What happened
On August 8, 2019, at approximately 20:40 UTC, a Beechcraft C-90, registration PT-LSO, was operating a private flight from Sebastião Leal, PI, to Teresina, PI. The aircraft was carrying one pilot and six passengers. While cruising at 17,000 feet, approximately 60 nautical miles from the destination, the right cockpit window suddenly shattered, resulting in an explosive decompression.
The pilot immediately initiated an emergency descent. Due to the intense noise generated by the airflow through the broken window, establishing communication with Air Traffic Control was difficult. The pilot and passengers did not use oxygen masks, as the aircraft's operating manual specifies their use only at altitudes exceeding 18,000 feet. The aircraft landed safely at Teresina (SBTE) with light damage to the airframe, and all seven occupants remained uninjured.
The investigation
CENIPA investigators examined the aircraft's pressurization system and maintenance history. The investigation confirmed that the pressurization system, including the Out Flow Valve and Safety Valve, was functioning correctly, ruling out structural failure caused by excessive internal pressure. The aircraft'17,000-foot altitude was within its operational limits, and the cabin was set to a pressure altitude of approximately 4,900 feet.
Investigators noted that the window, made of single-layer stretched acrylic, had recently undergone maintenance. While the maintenance logs indicated that a scheduled inspection had been performed in April 2019, investigators could not verify if the specific procedures for inspecting the critical areas of the side windows were strictly followed or properly supervised. Evidence suggested a potential pre-existing condition, as the window had exhibited fogging on its lower portion during the flight, which may have indicated a slow pressure leak prior to the total failure.
Findings
- Maintenance and supervision: The investigation could not definitively determine the exact cause of the window's structural failure, but identified uncertainties regarding the adequacy of the maintenance inspection and management supervision.
- The window failure occurred in a critical area of the component that requires heightened scrutiny during maintenance.
- The pilot's instrument rating (IFRA) had expired in July 2019, though the pilot was experienced in the aircraft type and held a valid medical certificate and multi-engine rating.