Narrative:

On jul/sun/04, I was PIC on a part 135 leg from jka to pvd. I had just leveled off at FL370 and was talking with ZTL when I began to hear a high pitch of whistling sound that I have never heard in-flight. I lifted my right ear cup off my ear to see if I could better pinpoint the area of the sound. I asked my co-pilot if he was hearing the noise as well. He stated that he was hearing something. I scanned the gauges and noticed that we were losing the noise as well. He stated that he was hearing something. I scanned the gauges and noticed that we were losing cabin pressure. I called 'mask' and flipped the microphone switch to mask. There was a loud sound from inside the plane and the cabin climb rate sprung to +6000 ft, the 10000 ft cabin warning light illuminated. Upon seeing this, I called 'emergency descent' to my co-pilot and immediately initiated the maneuver. I had the plane descending when I heard center asking where we were going. The passenger masks did not drop automatically or when the manual drop lever was positioned to manual! I was worried about my passenger passing out due to the addition of cabin masks failing to deploy. An emergency was declared but only after my descent maneuver was already initiated and a lot of altitude lost. My co-pilot was young and low time and I have never had decompression occur at altitude. I have since been told, through maintenance, that the masks did not deploy due to a faulty check valve at the passenger/crew only switch. The loss of cabin pressure, I was told by maintenance, was due to oil/grease at the hinges getting wiped onto the door seal as well as co-pilots opening the cabin door by force before the door seal has a chance to deflate and thereby causing damage and weak points. I probably broke some far during this event, but certainly not purposely, only to get out of high altitude. I am very happy to report no deaths or injuries during this event. Diversion was to mcn. Last night I remembered that I did not place my mask on passing FL350 only because 99% of my flts are part 91 and I have quick-donning masks, and few flts are above FL350, so it simply was an oversight on my part.

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Original NASA ASRS Text

Title: DIVERSION TO ANOTHER ARPT AFTER AN EMER DSCNT BY A C550 PIC WHEN THE ACFT RAPIDLY LOSES PRESSURE WITHOUT THE PAX OXYGEN MASKS DEPLOYING AS DESIGNED WHILE ON FREQ WITH ZTL.

Narrative: ON JUL/SUN/04, I WAS PIC ON A PART 135 LEG FROM JKA TO PVD. I HAD JUST LEVELED OFF AT FL370 AND WAS TALKING WITH ZTL WHEN I BEGAN TO HEAR A HIGH PITCH OF WHISTLING SOUND THAT I HAVE NEVER HEARD INFLT. I LIFTED MY R EAR CUP OFF MY EAR TO SEE IF I COULD BETTER PINPOINT THE AREA OF THE SOUND. I ASKED MY CO-PLT IF HE WAS HEARING THE NOISE AS WELL. HE STATED THAT HE WAS HEARING SOMETHING. I SCANNED THE GAUGES AND NOTICED THAT WE WERE LOSING THE NOISE AS WELL. HE STATED THAT HE WAS HEARING SOMETHING. I SCANNED THE GAUGES AND NOTICED THAT WE WERE LOSING CABIN PRESSURE. I CALLED 'MASK' AND FLIPPED THE MIKE SWITCH TO MASK. THERE WAS A LOUD SOUND FROM INSIDE THE PLANE AND THE CABIN CLB RATE SPRUNG TO +6000 FT, THE 10000 FT CABIN WARNING LIGHT ILLUMINATED. UPON SEEING THIS, I CALLED 'EMER DSCNT' TO MY CO-PLT AND IMMEDIATELY INITIATED THE MANEUVER. I HAD THE PLANE DSNDING WHEN I HEARD CTR ASKING WHERE WE WERE GOING. THE PAX MASKS DID NOT DROP AUTOMATICALLY OR WHEN THE MANUAL DROP LEVER WAS POSITIONED TO MANUAL! I WAS WORRIED ABOUT MY PAX PASSING OUT DUE TO THE ADDITION OF CABIN MASKS FAILING TO DEPLOY. AN EMER WAS DECLARED BUT ONLY AFTER MY DSCNT MANEUVER WAS ALREADY INITIATED AND A LOT OF ALT LOST. MY CO-PLT WAS YOUNG AND LOW TIME AND I HAVE NEVER HAD DECOMPRESSION OCCUR AT ALT. I HAVE SINCE BEEN TOLD, THROUGH MAINT, THAT THE MASKS DID NOT DEPLOY DUE TO A FAULTY CHK VALVE AT THE PAX/CREW ONLY SWITCH. THE LOSS OF CABIN PRESSURE, I WAS TOLD BY MAINT, WAS DUE TO OIL/GREASE AT THE HINGES GETTING WIPED ONTO THE DOOR SEAL AS WELL AS CO-PLTS OPENING THE CABIN DOOR BY FORCE BEFORE THE DOOR SEAL HAS A CHANCE TO DEFLATE AND THEREBY CAUSING DAMAGE AND WEAK POINTS. I PROBABLY BROKE SOME FAR DURING THIS EVENT, BUT CERTAINLY NOT PURPOSELY, ONLY TO GET OUT OF HIGH ALT. I AM VERY HAPPY TO RPT NO DEATHS OR INJURIES DURING THIS EVENT. DIVERSION WAS TO MCN. LAST NIGHT I REMEMBERED THAT I DID NOT PLACE MY MASK ON PASSING FL350 ONLY BECAUSE 99% OF MY FLTS ARE PART 91 AND I HAVE QUICK-DONNING MASKS, AND FEW FLTS ARE ABOVE FL350, SO IT SIMPLY WAS AN OVERSIGHT ON MY PART.

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.