Narrative:

Just after refueling and leveling off VFR in cruise flight the engine cowling popped open and began flapping in the slipstream. I had just flown a 2.5 hour flight with no issues and was surprised to see this happen after departure; as the cowling had not been opened since preflight that morning. I slowed the aircraft and looked for a close airport to land and secure the cowling. Directly below me was [a suitable] airport. I began a circle around to land. I set up for final approach and checked mixture rich prop forward and on final flaps full for landing. My concern was that the cowling would tear off before I got on the ground and cause damage to the windshield or worse. Due to my attention to the flapping cowling I neglected to select the gear down and executed a gear up landing. When I did finally hear the gear horn buzzing I mistakenly thought I was hearing the stall horn warning. Although I have flown this aircraft in the past; it had been over three years since I flew it. The day before I took this flight I went up for a 45 minute familiarization flight and executed four take offs and landings in the process. In retrospect I believe I should have gone up with someone who has been flying this aircraft on a regular basis and gone over all the emergency procedures that could be anticipated and not simply a local area flight and normal take offs and landings. It had been a long time since I flew retractable gear aircraft and while I have many thousands of hours in them my recent experience has all been in helicopters with fixed gear. This combined with the distraction of an engine cowling loose in my opinion contributed to my error in not having the gear down upon landing.

Related reports:

Google
 

Original NASA ASRS Text

Title: BE36 pilot reports the engine cowling coming open in flight and a diversion to a suitable airport. The distraction caused by the flapping cowl results in the landing gear being forgotten and a gear up landing.

Narrative: Just after refueling and leveling off VFR in cruise flight the engine cowling popped open and began flapping in the slipstream. I had just flown a 2.5 hour flight with no issues and was surprised to see this happen after departure; as the cowling had not been opened since preflight that morning. I slowed the aircraft and looked for a close airport to land and secure the cowling. Directly below me was [a suitable] airport. I began a circle around to land. I set up for final approach and checked mixture rich prop forward and on final flaps full for landing. My concern was that the cowling would tear off before I got on the ground and cause damage to the windshield or worse. Due to my attention to the flapping cowling I neglected to select the gear down and executed a gear up landing. When I did finally hear the gear horn buzzing I mistakenly thought I was hearing the stall horn warning. Although I have flown this aircraft in the past; it had been over three years since I flew it. The day before I took this flight I went up for a 45 minute familiarization flight and executed four take offs and landings in the process. In retrospect I believe I should have gone up with someone who has been flying this aircraft on a regular basis and gone over all the emergency procedures that could be anticipated and not simply a local area flight and normal take offs and landings. It had been a long time since I flew retractable gear aircraft and while I have many thousands of hours in them my recent experience has all been in helicopters with fixed gear. This combined with the distraction of an engine cowling loose in my opinion contributed to my error in not having the gear down upon landing.

Data retrieved from NASA's ASRS site 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.