As V-22 Osprey tilt-rotor aircraft are increasingly deployed around the world, the Marine Corps said a May 17 "hard landing" by a packed aircraft at Bellows that killed two Marines and injured others was the result of pilot error in "severe brownout conditions."

"This tragic mishap led to the loss of two Marines, major aircraft damage, and injuries to most Marines aboard," Marine Corps Forces Pacific said in a news release Monday.

Lance Cpl. Joshua E. Barron, 24, assigned to Marine Medium Tiltrotor Squadron 161, died that day in the crash at Marine Corps Training Area Bellows. Lance Cpl. Matthew J. Determan, 21, with the 3rd Battalion, 1st Marines, died two days later. Both Marines were based in California.

The investigation found the "main contributing factors" in the crash were pilot performance and improper site survey of Landing Zone Gull.

"The pilots did not violate any regulations or flight standards," the Marine Corp said. But pilot decision-making failed to take into account "contributory events" that led to the MV-22 mishap.

The first landing attempt indicated the "reduced visibility landing" level of the landing zone was much higher than anticipated. A proper risk assessment would have prompted the pilots to choose an alternate flight profile, path or landing site to avoid the "severe brownout conditions," the release said.

The Osprey takes off and lands like a helicopter but tilts its rotors forward to fly like a plane.

The investigation found that repeated, sustained flight time in brownout conditions due to dust or sand in the air while attempting to land caused the left engine to stall, resulting in an unavoidable free fall.

Specifically, the sand and dust ingestion caused a buildup of material on the turbine blades and vanes, leading to a compressor stall, which decreased lift and resulted in the crash, the Corps said.

As a direct result of the crash, a Naval Air Training and Operating Procedures Standardization interim change was published Nov. 17 calling for reduced Osprey exposure time in reduced-visibility landings.

"The investigation has also recommended improving the engine air filtration systems for the MV-22," the Marines release said. "The investigation recommendations also include the potential for disciplinary and administrative actions."

The Marine Corps concluded that the mishap did not occur due to any misconduct or negligence on the part of the air crew.

Twenty-one Marines and a sailor were aboard the Osprey from the 15th Marine Expeditionary Unit. The aircraft had taken off from the amphibious ship USS Essex, 100 miles offshore, for training on Oahu.

Dr. David Kaminskas, a physician camping at Bellows, arrived at the crash less than five minutes later to find all the crew and passengers clear of the burning aircraft.

One man was unresponsive and didn’t have a pulse, so he attended to others who were complaining of severe back pain and unable to move, he said previously. Some appeared uninjured and asked to help.

One of the men told him the Osprey had touched down on the ground in a cloud of dust, prompting him to take off his safety belt, but then the aircraft suddenly leaped up and then fell back to the ground.

First Lt. Natalie Poggemeyer, a spokeswoman for Marine Corps Forces Pacific, said that "factually, the MV-22 is safe." In development, the Bell Boeing Osprey experienced some deadly crashes, claiming dozens of lives.

"(The Osprey) has a Class A mishap rate (which result in fatality or total permanent disability, loss of an aircraft, or property damage of $2 million or more) on par with other Marine Corps aviation platforms," Poggemeyer said in an email. "The MV-22B Osprey provides commanders with unprecedented agility and operational reach, and the aircraft’s effectiveness and survivability have been demonstrated from land-based operations in Iraq and Afghanistan to sea-based operations in Haiti, Libya, the Philippines, and most recently in Nepal and Saipan."

The Marine Corps’ 2015 aviation plan said Marine Medium Tiltrotor Squadron 268, VMM-268, will relocate with Ospreys to Kaneohe Bay at the beginning of fiscal year 2017. They will be followed by VMM-363 beginning in the first quarter of fiscal 2018. A total of 24 Ospreys are expected to be based in Hawaii.

Honolulu Star-Advertiser reporter Timothy Hurley contributed to this report.

151123 Osprey Release by Honolulu Star-Advertiser