The Corps, in a statement released Sunday, said that the Osprey conducted a training flight and returned to base near Bodø, Norway, on March 18 as part of Exercise Cold Response 2022. After refueling, the aircraft left base again but "deviated from the preplanned and authorized flight and entered the Gråtådalen Valley" where it "impacted the eastern side of the valley."
Investigators concluded that, once inside the valley, the pilots "exceeded the maximum angle-of-bank" for an Osprey, meaning it turned too sharply, which caused it to lose altitude and speed, and ultimately crash.
"Analysis of the recovered aircraft data shows the aircraft, while maneuvering within the valley, made a left turn at 68 degrees angle-of-bank ... followed by an overcorrected maneuver with a right turn in excess of 80 degrees from which the aircraft could not recover," the statement explained, adding that the Osprey is rated to bank a maximum of 60 degrees.
The Marine Corps said investigators also looked at five other factors as possible causes: weather, procedures for low-altitude training, problems with maintenance paperwork, inexperience flying in the mountains, and the use of recording devices.
"It was determined that none of the five factors investigated were causal or contributing factors to the mishap," the statement concluded.
The four Marines who perished on the flight were identified days after the crash as Capt. Matthew J. Tomkiewicz, the aircraft commander; Capt. Ross A. Reynolds, the co-pilot; Gunnery Sgt. James W. Speedy, the aerial observer; and Cpl. Jacob M. Moore, the crew chief.
Investigators said they weren't able to determine which of the aircraft's two pilots had control at the time of the crash and there are "currently no recommendations for disciplinary or punitive action for any service members."
Since the crash, the service said that salvage and environmental cleanup efforts have been completed.
The Marine Corps had another Osprey crash in June in Southern California that claimed the lives of all five Marines aboard. The investigation results into that incident have not been released.
-- Konstantin Toropin can be reached at email@example.com. Follow him on Twitter @ktoropin.