The National Transportation Safety Board (NTSB) revealed on Tuesday that it is reviewing reports of cracks in a wing mount before the left engine sheared off from a UPS freight airplane on takeoff from Louisville, Kentucky, in November, resulting in a crash that killed 15 people.

That information surfaced at the beginning of a two-day hearing into the crash of the delivery service’s MD-11, which left all three crew members and 12 people on the ground dead. An additional 23 people on the ground were injured as an auto parts recycling ignited after the freighter crashed into it.

Between the crash and the NTSB hearing, the board said that a cracked part on the doomed jet was flagged in a Boeing 2011 report which said there had previously been four such failures on three different airplanes.

The NTSB said its investigation had found fatigue cracks in a support structure on the left pylon that connects to the wing and the plane’s engine known as the bearing race.

The agency also said there were a series of reports of cracks in race parts on MD-11 planes in the prior decade.

The NTSB’s hearing is also meant to review the design requirements for those components, along with the Federal Aviation Administration (FAA)’s oversight of the problem over the last two decades.

The FedEx delivery service said it had again started using its fleet of MD-11s after the FAA lifted an order that had barred flying those airplanes after the UPS crash. That came after UPS retired its remaining two dozen MD-11 jets soon after the crash.

Ahead of the hearing, the NTSB released an animated video of the components that failed on 11 November. It also released airport surveillance video that showed the engine breaking off the jet, which was unable to climb on its remaining two engines and slammed into the ground in a fireball.

The families of several victims who were injured or killed in the crash were present for the hearing in Washington DC.

“These families are devastated and certainly deserve answers,” said attorney Bradley Cosgrove, partner at Clifford law offices, which is believed to have filed the first wrongful death claim in Kentucky regarding the crash.

Cosgrove, who heads up the team of lawyers, pilots, and technical experts at the firm, was also attending.

In her opening statement on Tuesday, Jennifer Homey, the NTSB chair, addressed the families of those who were killed in the crash, saying: “Please know: Your loved ones are the reason we’re here. We want to find out what happened.

Furthermore, additional details emerged as the NTSB released more than 2,000 pages of documents related to the plane crash. The ill-fated plane had been pressed into service to substitute another which had a fuel leak, investigators said.

And the flight crew who ultimately died had shared good-natured banter with the maintenance team during a second pre-flight inspection about “meeting again” so soon.

The NTSB was prepared to call several witnesses, including representatives from Boeing, who manufactured the plane. The agency’s final report likely won’t be ready until more than a year after the crash.