The military surveillance blimp that broke free of its mooring at Aberdeen Proving Ground Wednesday morning has returned to Earth after a four-hour, 160-mile, power line-snapping odyssey, authorities said.
NORAD spokesman Michael Kucharek said the runaway aircraft was on the ground near Moreland Township, Pa. — 160 miles north of its mooring in Edgewood — and was deflating. The blimp had slowly been losing helium, he said, and appears to have drifted to the ground.
Pennsylvania State Police Trooper Angela Bieber said the balloon was "contained."
"It is no longer moving," she said.
Beiber said police had not received any reports of injuries. She said the military was trying to recover the blimp.
"It's still definitely in progress," she said.
The 243-foot-long, helium-filled JLENS aerostat, part of an over-the-horizon surveillance system being tested at Aberdeen Proving Ground, detached from its mooring in Edgewood at about 11:54 a.m., a spokeswoman for the Army installation said.
Two F-16 fighter jets were scrambled from an Air National Guard base in Atlantic City, N.J., to monitor the unmanned aircraft, and NORAD said it was working with the Federal Aviation Administration to ensure air traffic safety.
The blimp was trailing 6,700 feet of cable. Authorities warned onlookers away.
"Anyone who sees the aerostat is advised to contact 911 immediately," Aberdeen Proving Ground spokeswoman Heather Roelker said. "People are warned to keep a safe distance from the airship and tether as contact with them may present significant danger."
State police in Columbia County, Pa., said they had received reports of blimp sightings. Witnesses reported seeing the blimp drifting between Jerseytown and Turbotville, a sparsely populated area north of the state capital of Harrisburg.
Its tether was snapping power lines. The local electric utility, PPL, reported about 20,000 customers without power in the area, although it was unclear how many could be attributed to the blimp. Bloomsburg University canceled classes, citing a "widespread power outage.
Similar aircraft have been used extensively in the Iraq and Afghanistan wars to provide ground surveillance around U.S. bases and other sensitive sites.
"My understanding is, from having seen these break loose in Afghanistan on a number of occasions, we could get it to descend and then we'll recover it and put it back up," Defense Secretary Ash Carter said in a brief exchange with reporters at the Pentagon. "This happens in bad weather."
NORAD spokesman Michael Kucharek said the command was working with other agencies "to address the safe recovery of the aerostat."
The office of Pennsylvania Gov. Tom Wolf said it was "closely monitoring the situation."
"The Governor's Office is in communication with the Pennsylvania Emergency Management Agency, the Pennsylvania State Police, the National Guard, and the appropriate authorities with the federal government," the office said in a statement. "We will work with the appropriate authorities to respond to any resource requests and assist in any way possible."
The Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System, or JLENS, has become a fixture of the Baltimore skyline since the first of the two blimps was launched over Middle River in December.
When aloft, the aircraft use sophisticated radar to see up to 340 miles in any direction, which covers an area from North Carolina to the Canadian border. It can be used to track ships at sea and cars on land.
Authorities say the system is intended to watch for and direct fire on incoming cruise missiles and other threats. NORAD is running a three-year exercise to test its effectiveness in the National Capital Region.
The effort has proved controversial. After 17 years of research and $2.7 billion in funding, the system has been hobbled by defective software, poor reliability and vulnerability to bad weather.
Privacy advocates, meanwhile, have expressed concern about deploying such sophisticated surveillance technology over the United States.
The blimps are moored to the ground with thick, 10,000-foot cables that can transmit the data they collect back to earth. They're designed to stay aloft in winds of up to 70 knots, and remain in the air even if their skin is pierced.
Raytheon, the contractor that makes the blimps, says the cable is unlikely to break.
"The chance of that happening is very small because the tether is made of Vectran and has withstood storms in excess of 100 knots," the company said on its website. "However, in the unlikely event it does happen, there are a number of procedures and systems in place which are designed to bring the aerostat down in a safe manner."
Bad weather has caused problems for JLENS in the past. In 2010 a blimp was completely destroyed when it collided with another blimp at a facility in North Carolina.
The Associated Press contributed to this article.