WASHINGTON, Nov 8 (Reuters) - The U.S. Federal Aviation

Administration on Saturday issued an order prohibiting MD-11

planes from flying for now, pending inspection, after a fiery

crash this week of a UPS MD-11 cargo freighter killed at

least 14 people in Louisville, Kentucky.

UPS and FedEx ( FDX ) said they have already grounded their

combined fleet of more than 50 McDonnell Douglas MD-11 cargo

planes following a recommendation by planemaker Boeing ( BA ).

The FAA said its emergency airworthiness directive was

prompted by the crash on Tuesday in which the left engine and

pylon detached from the airplane during takeoff. The cause of

the detachment is under investigation.

"This condition could result in loss of continued safe

flight and landing," the U.S. regulator said.

UPS said it was in compliance with the directive because it

has grounded its fleet of 26 MD-11 planes, representing about 9%

of its fleet.

Boeing ( BA ) said on Saturday that it supports the FAA order.

FAA LIKELY TO REQUIRE COMPREHENSIVE INSPECTIONS

Boeing ( BA ) acquired the MD-11 program through its 1997 merger

with McDonnell Douglas.

Officials said the FAA is likely to require comprehensive

engine and pylon inspections before allowing the planes to

resume service.

The U.S. National Transportation Safety Board is leading the

probe into the crash of the 34-year-old MD-11 freighter at the

airport. The plane reached about 100 feet (30.5 meters) above

ground level before plunging in flames off the runway and

destroying two nearby businesses.

One of the plane's three engines detached from the left wing

as it rolled down the Louisville airport runway.

On Friday, U.S. safety investigators said that as a warning

bell sounded in the cockpit, three UPS pilots had tried to

wrestle control of the plane just before it crashed.