PA-34-200 Seneca I
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 100; Flight Crew Total 2800; Flight Crew Type 30
Aircraft Equipment Problem Critical; Ground Event / Encounter Ground Strike - Aircraft
Aircraft Aircraft Damaged; General Maintenance Action
Aircraft
I was instructing a pilot working on his commercial multi-engine rating.  We departed ZZZ1 headed out to a practice area and accomplished multi-engine maneuvers to include: slow flight; stalls; steep turns; climbs; and emergency descent.  We then accomplished 'engine failure' procedures in the practice area at altitude to include a drag demo and how to handle an in-flight engine failure.  Following those maneuvers; which were all uneventful; we proceeded to ZZZ.  We entered the VFR traffic pattern for runway XX; and accomplished 5 'stop-and go's'.  The first 3 stop and go's were normal; 2 engine landings.  The next two were 'single engine' landings; with one engine at idle. All 5 landings were stable approaches; with smooth touchdowns.  On each pattern we ran the before landing checklist on downwind; confirmed gear down and locked by checking for 3 green lights and no red 'gear unsafe' light.  Additionally; we check the gear status and accomplish a GUMPS check on base and final.On the 6th and final pattern; we again ran the before landing checklist at midfield downwind; accomplished a GUMPS check on base and final; each time visually confirming and noting verbally 'gear down; 3 green'.  Upon landing; the student landed at a normal touchdown rate; and after touchdown; as he released back pressure on the yoke; the nose gear collapsed and the nose of the aircraft struck the runway.  The props came to a stop after striking the runway; and I immediately proceeded to secure the engine to prevent any risk of fire or additional damage to the airplane.  I pulled the throttles to idle; mixtures to cut-off; fuel selector to off; mags off; master off; flaps up; and we egressed the aircraft. As mentioned; we had a gear down indication with 3 green gear lights; and no red gear unsafe light.  Both the student and I confirmed gear position 3 times during each VFR pattern.  I believe this to be a mechanical failure of either the nose gear position indicator sensor; and/or failure of the hydraulic pump.
A commercial rated pilot and his flight instructor in a PA-34 Piper Seneca experienced a nose landing gear collapse after landing for unknown reasons.