On December 12, 1999, at 1800 central standard time, a Piper PA-28-180, N41910, piloted by a private pilot, sustained substantial damage after colliding with trees while landing on runway 22 (3,999 feet by 75 feet, dry/asphalt) at the Mankato Municipal Airport (MKT), Mankato, Minnesota. The 14 CFR Part 91 personal flight was not operating on a flight plan. Visual meteorological conditions prevailed at the time of the accident. The pilot and his one passenger received minor injuries. The flight departed from the L J Bose Airstrip, Orleans, Nebraska, at 1455, and was en route to MKT. The Federal Aviation Administration conducted an on scene examination of the aircraft and found no anomalies that could be associated with a preexisting condition. In his written statement, the pilot listed no mechanical malfunction. In a written statement, the pilot stated that he "...remained at 150 feet above ground level until I felt we needed to expedite our descent to make the runway. Position calls were made at downwind entry, and upon turning final. My only explanation is that I was experiencing the classic optical illusion of thinking I was closer to the approach end of the runway, than I actually was. As the landing light had been turned on during the downwind leg, we saw the tree top just before we hit it." The pilot stated, in his written statement, that the accident could have been prevented by receiving additional night dual instruction and a visual approach slope indicator (VASI) on runway 22. According to the Airport/Facility Directory (A/FD), runway 22 has a VASI system that is activated using the aircraft radio tuned to the airport common traffic advisory frequency (CTAF). According to a statement from the airport manager, three flight instructors that operated aircraft during the late afternoon and early evening on the day of the accident were contacted. All three flight instructors indicated that the VASI lights were operational at the time of their flights. On the day following the accident, the airport maintenance manager conducted a daily inspection and determined that the VASI system was operational and in working order.