Last October, a Defense Department tethered radar blimp broke loose of its moorings near Baltimore and drifted across two states—taking out power lines as it dragged its tether cable behind it in a 13-hour, unguided flight. A new investigation into the incident has revealed that most of the damage could have been avoided. The aerostat—half of the pair used by the Joint Land Attack Cruise Missile Defense Elevated Netted Sensor (JLENS) System—would have come down without causing nearly as much damage if someone had remembered to install its batteries.

The JLENS program, which uses two high-flying aerostats with radar domes (one a search radar system and the other a targeting radar to lock onto low-flying cruise missiles and other potential threats), has cost over $2.7 billion since the program began in 1998. Each aerostat was equipped with an automatic deflation system to bring the giant floating sensor to the ground quickly in the event of a cable break. But the system's batteries had not been installed at the time of the accident, so the system failed to activate when main power was lost.

The report, a summary of which was obtained by the Los Angeles Times, found that "design, human, and procedural issues all contributed" to the aerostat breaking loose, disrupting air traffic and causing jets to be scrambled to track its progress. When it finally came down 160 miles north in Moreland Township, Pennsylvania, the Army had state police bring it down the rest of the way with approximately 100 shotgun blasts. At the time, authorities believed they had no other way under the circumstances to deflate it.

According to the report obtained by the LA Times, a pitot tube within the blimp failed to detect a change in its internal air pressure. High winds caused it to lose air pressure and begin to lose its shape. As a result, the wind caught the aerostat perpendicularly rather than head on, causing aerodynamic forces that wrenched the aerostat's mooring tether.

The JLENS' tether, made of Vectran (a substance similar to kevlar), was 1 1/8 inches thick and was allegedly designed to withstand 100 mile-per-hour winds. But the combination of forces snapped the tether, which also carried the aerostat's power. At this point, the safety deflation mechanism should have kicked in, and the blimp would have come down within two miles of its tether. But as North American Aerospace Defense Command and US Northern Command spokesman Michael Kucharek told the paper, "The lack of batteries prevented the automatic rapid deflation device from deploying."