Narrative:

I departed in a L39C albatross after a weekend of flight training including an FAA part 61.58 check ride. All systems including pressurization and oxygen were functional and checked during the weekend flights. I filed IFR and flew to ZZZ1; landed and topped off fuel. After one hour I departed ZZZ1 for my home base; on an IFR flight plan. Weather brief was obtained via foreflight and the NOAA website. While north of ZZZ2 the controller offered direct and I accepted. Flight was at 15;000. Weather enroute was mixed but predominantly VFR. East of ZZZ VOR cloud cover increased and I requested 17;000. While flying at 17;000 I noticed that I was focusing very intensely on the gauges; more than usual. I checked cabin pressure (two separate gauges installed) and both reading just over 12;000 ft. At this point I wondered whether or not my increased focus on the instruments may have been due to hypoxia. I was in VMC but became anxious thinking that my judgment may have been impaired. As I was attaching the oxygen mask to my helmet there was a large cloud build up ahead and I asked for an altitude change (I cannot recall the exact request). The controller refused; so I cancelled the IFR plan and planned to turn back and stay in VMC to get my oxygen mask on. I was able to attach the mask and maintain VFR as I began a 180 degree turn but I found that it was difficult to breathe. The valve in the mask seemed to be opening for only the first part of each inhalation. I panicked; realizing that I was probably becoming more hypoxic and my oxygen wasn't working. I checked the gauge and noted that the oxygen tank was near full. I considered performing a rapid descent as I was in VMC and I could see the ground from where I was but I could not judge the height of the ceiling at the bottom and was afraid that I may not be able to pull out in time and could impact the ground at high speed.I continued the turn to maintain VFR as I considered my options. I do not recall if I was at 15;000 or 17;000 at the time. I could see clear blue sky above and to my left. At the same time I reached to my left console and flipped on the emergency O2 switch and oxygen began to flow continuously in my mask. I noticed that my respiratory rate was high and I remember wondering whether or not this was due to hypoxia or panic. I didn't feel much differently; but I had some relief knowing that I was breathing 100% O2. There was a large build up at my 12 o'clock and I knew I needed to stay visual since I had cancelled IFR. I selected full power and climbed to the clear; so that I could maintain VFR and continue to breathe the oxygen. I immediately contacted the controller that I had cancelled with and said something to the effect of 'I need help...I need a vector to VFR' I cannot recall exactly what I said; I remember thinking that I was babbling a bit which I thought was odd since I am usually concise in my radio calls. The controller was calm and immediately helpful. Just hearing his voice calmed me even more. He gave me a squawk code and said 'squawk wxyz when able.' the words 'when able' made me think that I must have sounded desperate in my radio call. I did manage to dial in the code and to maintain the heading he suggested and within about ten minutes I was at the shoreline and had a clear view to the airport. I then did a circling descent and landed; breathing 100% O2 the whole time except when I had to lift the mask to speak into the boom mic.about one hour later I departed with the intent of flying south along the shoreline to my original destination. As I was taxiing the tower controller informed me that center wanted me to call a number when I landed and I wrote the number on my knee board. Just off the coast I contacted center for flight following and the controller told me that he had a message for me. I told him that I had the message and I read the number back to him. He then said that his supervisor was 'standing by' and insisted that he read the message to me again. As I took the message for the second time I realized that my mind was racing wondering why he insisted on giving me the same message twice. It was then that I realized I was still not thinking as clearly as usual and that taking off for the second flight was a bad idea; so I told the controller to cancel flight following as I planned to turn around and head back for landing. I contacted the tower and made an easy landing and spent the night in a hotel. Much of what had transpired began to make more sense as I mentally reviewed the events that had occurred later that night and the next morning.facts:I did not 'declare an emergency' even though an emergency clearly existed. I did manage to maintain flight in VMC at all times after I cancelled the flight plan. I realized that I needed to get oxygen as soon as possible and I was able to do so despite the regulator malfunction by using the emergency bypass switch. I did ask for help once I knew that I was addressing the hypoxia by breathing 100% O2. I suspected that my judgment was impaired; but I continued to work to solve each problem as it arose. The decision to take off the second time was very poor judgment as I was not really back to my normal mental clarity but did not realize this at the time.corrective action:I have contacted my mechanic and will not fly the plane above 10;000 ft until the pressurization and normal oxygen mask functions are evaluated and fixed. From now on I will always test and attach my oxygen mask to one side of my helmet when flying above 10;000 ft so that I can don the mask quickly if necessary.lessons:I should have declared an emergency immediately upon suspecting that I was becoming/was hypoxic instead of believing that I could solve the problem myself. I will continue to concentrate on recurrent training as I realized later how important it was that I had done these things in my training. I am sure that training is the reason I knew to check the gauges; don the mask; and use the bypass switch.

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Original NASA ASRS Text

Title: L39 pilot reports possible hypoxia at 17;000 FT after noting that cockpit altitude is 12;000 FT. The oxygen mask is donned but does not appear to function normally. Emergency is selected and with good oxygen flow the reporter elects to divert to a suitable airport. After an hour on the ground he elects to depart again only to decide airborne that the best course of action is to return and spend the night.

Narrative: I departed in a L39C Albatross after a weekend of flight training including an FAA part 61.58 check ride. All systems including pressurization and oxygen were functional and checked during the weekend flights. I filed IFR and flew to ZZZ1; landed and topped off fuel. After one hour I departed ZZZ1 for my home base; on an IFR flight plan. Weather brief was obtained via Foreflight and the NOAA website. While North of ZZZ2 the Controller offered direct and I accepted. Flight was at 15;000. Weather enroute was mixed but predominantly VFR. East of ZZZ VOR cloud cover increased and I requested 17;000. While flying at 17;000 I noticed that I was focusing very intensely on the gauges; more than usual. I checked cabin pressure (two separate gauges installed) and both reading just over 12;000 FT. At this point I wondered whether or not my increased focus on the instruments may have been due to hypoxia. I was in VMC but became anxious thinking that my judgment may have been impaired. As I was attaching the oxygen mask to my helmet there was a large cloud build up ahead and I asked for an altitude change (I cannot recall the exact request). The Controller refused; so I cancelled the IFR plan and planned to turn back and stay in VMC to get my oxygen mask on. I was able to attach the mask and maintain VFR as I began a 180 degree turn but I found that it was difficult to breathe. The valve in the mask seemed to be opening for only the first part of each inhalation. I panicked; realizing that I was probably becoming more hypoxic and my oxygen wasn't working. I checked the gauge and noted that the oxygen tank was near full. I considered performing a rapid descent as I was in VMC and I could see the ground from where I was but I could not judge the height of the ceiling at the bottom and was afraid that I may not be able to pull out in time and could impact the ground at high speed.I continued the turn to maintain VFR as I considered my options. I do not recall if I was at 15;000 or 17;000 at the time. I could see clear blue sky above and to my left. At the same time I reached to my left console and flipped on the Emergency O2 switch and oxygen began to flow continuously in my mask. I noticed that my respiratory rate was high and I remember wondering whether or not this was due to hypoxia or panic. I didn't feel much differently; but I had some relief knowing that I was breathing 100% O2. There was a large build up at my 12 o'clock and I knew I needed to stay visual since I had cancelled IFR. I selected full power and climbed to the clear; so that I could maintain VFR and continue to breathe the oxygen. I immediately contacted the Controller that I had cancelled with and said something to the effect of 'I need help...I need a vector to VFR' I cannot recall exactly what I said; I remember thinking that I was babbling a bit which I thought was odd since I am usually concise in my radio calls. The Controller was calm and immediately helpful. Just hearing his voice calmed me even more. He gave me a squawk code and said 'Squawk WXYZ when able.' The words 'when able' made me think that I must have sounded desperate in my radio call. I did manage to dial in the code and to maintain the heading he suggested and within about ten minutes I was at the shoreline and had a clear view to the airport. I then did a circling descent and landed; breathing 100% O2 the whole time except when I had to lift the mask to speak into the boom mic.About one hour later I departed with the intent of flying South along the shoreline to my original destination. As I was taxiing the Tower Controller informed me that Center wanted me to call a number when I landed and I wrote the number on my knee board. Just off the coast I contacted Center for flight following and the Controller told me that he had a message for me. I told him that I had the message and I read the number back to him. He then said that his Supervisor was 'standing by' and insisted that he read the message to me again. As I took the message for the second time I realized that my mind was racing wondering why he insisted on giving me the same message twice. It was then that I realized I was still not thinking as clearly as usual and that taking off for the second flight was a bad idea; so I told the Controller to cancel flight following as I planned to turn around and head back for landing. I contacted the Tower and made an easy landing and spent the night in a hotel. Much of what had transpired began to make more sense as I mentally reviewed the events that had occurred later that night and the next morning.Facts:I did not 'declare an emergency' even though an emergency clearly existed. I did manage to maintain flight in VMC at all times after I cancelled the flight plan. I realized that I needed to get oxygen as soon as possible and I was able to do so despite the regulator malfunction by using the Emergency bypass switch. I did ask for help once I knew that I was addressing the hypoxia by breathing 100% O2. I suspected that my judgment was impaired; but I continued to work to solve each problem as it arose. The decision to take off the second time was very poor judgment as I was not really back to my normal mental clarity but did not realize this at the time.Corrective action:I have contacted my Mechanic and will not fly the plane above 10;000 FT until the pressurization and normal oxygen mask functions are evaluated and fixed. From now on I will always test and attach my oxygen mask to one side of my helmet when flying above 10;000 FT so that I can don the mask quickly if necessary.Lessons:I should have declared an emergency immediately upon suspecting that I was becoming/was hypoxic instead of believing that I could solve the problem myself. I will continue to concentrate on recurrent training as I realized later how important it was that I had done these things in my training. I am sure that training is the reason I knew to check the gauges; don the mask; and use the bypass switch.

Data retrieved from NASA's ASRS site as of July 2013 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.