Narrative:

How the problem arose: on climb out to FL290, radio xmissions to ZLA as well as intercom communications began to deteriorate. The problem was traced to radio pressurization problems and a helmet aircraft mating connection. How the problem was discovered: increases in altitude resulted in worse and worse radio communication. The last clearance 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 aircraft mating problem, 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 control of the aircraft. The rear crewmember took control of the aircraft and due to the nature of the problem, 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 problem was affecting the front crewmember, elected to start an emergency descent, fearing that the front crewmember was incapacitated. During this descent (carried out in VMC conditions and turning so as to avoid other traffic), 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 aircraft was below FL180. ZLA was contacted as soon as possible at this point, explaining that the descent was conducted visually and stating that the remainder of the flts would remain below FL180 where the radios were not a problem. 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 flight being conducted on an IFR leg for subsequent chkout in the bd-10 aircraft for the rear crewmember. Human performance considerations. Perception, judgements, decisions: when the rear crewmember determined that an oxygen problem, accompanied with communication problems, was happening, he had very little choice but to start an emergency descent. Factors affecting the quality of human performance: this aircraft, being the prototype of the bd-10, is not pressurized. Both crew members, being USAF pilots, have had all the USAF oxygen/chamber training, and as such, recognize the significance of operating an unpressurized aircraft at high altitudes, and the timing to make decisions relating to this.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 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.