A bird strike caused the 2007 crash of a University of North Dakota airplane that killed two people, the National Transportation Safety Board says.

Student Adam Ostapenko, 20, of Duluth, Minn., and instructor Annette Klosterman, 22, of Seattle, died when the twin-engine Piper Seminole crashed in a swampy area in central Minnesota on Oct. 23, 2007. They were on a routine training flight from St. Paul, Minn., to Grand Forks when the plane went down near Browerville, Minn.

The NTSB’s probable cause report, dated Sunday, said DNA from a Canada goose was found on the plane’s left tail wing. It said the damage “caused the airplane to become uncontrollable.”

The report said the night flight contributed to the crash because the pilots could not have seen the goose.

Flight data indicated the plane was flying at about 185 mph, at an altitude of 4,500 feet. The airplane “abruptly departed from controlled flight” and crashed into the ground in about 25 seconds, the report said.

NSTB said autopsies three days after the crash found Ostapenko and Klosterman suffered “multiple blunt force injuries due to an aircraft accident.” Tests for drugs and alcohol were negative, the NTSB said.

The NTSB report said UND flight school officials helped with the investigation. UND released its own report in April, concluding the plane likely crashed after a bird strike.

Neither NTSB nor UND officials could be reached for comment today.

The NTSB report said UND now provides more pilot training about bird strike hazards and recommends that pilots cruise at higher altitudes to avoid them.

Canada geese, which can weigh more than 10 pounds, are one of the most hazardous species of bird for aircraft because of their large size and flocking behavior, the NTSB report said.

NTSB figures show 668 Canada goose strikes to civil aircraft in the United States from 1990 to 2002, resulting in “substantial damage” to 112 airplanes.