Well, although the first accident may be  related to mechanical causes based on comments by the pilot of engine failure, it could be as  simple as fuel starvation due to water in the system.  I would not jump to any conclusions as to the cause, but  there is probably a correlation to the age of any aircraft and higher maintenance needs.  The commentary by the FAA is a little indifferent and bureaucratic in saying no need to observe a plane that was probably still on radar, due to absence of a flight plan. The rules may be the rules, but where is the humanity?  Why is the computer software in this day and age not sophisticated enough to indicate an aircraft unexpectedly disappearing off the display when it probably should still be indicating a within range return, despite not being in positive control?