Adds FedEx grounding, details, background

By Rishabh Jaiswal and Dheeraj Kumar

Nov 7 (Reuters) - UPS UPS.N and FedEx FDX.N said on Friday they have grounded their combined fleet of more than 50 McDonnell Douglas MD-11 cargo planes following a crash in Louisville, Kentucky this week that killed at least 14 people.

A UPS MD-11 crashed late on Tuesday, erupting into a fireball moments after takeoff from Louisville's international airport. The death toll from the crash, the cause of which is still under investigation, has risen to 14, according to a post on X by Louisville Mayor Craig Greenberg on Friday.

UPS and FedEx, the world's largest cargo carriers, said in separate statements that they grounded the aircraft "out of an abundance of caution."

FedEx said it operates 28 MD-11s and, according to a UPS factsheet, UPS had 27 in its fleet prior to the crash.

"We made this decision proactively at the recommendation of the aircraft manufacturer," UPS said in its statement.

Boeing BA.N, which acquired the MD-11 program through its 1997 merger with McDonnell Douglas, did not immediately respond to Reuters requests for comment. Production of the MD-11 planes ended in 2000, and passenger service officially ended in 2014.

FedEx, which has a total fleet of 700 aircraft, said it was "immediately implementing contingency plans" to avoid disruptions. UPS said that its MD-11s account for only 9% of its fleet.

Still, any potential disruptions could have far-reaching consequences as FedEx and UPS are the workhorses for transferring goods around the world for major retailers like Amazon.com AMZN.O, Walmart WMT.N and Target TGT.N, as well as for manufacturers and businesses.

UPS is the No. 1 air cargo service provider for the U.S. Postal Service, transporting Priority and other speedy mail products.

NTSB LEADS PROBE

The U.S. National Transportation Safety Board 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 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.

While UPS flight 2976 began uneventfully, a repeating bell was heard on the aircraft's cockpit voice recorder just 37 seconds after the crew called for takeoff thrust, NTSB member Todd Inman told reporters.

NTSB anticipates issuing a preliminary investigation report into the crash in about 30 days.

The last UPS cargo plane to crash was in August 2013, when an Airbus aircraft went down on a landing approach to the international airport in Birmingham, Alabama, killing both crew members.

(Reporting by Rishabh Jaiswal and Dheeraj Kumar in Bengaluru and Joe Brock in Los Angeles; Editing by William Mallard, Thomas Derpinghaus and Himani Sarkar)

((rishabh.jaiswal@thomsonreuters.com; +91 9916719147))