Flight procedures for the Northrop Grumman RQ-4A Global Hawk high-altitude, long-endurance unmanned air vehicle (UAV) have been modified following the US Air Force's investigation of the crash on 29 March last year that destroyed a $45 million Global Hawk.
The accident occurred when the UAV inadvertently received a flight termination signal broadcast from Nellis AFB, Nevada, which was outside the frequency co-ordination zone in which the UAV was being flown (Flight International, 6-12 October, 1999).
Frequency deconfliction is required only within one training area. The Edwards, California, and Nellis ranges are in separate areas, and frequency management is not required during daily operations.
Investigators say there is a greater potential for signal overlap because of the RQ-4A's high altitude operations. Col Craig McPherson, director of the Global Hawk project says: "The flight termination approach for the Global Hawk has been modified to preclude the type of incident experienced on 29 March."
No Edwards test range flight termination transmitters were operating at the time of the RQ-4A flight, but one at Nellis, north-east of Edwards, was being tested in preparation for Global Hawk flights the month after the accident.
Source: Flight International
