Date: 201210
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: Mixed
Weather elements / visibility: 7
Light: Daylight
Aircraft: Albatros (L39)
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Training
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pressurization System
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Private
Human factors: Physiological - Other; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed As Precaution; Flight Crew Diverted; Flight Crew Returned To Departure Airport; General Maintenance Action; General Physical Injury / Incapacitation
Contributing factors: Aircraft; Human Factors
Primary problem: Ambiguous

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.




Synopsis: 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.