After taking off in calm, fine weather conditions, the pilot climbed the aircraft to a height of about 500 above the ground and commenced a series of manoeuvres incorporating steep angles of bank. During the nose-down segment of a wing-over, the aircraft was seen to be near vertical and to accelerate rapidly before pulling up into a steep turn at about 200 feet above the ground. The turn was tightened to at least 60 degrees of bank, and shortly afterwards the right wing failed. The aircraft fell to the ground at high speed and collided with a fence post after sliding for 18 metres. The aircraft had been substantially modified by the pilot, and was being operated at well in excess of the design weight. The wing spar had failed as a result of the overload forces applied to the structure during the sequence of manoeuvres.