Airworthiness Directives; Hawker Beechcraft Corporation Model 390 Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Hawker Beechcraft Corporation Model 390 airplanes. This AD requires you to modify the cabin barometric pressure switch and cabin altitude high switch installations and perform a functional test of the switches and related systems. This AD results from the possibility of barometric pressure switch electrical connections being incorrectly connected or inadvertently disconnected. We are issuing this AD to modify the cabin barometric pressure switch and cabin altitude high switch to prevent them from becoming incorrectly connected or inadvertently disconnected, which may result in no CABIN ALT HI annunciation in the cockpit and no automatic deployment of the cabin oxygen masks. This failure could lead to incapacitation of the crew due to hypoxia with possible inability to control the airplane.