MANSFIELD, Mass. (AP) – A small plane that crashed nose-first into the ground, killing two people at Mansfield Airport, appeared as if it could not maintain enough lift to stay in flight, a federal investigator said on Sunday.

The plane took off at about 10:30 a.m. Saturday, but issued a mayday call because it wasn’t climbing at a sufficient rate. When the plane turned back, it appeared to go into a stall before crashing. In aviation terms, a stall refers to a loss of lift.

Killed in the accident were pilot Lawrence Mann and passenger Cabot Squire, both from Portland, Maine. Injured were Jared Lamey of Saco, Maine, and Mathew Kramer of Mansfield.

Eric Alleyne, an investigator with the National Transportation Safety Board, said he watched a video of the takeoff and crash.

“He did take off. He was climbing. At some critical point, the airplane banked over and nose-dived into the ground. There appears to be a stall,” Alleyne said. “We don’t know why it stalled.”

The investigation will also consider “the pilot’s medical records and his experience,” Alleyne said.

Lamey remained in serious condition Sunday at Beth Israel Deaconess Medical Center, a spokesman said.

Kramer was listed in critical condition at Brigham and Women’s Hospital after the crash, but a hospital spokeswoman on Sunday said she had no information to update his condition.

The four-seat Cessna 172 is registered to Twin Cities Air Service of Auburn, Maine. The company offers charter air service, aviation services and flight instruction.