With a few exceptions, the typical personal aircraft is relatively reliable. Modern, solid-state avionics rarely break, we long ago figured out how to build and maintain mechanical flight instruments and, presuming the airframe is both flown and maintained regularly, dispatch reliability of personal aircraft often can be compared to the modern automobile. But, stuff does break every now and then, usually right before were prepping to launch for a family vacation or an important business trip. Some failures automatically mean going via human mailing tube; others often can be resolved after a couple of hours in the shop. In between those two extremes are equipment failures which may reduce the aircrafts capabilities, but dont materially affect either its airworthiness, ability to fly or safety.