Boeing MD-11 Plane That Crashed Had ‘Fatigue Cracks,’ NTSB Says

The Boeing MD-11 cargo plane that crashed in Louisville, Kentucky, earlier this month showed signs of “fatigue cracks” and “overstress failure” in a piece of the McDonnell Douglas-built plane that connects the engine to the wing, the National Transportation Safety Board said in a preliminary report Thursday.

The NTSB’s report does not explain what caused those cracks in the UPS freighter, and it will be several months before the safety board releases a final accident report that diagnoses a probable cause. But the focus of the preliminary findings could indicate what went wrong.

The crash grounded the MD-11 fleet and other similar cargo planes, with the Federal Aviation Administration writing in an emergency directive that “the unsafe condition is likely to exist or develop in other products of the same type design.”

The MD-11 that crashed was manufactured by McDonnell Douglas in 1991, six years before the company's merger with Boeing. The cargo plane model is no longer in production, but dozens still fly, operated by UPS, FedEx and Western Global Airlines, another cargo carrier.

On Nov. 4, the UPS MD-11 was heading from Louisville to Honolulu when it crashed shortly after takeoff. The plane’s left engine and pylon — essentially a mount for the engine — separated from the aircraft’s wing and caught fire, the NTSB said in its report. The plane, heavy with fuel for the long flight, became engulfed by the flames.

The plane only climbed about 30 feet into the air before it began to lose altitude, crashing into three nearby buildings, including a UPS warehouse and a petroleum recycling facility. The crash killed all three crew members aboard the plane and 11 people on the ground, and injured 23 others.

UPS grounded its MD-11 fleet three days after the crash, following a recommendation from Boeing. The FAA issued its emergency directive for all carriers to ground the MD-11 and MD-11F the following day, and later extended its order to include grounding the DC-10 series of planes, which are similar in design to the MD-11.

“We continue to grieve for the lives lost in the tragic accident involving Flight 2976,” UPS said in a statement Thursday. “We appreciate the National Transportation Safety Board’s prompt release of preliminary findings and will fully support the investigation through its conclusion.”

A spokesperson for Boeing said the company is supporting the NTSB in its investigation.

Our deepest condolences go out to the families who lost loved ones and our thoughts remain with all those affected," the spokesperson said.

In its preliminary report, the NTSB focused on the equipment that secures the plane’s engines to its wings.

The MD-11 has three engines, one on each wing and one center engine attached to the vertical stabilizer in the plane’s tail. It can have two engine types, one model from GE Aerospace and one from Pratt & Whitney. The plane that crashed had GE CF-6 engines.

In this case, the right engine remained attached to the wing but the left engine and pylon separated from the rest of the plane. The left engine then flew above the plane’s fuselage and hit the ground on the opposite side.

On the MD-11, the left and right engines are attached to the underside of pylons, which are then attached to the underside of each wing.

That pylon attachment consists of several pieces of hardware, including a forward mount bulkhead, a thrust link assembly and an aft mount bulkhead. Each of those pieces has its own set of hardware, including spherical bearings and fittings bolted together with lugs.

In its investigation, the NTSB found fractures on the left pylon aft mount lugs and the spherical bearing. In examining those fractures, it found evidence of “fatigue cracks” and “overstress failures” on the aft mount lug.

It did not find evidence of preexisting fractures or deformations on the structure.

The NTSB is continuing to examine several pieces of hardware, including the left and right pylon aft mount, the fractured lugs and two engine fan blade fragments that were recovered from the scene of the crash.

Anthony Brickhouse, an aviation safety expert, said the NTSB will now turn to studying the metal to understand when it started to crack and when the stress became too much for the structure to bear.

"The good thing about traditional metals is they tell a story," Brickhouse said. "With the right equipment, the metals will paint a picture and the investigators will try to piece together what happened."

In its report, the NTSB also described the plane’s maintenance history, including an inspection of the left pylon aft mount in October 2021.

Just before the crash, on Oct. 18, the carrier had completed a “lubrication task” for the pylon thrust links and spherical bearings, the NTSB said.

The aircraft was not yet due for a special detailed inspection of the left pylon aft mount lugs or other wing support, the NTSB said. Those inspections are scheduled for 29,200 cycles and 28,000 cycles, respectively. The plane that crashed had accumulated 21,043 cycles and 92,992 hours of flight time.

Fatigue cracks are typically “gradual failures over time,” said Jeff Guzzetti, a former accident investigator with the NTSB. They can be caused by a variety of factors, from corrosion to natural wear and tear to issues with another piece of equipment that puts too much load on one part of the plane.

It’s too soon to know what happened in this case, Guzzetti continued, but said the NTSB will likely focus its investigation on why the cracks weren’t caught during an inspection.

Boeing, as the manufacturer, would have determined when the aircraft needed certain inspections and UPS, as the carrier, was then responsible for facilitating those inspections.

The NTSB is going to be deep diving into how Boeing came up with the inspection interval, and they’re going to be looking into how UPS conducts maintenance, what tools they use. And they’re going to be looking into considerations of an aircraft aging issue,” Guzzetti said.

The NTSB’s report did not indicate that UPS failed to properly maintain the plane, Guzzetti said, but it raises questions about the maintenance protocol overall. The report also doesn’t indicate any problems with the left engine.

In its report, the NTSB related this crash to an American Airlines DC-10 crash in 1979 that killed 271 people on board and two others on the ground.

In that case, the left engine and pylon assembly separated from the airplane and fell to the runway. The plane rolled to the left and crashed into an open field.

A spokesperson for GE Aerospace said Thursday, “we extend our heartfelt sympathies to the families and loved ones of those impacted. Safety is our first priority, and we are supporting the NTSB’s investigation.”

Boeing, GE and UPS already face a proposed class-action lawsuit in Kentucky from people who live or work near the airport and scene of the crash. Those who are suing the companies say they faced property damage and health risks from debris and hazardous chemicals following the crash.

Robert Clifford, an attorney who has previously represented the families of airplane crash victims, including those who died in two fatal 737 MAX crashes in 2018 and 2019, said Thursday he has been in touch with those who lost loved ones from the MD-11 crash.

The NTSB’s preliminary report, Clifford said, “suggests that this plane was old, tired and well beyond its useful life. … More information will be revealed as the investigation continues.”

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