The US Customs and Border Protection (CBP) Agency has grounded its fleet of nine remaining General Atomics Aeronautical Systems Predator Bs, as a safety investigation continues over a crash caused by a mechanical failure.

A CBP flight crew intentionally ditched the medium-altitude, long-endurance unmanned air vehicle at about 23:15 local time on 27 January in the Pacific Ocean, about 17.4nm (32.2km) off the coast of San Diego, the agency says in a statement. The action was performed because of a mechanical failure, which was believed to have been related to the UAV’s electrical power system.

“The crew determined that the [UAV] would be unable to return to where it originated in Sierra Vista, Arizona, and put the aircraft down in the water,” the CBP says.

The US National Transportation Safety Board (NTSB) has joined the CBP’s investigation of the mishap, which is the second involving one of its Predator Bs. The CBP has also informed the US Federal Aviation Administration, it says.

The CBP's Predator Bs are equipped with the Raytheon SeaVue maritime surveillance radar, and used to detect smugglers.