The U.S. Army and National Guard have grounded their fleets of UH-1 Huey helicopters, which have an unexplained history of potentially catastrophic mechanical problems.
The military has placed wide restrictions on the Vietnam-era helicopters since November -- including barring flights in clouds and over water -- but declared Hueys safe to fly as recently as last week.
On Friday, military officials changed their minds.
"After careful consideration and as a prudent measure of safety, the Army is grounding its fleet of UH-1 helicopters until each helicopter engine can be tested to determine if there are excessive vibrations," Bob Hunt, spokesman for Army Aviation Missile Command at Redstone, Ala., told the Boston Globe in Sunday's editions.
In all, 907 Huey helicopters are expected to be grounded for six months to two years. The majority of those are used by the National Guard. Gearbox problems in the Hueys were blamed for some near disasters last year.