Members of Congress pressed for more information about how a giant surveillance balloon broke free of its moorings at Aberdeen Proving Ground, as Pennsylvania state troopers resorted to shotgun blasts Thursday to deflate the grounded aircraft.
The unmanned aerostat escaped from the Army installation about noon Wednesday and drifted 160 miles north before returning to earth near Moreland Township, Pa., some four hours later.
The 243-foot JLENS balloon, one of two that have hovered over the Baltimore area this year, traveled at an average speed of 40 mph while trailing 6,700 feet of cable. Authorities scrambled two F-16 fighter jets from a base near Atlantic City, N.J., and warned onlookers away.
The aircraft eventually lost helium and came down, the military said. No injuries were reported, but the balloon snapped power lines in Pennsylvania, cutting power to thousands of customers.
Rep. C. A. Dutch Ruppersberger, whose district includes Aberdeen Proving Ground — and who in 2013 promoted the Pentagon's plan to bring the JLENS over-the-horizon radar system to Maryland for a three-year exercise — said Thursday he had asked the military for a full report on the incident.
"I want to find out what happened, who's accountable and how we're going to fix it," he said.
Officials had few answers Thursday. The Army pledged a thorough investigation; a second balloon was hauled down Wednesday and grounded indefinitely.
Sen. Barbara A. Mikulski asked commanders to review whether the exercise should continue.
"The Army must investigate the danger this incident posed to communities and determine what action needs to be taken to ensure this never happens again," Mikulski wrote in a letter to Army Secretary John McHugh. "Determine whether operational testing for JLENS should continue."
Reps. Jason Chaffetz and Elijah e. Cummings, the Republican chairman and the top Democrat, respectively, on the House Committee on Oversight and Government Reform, sent letters to the secretaries of defense and transportation demanding information about JLENS contracts and reliability studies and a briefing by the end of next week.
"This event raises questions about the value and reliability of JLENS," the congressmen wrote. They noted that the system, which is supposed to detect incoming cruise missiles and other threats to the National Capital Region, failed to spot a gyrocopter in April as it approached and landed on the West Lawn of the Capitol.
There were indications Thursday that the balloon's emergency systems might have functioned improperly.
In NORAD briefing documents obtained by The Baltimore Sun, military planners wrote last year that the aircraft would deflate automatically if it lost power or reached a certain altitude. If that didn't occur, the planners wrote, the deflation system could be activated remotely.
Once it was deflated, planners wrote, the balloon would be on the ground in four minutes.
A NORAD spokesman said the performance of that system would be part of the military investigation.
The balloon also defied the planners' expectations about how far it would travel from its mooring at G-Field in the Edgewood Area of Aberdeen Proving Ground.
In a past briefing for the Maryland Emergency Management Agency, planners said there was a 90 percent chance the balloon would come down within 12.5 miles of its base, most likely to the south or east.
Given those predictions, officials in Kent County say they have been raising questions about the safety of the balloon system for months. County Commissioner William A. Short said he asked military leaders a year ago about the danger, if the balloon ever escaped, of the dangling tether.
"They assured it was in good standing and it would never happen," Short said.
"They shouldn't go back up, they really shouldn't. They should learn a valuable lesson."
While NORAD and Raytheon, the contractor that manages JLENS, said the chance of a balloon coming loose was exceedingly remote, the briefing documents show that the military was aware of the dangers if it did.
In the MEMA briefing, planners warned that the batteries in the deflation system could cause burns, the balloon could suffocate or crush anyone trapped underneath, and the helium could asphyxiate people nearby.
Planners also warned of the possibility that the tether could drag behind and damage power lines.
That appears to have happened Wednesday, when about 27,000 people in central Pennsylvania lost power as the balloon passed overhead.
The balloon eventually came down in a remote wooded area.
Capt. Matt Villa, an Army planning officer who was on the scene Thursday, said the balloon's tail had come off and crews had to cut parts of the tether that had tangled in power lines. About 60 troops were working with a team of contractors and local authorities to recover the aircraft.
"We're focused on safety at this point," Villa said. He said he expected the cleanup to take another day or so.
The three-year exercise of the Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System is a critical phase for the 17-year, $2.7 billion program.
Throughout its history, the system has been hobbled by defective software, poor reliability and vulnerability to bad weather.
The balloons, which are designed to remain aloft at an altitude of up to 10,000 feet, have become a fixture on the Baltimore skyline. They carry sophisticated radar capable of seeing 340 miles in any direction, covering an area from North Carolina to Canada, with fire-control systems to help aim weapons at incoming threats.
Ruppersberger acknowledged questions about the program, but said its goal remains worthy.
"As long as JLENS is there, we will have advance notice of any attack," he said. "We have to be ready to protect our citizens."