What happened
During an approach to land, the pilot initiated the flare maneuver while over a river. The pilot reported that the aircraft encountered a severe dowundraft, noting that applying back pressure on the elevator was insufficient to arrest the resulting rapid descent.
A flight instructor accompanying the flight observed that the pilot's approach angle was slightly high and noted that the pilot applied heavy back pressure on the control wheel immediately before touchdown.
The right main landing gear struck rapidly upsloping terrain located just short of the runway threshold. Following this impact, both main landing gears collapsed. The aircraft then proceeded to skid approximately 750 feet down the runway, supported by the nose wheel and the collapsed main gear.