Narrative:

Loud bang with an instant loss of cabin pressure. Oxygen masks which were placed on the back seat were not there. Deployed speed brakes; reduced power to idle; pointed nose down until speed reached red line. Contacted ATC while descending in VFR conditions and got clearance for 11;000 ft. Entered IMC and leveled and stabilized the aircraft with lower speed at 11;000 ft. Started looking for the reason for cabin pressure drop; found that the rear window on driver side was missing. Verified that all controls were working properly. Advised controller about missing window and that everything was ok and under control. Received clearance for 9;000 ft. Continued flight to destination at 9;000 ft without window with 170 KTS IAS. Landed without any problems.

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Original NASA ASRS Text

Title: A Lancair 4P lost cabin pressure at FL200 when a passenger window failed.

Narrative: Loud bang with an instant loss of cabin pressure. Oxygen masks which were placed on the back seat were not there. Deployed speed brakes; reduced power to idle; pointed nose down until speed reached red line. Contacted ATC while descending in VFR conditions and got clearance for 11;000 FT. Entered IMC and leveled and stabilized the aircraft with lower speed at 11;000 FT. Started looking for the reason for cabin pressure drop; Found that the rear window on driver side was missing. Verified that all controls were working properly. Advised Controller about missing window and that everything was OK and under control. Received clearance for 9;000 FT. Continued flight to destination at 9;000 FT without window with 170 KTS IAS. Landed without any problems.

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.