The Boeing 707, named “Flagship Connecticut”, was being operated on a training flight. It departed New York-Idlewild at 13:40. Training flight 514 accomplished high altitude air work after takeoff to permit sufficient fuel burnoff for airport transition training which was planned at Peconic River Airport (CTO). The 707 arrived in the Peconic area about 15:11. The crew of flight 514 accomplished several maneuvers, including full-stop landings, crosswind landings and takeoffs, a high off-set approach, simulated engine(s) out landings, and a no-flap aborted approach to landing. The aircraft did not retract its landing gear following the last aborted approach to landing on runway 23 but continued in the traffic pattern at an estimated altitude of 1,000-1,100 feet. The crew reported on left base leg for runway 23, was given clearance to land, and was informed that the wind was from 230 degrees at 10 to 15 knots. As it approached the extended centerline of runway it made a left bank, steepening to approximately 45 degrees. The aircraft was then observed to recover immediately to level flight and to begin a bank to the right which became progressively steeper. The right bank continued until the aircraft was inverted, at which time the nose dropped and a yaw to the left was observed. The 707 then continued to roll to the right in a nosedown configuration. The wings then levelled. Investigation revealed the aircraft struck the ground in a wings-level attitude, in a nearly stalled condition, yawed to the left approximately 12 degrees, with considerable and nearly symmetrical power. A fire erupted. PROBABLE CAUSE: “The crew failed to recognize and correct the development of excessive yaw which caused an unintentional rolling manoeuvre at an altitude too low to permit complete recovery.”