Incident Summary
On December 20, 2017, at approximately 0850 mountain standard time, an American Champion Aircraft 7GCAA, registered as N519MA, landed hard and departed the left side of runway at Vance Brand Airport (LMO) in Longmont, Colorado. The flight instructor and private pilot on board were not injured, and the airplane sustained substantial damage during the runway excursion.
Aircraft and Flight Details
The aircraft was registered to CAG International Inc. and operated by Fly Elite Aviation under 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed at the time, and no flight plan was filed. The local flight had departed at about 0845.
Damage and Investigation
The flight instructor reported that the private pilot made a hard landing. During the landing, the instructor heard a "snapping" sound and took over the flight controls. He increased throttle to compensate for the bounced landing and then landed the airplane on the runway. Subsequently, the left landing gear collapsed upward and aft, damaging the left wing strut. The airplane continued forward on its nose and left wing, departing the left side of the runway near taxiway A2.
A Federal Aviation Administration (FAA) inspector reported that the left landing gear thru-bolt was fractured. The left wing was bent upward, and the bottom and left side of the fuselage were damaged.
Metallurgical Findings
A metallurgical examination of the landing gear thru-bolt fracture revealed a primary fatigue fracture that initiated at the shank surface and propagated through about 60% of the bolt diameter. A second fatigue crack initiated on the shank surface about 180° from the primary crack and propagated through 20% to 30% of the bolt diameter. The fracture surface exhibited a narrow region of overstress fracture between the two fatigue crack regions.
Maintenance History
On December 13, 1978, Bellanca Aircraft Corporation issued FAA-approved service letter C-135 for inspecting landing gear thru-bolts and U-bolts. This service letter applied to the accident airplane and was issued due to reports of cracked and failed thru-bolts and U-bolts used to attach the landing gear to the fuselage frame. The service letter stated that these problems could result from one or more of the following: excessive loads during soft or rough runway operations, improper torque, or corrosion. It recommended inspections be performed on or before the next 100-hour inspection and at 100-hour intervals thereafter, with more frequent intervals if the aircraft is used in soft or rough runway operations.
The airplane owner stated that the Bellanca service letter C-135 had not been complied with, nor was it required under FAA regulations. The owner provided documentation that on September 7, 2017, an airframe annual inspection and engine 100-hour inspection were completed at tachometer time 1,817.5 hours.