BROOKSHIRE, Texas (KXAN) — Federal investigators began interviewing the passengers and crew members who escaped a fiery plane crash in Brookshire, Texas as part of a lengthy effort to figure out what happened.

Michael Graham, a member of the National Transportation Safety Board (NTSB), told reporters Wednesday the MD-87 plane tried to take off Tuesday morning at about 10:08 a.m. from the Houston Executive Airport. However, the plane veered off the runway and went through a perimeter fence. It stopped when the left wing struck some trees, and then all 21 people on board managed to get off the plane safely. The NTSB only reported two minor injuries from the crash.

“We are extremely thankful that there were no fatalities,” Graham said.

Interviews began Wednesday for the 18 passengers, three crew members and other witnesses. Graham could not share any information yet about how everyone managed to escape the plane, though the investigation will focus on that, too, because he said it’s important to know why no deaths happened.

Graham also noted the majority of the fire damage appears to have happened after everyone escaped the plane. He said investigators already found two heavily-burned black box recorders in the wreckage. Those are on their way back to Washington, D.C., where they’ll be downloaded and used to assist the ongoing investigation into the crash. Graham explained the investigation could last anywhere from 12 to 18 months.

According to KPRC, the plane crash is believed to be caused after it failed to gain altitude at the end of the runway. However, the NTSB would not comment Wednesday on any potential causes of the crash.

Waller County Judge Trey Duhon told KPRC, the Houston NBC station, he believed the plane was headed to Boston to watch the Astros play in the American League Championship Series.

Witnesses who captured any photos or videos of the plane crash are asked to send an email to witness@ntsb.gov.