Narrative:

We were on the arrival to ZZZ at FL410. Center cleared us to descend to FL330. I initiated the descent and called for descent checklist. As the cabin was set to field elevation I noticed the cabin altitude climbing rapidly. I put on my oxygen mask and began an emergency descent. The first officer also put on his oxygen mask and began to attempt manual control of the cabin. The first officer squawked 7700 and attempted contact with the center. A faulty oxygen mask microphone prevented contact. Center had us acknowledge their instructions with squawk identify. We continued the emergency descent to 16000 ft MSL at which point center cleared us to 11000 ft MSL. Contact with center was re-established through the normal microphone at this point. We reset the emergency bleed air and continued to our destination using manual control of the cabin altitude. Establishment of periodic functionality tests of the oxygen microphone system may prevent loss of communication in certain sits as this. Supplemental information from acn 624608: the captain initiated a normal descent to 33000 ft until the cabin had climbed from 6000 ft cabin altitude to 8000 ft cabin altitude. At that point we tried to bring the cabin down manually (in automatic mode) with the cherry picker. The pressurization would not respond and the captain called for an emergency descent checklist. Once the checklist got us to a point that we had the cabin under control, the PF stayed on oxygen and the PNF took off his oxygen mask to establish effective communication. This was at approximately 23000 ft MSL with a cabin altitude of approximately 8000 ft. It is now part of company operations to check the microphone in the oxygen mask when checking the availability of oxygen from the mask.

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Original NASA ASRS Text

Title: EMER DSCNT INITIATED BY THE PIC OF AN LR25 WHEN THE CABIN STARTS A RAPID CLB. FLT CREW UNABLE TO COMMUNICATE WITH ATC WHEN OXYGEN MASK MIKES ARE MALFUNCTIONING, ON FREQ WITH ZZZ.

Narrative: WE WERE ON THE ARR TO ZZZ AT FL410. CTR CLRED US TO DSND TO FL330. I INITIATED THE DSCNT AND CALLED FOR DSCNT CHKLIST. AS THE CABIN WAS SET TO FIELD ELEVATION I NOTICED THE CABIN ALT CLBING RAPIDLY. I PUT ON MY OXYGEN MASK AND BEGAN AN EMER DSCNT. THE FO ALSO PUT ON HIS OXYGEN MASK AND BEGAN TO ATTEMPT MANUAL CTL OF THE CABIN. THE FO SQUAWKED 7700 AND ATTEMPTED CONTACT WITH THE CTR. A FAULTY OXYGEN MASK MIKE PREVENTED CONTACT. CTR HAD US ACKNOWLEDGE THEIR INSTRUCTIONS WITH SQUAWK IDENT. WE CONTINUED THE EMER DSCNT TO 16000 FT MSL AT WHICH POINT CTR CLRED US TO 11000 FT MSL. CONTACT WITH CTR WAS RE-ESTABLISHED THROUGH THE NORMAL MIKE AT THIS POINT. WE RESET THE EMER BLEED AIR AND CONTINUED TO OUR DEST USING MANUAL CTL OF THE CABIN ALT. ESTABLISHMENT OF PERIODIC FUNCTIONALITY TESTS OF THE OXYGEN MIKE SYS MAY PREVENT LOSS OF COM IN CERTAIN SITS AS THIS. SUPPLEMENTAL INFO FROM ACN 624608: THE CAPT INITIATED A NORMAL DSCNT TO 33000 FT UNTIL THE CABIN HAD CLBED FROM 6000 FT CABIN ALT TO 8000 FT CABIN ALT. AT THAT POINT WE TRIED TO BRING THE CABIN DOWN MANUALLY (IN AUTOMATIC MODE) WITH THE CHERRY PICKER. THE PRESSURIZATION WOULD NOT RESPOND AND THE CAPT CALLED FOR AN EMER DSCNT CHKLIST. ONCE THE CHKLIST GOT US TO A POINT THAT WE HAD THE CABIN UNDER CTL, THE PF STAYED ON OXYGEN AND THE PNF TOOK OFF HIS OXYGEN MASK TO ESTABLISH EFFECTIVE COM. THIS WAS AT APPROX 23000 FT MSL WITH A CABIN ALT OF APPROX 8000 FT. IT IS NOW PART OF COMPANY OPS TO CHK THE MIKE IN THE OXYGEN MASK WHEN CHKING THE AVAILABILITY OF OXYGEN FROM THE MASK.

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.