Air Force officials say design and training improvements have lowered the Predator's accident rate. They say lessons learned from that plane's problems have solved some issues for the larger and more potent Reaper, in use in combat since 2007. Accident rates per 100,000 hours dropped to 7.5 for the Predator and 16.4 for the Reaper last year, according to the Air Force. The Predator rate is comparable to that of the F-16 fighter at the same stage, Air Force officers say, and just under the 8.2 rate for small, single-engine private airplanes flown in the U.S.
The crash figures do not include drones flown over Pakistan by the CIA, which does not acknowledge the covert program. But independent experts said Predators flown over Pakistan probably experience problems similar to those flown by the Air Force in Afghanistan and Iraq.
Four Air Force Predators have crashed this year, three of them in Afghanistan — on Jan. 15 in southern Afghanistan, one on takeoff Feb. 9 in eastern Afghanistan, and a third March 14 in the southern part of the country. All were total losses, the Air Force said. Another Predator crashed in California during a training exercise April 20.
In the 12 months ended Sept. 30, the Air Force reported 16 Predator and Reaper accidents. Four involved crashes during a 15-day period in September. On Sept. 13, a pilot inside a ground station in Nevada lost video and data links to a Reaper over Afghanistan. As it was about to exit Afghan airspace and crash, an F-15 pilot was ordered to shoot it down and ground troops recovered the wreckage to keep top-secret technology out of insurgents' hands.
In another case, a drone crashed into a Sunni political headquarters in Mosul, Iraq. No injuries were reported.
In some cases, a cause is never determined and no wreckage is recovered. On May 13, 2009, a crew in Nevada lost contact with a Predator, and it was listed as "presumed crashed" somewhere in Afghanistan, according to an Air Force report.
Retired Gen. Wesley K. Clark, asked whether high drone mishap rates concerned him, replied: "Not really. They're expendable." Others disagree, saying every drone that goes down is one less available for troops in need.
"We can't treat these things like disposable diapers and just throw them out," retired Air Force Gen. Hal Hornburg, former chief of the Air Force Air Combat Command, warned officers at a conference on drones.
Kyle Snyder, who tracks military drones for the Assn. for Unmanned Vehicle Systems International, a nonprofit research group, said he had never heard anyone in the Air Force call drones expendable.
A 2007 study by the Air Force Research Laboratory found that up to 80% of Predator crashes involved some degree of human error. Updated studies attribute more recent accidents to inadequate manuals, crew coordination mistakes and crews being asked to perform tasks for which they are not fully trained, according to an analysis by the Air Force and a private contractor.
After a Predator crashed during a landing at Kandahar air base in March 2007, investigators faulted the Predator system for a "lack of visual cues" to help pilots understand the position of a plane flying half a world away. The pilot in Nevada misjudged the drone's altitude, the investigative report said.
The Predator that ran out of fuel over Iraq had a leak, but there was no gauge to warn the pilot, an Air Force crash researcher said. And a pilot trainee at Creech Air Force Base in Nevada crashed a Predator by hitting the "kill engine" switch instead of the adjacent landing gear switch, according to an investigative report.
Some ground control stations, where pilots and camera operators sit, still have 1990s-era text-based computer systems. Pilots have to type function and control commands rather than clicking on icons.
"There's a control delay between typing something and having it actually happen on the airplane," said Gregg Montijo, a contractor who trains drone crews. "When the heat is on, sometimes guys will type something in, then type it again real quickly. They'll confuse the computer and get the wrong display and get into a vicious cycle."
Despite the mishaps, Burdine said, Predators and Reapers are doing great work. "It's a big payoff for the Air Force to make sure the next generation of systems learns from the first generation," he said. "And that's what we're doing."