Narrative:

Working with center we were cleared to climb to FL410 and cross a lat/long fix at FL410. In the climb we noticed that the OAT was climbing to isa +10 and rate of climb was deteriorating. To make the crossing restriction we increased power to maximum. Within 15 miles of the fix we heard the main cabin door seal start to whistle and the outflow valve completely shut trying to maintain pressure in the cabin. We read the checklist for suspected main door seal failure and its indicated procedure was to engage the cowl anti-ice to increase seal airflow; which we did. As we approached the fix we were slightly below our restriction altitude. Due to decreased performance by having the cowl anti-ice selected on. About this time the door seal airflow became much more pronounced and the cabin started to climb approximately 2000 FPM. The first officer was flying the aircraft. We both went on oxygen and I called ATC requesting an emergency return to our departure airport. We were given a turn off track and I requested lower. We were advised of two aircraft in our vicinity; which we verified and had on TCAS. Our cabin altitude had exceeded 15;000 ft and I declared an emergency. Once clear of the traffic we initiated a descent to 10;000 ft. After descent was initiated we lost communication with center and an air carrier was relaying radio traffic on our behalf. We were cleared to 10;000 ft and given direct to the airport. Upon reaching 10;000 ft we canceled the emergency and proceeded for an uneventful landing. I called the center and talked with the shift manager and gave him a detailed account of all events as transpired.

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Original NASA ASRS Text

Title: G-IV Captain reported a door seal failure attempting to climb to FL410. An emergency was declared and descent initiated with a return to the departure airport.

Narrative: Working with Center we were cleared to climb to FL410 and cross a lat/long fix at FL410. In the climb we noticed that the OAT was climbing to ISA +10 and rate of climb was deteriorating. To make the crossing restriction we increased power to maximum. Within 15 miles of the fix we heard the main cabin door seal start to whistle and the outflow valve completely shut trying to maintain pressure in the cabin. We read the checklist for suspected main door seal failure and its indicated procedure was to engage the cowl anti-ice to increase seal airflow; which we did. As we approached the fix we were slightly below our restriction altitude. Due to decreased performance by having the cowl anti-ice selected on. About this time the door seal airflow became much more pronounced and the cabin started to climb approximately 2000 FPM. The First Officer was flying the aircraft. We both went on oxygen and I called ATC requesting an emergency return to our departure airport. We were given a turn off track and I requested lower. We were advised of two aircraft in our vicinity; which we verified and had on TCAS. Our cabin altitude had exceeded 15;000 FT and I declared an emergency. Once clear of the traffic we initiated a descent to 10;000 FT. After descent was initiated we lost communication with Center and an air carrier was relaying radio traffic on our behalf. We were cleared to 10;000 FT and given direct to the airport. Upon reaching 10;000 FT we canceled the emergency and proceeded for an uneventful landing. I called the Center and talked with the shift manager and gave him a detailed account of all events as transpired.

Data retrieved from NASA's ASRS site as of April 2012 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.