Extract from one report, "It proceeded to the south, where it flew a pattern at altitudes between 2,000 and 3,000 feet. The last data point is at 1,975 feet at a speed of 199 knots at 11:47 a.m. A witness on the ground reported hearing a loud twin boom sound before seeing the helicopter make an immediate descent. Most of the helicopter debris is highly compact, though some is hundreds of feet away from the primary crash site. Dallas television station KXAS reports a section of the tail boom was located 1,500 feet southeast of the primary crash site."