Blackhawk XR Upgrade Kit Certified By FAA The Federal Aviation Administration (FAA) has given Blackhawk the Supplemental Type Certificate (STC) for its XR Upgrade Kit designed for the King Air 350-series. The XR kit allows a number of performance increases over the standard King Air 350. Notably there is a 30 to 40-knot increase in the cruising speed of the aircraft. The Maximum Take Off Weight (MTOW) of the aircraft also increases to 16,500 lbs. Climb performance is also better reaching FL350 in 18 minutes.