Incident Overview
On April 25, 2010, at approximately 1640 central daylight time, a Piper PA-46-350P, registration N46PT, incurred minor damage when the pilot side window shattered and departed the aircraft during cruise flight near Owensboro, Kentucky. The aircraft was operating under instrument meteorological conditions on an instrument flight rules flight plan. The flight, a personal trip, had departed Southern Illinois Airport in Carbondale, Illinois, and was en route to Smith Reynolds Airport in Winston-Salem, North Carolina. The certificated commercial pilot and two passengers were not injured.
The pilot reported that after leveling off at 15,000 feet mean sea level and adjusting to cruise power, the pilot side window suddenly blew out, resulting in immediate depressurization. The pilot's headset was pulled out of the aircraft. He then used the copilot-side headset to contact air traffic control, who provided radar vectors and cleared the aircraft for an instrument landing system approach to Owensboro-Daviess County Airport. The pilot landed without further incident.
Examination and Findings
Approximately 30 percent of the window's original surface area remained attached to the aircraft. This portion was sent to the NTSB Materials Laboratory for analysis. The laboratory report indicated that a primary overstress fracture originated from the radius of the storm window cutout on the pilot side window. The fracture propagated aft and downward relative to the window's installed position. Additional fractures along the top and forward edge of the window were secondary overstress cracks associated with the overall in-flight loss. Detailed examination near the initiation point revealed preexisting craze cracks with a thumbnail shape, emanating from the edge radius or flat face of the storm window cutout.
Service Bulletin History
On December 13, 2006, the airframe manufacturer issued Service Bulletin (SB) Number 1175, which required repetitive inspections or replacement of the pilot side window. The inspection focused on the lower aft corner of the storm window for cracking, mandated after the first 350 hours in service and every 50 hours thereafter. If cracks were detected, replacement was required, with continued inspection at the same intervals. In May 2007, the bulletin was superseded by Revision A (SB 1175A), which allowed installation of a newly designed window without the storm window. Upon installation, the repetitive inspection requirement was eliminated. After the incident, Revision B was released, expanding the inspection area and including a photograph from the incident window as an example of the cracking to inspect for.
Maintenance Records
Review of the incident airplane's available airframe maintenance records by a Federal Aviation Administration inspector revealed no evidence that the inspection or replacement of the window had been performed in compliance with any revision of the service bulletin.