Maintenance Inspection Authority; Maintenance Powerplant; Maintenance Airframe
Maintenance Inspector 6; Maintenance Technician 13
Communication Breakdown; Situational Awareness
Aircraft Equipment Problem Critical; Ground Event / Encounter Ground Strike - Aircraft; Inflight Event / Encounter Loss Of Aircraft Control
Aircraft Aircraft Damaged; General Maintenance Action; General Flight Cancelled / Delayed
Human Factors; Manuals; Chart Or Publication; Aircraft
Stinson L-5C aircraft has conventional gear equipped with a Scott tailwheel. This tailwheel is not original equipment; but paperwork in the aircraft forms appears proper for this modification. The Tail Wheel connections were made using compression springs and tail wheel connection clips typical for small aircraft. The aircraft had been previously flown using this tail wheel set up with no difficulties. The plane had been down for an Annual Inspection during which time significant maintenance was accomplished on the fuel tanks and wings. Also during the maintenance period; some rudder cables were replaced which required the tailwheel to be disconnected. Upon completion of the rudder cable maintenance; the tailwheel was re-connected and the rudder cables were tensioned In Accordance With (IAW) the Aircraft Maintenance Manual (AMM). Taxi tests showed that the tail wheel was performing correctly. I signed-off the aircraft as having completed the Annual Inspection. An experienced L-5 Instructor Pilot flew the plane on a Return to Service flight without incident. After the Return to Service flight; the Instructor Pilot put a trainee with zero L-5 experience in the aircraft and they began a training sortie. The trainee is qualified in other conventional gear aircraft and is an experienced pilot. The trainee executed a full-flap three point landing on his first attempt to land the plane. The trainee stated that this was what the Instructor wanted him to do. L-5 Landing Main Gear has a very long throw on their oleos because they were made to land in rough terrain. It is important that weight on wheels be maintained so that the gear remains at full deflection during roll-out. If the aircraft rises back into the air or partial so; the tires will drop to a position nearly below the fuselage longerons in a very narrow track. This can contribute to a ground loop on the L-5 and therefore bounces are to be avoided. The trainee reported that the aircraft bounced twice to the top of the landing gear throw; but probably not back into the air. Given the oleo travel and shock absorption capacity of the L-5 gear; this indicated that the landing was firm. At some point during the landing it appears that the connections on the tailwheel were stretched beyond their ability and broke. The aircraft executed a ground loop to the left and dragged the right wing tip causing significant damage the wing. Wind was light and down the runway. Two other pilots who were qualified in this aircraft had only done wheel landings at the advice of a different Check Pilot. The L-5 is fairly heavy on the controls and can establish a high sink rate if the pilot allows it. As per most heavy; conventional gear aircraft; the mechanic and other qualified pilots recommended that the aircraft be wheel landed. The other qualified pilots had not executed a three point landing in this plane. Compression springs have a sufficient but limited amount of travel before they reach full compression and thereupon have no more travel. If the tailwheel spring is deflected far enough on a firm landing; the compression springs can reach full travel which they apparently did and then certain connecting hardware let go. At that point there was no tailwheel steering and rudder control. At landing speed; rudder authority in the L-5 is very limited. Had the pilot applied full left aileron; the extra drag on the right wing may have mitigated the ground loop but this can't be known for certain.
Reporter stated the original tailwheel utilized an actuator as part of tailwheel assembly that could accommodate the 18 inch deflection of the Main Landing Gears (MLG). The tailwheel had previously been replaced with a Scott Leaf Spring Tail Wheel Assembly using directions from an FAA 337 Form: Major Repair and Alteration information. The modification appeared correct per the forms included in the aircraft's history. The original tailwheel could handle a three-point landing and deflection of the tail wheel; but not the Scott design that is similar to a Piper Shawnee tailwheel. During a three-point landing; the leaf spring assembly could only straighten out so far before collapsing; damaging the underside of the aft fuselage; causing a ground loop and cracking the Right Rear Spar. Reporter stated the FAA 337 Form does not require a placard in the cockpit or logbook notifying pilots of the limitations of the modified tailwheel assembly and to 'not' attempt a three-point landing. Most pilots end up learning about the different tail wheel assemblies on Stinson L-5 aircraft through 'Tribal Knowledge'.
An Aircraft Maintenance Technician (AMT) with Inspection Authority (I/A) reports about a ground loop incident involving a Stinson L-5 aircraft with a modified Tailwheel Assembly.