As a second RQ-4A Global Hawk was lost last week over Afghanistan, Northrop Grumman was playing down the significance of a structural failure which caused an earlier loss of the unmanned air vehicle (UAV) during Operation Enduring Freedom. The first crash occurred on 30 December last year as the UAV was returning from a mission over Afghanistan.

The final US Air Force accident investigation report concludes an actuator mounting bolt and nut had been installed backwards, leading to structural failure of the Global Hawk's right V-tail and ruddervator due to massive delamination of the main spar. The Global Hawk was returning early because operators had identified an actuator problem and it went out of control while descending to land. Investigators concluded the wrongly installed bolt touched the control rod, causing it to bend. The resulting actuator's movement put the UAV into a spin, causing the tail to fail.

Northrop Grumman stresses the UAV was hand-built for the Global Hawk advanced concept technology demonstration and was not representative of production aircraft. Assembly processes and procedures are being improved.

Source: Flight International