Lancair IV/IVP
Flight Crew Instrument
Flight Crew Last 90 Days 8.4; Flight Crew Total 1111; Flight Crew Type 175
Time Pressure; Physiological - Other; Communication Breakdown; Workload
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Illness / Injury
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Returned To Departure Airport; Flight Crew Took Evasive Action; General Maintenance Action
Human Factors; Aircraft; Procedure
As I was traveling in a experimental Lancair IV-PT pressurized aircraft; I experienced a cabin depressurization at FL240. I contacted center and requested 'Aircraft X needs to descend-lost pressurization'. I got no response; so I initiated a descent to 12;000FT. I then put on my oximizing cannula and opened the oxygen bottle valve. I then called Center again (sorry I can't remember the time interval) and got no response. I believe at FL190 I made third request for a lower altitude due to a loss of pressurization. I was having a difficult time keeping the cannula in my nose and thought at one point I was getting light headed. The controller asked if I wanted to declare an emergency; I replied 'no I now have my oxygen mask on'. The controller requested I turn right 30 degrees and ident; but in the challenge of keeping the cannula in my nose and flying the plane (at this point I realized the electric elevator trim servo was inoperative) I turned 30 degrees left and idented. The controller instructed me to continue a left turn back to my original heading and ident; which I did. The entire flight was in visual meteorological conditions.I descended down to 12;000FT and gained my composure. I then had time to anaylse the situation and thought the door seal was the culprit; (I had realized when the cabin depressurized I could hear the air leaving from the cabin door) but after bleeding the air from it I realized that wasn't the problem. I then looked further back and saw a 6 inch long crack in the aft upper cabin door window. Once I saw this I requested and received a 180 degree turn back to my departure airport.  I have ordered a new window and the factory has a new procedure of installing it; which is better than the original build manual.
The reporter stated his aircraft is over 10 years old with a different door design than current aircraft. The Lancair door windows have departed aircraft in the past; he feels fortunate his only cracked. The issue he believes is the potential for home builders of this door to drill the mid-door hinge holes incorrectly ultimately placing stress on the windows. He believes ATC did not immediately answer his request for a lower altitude because he may has activated the microphone switch while dealing with his cannula which was located on the seat next to him. Because of his experience putting the cannula on; in the future he will have the cannula around his neck and the oxygen bottle immediately available. Additionally; the Reporter stated he will in the future declare an emergency to enlist ATC's immediately assistance after establishing communications.
A Lancair LNC4 door window developed a six inch crack at FL240 and depressurized. The pilot had difficulty keeping his oxygen cannula on his face in place and calling ATC for a lower altitude but he was ultimately successful.