WASHINGTON (REUTERS/AFP) - A massive high-tech US military blimp designed to detect a missile attack came loose on Wednesday and wreaked havoc as it floated from Maryland into Pennsylvania, dragging its 3,000 metre long cable behind it and knocking out power to thousands.
The US military scrambled two armed F-16 fighter jets to keep watch as the blimp - the size of an American football field -travelled into civilian airspace after coming loose shortly after mid-day from its mooring station at Aberdeen Proving Grounds, a US Army facility 64 kilometres northeast of Baltimore.
It came down several hours later in two parts in Montour County, Pennsylvania, the US military's North American Aerospace Defence Command (NORAD) told reporters.
First, the tail portion of the blimp detached and came to the ground "with no reports of other damage or casualties," Navy Captain Scott Miller said. "The remainder of the aerostat has also grounded itself in Montour County," Miller said.
It was not immediately clear how the blimp became detached from its mooring station at Aberdeen Proving Grounds.
PPL Electric Utilities Corp said that as of 3:45 am Singapore time there were about 17,800 customers without power in Columbia County, Pennsylvania, with another 9,000 out in Schuylkill County.
A local television news station said the cable attached to the helium-filled blimp was "hitting power lines and causing blackouts" in Bloomsburg.
The blimp broke loose from its mooring at Aberdeen Proving Grounds, an army installation in Maryland some 64 metres northeast of Baltimore, Maryland at around 12:20 am Singapore time on Wednesday, NORAD said.
"Anyone who sees the aerostat is advised to contact 911 immediately; people are warned to keep a safe distance from the airship and tether as contact with them may present significant danger," a statement from the Aberdeen Proving Ground said.
"NORAD officials are working closely with the FAA (Federal Aviation Administration) to ensure air traffic safety, as well as with our other interagency partners to address the safe recovery of the aerostat," NORAD said.
Pennsylvania Governor Tom Wolf's office said state and federal authorities were in contact.
"We are closely monitoring the situation, and we will work with the appropriate authorities to respond to any resource requests and assist in any way possible," it said.
The blimp is known as the Joint Land Attack Cruise Missile Defence Elevated Netted Sensor System or JLENS.
JLENS carry powerful radars that can protect an area about the size of Texas from airborne threats including unmanned aircraft, cruise missiles and other objects.
The aerostats normally fly at about 3,000 metres, and when on the ground are tied down with a Kevlar-like cable a little more than 2.5 centimetres thick.
Even before the current incident, its presence in the skies over the eastern United States had generated controversy.
Civil liberties activists worried it could be used for domestic surveillance, something the Pentagon strongly denies, saying it cannot see people and does not have cameras aboard.
Last year, the Government Accountability Office estimated the cost of the JLENS programme at US$2.8 billion (S$3.9 billion) so far. Congress, meanwhile, nearly halved JLENS' US $54 million budget for fiscal 2015.
Nearly a decade in development, only two JLENS blimps are operational.
Together the pair make up an "orbit", with the ground crew of one aerostat assigned to 24/7 surveillance and the other tasked with directing air defence missiles to intercept a cruise missile in mid-flight.
Each blimp can stay aloft up to 30 days at a time, tethered to a dark green mobile mooring station, coming down to Earth only for maintenance - like a fresh shot of compressed helium - or extreme weather.
The main JLENS contractor is Raytheon, which ironically also makes the US military's sea-launched Tomahawk guided cruise missile.
Michael Kucharek, a spokesperson for NORAD said the blimp is specifically meant to detect cruise missile attacks on the Washington, DC, region.