What happened
On June 17, 2005, a Piper PA 36-285, registration F-GRDJ, was engaged in agricultural spraying operations. After completing an initial mission, the pilot landed at Montpellier Méditerranée airport to refuel. During the refueling stop, the pilot opened the right side window and exited the aircraft. To improve cockpit ventilation during the subsequent flight, the pilot decided to leave the right window in the open, folded position against the fuselage.
Following refueling, the pilot departed from runway 31. Shortly after takeoff, air traffic control notified the pilot that something appeared to have been lost from the aircraft. The pilot, noticing no immediate abnormalities, continued the flight to the home base at Montpellier Candillargues. Upon arrival and after exiting the aircraft, the pilot discovered that the right window was missing.
The investigation
The investigation focused on the window's locking mechanism, which utilizes two pins that slide into hinges and fuselage fittings. These pins feature spring-loaded balls to ensure they remain locked in place. A red release handle, connected to the pins via a cable, is used for emergency window jettisoning.
Examination of the hinges and fittings revealed that while the pins could slide normally, the internal spring-loaded balls did not protrude sufficiently to ensure a secure lock. Furthermore, the release handle was found to have moved out of its retaining clips. The investigation also noted that the aircraft had flown 180 hours since its last major overhaul, and while 50-hour inspections had been performed, the current state of the locking balls could not be verified during a standard pre-flight inspection without dismantling the release system.
Findings
- The primary cause of the window loss was the inadequate protrusion of the locking balls on the window pins, which prevented a secure engagement with the fuselage fittings.
- An involuntary movement of the release handle likely contributed to the failure, as the handle can be accidentally displaced when accessing the cockpit via the wing root.
- The pre-flight inspection was incomplete, as the pilot did not perform a secondary walk-around after refueling to re-verify the window's position and the handle's security.
- The window lacked a dedicated fastening system to hold it securely in the open, folded position during flight.