What happened
On June 12, 2012, a Hawker Beechcraft Beechjet 400A, modified to a Nextant 400XT with registration N400AJ, experienced a significant electrical failure during its departure from Zurich Airport. During the pre-takeoff phase, the crew performed a master test sequence. This procedure, which involved rotating a test switch, inadvertently disconnected both generators from the aircraft's electrical bus. Because the crew did not notice that the generators remained offline, the aircraft's entire electrical system began running solely on the main battery and uninterrupt and power supplies (UPS).
As the aircraft entered cloud cover, the depletion of the battery caused the failure of the Flight Management System (FMS) 2 and subsequent system outages. The pilot in command eventually informed Air Traffic Control that the aircraft had lost almost all electrical power. To manage the situation, the pilot switched the battery to emergency mode. While the pitch trim remained functional, roll trim capabilities were lost. The crew decided to perform an immediate emergency landing at Zurich.
The aircraft touched down on runway 14 shortly before the midpoint of the runway at a high speed. The heavy braking required to stop the aircraft before taxiway H1 caused the wheel brakes to exceed their maximum operating temperature, resulting in the loss of pressure in the main landing gear tires due to overheated fuse plugs.
The investigation
An investigation by the Swiss Transportation Safety Investigation Board (SUST) examined the technical modifications of the aircraft, the crew's training, and the operational procedures used during the flight. The investigation focused on the electrical system changes following the conversion from a standard 400A to the 400XT model, specifically how the master test switch interacts with the generators and how the repositioning of warning indicators affected crew awareness.
Findings
- The N400AJ had undergone significant modifications, including new engines and upgraded avionics.
- The master test switch, while physically unchanged, functioned in a way that disconnected both generators from the bus when moved from the OFF position to certain test sequences.
- The modification to the 400XT moved the Master Caution/Master Warning panel from the instrument panel to the lower edge of the overhead panel, altering the crew's field of view for warnings.
- The crew used a mix of outdated and current checklists during operations.
- The crew error during pre-takeoff preparations was the primary cause of the electrical failure.
- Contributing factors included a lack of systematic work patterns, inadequate crew documentation, and insufficient difference training regarding the modified cockpit layout and new working documents.