Narrative:

While cruising at FL250; the aircraft experienced a total cabin pressurization loss. I immediately attempted to define the problem; what happened; and consider any available solution. I immediately attempted to place my face mask into operation. I was having an issue with turning on the O2 supply and decided to start an autopilot descent. I thought that if I encountered a loss of consciousness; the aircraft would level at a safe altitude; the aircraft would still be in control until I regained consciousness. After checking to make sure there was no damage and that the plane was safe to operate. I proceeded to review the emergency checklist for the problem. I reset the system numerous times but to no avail. I attempted to contact ATC but forgot to change over the mike switch from boom to mask. As soon as I had gotten O2 flow; I then proceed to change the mask mic over to mask. I contacted ATC to let them know of my situation and they cleared me to 11;000 feet. The controller indicated that the supervisor had cleared the way for me and they were most helpful. Once everything returned to normal; pressurization was restored and I was cleared to higher altitudes. My final was FL230. The rest of the flight was uneventful.after a thorough review of the events; I can say that I did not know how long the entire situation took to get my clearance to 11;000 feet. While I would anticipate 4-5 minutes before loss of consciousness; I completely lost track of the time of the event. My aircraft pressurization system was recently checked; door gasket replaced and passed a thorough check out and pressurization test. This situation occurred because I believe that the main squat switch on the left main gear had gotten moisture in it and after some time at FL250; it froze and therefore shorted out. This switch controls the outflow valve and once it thaws out; everything returns to normal. This switch will be replaced as soon as possible. Regarding the interaction with ATC; I cannot say enough. They were professional; thoughtful; and assisted me in whatever I requested. They followed up to make sure everything was good to go. I have spoken to my flight instructor about the incident and he felt that it was handled in an acceptable manner. Unlike most accidents where there is a chain of events; this came out of nowhere and demanded immediate attention and resolution.

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Original NASA ASRS Text

Title: Piper 46 pilot reporter a total loss of cabin pressurization while at FL250. Pilot reported having issues with the O2 mask and elected for an autopilot descent to 11;000 feet and pressurization was restored.

Narrative: While cruising at FL250; the aircraft experienced a total cabin pressurization loss. I immediately attempted to define the problem; what happened; and consider any available solution. I immediately attempted to place my face mask into operation. I was having an issue with turning on the O2 supply and decided to start an autopilot descent. I thought that if I encountered a loss of consciousness; the aircraft would level at a safe altitude; the aircraft would still be in control until I regained consciousness. After checking to make sure there was no damage and that the plane was safe to operate. I proceeded to review the emergency checklist for the problem. I reset the system numerous times but to no avail. I attempted to contact ATC but forgot to change over the mike switch from boom to mask. As soon as I had gotten O2 flow; I then proceed to change the mask mic over to mask. I contacted ATC to let them know of my situation and they cleared me to 11;000 feet. The Controller indicated that the Supervisor had cleared the way for me and they were most helpful. Once everything returned to normal; pressurization was restored and I was cleared to higher altitudes. My final was FL230. The rest of the flight was uneventful.After a thorough review of the events; I can say that I did not know how long the entire situation took to get my clearance to 11;000 feet. While I would anticipate 4-5 minutes before loss of consciousness; I completely lost track of the time of the event. My aircraft pressurization system was recently checked; door gasket replaced and passed a thorough check out and pressurization test. This situation occurred because I believe that the main squat switch on the left main gear had gotten moisture in it and after some time at FL250; it froze and therefore shorted out. This switch controls the outflow valve and once it thaws out; everything returns to normal. This switch will be replaced as soon as possible. Regarding the interaction with ATC; I cannot say enough. They were professional; thoughtful; and assisted me in whatever I requested. They followed up to make sure everything was good to go. I have spoken to my flight instructor about the incident and he felt that it was handled in an acceptable manner. Unlike most accidents where there is a chain of events; this came out of nowhere and demanded immediate attention and resolution.

Data retrieved from NASA's ASRS site 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.