Narrative:

Door opened during cruise flight resulting in landing at an airport that was not the destination; and also resulted in loss of altitude that was unpredicted. When ATC was notified of the problem I was not able to hold altitude when landing was required; which resulted in a conflict for ATC. I did not notify them that it was emergency; because I did not believe it was; but while controlling the aircraft it became apparent that I could not hold altitude before I was cleared to land.

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Original NASA ASRS Text

Title: An IFR Bonanza 33 pilot was unable to maintain altitude when the entry door opened in flight. A loss of separation occurred while diverting to a nearby airport where he landed without declaring an emergency.

Narrative: Door opened during cruise flight resulting in landing at an airport that was not the destination; and also resulted in loss of altitude that was unpredicted. When ATC was notified of the problem I was not able to hold altitude when landing was required; which resulted in a conflict for ATC. I did not notify them that it was emergency; because I did not believe it was; but while controlling the aircraft it became apparent that I could not hold altitude before I was cleared to land.

Data retrieved from NASA's ASRS site as of April 2012 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.