PONCA CITY, Okla. (AP) — An investigator with the National Transportation Safety Board has examined debris from a small aircraft that crashed in a northern Oklahoma field, killing all five people on board.

NTSB spokesman Peter Knudson said Sunday the investigator will remain at the site through Monday looking for clues into the cause of the crash about 90 miles (145 kilometers) north of Oklahoma City.

The Oklahoma Highway Patrol says the plane, an Extra EA-400 corporate aircraft, was northbound from Ponca City's airport when it lost altitude and crashed about 10:45 a.m. Saturday. Troopers say the aircraft burst into flames and five people on board were killed. They have not been identified.

The bodies were sent to the Oklahoma medical examiner's office for identification. Local media reported that the plane was registered in Kansas.