Summary
We propose to adopt a new airworthiness directive (AD) for certain Hawker Beechcraft Corporation Model 390 airplanes. This proposed AD would require you to inspect the essential bus lightning strike protection for proper installation of metal oxide varistor (MOV) and spark gap wiring. This proposed AD would also require you to rework the wiring as necessary to achieve the required lightning strike/surge protection. This proposed AD results from a report that the wires to the MOV and spark gap were swapped. We are proposing this AD to detect and correct improper installation of the MOV and spark gap wiring, which could result in overload of the MOV in a lightning strike and allow electrical energy to continue to the essential bus and disable equipment that receives power from the essential bus. The disabled equipment could include the autopilot, anti-skid system, hydraulic indicator, spoiler system, pilot primary flight display, audio panel, or the 1 air data computer. This failure could lead to a significant increase in pilot workload during adverse operating conditions.