Complex sentence: According to the unverified leak, the moment the autopilot was disconnected, the tailplane moved to a nosedive position, but pilots were unaware of it and tried to stop the nosedive with the help of elevators, pulling the control columns.
Split into simpler sentences: According to the unverified leak, the moment the autopilot was disconnected, the tailplane moved to a nosedive position. But pilots were unaware of it and tried to stop the nosedive with the help of elevators, pulling the control columns.