PA-23 Apache/Geronimo Apache
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 72; Flight Crew Total 2252; Flight Crew Type 78.3
Aircraft Equipment Problem Critical; Ground Event / Encounter Ground Strike - Aircraft; Ground Excursion Runway
Aircraft Aircraft Damaged; General Evacuated
Aircraft
I was providing flight instruction in a Piper Apache Geronimo with the student practicing take off and landings. The student was performing very well with well-executed gentle landings. On this landing; the aircraft touched down short of the approach-end fixed distance markers on Runway 34 and rolled about 1000ft. The aircraft then began drifting to the right of the center line. The student double-checked engines at idle (for a potential engine-failure induced loss of directional control) and began working the rudder to stay on the runway. Just about that time; the right wing started to settle and then it dropped. The propeller started hitting the runway.  The student steered the aircraft into the grass in an attempt to minimize the risk of generating fire-igniting sparks on the runway as the wing slid along the pavement.  About the time the right wing dropped; the gear down horn came on. During the approach; there were three green lights (gear down and locked) noted during the start of the base leg turn; again at the start of the final approach leg; and again on short final (I teach the student to double-check one final time when the runway numbers become readable). Both I and the student verbally called attention to the three greens at each of these point. The landing was soft and normal until the plane passed Taxiway A. Shortly after that is when the sideways drift began and the soon after that the right wing began to settle - and moments later the gear warning horn began to sound as the wing started dropping more rapidly.  When the wing hit the runway; I pulled the mixtures to stop the engine. The airplane came to a rest in the grass just past Taxiway G on the right side of Runway 34. When the plane stopped sliding; I killed the magneto switches; master switch; and electrical switches. The Fuel selectors were moved to the OFF position for both engines in an attempt to ensure no fuel leakage from the then unknown damage that might have occurred under the plane.  I honestly don't know what caused the right main gear to collapse and am anxiously awaiting the outcome of the mechanical diagnosis and assessment. The FBO attempted to jack up the plane so the right gear could be extended - but the plane fell off the jack; hard to the ground.  This happened twice.  As the plane fell; the underside of the right side wing - between the engine cowling and the wing root - impacted on the jack equipment hard - both times.  The Airport Manager then called for a crane to lift the right side of the airplane. Once lifted; I used the hand hydraulic pump to pump down the gear.  When the hydraulic action reached its limit; the gear handle popped back into the off position. I checked the gear status by turning on the master switch but the horn sounded and the right main gear green light was dark. The mechanic then pounded on the gear locking mechanism to force it into place. Another check of the master switch still resulted in a warning horn and no right main gear green light. The FBO line technicians elected to attempt to tow the airplane back to the hangar anyway asking the crane operator to stand by until the plane was successfully moved into the hangar.  The tow operation was successful. The gear failure is scheduled for further investigation beginning tomorrow. One decision I don't know if it was prudent or not was to steer the aircraft into the grass at the edge of the runway in an attempt to minimize the risk of fire from metal scraping the concrete. It did make for a gentle stop however. Both occupants of the aircraft (student and instructor) were uninjured.
A pilot and flight instructor experienced a right main landing gear collapse during landing rollout.