Narrative:

We departed right at sunset. I took off and headed northwest towards our destination, a private grass field. Most of the direct flight path follows a broad valley. To allow sufficient altitude for the trip I climbed to 2100 ft MSL. This would put us about 1500 ft AGL for our flight up the valley, and about 1200 ft AGL for the last 10 mi. My passenger pointed out an area of very bright lights that he did not recognize. As we were approaching the lighted area, we recognized that it was an automobile dealership. I flew over the village so that my passenger could get a good look at the dealership and the village. While I was overflying the village, I spotted an airport, which is located about 3 mi west of the village. I then recalled that the pattern altitude is 2350 ft MSL. The airport elevation is 1559 ft. Since we were still at 2100 ft MSL, that meant that we were only about 550 ft AGL above the village. Since the village is a 'congested area of a city, town or settlement' we were too low. I then turned away from the village and continued the flight to our destination, while climbing higher and avoiding other congested areas. Contributing factors: since it was getting dark, it was much harder to recognize that the terrain was rising beneath us as we flew out of the valley. During daylight this transition is more obvious. Human performance factors: I had planned our flight to be direct. Once I decided to divert from the plan I needed to reconsider the elements of the flight plan, such as altitude. If you divert from the plan, you have to look ahead at what you're doing, and revise the flight plan.

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Original NASA ASRS Text

Title: C150 PLT INADVERTENTLY FLIES OVER A POPULATED AREA BELOW 1000 FT AGL AT NIGHT.

Narrative: WE DEPARTED RIGHT AT SUNSET. I TOOK OFF AND HEADED NW TOWARDS OUR DEST, A PVT GRASS FIELD. MOST OF THE DIRECT FLT PATH FOLLOWS A BROAD VALLEY. TO ALLOW SUFFICIENT ALT FOR THE TRIP I CLBED TO 2100 FT MSL. THIS WOULD PUT US ABOUT 1500 FT AGL FOR OUR FLT UP THE VALLEY, AND ABOUT 1200 FT AGL FOR THE LAST 10 MI. MY PAX POINTED OUT AN AREA OF VERY BRIGHT LIGHTS THAT HE DID NOT RECOGNIZE. AS WE WERE APCHING THE LIGHTED AREA, WE RECOGNIZED THAT IT WAS AN AUTOMOBILE DEALERSHIP. I FLEW OVER THE VILLAGE SO THAT MY PAX COULD GET A GOOD LOOK AT THE DEALERSHIP AND THE VILLAGE. WHILE I WAS OVERFLYING THE VILLAGE, I SPOTTED AN ARPT, WHICH IS LOCATED ABOUT 3 MI W OF THE VILLAGE. I THEN RECALLED THAT THE PATTERN ALT IS 2350 FT MSL. THE ARPT ELEVATION IS 1559 FT. SINCE WE WERE STILL AT 2100 FT MSL, THAT MEANT THAT WE WERE ONLY ABOUT 550 FT AGL ABOVE THE VILLAGE. SINCE THE VILLAGE IS A 'CONGESTED AREA OF A CITY, TOWN OR SETTLEMENT' WE WERE TOO LOW. I THEN TURNED AWAY FROM THE VILLAGE AND CONTINUED THE FLT TO OUR DEST, WHILE CLBING HIGHER AND AVOIDING OTHER CONGESTED AREAS. CONTRIBUTING FACTORS: SINCE IT WAS GETTING DARK, IT WAS MUCH HARDER TO RECOGNIZE THAT THE TERRAIN WAS RISING BENEATH US AS WE FLEW OUT OF THE VALLEY. DURING DAYLIGHT THIS TRANSITION IS MORE OBVIOUS. HUMAN PERFORMANCE FACTORS: I HAD PLANNED OUR FLT TO BE DIRECT. ONCE I DECIDED TO DIVERT FROM THE PLAN I NEEDED TO RECONSIDER THE ELEMENTS OF THE FLT PLAN, SUCH AS ALT. IF YOU DIVERT FROM THE PLAN, YOU HAVE TO LOOK AHEAD AT WHAT YOU'RE DOING, AND REVISE THE FLT PLAN.

Data retrieved from NASA's ASRS site as of July 2007 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.