On November 25, 1998, at 1330 hours Pacific standard time, a Boeing A75N1, N59734, ground looped and nosed over during landing at the Vacaville, California, airport. The aircraft was owned and operated by the pilot under 14 CFR Part 91, and was on a personal flight from Executive Airport, Sacramento, California. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft sustained substantial wing damage. The private pilot, the sole occupant, was not injured. In a written statement, the pilot reported he had his landing gear serviced in Sacramento, and was returning back to Vacaville. Prior to his arrival in Vacaville, he monitored the ASOS, which reported winds as variable at 4 to 5 knots. There were two other aircraft in the traffic pattern, and they were using runway 02. The pilot said he did not notice that the winds had changed to a slight tailwind, and on touchdown, he lost directional control and the left wing touched the runway. The aircraft then turned sharply off the runway, encountered soft mud, and nosed over. The pilot stated that there were no mechanical discrepancies with the aircraft. The pilot went on to state that a few pilots had commented on the unreliability of the ASOS located on the field. In a telephone interview with the airport manager of Nut Tree Airport, Vacaville, he stated that the ASOS is located in an open field, and there are no restrictions to the sensors. He said that pilots have not complained about the ASOS, but have commented on how accurate and reliable it is. The ASOS is Federal Aviation Administration approved, and it is the only certified ASOS in the county.