(Reuters) -U.S. safety investigators said on Thursday they are probing the maintenance history of a UPS cargo plane that was in Texas for repairs weeks before crashing in flames in Louisville, Kentucky, on Tuesday, killing at least 13 people.

The National Transportation Safety Board has said a large "plume of fire" erupted around the 34-year-old MD-11 freighter's left wing and one of its three engines detached from that wing as it rolled down a Louisville airport runway.

Flight tracking data show the plane was on the ground in San Antonio, Texas, from September 3 to October 18.

"We are aware that this aircraft was there in San Antonio," NTSB member Todd Inman told reporters on Thursday, without giving a specific time frame. "We will look at every piece of maintenance that was done, even from the San Antonio time, all the way to the date of the flight."

Singapore-based ST Engineering, which said it provides airframe maintenance for UPS's MD-11 aircraft and operates a repair facility in San Antonio, declined to comment but said it would cooperate fully when relevant authorities reached out to it.

According to Federal Aviation Administration records dated September 18, a crack on a structural piece inside the center wing fuel tank required repairs.

UPS referred queries to the NTSB, as is standard in air crash investigations.

The cargo giant on Thursday named the pilots operating the flight as Captain Richard Wartenberg, First Officer Lee Truitt, and International Relief Officer Captain Dana Diamond. All three died in the crash.

There is currently no evidence that poor maintenance caused the crash of the freighter bound for Honolulu, which also killed at least 10 people on the ground after the burning plane struck a number of structures just beyond airport property.

Air crashes are normally caused by multiple factors, with a preliminary report generally expected 30 days after the incident.

The NTSB said the download of the plane's two "black boxes", the cockpit voice recorder and flight data recorder, was successful and a transcript of the cockpit conversation was being put together.

Inman said the NTSB had no immediate safety concerns about the broader MD-11 program owned by Boeing ( BA ) since its 1997 merger with McDonnell Douglas. For cargo operations, there are about 50 MD-11 planes being operated by FedEx and UPS worldwide.

On Thursday evening, Louisville Mayor Craig Greenberg said on social media site X that the death toll had grown to 13.

Earlier in the day, he told reporters that investigators and others were still searching through the crash debris for clues and possible victims.

"There is so much charred, mangled metal that not all of the bodies may have been located," Greenberg said.