The Osprey crash in Waimanalo that killed two Marines in May was due to “pilot performance,” the Marines said today after completing an investigation.

The Marines found that the pilots did not properly survey the landing zone site. A proper risk assessment of the site would have prompted the pilots to choose another flight path or landing site that would have avoided severe brownout conditions, the statement said.

“The investigation found that repeated, sustained flight time in brownout conditions (an in-flight visibility restriction due to dust or sand in the air) while attempting to land caused the left engine to stall, resulting in a loss of power that placed the aircraft in an unavoidable freefall to the ground,” the Marines said.

The MV-22 Osprey crashed while trying to land during a training exercise on May 17 at Bellows Air Force Station with 21 Marines and a Navy corpsman on board. The crash killed Lance Cpl. Joshua Barron, 24, of Spokane, Wash., and Lance Cpl. Matthew J. Determan, 21, of Maricopa, Ariz. Most of the others on board were injured.

Engine power from the Osprey decreased on both engines each time the aircraft entered a low-altitude hover over the landing zone as dust and sand particles increased in the air due to rotor wash, the Marines said today. The sand and dust caused a buildup on the turbine blades which led to a compressor stall in the left engine, decreasing lift and resulting in the hard landing.

The Marines added that the crew performed all emergency procedures accordingly and the crash was not due to any crew misconduct.

“The pilots did not violate any regulations or flight standards; however, pilot decision-making failed to take into account the contributory events that led to the mishap,” the Marines’ report concluded.

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