What happened
On 23 October 2020, a Beech B2/200, registration G-YVIP, was performing a private flight on final approach to Bournemouth Airport. While at an altitude of approximately 1,200 ft, the crew observed a yellow glow and smoke emanating from behind the commander's circuit breaker panel shortly after deploying the approach flaps.
In an attempt to manage the emergency, the crew operated the master switch gang bar to disconnect the battery and generators, but the smoke and glow persisted. The crew declared a mayday. During the descent, the first officer attempted to access the fire extinguisher located under his seat, though shoulder straps hindered his movement. The aircraft landed safely on the runway, and the crew evacuated. Although the airport fire service attended, the smoke dissipated once the aircraft engines and systems were shut down.
The investigation
An investigation by the operator identified that the commander's circuit breaker panel had sustained damage from overheating and moisture. Specifically, the back-lighting circuit board showed evidence of burning.
The panel is situated directly beneath the left storm window. While the window seal was found to be serviceable, the investigation noted that water often accumulates on the exterior of this window and can leak into the cockpit when the window is opened. The operator noted that while they typically hangar their aircraft, G-YVIP had recently joined the fleet and had likely been parked outside during rain. Additionally, the crew had been frequently opening the storm window to ventilate the cockpit following the use of a sterilization agent used during the COVID-19 pandemic, which may have facilitated the entry of rainwater.