PA-18/19 Super Cub
Flight Crew Commercial; Flight Crew Flight Instructor
Ground Event / Encounter Ground Strike - Aircraft; Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Runway
Aircraft Aircraft Damaged
Human Factors; Aircraft
The night before the flight; a friend called and asked if I wanted to go flying in his Super Cub the next day; the weather had recently cleared; and he was looking for some company to go for a ride. It had been over a year since I had flown in the airplane; I only have about ten hours in the type; and was not tailwheel current so I rode as a passenger in the back seat. Prior to the flight; the pilot and I discussed our roles and confirmed that he was pilot in command and I was present only as a passenger. After flying to an airport about forty miles away; with an 1800 ft paved strip about thirty feet wide; the pilot made a couple landings. I was enjoying the ride; I'm no expert on Super Cubs; but the pilot seemed to be doing a great short-field technique and handling the airplane well. The third landing started out no differently; the approach and three-point touchdown were well-executed from my vantage point. After touchdown the pilot appeared to have good directional control of the airplane. As the airplane slowed; however; I felt a subtle; then very noticeable vibration coming from the tail; followed by a sudden jerk to the left. As the airplane rolled off the runway into the grass; it decelerated quickly as the pilot applied the brakes; the tail lifted; and I could see a tetrahedron and runway sign directly ahead of us. The prop struck the sign and stopped the engine; and the tail came back down as the aircraft came to a stop. We both exited the airplane.  Although I was not in any manner acting as crew on this flight; as a CFI who had formerly given instruction to the pilot; I am concerned that I will be viewed as having failed at some implied responsibility with respect to this flight.
After landing and during taxi in a Piper PA18 the pilot lost control of the steering and ran off the runway.