What happened
During cruise flight, the pilot heard a loud noise followed by air entering the cockpit. The pilot initially reduced power, unsure of the issue. After checking for visible problems and finding none, the pilot added power but could not maintain altitude or control direction. A forced landing was attempted, during which the aircraft nosed over onto its back.
The investigation
Examination revealed that fabric at the top of the outside windscreen had separated, creating a large scoop area. This defect occurred because Airworthiness Directive 74-17-04, requiring installation of Piper Service Kit #754-404, had not been complied with.
Findings
The structural failure of the windscreen fabric directly caused the loss of control and subsequent ground impact. The root cause was non-compliance with a mandatory airworthiness directive designed to prevent this specific failure mode.