Event Summary
A transport airplane encountered severe turbulence while cruising at flight level 420 (FL420). The crew observed a rapid decay in airspeed and responded by lowering the aircraft's nose. This action induced negative G forces on the airplane.
Crew Actions
The negative G maneuver caused the integrated drive generators to trip offline. The crew then executed the emergency procedures for a complete electrical failure. During this time, they flew the airplane using only the standby flight instruments while electrical power was absent.
Restoration of Power
The crew successfully reestablished electrical power by starting the auxiliary power unit (APU). Subsequently, both main generators were reinstated, restoring normal electrical system operation.