Domestic US training flights with the Northrop Grumman RQ-4 Global Hawk could resume this month if the US Air Force and Federal Aviation Administration agree new procedures for operating the unmanned air vehicle from Beale AFB in California.

Flights were halted on 21 November after a Global Hawk briefly lost datalink communications with the ground while recovering to Beale, after the first routine training mission in US civil airspace. Beale crews are continuing to fly RQ-4s over Iraq.

The link was interrupted as the Global Hawk was spiralling down to land at Beale, using a profile similar to that for the manned Lockheed U-2. This was designed to keep the UAV within an 18.5km (10nm) radius of the base while descending through civil airspace below 18,000ft (5,500m).

Following a pre-programmed 30s delay after loss of the link, the UAV autonomously initiated a climb and transmitted an alert to air traffic control. Communications with the ground station were quickly regained and the Global Hawk resumed its approach.

Northrop believes the link loss may have been caused by the UAV entering a communications dead zone over its ground station. This could be overcome by changing the descent profile and providing redundant datalinks, it says.

Source: Flight International