What happened
On March 12, 2004, a Cessna 421C, registration OK-JIP, was performing an IFR flight between Prague Kbely (LKKB) and Vlašim (LKVO). While climbing through FL 210 at a rate of 800 ft/min, the crew noted a hollow sound and a slight change in cabin noise. After verifying that all instruments were operating normally, the pilot continued the climb.
Upon reaching FL 230, the aircraft suffered a rapid cabin decompression caused by the shattering of the right pilot-side windshield. The pilot immediately terminated the climb and initiated an emergency descent to a safe altitude. Following an assessment of the situation, the pilot decided to return to Prague Kbely. The subsequent landing on runway 2ical 24 was hard due to a crosswind and ground turbulence.
No injuries were sustained by the crew. However, the aircraft sustained extensive damage, including a shattered windshield, damaged cockpit frame, and damage to both engines and avionics resulting from the steep descent. The pressure change also damaged the aircraft's airframe, landing gear, and interior components, with some items being sucked out of the cabin during the event. Total damages were estimated at approximately 10,000,000 CZK.
The investigation
The ÚZPLN investigation focused on the structural failure of the cockpit glazing and the subsequent emergency descent. The investigation examined the aircraft's maintenance history, noting that a manufacturer service bulletin (MEB03-4) had been implemented during a recent annual inspection with no defects found. The investigation also reviewed the meteorological conditions, which were found to be suitable for flight, and the pilot's qualifications, which were confirmed to be valid and in order.