This June 2007 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Aircraft: Cessna 172.
Location: Amarillo, Texas.
Aircraft damage: Substantial.
What reportedly happened: The 45-hour student pilot was attempting to land in a crosswind. According to the student, the right main tire touched down first. As the left tire touched down, the airplane veered to the left. The student thought he had a flat tire and he held the left wing up for as long as possible to minimize the amount of weight on the tire. The airplane went off the left side of the runway
Examination of the airplane revealed the left main landing gear spring had fractured into two sections at the point where the foot-step attached to the spring. The fractured spring assembly, including the foot-step and bracket, were shipped to a metallurgical laboratory for further examination. It was discovered that the step was welded to the spring gear by two transverse weld beads on the top and side of the spring. In addition, there were two longitudinal weld beads on the lower surface of the spring. The welds were not consistent with good quality workmanship. A magnified examination of the fracture surface revealed that the fracture initiated at this weld bead. The airplane’s last annual inspection was completed in January 2007. There were no entries relating to a weld repair in the aircraft maintenance logbooks.
According to the owner, who just recently purchased the airplane, no maintenance had been performed on the airplane since it was purchased. According to the manufacturer’s Service Manual, the foot-step should be bonded to the steel landing gear spring with EA9303 or a similar adhesive. In addition, FAA Advisory Circular AC43.13-1B CHG 1, Acceptable Methods, Techniques, and Practices-Aircraft inspection and Repair, section 4-89, titled Aircraft Parts Not To Be Welded, part (A), stated, “Do not weld alloy steel parts such as aircraft bolts, turnbuckle ends, etc., which have been heat treated to improve their mechanical properties.”
Probable cause: The failure of the left main landing gear spring assembly as a result of an unapproved repair by an unknown person, which resulted in a loss of directional control during the landing roll.
For more information: NTSB.gov/ntsb/brief2.asp?ev_id=20070621X00767&ntsbno=DFW07LA130&akey=1.