Global Hawk Crashes: Who’s to Blame?

By Michael Peck

Mishaps that destroyed or badly damaged four out of seven Global Hawk prototypes resulted from errors or decisions made by Air Force operators, said the Global Hawk manufacturer, Northrop Grumman Corp.

Though Air Force statements generally match Northrop Grumman’s version of events, the manufacturer claims that the crashes were preventable, and do not reflect any flaws in the Global Hawk’s design.

Without disputing the findings of the Air Force’s accident boards, which mostly suggest manufacturer responsibility, Northrop Grumman argues that there is another side to the story. “We look much better than many people think,” said Timothy Beard, Northrop Grumman’s director of business development for unmanned vehicles.

For its part, the Air Force declined to provide additional information on the incidents, beyond what already was published in news releases and accident reports.

The Air Force said that a March 1999 mishap occurred when a Global Hawk controlled by operators at Edwards Air Force flew so high that it lost the Edwards signal and inadvertently responded to a termination signal emanating from Nellis Air Force Base. In a December 1999 incident, a Global Hawk was badly damaged when it overran the runway during a taxiing test. The Air Force investigation blamed it on a combination of known software problems between the aircraft’s mission planning systems. Beard said operators ignored Northrop Grumman’s warning that a ground speed of 155 knots was excessive given the length of the Edwards AFB runway and the aircraft’s braking capacity.

The two most recent crashes occurred over Afghanistan in December 2001 and July 2002. According to an Air Combat Command Accident Investigation Report, the primary cause was structural failure of the right V-tail and rudder-elevator assembly, due to a control rod bent “by coming in contact with an improperly installed actuator nut plate bolt.” Beard acknowledged that the problem was mainly “due to maintenance manufacturing and installation error.” Yet, he also said that it was not fatal, and that the Global Hawk could have been saved had Air Force rules of engagement allowed the operators to divert it to bases in nearby friendly nations, rather than returning it to its launch point after the problem was detected.

If the aircraft had been a manned U-2, it would have been diverted to the first available base, Beard said. He added that the Global Hawk managed to fly 6.5 hours after the tail mechanism failed, but crashed during landing.

For a July 2002 mishap, Air Force investigators blame an engine malfunction on “failure of a single fuel nozzle in the high-flow position that eventually caused internal failure of the engine,” leading to a crash during an attempted emergency landing. Beard counters that although operators did not know why the Global Hawk was losing altitude—because the aircraft’s telemetry did not indicate a reason—they should have stopped running the engine at 100 percent power.

“Most of us who have flown airplanes realize that if something like this happens, and I’m not getting any information as to why, we’ve got a problem, and we had better bring it on home and reduce the throttle,” said Beard, a retired admiral and naval aviator. As with the previous mishap, the aircraft could also have been diverted to a friendly country, Beard added.

He said that it was ironic that the reliability goals initially set for Global Hawk by the Defense Advanced Research Projects Agency were too low. “Predicted Global Hawk reliability exceeds those goals today,” he said, estimating reliability at the current test stage at 9.5 per 100,000 flight hours, and rising to 5.1 when Global Hawk enters production. Two are scheduled to be built this year, four next and then six every subsequent year. Beard estimated the cost of production models at about $35 million, though other estimates put the price tag as high as $50 million, depending on the sensor package.


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