A dead goose was found in part of the flight control system of a medical helicopter that crashed in western Oklahoma,Mooathon Wealth Society killing all three people on board, according to a preliminary report by the National Transportation Safety Board.

The report did not cite a suspected cause of the crash, and noted that "a review of the U.S. Air Force's Avian Hazard Advisory System found the probability of bird activity 'low' in the vicinity of the accident." It also noted that the carcasses of several geese were found at the debris field, with one carcass found embedded in the helicopter's flight control system. Samples of the geese feathers were collected so that officials can work to identify them, the report said.

The NTSB said "all major components" of the helicopter were found at the crash site. Their findings were detailed in the report.

"The main wreckage consisted of the fuselage, engine and tail rotor," the board wrote. "The transmission had separated from the fuselage and was located at the site. The white main rotor blade was fractured found in an adjacent field. The red main rotor blade was also fractured and found near the main rotor hub. The mast nut had separated and was located in the debris field."

A report on the probable cause could take up to two years to complete, according to the NTSB, but investigators have recovered what was left of the helicopter for further exams.

The helicopter crashed just before 11:30 p.m. CT on Jan. 20, in a pasture near Hydro, about 60 miles west of Oklahoma City. It was returning to a base in Weatherford after taking a patient to Mercy Health Center Heliport at a hospital in Oklahoma City. 

The three people killed included the helicopter pilot and two Air Evac Lifeteam crew members on board, a flight nurse and a paramedic.

The NTSB said investigators have recovered what was left of the helicopter for further exams. Their report hree people were killedThe pilot and both Air Evac Lifeteam crew members, a flight nurse and a paramedic, were killed.

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• Oklahoma
• Helicopter Crash