The blimp that broke loose from an Army facility in Maryland last fall, wreaking havoc with its milelong tether, flew uncontrolled for hours because someone neglected to put batteries in its automatic-deflation device, Pentagon investigators have found.
The pilotless, radar-carrying blimp was part of the troubled JLENS missile-defense system, which has failed to perform as promised while costing taxpayers more than $2.7 billion since 1998.
The runaway blimp episode was caused by a cascade of events spanning 13 hours, according to people familiar with the investigation, an overview provided to congressional staff members and a summary released by a military spokeswoman.
The six-sentence summary of the investigation said that "design, human, and procedural issues all contributed" to the mishap. Pentagon officials declined to release a copy of the investigative report.
The blimp was one of two moored at the Army's Aberdeen Proving Ground. On Oct. 28, it was floating at an altitude of about 5,200 feet when its tether tore apart.
Fighter jets were scrambled to track the blimp as it wafted over Maryland and Pennsylvania, and commercial air traffic had to be diverted. The blimp's tether damaged power lines, knocking out electricity to 35,000 rural Pennsylvania residents. The tattered blimp finally came to rest in high trees in rural Moreland Township, Pa.
The incident made JLENS a target of widespread ridicule and provoked fresh questions about the program.
JLENS — short for Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System — is designed to provide early warning of enemy cruise missiles, drones or other low-flying threats.
The blimps, also called aerostats, can float as high as 10,000 feet. At that altitude, their powerful radar can see 340 miles in any direction, farther than land- or sea-based radar, according to the system's prime contractor, Raytheon Co.
The 7,000-pound aerostats are anchored to the ground by 11/8-inch-thick Kevlar tethers, which also hold wiring for electricity.
The two blimps at Aberdeen were participating in an "operational exercise" intended to test the system's ability to defend the Washington, D.C., area. The exercise was suspended after the accident.
The sequence of events that caused the blimp to break away began when a pitot tube, a narrow 18-inch-long device intended to measure air pressure within the blimp, malfunctioned. Ground personnel failed to detect or address the problem, investigators found.
Ordinarily, fans within the blimp would activate in response to a change in atmospheric conditions, such as increased winds. But because the pitot tube failed, the fans did not operate — and air pressure within the blimp started to drop.
The blimp turned so that it was perpendicular to the prevailing wind, instead of the desired parallel position. Gusts that reached 69 mph bent its vertical tail fins out of their normal shape.
This made the blimp unstable in the air, putting greater pressure on the mooring tether than it was designed to withstand, according to the investigative documents.
Still, the blimp was equipped with an automated device that should have caused it to deflate promptly and return to ground within two miles. The device failed to activate, because batteries had not been installed as a backup power source, according to people familiar with the investigation.
Michael Kucharek, a spokesman for the North American Aerospace Defense Command and the U.S. Northern Command, confirmed the lapse: "The lack of batteries prevented the automatic rapid deflation device from deploying."
Military officials declined to say who was responsible for failing to load the batteries. The blimps were managed by Army and contractor personnel.
The breakaway was the most conspicuous of many setbacks for JLENS, detailed in a Times report published last September. In tests, the system has struggled to track flying objects and to distinguish friendly aircraft from threatening ones.
A 2012 report by the Pentagon's Operational Test and Evaluation office faulted the system in four "critical performance areas" and rated its reliability as "poor." A year later, in its most recent assessment, the agency again cited serious deficiencies and said JLENS had "low system reliability."
A spokesman for Defense Secretary Ashton B. Carter said Carter "concurred" with a recommendation from military officials to resume the JLENS operational exercise.
"A thorough and complete test will allow us to determine if this technology will contribute to the overall homeland defense architecture here in the National Capital Region," said the spokesman, Air Force Lt. Col. Tom Crosson.
Now it will be up to Congress to decide whether to provide the additional funds needed to return JLENS to the skies. In the last week, military officials have privately told congressional staff that they would like an additional $27 million to restart the operational exercise as of Oct. 1.
A spokesman for Sen. Barbara A. Mikulski of Maryland, the ranking Democrat on the Senate Appropriations Committee and a supporter of JLENS, said the senator "is reviewing the findings of the investigation as Congress examines next steps in funding for the program."
Army Major Beth R. Smith said that officials in charge of the operational exercise plan to "fix any issue identified'' by the investigation and will follow recommendations to add personnel to JLENS and improve training and equipment.
Click here to read previous articles by David Willman about problems in the nation's missile-defense programs.