EASTON, Mass. (AP) – A pilot of a plane that crashed into shopping plaza parking lot did not make a distress call and was repeatedly warned that he was flying too low shortly before the plane spiraled to the ground, killing all three on board, according to a federal investigator.

Meanwhile, audio recordings of the plane’s final minutes showed frantic attempts by a Boston air traffic controller to urge the pilot to climb, just before the plane disappeared from radar.

The charity flight was carrying Robert Gregory of Riverhead, N.Y., a cancer patient, and his wife, Donna, to Boston’s Logan International Airport for treatment at the nearby Dana-Farber Cancer Institute. Witnesses said the plane appeared to lose power, then nosedive into the parking lot in Easton, about 25 miles south of Boston.

Joseph Baker of Brookfield, Conn., a U.S. Navy submarine veteran and volunteer pilot for the charity group, Angel Flight Northeast, was also killed.

Baker did not make a distress call before the crash and there was no other indication from the pilot that he was in trouble, senior NTSB investigator Tim Monville said at the crash site.

The NTSB has received air traffic-control data and radar information from the Federal Aviation Authority and is studying the new information to determine the sequence of events before the crash, Monville said.

It’s the third fatal crash of an Angel Flight plane since June.

On July 17, an Angel Flight plane crashed shortly after takeoff near Tampa, Fla., killing all three on board, including a 49-year-old cancer patient, a 15-year-old boy and the 81-year-old pilot. On June 3, a Georgia toddler was fatally injured when an Angel Flight plane crashed in Iowa City as it was flying the little girl home.

Monville has interviewed witnesses to the Easton crash and plans to move the wreckage to a secure location for detailed examination of the airframe and engine.

“We are going to be examining maintenance records, pilot training records, obviously we will be waiting on autopsy and toxicology reports, as we always do – and in addition, learning more about this operation, Angel Flight, and how they operate,” Monville said.

Recordings just before the crash indicate that an air traffic controller in Boston knew the plane was in serious trouble. He warns Baker that he was flying at 1,200 feet and orders him to “climb immediately!” and remain at the assigned altitude of 3,000 feet.

“The pilot acknowledged by responding: ‘1-5 Delta climbing”‘ Monville said.

Shortly afterward, the controller was heard to say, “Your altitude is going up and down, are you all right, sir?”

The pilot did not respond to that query.

The air traffic controller then asks other pilots in the area if they picked up any response from Baker, but none had heard from him. The air traffic controller again tells Baker his altitude is too low and orders him to climb.

In the next transmission, he reports, “Radar contact lost.”

Several witnesses in Easton told investigators that they saw the aircraft circling the area, flying low and then plunging to the ground, Monville said.

The examination of the crash site and the wreckage indicates that the right wing was first to hit the ground before the plane rotated 45 degrees and came to rest upright, Monville said. “A post-crash fire consumed the cockpit, cabin and portion of the left wing.”