A Predator B just prior to touchdown at Libby Army Airfield in Sierra Vista in November 2010. 

Benjie Sanders/Arizona Daily Star

A new Predator B unmanned aircraft arrived Tuesday in Arizona, becoming the fourth in U.S. Customs and Border Protection's Arizona fleet.

The aircraft, also known as a "drone," will be used to patrol the U.S.-Mexico border.

The agency now has six Predator B's available to patrol the U.S.-Mexico borderland from the eastern tip of California and across Arizona, New Mexico and Texas. The two others are based in Corpus Christi, Texas, said a news release from Customs and Border Protection.

The aircraft, which are flown remotely by pilots in cockpits on the ground, are a valuable border enforcement tool because they can do things most manned aircraft cannot, agency officials say.

The Predator B can fly for 20 hours at a time. Its cameras can determine from as far as 10 miles away if a ground sensor was set off by armed drug smugglers or cows. And it can collect intelligence on suspicious behavior at houses without anybody below knowing because it flies so high and is quieter than other aircraft.

But critics question if this is the best use of taxpayer money and whether the Predator B might crash into other planes in the sky or people on the ground. The Federal Aviation Administration hasn't fully accepted unmanned aircraft into the national airspace because of safety concerns, limiting the hours and places they can fly.

The aircraft weighs 10,500 pounds, has a 66-foot wingspan and stretches 39 feet from front to back. The Predator B costs about $6 million, and the rest of the system needed to fly it - antennas, sensor, radar, satellite bandwidth, systems spares, maintenance and ground support - brings the per-unit total to $18.5 million.

Since the unmanned aerial system program was started in 2006, the Predator B's have flown 12,000 hours, helping to seize 46,600 pounds of drugs and apprehend 7,500 illegal border crossers and drug runners, the agency said.

On StarNet: Find extensive coverage of immigration issues at azstarnet.com/border

Contact reporter Brady McCombs at 573-4213 or bmccombs@azstarnet.com