Narrative:

Aircraft X was climbing west. Aircraft Y was being stepped up below him; 7 mi behind and 40 KTS faster. Aircraft X advised they needed to descend to FL240. Radar controller asked if they were an emergency. Aircraft X replied 'yes sir.' they were issued a turn and told to stop climb at FL300. The aircraft did not reply. They continued on assigned route. The altitude stopped at FL295 and started dropping. The radar controller assigned FL280 (aircraft Y was climbing through FL265). Communication was still not established. The sector controling aircraft Y was told to turn aircraft Y out from underneath aircraft X. The turn kept the aircraft at least 3 mi apart as aircraft X descended to FL240. Communication was reestablished and aircraft X advised they had a pressurization problem and were having trouble controling the aircraft. They were given clearance back to ZZZ and 19000 ft. I believe all persons involved acted in an exemplary manner. The pilots did what they had to do to control the aircraft. My radar controller was quick to recognize that aircraft X would be making a descent without clearance and took quick and accurate measures to avoid a midair collision. Supplemental information from acn 703423: while climbing to cruise altitude; we received aural and visual warnings that pressurization had failed. According to the emergency checklist; we immediately initiated a descent then declared an emergency with ATC. We returned to ZZZ without further incident and made a normal landing. ATC advised of a possible loss of separation. There was no TA or RA. Our corporate maintenance staff determined that the pressurization controller failed.

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Original NASA ASRS Text

Title: CTLR DESCRIBED LOSS OF SEPARATION AT FL280 INVOLVING AN ACFT WITH PRESSURIZATION PROBS IN AN EMER DSCNT.

Narrative: ACFT X WAS CLBING W. ACFT Y WAS BEING STEPPED UP BELOW HIM; 7 MI BEHIND AND 40 KTS FASTER. ACFT X ADVISED THEY NEEDED TO DSND TO FL240. RADAR CTLR ASKED IF THEY WERE AN EMER. ACFT X REPLIED 'YES SIR.' THEY WERE ISSUED A TURN AND TOLD TO STOP CLB AT FL300. THE ACFT DID NOT REPLY. THEY CONTINUED ON ASSIGNED RTE. THE ALT STOPPED AT FL295 AND STARTED DROPPING. THE RADAR CTLR ASSIGNED FL280 (ACFT Y WAS CLBING THROUGH FL265). COM WAS STILL NOT ESTABLISHED. THE SECTOR CTLING ACFT Y WAS TOLD TO TURN ACFT Y OUT FROM UNDERNEATH ACFT X. THE TURN KEPT THE ACFT AT LEAST 3 MI APART AS ACFT X DSNDED TO FL240. COM WAS REESTABLISHED AND ACFT X ADVISED THEY HAD A PRESSURIZATION PROB AND WERE HAVING TROUBLE CTLING THE ACFT. THEY WERE GIVEN CLRNC BACK TO ZZZ AND 19000 FT. I BELIEVE ALL PERSONS INVOLVED ACTED IN AN EXEMPLARY MANNER. THE PLTS DID WHAT THEY HAD TO DO TO CTL THE ACFT. MY RADAR CTLR WAS QUICK TO RECOGNIZE THAT ACFT X WOULD BE MAKING A DSCNT WITHOUT CLRNC AND TOOK QUICK AND ACCURATE MEASURES TO AVOID A MIDAIR COLLISION. SUPPLEMENTAL INFO FROM ACN 703423: WHILE CLBING TO CRUISE ALT; WE RECEIVED AURAL AND VISUAL WARNINGS THAT PRESSURIZATION HAD FAILED. ACCORDING TO THE EMER CHKLIST; WE IMMEDIATELY INITIATED A DSCNT THEN DECLARED AN EMER WITH ATC. WE RETURNED TO ZZZ WITHOUT FURTHER INCIDENT AND MADE A NORMAL LNDG. ATC ADVISED OF A POSSIBLE LOSS OF SEPARATION. THERE WAS NO TA OR RA. OUR CORPORATE MAINT STAFF DETERMINED THAT THE PRESSURIZATION CTLR FAILED.

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.