Great Moments in Military Aviation: Death of a Blimp

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Lockheed Martin

A blimp like this -- more than 200 feet long -- was lost last August

How can the Air Force lose a blimp two-thirds the size of a football field? When the winds are wrong, alas, anything can happen.

Battleland readers of a certain vintage may recall, with wonder and delight, the goofy mid-1960s’ Ideal Toys’ Mouse Trap Game, where players had to assemble a rickety Rube Goldberg structure of plastic pieces that launched a series of improbable actions that ultimately caught the mouse and made someone the winner.

A similar string of unlikely steps made the Air Force the loser – of an $8 million blimp. Here’s how it happened:

— The Air Force’s ITT contractor launched a drug-hunting Tethered Aerostat Radar System into the skies over Puerto Rico’s Lajas Tethered Aerostat Radar System (TARS) Site last August 15 at 8:41 a.m.

— Slightly more than 24 hours later, a line of thunderstorms approached the blimp from the southeast.

— This is no modest blimp: at 208.5 feet long and 69.5 feet in diameter, and filled with 420,000 cubic feet of helium and air, it’s nearly double the size of the MetLife blimps orbiting over sporting events.

— This was no modest storm: this “tropical wave” eventually grew up and became Hurricane Irene, which battered the east coast of the U.S. late last summer. Winds aloft at the blimp site topped 50 knots.

— The ground crew desperately tried to bring the blimp down from its 2,100-foot altitude before the storm hit. They connected the blimp’s line to the winch truck that would reel it in. Bad weather had already forced them to move it from 9,800 feet to 4,000 feet about an hour before the storm hit.

— The ground crew failed to place chock blocks at the winch truck’s wheels to help keep it immobile when tugged by the blimp.

— But even with the blimp at only 2,100 feet, the storm blew in before the six-member ground crew could winch it in and moor it securely on a mast that would allow it to spin like a weather vane and survive bad weather.

— The ground crew was forced to slow the rate of tether winching from 250 feet per minute to 100 feet per minute because of excessive tension the higher rate was putting on the tether line.

—  Battered by the approaching storm, the blimp’s tail fins collapsed. It quickly nosed over, and moved rapidly from the west to the north, as it fell from 1,200 to 300 feet in less than 25 seconds.

— The squall grabbed the truck and began pushing it to the northwest, pulling it off its large circular operating pad.

— The 43-ton winch truck remained connected to the blimp via the tether line.

— The blimp pulled the truck backwards, to the northwest, off the operating pad, and rotated it to the right. The wheels were torn off the truck’s stability outriggers as it careened out of control, hitting a storage container and a diesel fuel trailer.

— The blimp pulled the truck over two embankments before the truck got stuck on a third, near the site’s perimeter and underneath its utility lines.

— The nylon and polyethylene tethering line crossed a steel anti-fouling line that was a remnant of an earlier kind of blimp.

— Like a buzz saw, the point where the two lines met generated sufficient force and friction to snap the tethering line within seconds.

— The untethered blimp soared skyward.

— The ground crew ordered the blimp down with its onboard Rapid Descent Device. It failed.

— The crew then ordered the helium blowers turned on in an effort to deflate the blimp.

— But the blimp was ascending too fast for that to bring it gently back to Earth.

— The blimp quickly reached 7,000 feet, where it exploded because of excessive helium pressure (the Air Force prefers the less cataclysmic “rupture.”)

— Everything aboard fell back to Earth, some up to two miles away from the pad, and was destroyed upon impact. All the wreckage was collected “with the exception of one section of aerostat fabric that remains unrecoverable in a swampy area, and a small carbon dioxide cylinder that was never found,” the Air Force investigation into the mishap concluded.

“The total cost for the destroyed [mishap aircraft], payload and damaged ground equipment is approximately $8,159,917.86,” it said. “Clean up costs are pending for 71 gallons of spilled diesel fuel from the Airborne Power Generation Subsystem (APGS) fuel tank.”

Cause of the accident: Air Force guidance waits too long before mandating such blimps be brought down. “This guidance,” the Air Force probe found, “does not take into account the speed of an approaching storm.” The missing chock blocks didn’t help things, either.

Air Force

Thankfully, no one was hurt. And some good did come out of it, at least for the local economy, according to the official Air Force probe:

“Lajas has been a hot-spot for UFO enthusiasts. UFO sightings in Lajas are frequently reported on UFO enthusiast web sites. Local government has only encouraged this speculation in hopes of spurring tourism, with the area immediately surrounding the aerostat site being dubbed the “UFO Capital of Puerto Rico.” The highway signs on PR-303 are labeled “Ruta Extraterrestre” and have a drawing of a flying saucer. News stories featuring UFO enthusiasts have attempted to connect the mishap to UFO activity. They claim to have spoken to witnesses who saw a ball or beam of fire from the sky attack the aerostat.”

Interesting. You note the Air Force doesn’t deny a UFO was involved.