Saratoga, WY, USA
N7569A
ABBETT GERRY LANCAIR EVOLUTION
While in cruise flight at 27,000 ft mean sea level, the experimental, amateur-built airplane’s windshield shattered, followed immediately by a rapid decompression of the cabin. The pilot performed an emergency descent and landed uneventfully. The windshield was substantially damaged. Examination revealed that the fracture originated from a small crack located at the exterior surface of the windshield within the bonded edge. The presence of parallel linear scratches near the fracture origin and on the windshield edge suggests that the bonded area was not sanded in accordance with the build instructions. The evidence also suggests that the in-service stresses in the as-manufactured windshield were high enough to cause fractures from scratches that deviated from the build instructions; therefore, it is likely that the windshield failure was the result of stress concentrations in the bond area due to scratches made with methods inconsistent with the build instructions.
On February 7, 2021, about 1844 mountain standard time, an experimental, amateur-built Lancair Evolution airplane, N7569A, was substantially damaged when it was involved in an accident near Saratoga, Wyoming. The pilot and the two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, while diverting to an airport to assess a landing gear issue and during cruise flight at 27,000 ft mean sea level (msl), he heard an “explosion” that knocked the headsets off the airplane occupants’ heads immediately followed by a rapid depressurization of the cabin. The pilot reduced power to idle, deployed the landing gear, and entered a rapid descent. Once the airplane was in an established descent, the pilot activated the autopilot and configured it to level off at 12,500 ft msl in the event they lost consciousness. The pilot stated that he did not don the oxygen mask or headset because he did not feel comfortable removing his hands from the controls given the operational and environmental conditions at the time. After leveling the airplane at 12,500 ft msl, the pilot searched for the closest airport and subsequently landed without incident. Postaccident photographs showed substantial damaged to the windshield. According to the pilot, the airplane received annual inspections from a maintenance facility in Redmond, Oregon, from its construction to the date of the accident. The maintenance facility that built the airplane in 2016 and performed condition inspections in the years that followed reported that they did not perform any work on the windshield. The windshield was manufactured from 3/8-inch-thick cast polymethyl methacrylate, commonly referred to as acrylic. According to the manufacturer’s build instructions, once the outer edges of the windshield are cut and smoothed to fit within a joggle around the windshield, the interior and exterior bond surfaces are sanded first with 80 grit abrasive paper along the edge of a reference tape. The entire bond area is then sanded with 40-grit paper using a dual action (DA) sander. Once the sanding is complete, the bond areas are cleaned using alcohol and the exterior bond surface is bonded to the frame using a Hysol 9360 epoxy. The interior bond surface is bonded with a wet layup of carbon fabric and Rhino 1307-LV epoxy resin and hardener. The manufacturer reported that the sanding would have taken place at the airplane kit manufacturer’s facility. Examination at the NTSB materials laboratory identified the primary crack origin at the lower right side of the windshield at the exterior surface of the windshield and a fracture that emanated from that origin area. Elliptical scratches were observed across most of the bond surface, consistent with the use of a DA sander; however, many edges around the circumference of the windshield exhibited a flat chamfer with linear grinding marks on the flat portion along with deep parallel grooves. According to the build instructions, the edge of the windshield required the use of a DA grinder for a rounded (bull nose) edge profile. The windshield also contained cracks emanating from elliptical scratches in bond areas on the exterior surface near the origin and the interior surface near the upper edge. The windshield edge was similar to the edge of a windshield that was analyzed as part of a separate accident investigation (NTSB accident number WPR17LA104), where cracks were observed emanating from grooves at the flat chamfered edge.
A windshield failure during cruise flight due to stress concentrations in the bond area as a result of improper assembly of the windshield.
Source: NTSB Aviation Accident Database
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