Narrative:

Part 91 flight from ZZZ to O69. Uneventful until the last 2 minutes of flight. The sun set about 20 minutes before landing at O69; and there was a thin broken layer over and south of the airport; with tops at perhaps 1;200-1;400 ft and bases at 1;000-1;200 ft. With the cloud cover; and the surrounding hills reaching to about 1;500 ft MSL; the airport (82 ft MSL) and environment was dark. Cleared for VOR 29 approach to O69; no procedure turn; I flew the approach normally; with a step descent from 1;900 ft MSL at aftin down to the MDA of 1;100 ft. That put me right at the base of the clouds. The airport was in sight at a distance of about 5 miles; and so I continued my descent to remain clear of the clouds and kept the airport in clear sight. Then I noticed something; a dark shape; to the left in my peripheral vision. I looked and saw it was a large eucalyptus tree on a small hill about 3 miles out on the extended centerline of the petaluma airport's runway. The tree was at most 200 ft below me. I had continued my descent to about 400 ft MSL. I added power and climbed back to about 800 ft; at which point I was back on the VASI 3 degree GS. I have flown this approach many times before. I have taken simulator training which graphically presents the danger of an approach over a dark terrain toward a lighted runway. In spite of that background; I descended well below the visual glide path to 'make sure' I did not re-enter the clouds; and nearly entered the terrain instead. I have for a decade had a self-imposed rule that I will not fly circle-to-land approaches in IMC. This approach made me realize that a straight-in non-precision approach at night has its own hazards. I; therefore; decided that I would add to my personal operations manual this: I will not fly non-precision approaches at night unless there is some form of vertical guidance -- either VASI or GPS-derived; and I will not descend below that glide path reference until reaching the runway. There is nothing particularly new or novel about the incident reported here. I have often read of pilots descending well below the MDA with sad consequences; and wondered why they would do so. Now I see that I; too; can be lulled into complacency and did the same thing. I'll stick to my newly added operations rule in the future.

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Original NASA ASRS Text

Title: A small aircraft pilot descended below the MDA for Petaluma airport's VOR approach shortly after sunset. A near CFIT event occurred but a nearby tree line provided a visual cue that made him climb back to the VASI.

Narrative: Part 91 flight from ZZZ to O69. Uneventful until the last 2 minutes of flight. The sun set about 20 minutes before landing at O69; and there was a thin broken layer over and south of the airport; with tops at perhaps 1;200-1;400 FT and bases at 1;000-1;200 FT. With the cloud cover; and the surrounding hills reaching to about 1;500 FT MSL; the airport (82 FT MSL) and environment was dark. Cleared for VOR 29 approach to O69; no procedure turn; I flew the approach normally; with a step descent from 1;900 FT MSL at AFTIN down to the MDA of 1;100 FT. That put me right at the base of the clouds. The airport was in sight at a distance of about 5 miles; and so I continued my descent to remain clear of the clouds and kept the airport in clear sight. Then I noticed something; a dark shape; to the left in my peripheral vision. I looked and saw it was a large eucalyptus tree on a small hill about 3 miles out on the extended centerline of the Petaluma Airport's runway. The tree was at most 200 FT below me. I had continued my descent to about 400 FT MSL. I added power and climbed back to about 800 FT; at which point I was back on the VASI 3 degree GS. I have flown this approach many times before. I have taken simulator training which graphically presents the danger of an approach over a dark terrain toward a lighted runway. In spite of that background; I descended well below the visual glide path to 'make sure' I did not re-enter the clouds; and nearly entered the terrain instead. I have for a decade had a self-imposed rule that I will not fly circle-to-land approaches in IMC. This approach made me realize that a straight-in non-precision approach at night has its own hazards. I; therefore; decided that I would add to my personal operations manual this: I will not fly non-precision approaches at night unless there is some form of vertical guidance -- either VASI or GPS-derived; and I will not descend below that glide path reference until reaching the runway. There is nothing particularly new or novel about the incident reported here. I have often read of pilots descending well below the MDA with sad consequences; and wondered why they would do so. Now I see that I; too; can be lulled into complacency and did the same thing. I'll stick to my newly added operations rule in the future.

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.