PA-23 Apache/Geronimo Apache
Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument
Flight Crew Last 90 Days 25; Flight Crew Total 586; Flight Crew Type 12.2
Other / Unknown
Ground Excursion Runway; Inflight Event / Encounter Loss Of Aircraft Control
Aircraft Aircraft Damaged
Aircraft; Human Factors
Landed on the runway a little hard and had a slight bounce. After bounce we maintained centerline for a few seconds and felt like the right strut collapsed.  The aircraft started to list to the right and off the runway.  Had full left rudder applied with no effect on aircraft movement.  The aircraft went off the runway and into the grass when I heard the prop strike on the right engine.  We immediately secured both engines and shut down power to the aircraft.  After egress we saw that the right gear had collapsed.  Due to the prop strike at the end of the landing roll out; I suspect that the gear collapsed when we went off the runway into the grass.  The ground was soft at the time and suspect that the gear getting caught in the grass caused the gear to fold back.  The gear retracts forward into the nacelle with a normal gear retraction.  I estimate that we were going about 15-20 MPH when we went off the runway.  Runway Length is under 2;700 feet by 36 feet.  It was a short field approach to land.Environment: VMC; and Dusk.  Pilot is night current.Human Factors:  Reduction of power causing a high sink rate while crossing the numbers during landing. Factors affecting Human Performance:  Stress and Fatigue due to impending check ride for multi add on rating.
A PA23 pilot receiving instruction reported a right gear collapse after a firm landing with a slight bounce. The aircraft became uncontrollable and went off the right side of the runway.