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

Administration on Saturday said it was prohibiting MD-11 planes

from flying for now, pending inspections, after a crash earlier

in the week of a UPS MD-11 cargo freighter killed at

least 14 people in 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 the emergency airworthiness directive was

prompted by the crash on Tuesday, when the left engine and pylon

detached from the airplane during takeoff in Louisville. 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.

FedEx ( FDX ), with 28 MD-11s in operation out of its 700 planes,

said on Saturday that it was "immediately implementing

contingency plans within our integrated air-ground network to

minimize disruptions."

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 FAA order requires any necessary fixes after

the inspections.

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

probe into the crash of the 34-year-old MD-11 freighter. 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, the three UPS pilots on board had

tried to wrestle control of the plane just before it crashed.

Earlier this week, the NTSB said it was probing the

maintenance history of the plane, which was in Texas for repairs

with the aircraft undergoing heavy maintenance weeks before the

accident. The aircraft was at a facility operated by

Singapore-based ST Engineering, according to a source

familiar with the matter.

ST Engineering has said it provides airframe maintenance

for UPS's MD-11 aircraft and operates a repair facility in San

Antonio, but declined further comment.