AUSTIN, Texas (AP) — The small plane that crashed while carrying four pickleball players to a tournament near Austin last month had problems with freezing instruments before it broke apart midair, according to a preliminary federal investigation report released Friday.

The Cessna 421C took off from Amarillo on April 30 at 9:10 p.m. and crashed at about 11 p.m. in Wimberley, a city about 40 miles (64 kilometers) southwest of Austin. Pilot Justin Appling and passengers Hayden Dillard, Brooke Skypala, Stacy Hedrick and Seren Wilson died.

The National Transportation Safety Board report said that during the flight, the pilot reported problems with the plane’s anti-icing system that protects onboard instruments.

He later reported an instrument that measures airspeed had “iced up” and that he was using backup gauges. He was cleared to descend to 4,000 feet (1,200 meters) and told air controllers he wanted to get to a lower altitude to try to “warm back up.”

Over the last 15 minutes before the crash, the plane flew at altitudes where temperatures hovered just below freezing, according to the report.

The pilot’s last radio transmission with air controllers was made at 10:59 p.m. The plane then made a series of descending left and right turns before crashing to the ground.

Investigators found pieces of the plane over a 1.25-mile (2-kilometer) debris field, distribution consistent with an “inflight breakup,” the report said.

It was mostly cloudy in the area shortly before the crash, and there was a thunderstorm two hours later, the National Weather Service said.

A second plane traveling with the group landed safely in New Braunfels.