Incident Overview
On September 3, 2020, a Cessna 340 airplane, registration N5178J, was substantially damaged during a personal flight operated under 14 CFR Part 91. The pilot, who was the sole occupant, was not injured. The flight originated from an airport in Oklahoma and was destined for Texas.
Flight and Pressurization Details
While climbing through 17,000 ft mean sea level (msl), the pilot performed a transition check. At that point, the cabin pressure altitude was 8,000 ft and the pressure differential was 3, below the maximum allowable differential of 4.3. Approximately 50 miles southwest of Oklahoma City, as the airplane passed 18,000 ft msl, the right windscreen suddenly blew out. The pilot immediately returned to the departure airport and landed without further incident.
Damage and Windscreen Examination
The loss of the windscreen, which is considered part of the pressure vessel structure, resulted in substantial damage to the airplane. Examination of the remaining windscreen material revealed six pieces of acrylic comprising the complete outer circumference of the windshield. When laid flat, the remnants measured approximately 35 inches tall by 31 inches wide. The blown-out section, measuring about 21 inches by 31 inches, was not recovered.
Laboratory examination of the remnants found no significant signs of aging or visible crazing. The fracture surfaces were consistent with overstress separation. However, the origination point of the failure could not be identified on the available remnants.