Elyria, OH, USA
N21ZA
FLIGHT DESIGN CTLS
The flight instructor reported that the airplane's fixed right main landing gear collapsed during landing. He reported that the landing was "not extraordinarily hard" and that it should have been well within the airplane's typical performance. Postincident examination of the composite right main landing gear leg revealed several manufacturing defects, including wrinkled layers and layers that terminated at the surface when they should have been continuous, which reduced the landing gear leg's strength and its ability to resist longitudinal cracks. As a result of this investigation, the airplane manufacturer conducted an audit of the subcontractor that manufactured the landing gear legs. The audit revealed that, before the incident, the landing gear manufacturer had become aware of quality issues related to the mold closing process of the landing gear legs during manufacture and had implemented steps to reduce the recurrence of these issues. Based on the available evidence, the manufacturing defects in the composite main landing gear leg likely reduced the leg's load-carrying capacity and resulted in its eventual failure.
On October 17, 2012, about 1330 eastern daylight time, a Flight Design GMBH model CTLS, N21ZA, sustained substantial damage while landing on runway 25 at the Lorain Couty Airport (LPR), Elyria, Ohio. The flight instructor and student pilot were not injured. The airplane sustained minor damage to the landing gear during the mishap. The aircraft was registered to RAS Aviation LLC, Elyria, Ohio, and operated by Zone Aviation, Elyria, Ohio, under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The local flight originated at an unconfirmed time. The flight instructor reported that the flight was a training flight and on the first landing the right main landing gear collapsed. He stated that the landing was "not extraordinarily hard". He went on to add that based on his experience in the same model airplane that the landing should have been well within typical performance of the airplane. During the investigation it was discovered that this same airplane was involved in a landing accident on July 19, 2012 (CEN12LA676). The July accident also resulted in a fracture of the right main landing gear leg. The damaged right main landing gear leg from this incident was retained for further examination. The main landing gear leg was made of composite material. The fiber reinforcements used in the composite construction included unidirectional glass fibers, glass fiber fabric, and basalt fiber fabric. Flexible plastic tubes extended the length of the legs enclosed within ribbed plastic tubes located near the leading and trailing edges of the leg. Foam filled space between the plastic tubes and a center internal cavity. The legs were manufactured in a mold with the split line at the leading and trailing edges. During the layup process, layers were placed in a mold half representing the upper half of the leg, and layers were wrapped around the internal tubes, foam, center cavity, and preformed layers. The mold was then closed with a mold piece representing the lower half of the landing gear, and the center internal cavity was pressurized during curing. Examination and sectioning of the landing gear leg showed wrinkling of the fibers resulting in their orientation being angled with relation to the surface rather than parallel to the surface. Additionally several layers terminated at the leading and trailing edges. The location of theses terminating layers corresponded with the location of longitudinal cracks found along the leading and trailing edges of the landing gear. As a result of the investigation, the manufacturer of the airplane was contacted regarding the landing gear manufacturing process. The landing gear legs were manufactured by a sub-contractor to the airplane manufacturer. The airplane manufacture conducted an audit of the sub-contractor and determined that there were some previous quality issues with regard to mold closing during the manufacture of the landing gear legs. It was reported that the landing gear manufacturer had recognized these issues and had implemented steps to reduce the risk of recurrence of these issues. The airplane manufacturer also conducted a search of part requests and difficulty reports related to the main landing gear. This records search showed 3 occurrences which resulted in complete collapse of the landing gear leg out of a fleet of 370 airplanes. All other reported landing gear leg fractures were discovered either during inspection after a hard landing, or during taxi operation when significantly reduced stiffness was encountered.
The manufacturing defects in the main landing gear leg, which resulted in its eventual failure.
Source: NTSB Aviation Accident Database
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