the observer's audio panel. He then replaced the observer's audio panel and we flew the aircraft for 2 more legs with no further problems with our communications. This was a very uncomfortable situation for all involved as communication problems in-flight can be quite dangerous.

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Original NASA ASRS Text

Title: AN MD80 EXPERIENCED ATC COM DIFFICULTY WHEN AN INTERNAL FAILURE OF THE OBSERVER'S AUDIO PANEL MADE THE OBSERVER'S OXYGEN MASK MIKE HOT.

Narrative: WE DEPARTED ON THIS FLT AND ALL COMS WERE INITIALLY NORMAL. AT CRUISE ALT WHILE ON ZFW FREQ; WE STARTED TO HAVE COM PROBS. AT FIRST WE HAD A DIFFICULT TIME CHKING IN. TRIED A DIFFERENT RADIO AND WE WERE ABLE TO REESTABLISH COMS FOR A SHORT WHILE. THEN THE PROBS RESTARTED. WE HAD INTERMITTENT COMS WITH ATC. THE CTLR SAID HE COULD HEAR US; BUT THAT WE APPEARED TO HAVE A HOT MIKE AND WERE BLOCKING HIS FREQ. NEEDLESS TO SAY; THE CTLR WAS IRRITATED AND THAT IS UNDERSTANDABLE. WE THEN SWITCHED FREQS AND HAD A DIFFICULT TIME CHKING IN. AFTER HAVING DIFFICULTIES ON THE SECOND FREQ; IT APPEARED FAIRLY OBVIOUS THAT THE PROB WAS WITH US AND THAT SWITCHING RADIOS DID NOT SOLVE THE PROB. WE TROUBLESHOT THE COM SYS AND UNPLUGGED VARIOUS MIKES; ETC; MADE SURE NO BUTTONS WERE PUSHED ON THE OBSERVER'S PANEL AND THOUGHT WE HAD THE PROB ISOLATED TO THE FO'S AUDIO PANEL. AT THAT POINT WE SWITCHED ROLES; WITH THE FO TAKING THE REMAINDER OF THE LEG AND I AS CAPT TOOK OVER RADIO COMS AS MY PANEL SEEMED TO WORK JUST FINE. WE NOTIFIED MAINT WHO MET THE ACFT AND DETERMINED THAT THE PROB ACTUALLY APPEARED TO INVOLVE A STUCK MIKE ON THE OBSERVER'S OXYGEN MASK MIKE. THE PROB WAS INTERNAL TO THE OBSERVER'S AUDIO PANEL. HE THEN REPLACED THE OBSERVER'S AUDIO PANEL AND WE FLEW THE ACFT FOR 2 MORE LEGS WITH NO FURTHER PROBS WITH OUR COMS. THIS WAS A VERY UNCOMFORTABLE SITUATION FOR ALL INVOLVED AS COM PROBS INFLT CAN BE QUITE DANGEROUS.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.