A Marine Corps investigation into the May 17 fatal crash of an MV-22 Osprey at Bellows, after consecutive landing attempts in the same severe brownout conditions, apportioned blame all the way around but said pilots could have picked an alternative flight profile or alternative landing site when it became clear the engulfing sand and dust were far worse than expected.

At 110 feet the tilt-rotor Osprey’s engine ingested enough grit to disrupt airflow to the port-side turbine engine, causing a compressor stall and engine failure, leading to a “rapid, unrecoverable descent.”

Two California-based Marines were killed. Lance Cpl. Joshua Barron, 24, died immediately following the crash of the aircraft, which has an empty weight of 33,000 pounds. Lance Cpl. Matthew Determan, 21, died days later. Most of the 20 other Marines aboard the Osprey sustained varying injuries.

The financial loss of the Osprey, which lands like a helicopter but tilts its propellers forward in level flight, was pegged at $67 million after it crashed, broke into pieces and burned.

Ironically, although the investigating officer said the pilots demonstrated “poor judgment” in trying to land after hovering for 35 seconds in brownout on the first try and 45 seconds on the second, they “followed all orders, directives and SOPs (standard operating procedures) related to operation of the MV-22B.”

Both attempts were within 60-second hover “warning” guidelines written by the Naval Air Training and Operating Procedures Standardization program, or NATOPS, said the investigator, whose name was redacted in the released report along with the names of most others involved.

It might have appeared that the crew of the Osprey called “Mayhem 11” failed to adhere to a NATOPS warning by exposing the aircraft to brownout conditions for a “prolonged period of time,” the investigator said. “However, the term ‘prolonged’ is not clearly defined,” the officer added.

NATOPS “does not adequately explain whether a single re-attempt of a landing following a wave-off in brownout conditions is appropriate,” the investigator said.

The 15th Marine Expeditionary Unit out of Camp Pendleton, Calif., was part of the Essex Amphibious Ready Group and participating in an exercise in Hawaii. Five Ospreys from the USS Essex were to drop off Marines at Marine Corps Training Area Bellows.

The Honolulu Star-Advertiser obtained the more than 2,200-page investigation into the crash of Mayhem 11 as the result of a Freedom of Information Act request. Although the pilots were faulted in the deadly accident for not using common sense, the Marine Corps investigation found much more in error.

Among the findings:

>> The medevac plan was not understood or known by all participants in the mission.

>> An on-site examination of the Bellows landing zones was never conducted.

>> The MV-22B procedure manual recommends a minimum 200-by-200-foot reduced-visibility landing zone. Landing Zone Gull where the crash occurred is 154 by 506 feet.

>> The unit did not adequately plan for the possibility of a mass-casualty event.

>> The battalion surgeon incorrectly stated CH-47 Chinook helicopters were available for medevac to Tripler Army Medical Center, a mistake that was corrected before the mission but which showed “a lack of rigor put into this plan.”

“In this case the MEU and ACE (Aviation Combat Element) had ample time and opportunities to conduct a site survey and complete detailed planning prior to execution but failed to do so,” the investigating officer said.

The investigation said “improper medevac planning” led to the arrival of first responders at locked gates or in the wrong area, evacuation was delayed and some casualties were transported via civilian vehicles rather than ambulances.

On the day of the crash, Mayhem 11 descended to 1,500 feet from 12,500 feet at about 11:30 a.m. Mayhem 11, 12 and 13 began a right turn to LZ Gull. Mayhem 14 and 15 were in a holding pattern.

Mayhem 11 lined up in the wrong landing spot and experienced brownout conditions that engulfed the aircraft for 35 seconds at 25 to 35 feet altitude. After a “wave off” and second try, Mayhem 11 was exposed to brownout for 45 seconds between 25 and 110 feet altitude before crashing, according to the investigation.

Mayhem 13 performed a steeper approach to the west resulting in less brownout and a successful landing.

One Marine on Mayhem 11 said after the engine died “we were free floating for a couple seconds then as if on a roller coaster ride.” He added that “I knew we were in trouble and it was going to crash. Before we hit the ground I closed my eyes and thought of my wife and child and how I was going to die before my child could understand who I was.”

Once on the ground and after the debris settled, he started looking for his team.

A witness near the landing site who said he had experienced a compressor stall in an Osprey before said he heard several loud “pops” and watched the aircraft disappear into the dust cloud. Running to the aircraft, he saw one of the proprotor hubs 100 feet from the fuselage. The tail section had separated, and the main fuselage was beginning to catch on fire. All the Marines had been evacuated.

The investigating officer recommended that four unnamed individuals receive evaluation, counseling and “appropriate disciplinary or administrative action” for their roles in the accident.

The same was recommended for the Aviation Combat Element commander for failing to supervise the landing site survey, and the 15th MEU commander for failing to supervise the landing zone selection and medevac plan.

Lt. Gen. John Toolan, commander of Marine Corps Forces Pacific at Camp H.M. Smith, said in his endorsement of the investigation that while the excessive intake of sand and dirt caused the engine to fail, “the failure of the pilots to fully appreciate the circumstances of the landing and adjust their actions accordingly were the primary factors that put the aircraft in danger.”

He also agreed there was inadequate planning for the mission.

Asked what disciplinary action was taken and against whom, Marine Corps spokesman Lt. Col. Chris Perrine said in an email, “The commanding general of I Marine Expeditionary Force has thoroughly reviewed the investigation conducted by U.S. Marine Corps Forces Pacific into the May 17, 2015, MV-22 mishap at Marine Corps Training Area Bellows. He has considered each individual case and directed appropriate administrative action. Please note that administrative actions are covered under the U.S. Privacy Act and not releasable.”

Other recommendations included expedited development of an improved dust and sand filtration system and clarification of the NATOPS manual regarding 60-second brownout hover guidelines.

Marine Corps Forces Pacific said in a news release in late November that as a direct result of the crash, a NATOPS interim change was published Nov. 17 decreasing exposure time in reduced-visibility landing profiles.

Capt. Sarah Burns, a Marine Corps spokeswoman at the Pentagon, said Naval Air Systems Command “is exploring solutions to reduce the ingestion of particles into the V-22 engines.”

An “improved inlet solution,” engine monitoring, improved engine air particle separator and improved procedures “are all possible solutions that are being explored. They are all being looked at to reduce particle ingestion,” Burns said.