NW Of Chicago/Crystal Lake, July 1958July 1958

On July 20, 1958, a private pilot flying a Cessna 182 near Crystal Lake, Illinois spotted an unusual object in the sky. The pilot was cruising at 8,500 feet when he noticed a disc or sphere-shaped object approaching from below and to the right of his aircraft. The object was about the size of a basketball, white in color, and non-reflective. It made no sound.

The sighting lasted only four to six seconds. The object traveled on a straight path at an altitude between 3,500 and 4,000 feet, moving on a heading of 280 degrees (roughly west). The pilot watched it pass from view behind his aircraft. Weather conditions at the time were clear, with a layer of haze around 4,200 feet. Wind at the time was easterly at about 10 knots near the surface, shifting to different directions at higher altitudes.

The Air Force's Aerospace Technical Intelligence Center analyzed the sighting and concluded the object was a balloon. According to their report, the object's appearance, the position of the sun, and the wind direction all supported this conclusion. The report noted that the pilot's aircraft was flying in the exact opposite direction from the wind, which created a high closure rate and explains why the sighting lasted only a few seconds. The report also suggested that scattered clouds between the aircraft and the object, combined with the fact that the object was positioned between the plane and the ground, may have made it harder for the pilot to identify what he was seeing.

The complete case file, comprising 9 pages as held by the National Archives, is reproduced below.