What happened
On the morning of 3 December 2025, the pilot of a Cessna Aircraft Company 340, with 4 passengers on board, departed Gnowangerup Airport for a private business flight to Jandakot Airport, Western Australia, under instrument flight rules (IFR).
After departure, as the aircraft was climbing through flight level 110 (11,000 ft above mean sea level), the left side cockpit window failed (Figure 1) and was ejected from the aircraft, which rapidly depressurised. The pilot assessed the situation, and after ensuring continued aircraft controllability, requested clearance to descend and traffic information from air traffic control. A descent to 8,000 ft followed and the aircraft was subsequently cleared for a direct track to Jandakot. With the aircraft stable, the pilot and passengers examined the exterior, and with no airframe or control surface damage evident, continued the flight to Jandakot, where the approach and landing were uneventful.
Figure 1: Failed left cockpit window
Source: Aircraft operator
Engineering information
The Cessna 340 is a 6-seat pressurised twin-engined aircraft with a maximum take-off weight of 2,717 kg. It was introduced in 1972, with production continuing until 1984, with 1,351 aircraft built. The 340 cockpit is framed with 4 acrylic (plexiglass) windows – 2 forward windscreens, each with adjacent side panel windows that have smaller, inward opening quarter vent panels. The initial design of the side windows with the vent panels has been found to be susceptible to cracking and in-flight failure, and in April/May 1982 Cessna introduced Service Kits SK340-26-1/2 and issued Service Information Letter ME82-18 for earlier build 340/340A aircraft. The letter and service kits provide instructions and equipment for the reinforcement of both pilot and copilot’s side windows by adding a diagonal brace (Figure 2) behind the quarter panel vent. This supports the larger window panel and reduces the pressurisation stresses that could lead to cracking or in-flight failure such as sustained in this incident. The service letter recommended compliance within the next maintenance period but not exceeding the next 200 flight hours.
Information from the aircraft owner advised that following the incident aircraft’s importation into Australia in mid-2021, the left and right window service kits had been procured, however due to pandemic-related delays, the kits had not yet been installed at the time of the occurrence.
Figure 2: Example of reinforced cockpit side window
Source: https://jet-shades.com/shop/propeller/cessna-335-340-ultrathins/, modified by the ATSB
Safety message
Owners and operators of Cessna Aircraft Company 340 and 340A aircraft are advised to check their aircraft for the installation of cockpit side window reinforcing in accordance with Service Letter ME82-18. Where such reinforcing has not been installed, regular inspection of the windows and surrounds for evidence of cracking and degradation is recommended – particularly in areas around the quarter vent panel. Installation of Cessna Service Kit SK340-26-1/2 (or approved equivalent) is recommended.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.