Accident Overview
On February 7, 2021, about 1844 mountain standard time, an experimental, amateur-built Lancair Evolution airplane, registration N7569A, was substantially damaged during an accident near Saratoga, Wyoming. The pilot and two passengers were not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Pilot Account
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), an “explosion” was heard that knocked the headsets off all occupants, immediately followed by a rapid cabin depressurization. The pilot reduced power to idle, deployed the landing gear, and entered a rapid descent. Once the airplane was in an established descent, the autopilot was activated and configured to level off at 12,500 ft msl as a precaution if consciousness were lost. The pilot 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. After leveling the airplane at 12,500 ft msl, the pilot located the closest airport and landed without further incident.
Aircraft and Windshield Details
Postaccident photographs showed substantial damage to the windshield. According to the pilot, the airplane had received annual inspections from a maintenance facility in Redmond, Oregon, from its construction until the accident. That facility, which built the airplane in 2016 and performed subsequent condition inspections, reported no work performed on the windshield. The windshield was manufactured from 3/8-inch-thick cast polymethyl methacrylate (acrylic). Per the manufacturer’s build instructions, after cutting and smoothing the outer edges to fit within a joggle, the interior and exterior bond surfaces are sanded first with 80-grit abrasive paper along a reference tape, then the entire bond area is sanded with 40-grit paper using a dual action (DA) sander. The bond areas are then cleaned with alcohol, and the exterior bond surface is bonded to the frame using Hysol 9360 epoxy, while the interior bond surface is bonded with a wet layup of carbon fabric and Rhino 1307-LV epoxy resin and hardener. The manufacturer noted that sanding would have been performed at the airplane kit manufacturer’s facility.
NTSB Materials Examination
Examination at the NTSB materials laboratory identified the primary crack origin at the lower right side of the windshield on the exterior surface, with a fracture emanating from that area. Elliptical scratches were observed across most of the bond surface, consistent with DA sander use. However, many edges around the windshield circumference exhibited a flat chamfer with linear grinding marks and deep parallel grooves. Per the build instructions, the edge required a rounded (bull nose) profile using a DA grinder. Additionally, cracks were found emanating from elliptical scratches in bond areas on the exterior near the origin and on the interior near the upper edge. The windshield edge resembled that of a windshield analyzed in a separate accident (NTSB accident number WPR17LA104), where cracks were observed emanating from grooves at the flat chamfered edge.