On Dec. 4, an RQ-170 Sentinel surveillance drone crashed in Iran; a U.S. official involved in the program blamed a lost data link and another unspecific malfunction. Two weeks later, an unarmed Reaper drone crashed at the end of a runway in the Seychelles. "This should not be a surprise," a defense official told Aviation Week & Space Technology, saying the United States had already lost more than 50 drones. As of July 2010, the Air Force had identified 79 drone accidents costing at least $1 million each. The primary reasons for the crashes: bad weather, loss or disruption of communications links, and "human error factors," according to the Air Force. As Lt. Gen. David Deptula, former Air Force deputy chief of staff for intelligence, has noted with refreshing honesty, "Some of the [drones] that we have today, you put in a high-threat environment, and they'll start falling from the sky like rain."