Broken engine parts shattered a window on a Ryanair flight shortly after takeoff in Greece last month, causing a man's head to be sucked through the opening before fellow passengers pulled him back inside, U.S. investigators said Thursday.

READ MORE: Man partly sucked out of broken window on flight from Greece was pulled back by passengers

A fan blade in the Boeing 737-800's right engine broke loose, sending fragments flying out of the engine that broke the window and damaged the fuselage in several other places, according to a preliminary report by the National Transportation Safety Board. Greece turned the investigation over to the U.S. agency under international aviation rules.

The July 10 accident happened after the flight departed the northern Greek city of Thessaloniki. Investigators found bird remains inside the engine, suggesting the plane may have struck birds during takeoff, though they haven't determined what caused the fan blade to break loose.

The 61-year-old passenger suffered neck and shoulder injuries and friction burns.