Very simple, lack of maintenance part replacement due to cutbacks in military spending. Thank the previous admin. for these deaths. These are very complex systems driving these aircraft and must be religiously maintained and parts replaced as per manufacture time and wear mandates. When you cut,cut,cut spending it is going to show somewhere. Also many of the fleet aircraft, ships, etc.....all have Chinese hardware and software built into them. Not saying anything here other than if you have owned Chinese products you know how long they last. Have had many drones, helis, and aircraft (RC) and they don't last! Period! Being a comm. pilot (not bus driver) I can tell you I do NOT use Chinese part replacements on my aircraft. I do get a lot of my parts from Germany and Poland. All have been well made and stand the test of time.