Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 25; Flight Crew Total 3200; Flight Crew Type 120
Aircraft Equipment Problem Critical; Ground Event / Encounter Ground Strike - Aircraft; Ground Event / Encounter Loss Of Aircraft Control
Aircraft Aircraft Damaged
Aircraft
Normal approach; wind out of the south at 3 kts. Pilot with tail wheel endorsement flying his plane made nice 3 point landing; no bounce. On rollout; the plane suddenly veered to the left and the right side of the airplane dropped to the runway. Pilot and I exited airplane.  The right main gear leg was lying beneath the airplane. I think there was a complete mechanical failure of the right main landing gear leg.
I was receiving instruction; we were attempting our first touch and go; uneventful three point landing; upon which the plane turned unexpectantly and violently to the left; right main landing gear collapsed.
Cessna 170 Instructor Pilot and student reported the right main landing gear collapsed after a normal landing.