UA Control System
The accident UA was operated by means of C-band (signal communications), which provided for LOS control. The UA descended below LOS after the engine stopped producing power.
A secondary means of control was provided through the Iridium satellite communication system. However, in the Iridium control mode, there is limited ability to control the UA; under Iridium control, the only way to control the UA is by using autopilot hold modes. All hold modes (altitude, airspeed, and heading) must be active for the Iridium satellite to control of the UA. The hold modes were on before the lost link. If both the Iridium and LOS uplinks are active, the LOS link has priority, and the Iridium data is ignored. However, when the fuel was cut off to the engine and the UA began shedding electrical equipment to conserve battery power, the Iridium system was one of the items that was shed. The UA is also equipped with an auto-ignition system, but this system will not work unless the Iridium system is operable.
This reads like a comedy of errors in the design cycle of the Predator. The FMECA (Failure Modes, Effects, & Criticality Analysis) has more holes in it than Swiss cheese.