Champion Citabria 7ECA
Flight Crew Flight Instructor; Flight Crew Instrument
Flight Crew Last 90 Days 76; Flight Crew Total 3580; Flight Crew Type 850
Aircraft Equipment Problem Less Severe; Ground Event / Encounter Object; Inflight Event / Encounter Loss Of Aircraft Control
Flight Crew Regained Aircraft Control; General Flight Cancelled / Delayed
Aircraft
I was conducting a training flight which included some air work and full stall landing practice. After entering the pattern; I made the first landing and the student made the next 3 landings without any problems. All controls responded normally. On the fourth landing the student touched down to the right of the centerline but we were aligned parallel to the centerline. Once the wheels were on the ground; the stick came full back and next second the aircraft tail swung to the right. Left rudder was added to counter the right turning tendency but it had no effect. The tail eventually swung around and hit a landing light. There were no injuries and the aircraft sustained no damage. While taxiing the aircraft back to its tie down I had to steer the aircraft with the brakes. Back at the tie down I lifted the tail off the ground and found I could spin the tail wheel 360 degrees without the tail wheel locking in position to allow the rudder pedals to steer the aircraft on the ground. The tail wheel was disassembled and it was found that the locking cam was stuck in a position that would allow the tail wheel to freely caster in any direction it wanted. A nudge from behind the cam was enough to unstick it and allow the spring to push it into the position for locking. The manufacture of the tail wheel was contacted to explain the situation. Not trusting this type of tail wheel any more it has been replaced with a different type tail wheel. I feel if the tail wheel lock had engaged properly there would have been sufficient control to avoid a ground loop. I believe this incident does drive home the point to land on the centerline since it gives you the most buffer zone. If we had landed on the centerline we may have still ground looped but we might not have hit anything.
Citabria instructor pilot reports a ground loop during the students forth landing with the tail hitting a runway light. A defective tailwheel locking mechanism is discovered on post flight.