The NTSB has found "pilot error" as the main causal factor behind a Predator crash back in April 2006 according to The Washington Post:
The pilot's computer console locked up, investigators said. He started to transfer control to a backup console used by Customs agents to operate the drone's cameras but did not follow a checklist that required him to make sure the engine controls on the second console matched the ones he had been using.Because the second console's controls were in the fuel shut-off position, investigators said, the Predator-B's engine quit when control was switched.The pilot, who did not understand why his plane kept descending, turned off ground communication with the drone to trigger its automatic emergency responses, according to investigators. Under such conditions, the plane should have climbed to 15,000 feet and circled above a designated spot until communication was reestablished. But without engine power, the plane crashed.The pilot told investigators that he didn't follow the checklist because he was in a hurry, said Pam Sullivan, an NTSB investigator.Under Customs guidelines, the pilot did not have enough hours on the Predator-B to fly the plane without an instructor in the room, and the instructor was in another building, Sullivan said.
Ah, sweet solace. It does an aging aviator's heart good to see the more things change, the more they stay the same.