Summary
During a landing on a 1,200-foot wet grass airstrip, the pilot touched down 400 feet beyond the threshold. The airplane overran the end of the strip and struck a ditch, resulting in the collapse of the main landing gear.
Full Account
The pilot reported that he used full flaps and an approach speed of 65 knots. He touched down 400 feet past the threshold of the 1,200-foot strip. The braking action on the wet grass was described as 'nil'. The airplane continued beyond the end of the airstrip and hit a ditch, collapsing the main landing gear.
Aircraft Performance Reference
According to the pilot operator's handbook supplement for the Robertson STOL conversion, the normal ground roll under conditions of full flaps, 58 knots indicated at 50 feet, and heavy braking on hard surfaced runways is 310 feet. The supplement notes that this distance should be increased by 20% for dry grass runways.