Narrative:

My airplane; a piper mirage; was parked in transient parking facing a cessna 400; across the taxiway. I started up my airplane to fly to my/its' home base. After getting the engine running and going through part of my start up procedures; I realized that one of the cabin lights behind me in the plane was on. At night; these lights create nontrivial light pollution in the cabin; so I wanted to turn it off. I put on the parking brake and went back to the cabin to turn the light off.while I was moving to the light switch; I heard my passenger screaming; 'the plane is moving!' I got back to the pilot seat as quickly as I could to put my feet on the brakes; but I couldn't get in quickly enough. My plane hit (at very slow speed) the cessna. My prop sliced the starboard side of the cessna's nose before coming to a stop in its starboard wing. The starboard side of the cessna's nose and its starboard wing were obviously damaged in the collision. There may be engine damage as well; although it appeared that my prop just barely penetrated the composite skin of the plane. All three prop blades on the piper were wrecked; and there is a minor scratch or two on the starboard side that I believe were caused by one blade of the cessna's [stationary] prop. The morning after the collision; an a and P opened the piper's cowling and verified that there was no firewall damage. Shortly after hearing the a and P's report; the NTSB ruled that the collision was an 'incident.'although it is possible that there was a problem with the piper's parking brake; I think it unlikely. It is much more likely that in my rush; I did not properly engage the parking brake. Clearly I was bitten by my own desire for haste. The safest course of action upon seeing the lit cabin light would have been to shut down the plane before going back to turn it off. My desire to save myself 5 minutes of shutdown/startup procedures cost me dear. While there is little question that the above is the best and safest protocol; two others come to mind:1. instead of going back to the light switch to turn it off; I could have just pulled the circuit breaker for cabin lights and flown that way for the entire flight.2. I could have given my passenger instructions in how to use the brakes before going back into the cabin.

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Original NASA ASRS Text

Title: PA46 pilot reports setting the parking brake after engine start and leaving the seat to turn off a cabin light. The aircraft starts to move during the reporters absence and contacts another aircraft parked opposite.

Narrative: My airplane; a Piper Mirage; was parked in transient parking facing a Cessna 400; across the taxiway. I started up my airplane to fly to my/its' home base. After getting the engine running and going through part of my start up procedures; I realized that one of the cabin lights behind me in the plane was on. At night; these lights create nontrivial light pollution in the cabin; so I wanted to turn it off. I put on the parking brake and went back to the cabin to turn the light off.While I was moving to the light switch; I heard my passenger screaming; 'The plane is moving!' I got back to the pilot seat as quickly as I could to put my feet on the brakes; but I couldn't get in quickly enough. My plane hit (at very slow speed) the Cessna. My prop sliced the starboard side of the Cessna's nose before coming to a stop in its starboard wing. The starboard side of the Cessna's nose and its starboard wing were obviously damaged in the collision. There may be engine damage as well; although it appeared that my prop just barely penetrated the composite skin of the plane. All three prop blades on the Piper were wrecked; and there is a minor scratch or two on the starboard side that I believe were caused by one blade of the Cessna's [stationary] prop. The morning after the collision; an A and P opened the Piper's cowling and verified that there was no firewall damage. Shortly after hearing the A and P's report; the NTSB ruled that the collision was an 'incident.'Although it is possible that there was a problem with the Piper's parking brake; I think it unlikely. It is much more likely that in my rush; I did not properly engage the parking brake. Clearly I was bitten by my own desire for haste. The safest course of action upon seeing the lit cabin light would have been to shut down the plane before going back to turn it off. My desire to save myself 5 minutes of shutdown/startup procedures cost me dear. While there is little question that the above is the best and safest protocol; two others come to mind:1. Instead of going back to the light switch to turn it off; I could have just pulled the circuit breaker for cabin lights and flown that way for the entire flight.2. I could have given my passenger instructions in how to use the brakes before going back into the cabin.

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.