(along with his brother Eduardo) runs a civilian research group in San Jose. In 1980 Mr. Vilchez met in person with Sergio L. V., the specialist in aerial photography who was aboard the aircraft that day. They discussed the circumstances surrounding the flight and the photograph without reaching a conclusion regarding the nature of the object. One of the authors saw the photograph while attending a meeting in Costa Rica in 1985, and Mr. Vilchez was kind enough to provide a second-generation negative to be taken back to the United States for analysis. Later we requested and obtained detailed maps of the area in question, as well as copies of the immediately preceding and following frames, respectively numbers 299 and 301. These photographs did not show the disc that was present on frame number 300.

In spite of the lack of a first-generation negative, we felt several unusual factors justified a detailed analysis of this photograph, if only to refine our methodology in dealing with such evidence: (1) it was taken by a high-quality professional camera; (2) the camera was looking down, which implies a maximum distance, hence a maximum size for the object; (3) the disc was seen against a reasonably uniform dark background of a body of water; and (4) the image was large, in focus and provided significant detail.

The disc was located about 3 miles North of the town of Arenal and some 25 miles South of the border with Nicaragua. The precise site was at latitude 10.583 degrees North and longitude 84.916 degrees West in the province of Alajuela above a small lake called "Lago de Cote" measuring approximately 1800 X 1600 meters. Lake level is about 640 m above sea level and the surrounding countryside consists of rolling and sharp hills rising several 100 meters above the valley floors. The region is densely wooded, with some broad grassy patches. A dirt road which is only passable in summer runs along the southern edge of the lake. It connects the small town of Cabanga to the northeast with Aguacate to the southwest. When the photograph is carefully examined, a few houses or other structures can be seen along this road, as well as animals in the fields.

The location of the disc was about 800 meters due North of the boundary between the province of AlaJuela and the province of Guanacaste.

Figure 1 is a black-and-white contact positive print of most of the aerial negative.

Figure 2 is a copy of the 1:50,000 chart in the region of Lago de Cote above which the disc was located.

Figure 3 is a copy of a geological chart with an arrow pointing to the Lago de Cote. A heavy long dashed line labelled "Fila Vieja Dormida" is seen passing almost directly through the location where the disc was recorded. This line represents a geological fault. The legend on the chart indicates that the dark areas are of volcanic origin.