?It flew so well that unless pilots were told they were in backup actuation mode I don?t think they would notice,? said test pilot Freeman. Typically, fly-by-wire uses a third hydraulic system to provide redundancy in the event of a dual hydraulic system failure. However, Gulfstream?s fly-by-wire architecture uses electric backup hydraulic actuators (EBHA): electrically controlled actuators that are primarily hydraulically powered but offer electric power as a backup. A self-contained hydraulic reservoir and motor pump allow full operation should hydraulic loss occur. 

The G650 has an EBHA at every primary control surface (elevator, rudder and aileron) as well as the outboard spoiler. These provide enhanced safety and aircraft availability because of the two different power sources. The self-contained actuators also offer an advantage following extremely rare failure scenarios, such as a rotor burst. 

The Dec. 21 G650 flight began with evaluating the electric backup-mode handling qualities in one axis and then progressed to full evaluations in all axes (pitch, roll and yaw). The test conditions consisted of all flap settings at 10,000 feet for speeds ranging from 1.13 reference stall speed (VSR) to maximum flap extended speed (VFe).