NTSB Identification: DFW07LA130.
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Accident occurred Thursday, June 07, 2007 in Amarillo, TX
Probable Cause Approval Date: 08/30/2007
Aircraft: Cessna 172K, registration: N7370G
Injuries: 1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The student pilot lost control of the airplane after the left main landing gear spring failed during the landing roll. According to the 45-hour student pilot, while attempting a crosswind landing in a single-engine airplane, the right main landing gear tire touched down first, followed by the left main landing gear tire; however, when the left hand tire made contact with the ground "something went wrong." The student pilot thought he may have 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 side of the runway after the student pilot was unable to maintain directional control of the airplane. Examination of the airplane revealed the left main landing gear spring 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. According to the Factual Report, the spring gear fractured at the point where the foot-step was installed to the spring. 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. According to the report, "...the weld beads were tall and rounded with weld spatter on the surrounding surfaces and not consistent with good quality workmanship." The spring gear fracture intersected the longitudinal weld on the lower surface of the spring. 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. A review of the maintenance logbooks revealed no entries relating to a weld repair on the spring gear. 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."
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The failure of the left main landing gear spring assembly as a result of an unapproved repair by an unknown person(s), which resulted in a loss of directional control during the landing roll. Full narrative available
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