Nov 7 (Reuters) - As a bell sounded in the cockpit,

three UPS pilots tried to control a cargo flight that

crashed this week in Louisville, Kentucky, killing at least 13

people, the National Transportation Safety Board said on

Friday.

While UPS flight 2976 started uneventfully, a repeating bell

was heard on the aircraft's flight cockpit voice recorder just

37 seconds after the crew called for takeoff thrust, NTSB member

Todd Inman told reporters.

The bell persisted until the end of the recording 25 seconds

later, which Inman believes signals the aircraft's crash.

"During this time, the crew engaged in efforts to attempt to

control the aircraft before the crash," Inman said.

CRASH DESTROYED TWO BUSINESSES

The independent U.S. safety agency is leading the probe into

the crash of the 34-year-old MD-11 freighter at the Louisville

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

ground level before plunging in flames off the runway and

destroying two businesses.

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

as it rolled down the Louisville airport runway.

The bulk of the left engine pylon, a structural component

connecting the aircraft engine to the wing or fuselage, was

still attached to the left engine when it separated from the

wing, Inman said.

"Now, subsequently, there could be damage that occurred upon

its impact with the terrain," he said.

Debris from the engine, an area of focus to investigators,

was found on the runway.

Investigators are also probing the aircraft's maintenance

history, including a six-week period this fall when it underwent

heavy maintenance at a San Antonio, Texas, repair facility.

A transcript of the cockpit voice recorder, which contained

two hours and four minutes of good quality digitally recorded

audio, will be made public in several months, Inman said.

Air crashes are normally caused by multiple factors, with a

preliminary report generally expected 30 days after the

incident.