Summary
We propose to adopt a new airworthiness directive (AD) for certain Hawker Beechcraft Corporation (HBC) Model 390 airplanes. This proposed AD would require you to remove the current preformed packing, elbow fitting, and jam nut from the left and right hydraulic pump pressure output port and replace with new parts. This proposed AD would also require you to install a hydraulic pump case drain check valve. This proposed AD results from nine occurrences of hydraulic fluid leaking from the engine hydraulic pump output fitting as a result of an improperly installed elbow connecting the output port to the pulse dampener hose. We are proposing this AD to prevent hydraulic fluid leaks from the left and right hydraulic fluid pump and to prevent the flow of hydraulic fluid into the engine compartment. The loss of hydraulic fluid can result in loss of airplane hydraulic system pressure and the consequent loss of hydraulic system functions including gear extension/retraction, spoiler functions, and anti-skid braking system actuation. The inability of the hydraulic installation to isolate flow of hydraulic fluid could result in a hazardous amount of flammable fluid in the corresponding engine compartment. These conditions, if not corrected, could result in loss of system functions and/or fire in the engine compartment.