KERRVILLE, Texas (AP) — Witnesses described hearing a twin-engine plane sputter and seeing its tail dragging before the small aircraft flipped over and crashed in central Texas, killing all six people on board.

The Texas Department of Public Safety said Jeffrey C. Weiss was piloting the Beechcraft BE58 Monday morning when it went down as it approached Kerrville Municipal Airport, about 70 miles (110 kilometers) northwest of San Antonio. Friends said Weiss, a 65-year-old investment manager, was an experienced pilot who often volunteered to fly sick people to Texas hospitals.

The family of Houston landscape architect Marc Teppesen, 45, told KTRK-TV that they believe an architectural client had chartered the doomed plane to survey some property. Teppesen was killed alongside his 58-year-old associate Mark Scioneaux, 55-year-old architect Scott Reagan Miller, 55-year-old Houston real estate investor Stuart Kensinger and his 54-year-old wife Angela Kensinger, officials said.

Federal Aviation Administration and National Transportation Safety Board investigators surveyed the site but provided no preliminary information on what might have caused the crash.

Witnesses described the plane’s last moments.

“It was making a sput-sput sputtering sound, like the engines were cutting out,” Treva Hardeman told the San Antonio Express-News . She said she was working at home about a quarter of a mile from where the aircraft crashed. “It was just a few seconds later that I heard the boom.”

Construction worker Rodney Simmons said he heard a plane struggling.

“I looked over and watched him drop down out of the clouds,” Simmons told the Express-News. “The rear end of the plane was real low, like he was trying to stay in the air. It was like he was dragging the tail end of that plane. Like he had a lot of weight in the back or something.”

The plane flew southward then “banked to the right, real hard, and just flipped on over, upside down, and nose-dived to the ground,” Simmons said.

The aircraft had taken off from an airport outside Houston earlier Monday and crashed just before 9 a.m. about 6 miles (10 kilometers) short of the Kerrville airport, FAA spokesman Lynn Lunsford said.

Weiss co-owned the plane with Charles Morina of Dallas, according to FAA records.

Weiss loved to fly and the pair volunteered their time transporting sick people from remote regions to Texas hospitals for Angel Flight, Morina said.

“We flew people from all over the country to Dallas and Houston” for medical treatment, he told The Associated Press.

Weiss also was active in charities supporting children with special needs or who suffered abuse, said friend Bob Fuller. He told KPRC-TV of Houston that Weiss helped him conduct his Keels and Wheels charity event in Seabrook each year to aid abused children, giving both his time and money.

“I loved the man, I’ll tell you that. He was generous to a fault,” Fuller said.