FLC OF A SMA JET MAKES AN EMER DSCNT AFTER LOSING COMS.

Narrative

HOW THE PROB AROSE: ON CLBOUT TO FL290; RADIO XMISSIONS TO ZLA AS WELL AS INTERCOM COMS BEGAN TO DETERIORATE. THE PROB WAS TRACED TO RADIO PRESSURIZATION PROBS AND A HELMET ACFT MATING CONNECTION. HOW THE PROB WAS DISCOVERED: INCREASES IN ALT RESULTED IN WORSE AND WORSE RADIO COM. THE LAST CLRNC FROM FL230 TO LEVEL AT FL290 WAS UNDERSTOOD AND ACKNOWLEDGED. HOWEVER; AT FL290; RADIO XMISSIONS WERE DETERIORATED TO THE POINT WHERE ZLA REQUESTED SEVERAL REPEATS AS BEING LEVEL AT FL290. CORRECTIVE ACTION: WHILE ATTEMPTING TO FIX THE HELMET ACFT MATING PROB; THE FRONT COCKPIT OXYGEN CONNECTOR WAS PULLED AND SEPARATED A PORTION OF THE CONNECTION; RESULTING IN AN OXYGEN LOSS TO THE FORWARD CREWMEMBER. THE FORWARD CREWMEMBER; REALIZING THAT HE WAS LOSING SOME OXYGEN SUPPLY AS WELL AS HAVING LOST INTERCOM AND RADIO XMISSIONS; SIGNALED TO THE REAR CREWMEMBER TO TAKE CTL OF THE ACFT. THE REAR CREWMEMBER TOOK CTL OF THE ACFT AND DUE TO THE NATURE OF THE PROB; WAS THE ONLY ONE WHO WAS HEARING BOTH INTERCOM AND ZLA. AT THIS TIME; ZLA WAS CALLING; WHICH THE REAR CREWMEMBER HEARD; BUT DETERMINING THAT THE OXYGEN SUPPLY PROB WAS AFFECTING THE FRONT CREWMEMBER; ELECTED TO START AN EMER DSCNT; FEARING THAT THE FRONT CREWMEMBER WAS INCAPACITATED. DURING THIS DSCNT (CARRIED OUT IN VMC CONDITIONS AND TURNING SO AS TO AVOID OTHER TFC); THE RADIOS CAME BACK AND THE FRONT CREWMEMBER; NOW BEING ABLE TO TALK TO THE REAR CREWMEMBER; DISCUSSED THE MANEUVER BEING FLOWN. THE FRONT CREWMEMBER THEN TURNED THE IFF TO 7700; THEN TO 7600 WHERE IT REMAINED UNTIL THE ACFT WAS BELOW FL180. ZLA WAS CONTACTED AS SOON AS POSSIBLE AT THIS POINT; EXPLAINING THAT THE DSCNT WAS CONDUCTED VISUALLY AND STATING THAT THE REMAINDER OF THE FLTS WOULD REMAIN BELOW FL180 WHERE THE RADIOS WERE NOT A PROB. CONTRIBUTING FACTORS: THE REAR CREWMEMBER; ALTHOUGH BEING ABLE TO HEAR EVERYTHING; WAS UNABLE TO MAKE ANY XMISSIONS OR CHANGE THE IFF FROM THE REAR COCKPIT. THIS WAS A TRAINING FLT BEING CONDUCTED ON AN IFR LEG FOR SUBSEQUENT CHKOUT IN THE BD-10 ACFT FOR THE REAR CREWMEMBER. HUMAN PERFORMANCE CONSIDERATIONS. PERCEPTION; JUDGEMENTS; DECISIONS: WHEN THE REAR CREWMEMBER DETERMINED THAT AN OXYGEN PROB; ACCOMPANIED WITH COM PROBS; WAS HAPPENING; HE HAD VERY LITTLE CHOICE BUT TO START AN EMER DSCNT. FACTORS AFFECTING THE QUALITY OF HUMAN PERFORMANCE: THIS ACFT; BEING THE PROTOTYPE OF THE BD-10; IS NOT PRESSURIZED. BOTH CREW MEMBERS; BEING USAF PLTS; HAVE HAD ALL THE USAF OXYGEN/CHAMBER TRAINING; AND AS SUCH; RECOGNIZE THE SIGNIFICANCE OF OPERATING AN UNPRESSURIZED ACFT AT HIGH ALTS; AND THE TIMING TO MAKE DECISIONS RELATING TO THIS.