NTSB investigators pinpoint failed aircraft part from UPS crash last year

The fire in the area of the left pylon attachment to the wing continued as the airplane cleared the blast fence. - UPS/NTSBInvestigators have pinpointed the exact part that failed in the fiery Louisville crash of a UPS cargo flight in November, killing 15 in all.The rare investigative update issued Wednesday by the National Transportation Safety Board says a 3-inch-wide metal housing around a bearing — central to the mount that kept the left engine attached to the MD-11F’s wing — showed signs of existing metal fatigue and cracking. Investigators identified the larger assembly as a problem early in the investigation.Three pilots on board UPS flight 2976 and 12 people on the ground were killed when the jet sliced a half-mile long debris field across a petroleum recycling facility and UPS warehouse, setting off a massive blaze of fire and black smoke visible for miles on November 4.As part of the update, investigators released previously unseen images of the so-called bearing race that was split into two halves, causing the left engine to go up and over the wing of the three-engine jet in a dramatic fireball.The NTSB underscored in its new update that the bearing housing was the subject of a 2011 Boeing letter to airlines—known as a service letter—alerting them to four failures of engine bearing races on three different MD-11s. But the NTSB notes the alert to operators, “Boeing determined it would not result in a safety of flight condition,” and called for visual checks of the part at normal five-year intervals.CNN has reached out to Boeing, which took over support for the McDonnell Douglas-made MD-11F after Boeing acquired the company in 1997.In November,the NTSB released a preliminary report into the incident which unveiled that a critical mount that kept the left engine attached to the UPS flight failed only moments after the flight left the ground. Data showed the plane failed to climb higher than 30 feet above Runway 17 Right at Louisville Muhammad Ali International Airport.The preliminary report also highlighted fatigue cracks found in the hardware attaching the engine to the wing and symptoms of over-stressing, but more is still to come as the agency conducts its full investigation.Investigators also reviewed the flight data recorder information which will be incorporated into a performance study to understand why the plane’s altitude did not increase.A final report from the NTSB is expected in 18 to 24 months from the incident detailing the probable causes of the crash. The agency does not place blame but gives further recommendations to improve safety.CORRECTION: An earlier version of this story misstated the death toll in the November crash of a UPS cargo flight. It was 15.For more CNN news and newsletters create an account at CNN.com