Cessna 310/T310C
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor
Flight Crew Last 90 Days 250; Flight Crew Total 850; Flight Crew Type 10
Training / Qualification; Communication Breakdown
Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Taxiway
Aircraft Aircraft Damaged; General Evacuated; General Flight Cancelled / Delayed; General Maintenance Action
Human Factors
Today I had an incident in an aircraft with a student. We had flown the aircraft two days prior and had just returned from a flight of about 1.6 hours. We were taxiing back to the runway from the taxi way connector when the aircraft began to pick up speed. I instructed the student to begin to slow the aircraft down which she agreed with and began to do so. While slowing the aircraft it began to veer to the right slightly. I instructed the student to gently apply some left rudder to straighten the airplane. The left input was initially given and I believe the student thought that she had given too much as she made a hard input to the right. The input was harsh enough that as I tried to block the large input with my foot it raised me up against my seatbelt. When a large input is made in this aircraft over 20 degrees the wheel begins to do what is known as free cast. All that can really be done at that point is stop the aircraft and straighten the wheel. The rudder can no longer move the nose wheel in the opposite direction. I sensed this happened and immediately pulled back the throttles and mixture to stop thrust and applied full brakes. The aircraft almost got stopped but as the nose of the aircraft fell over the edge of the hill next to the taxi way; the momentum pulled us over the edge. At this point I continued to stand on the brakes to attempt to stop the aircraft but the downward momentum was too great. The aircraft came to rest against a chain link fence and some small brush. I secured the aircraft by shutting off battery power and fuel selectors and helped the student safely exit the plane. I carry insurance but found out after the fact that the owner did not have an insurance policy.
Reporter stated that the student had almost no multi-engine time and that student had a tendency to over control while taxiing. Reporter also stated that the likely cause of the aircraft initially veering to the right was a slightly advanced left throttle and uneven braking.
CE310 Instructor reported exiting the taxiway and proceeding down an embankment after the student applied improper rudder steering input.