An US Marine Corps investigation of the crash of a MV-22B Osprey into an amphibious transport ship in August 2017, which killed three, found that the rotorcraft suffered no mechanical or electrical problems and the flight crew was not at fault.
A paragraph containing the service’s "most probable" explanation of the mishap was redacted in the report, though engineers with Naval Air Systems Command noted problems with the aircraft’s rotor downwash in a non-redacted section.
The heavily redacted report offered few other clues as to what caused the tiltrotor aircraft to strike against the side of the USS Wisconsin off the eastern coast of Australia last year. The aircraft rapidly lost altitude on its approach for landing on the ship’s deck, hit the vessel's side and fell into the Pacific Ocean, resulting in the deaths of three and injuries to 23 others on board.
The MV-22B Osprey was participating in a training mission, simulating the evacuation of a US embassy in Raspberry Creek, Queensland, Australia.
While withholding an official explanation for the mishap, engineers with NAVAIR “discovered the presence of recirculated downwash reflecting off the hull of the ship and back into the rotor arc."
The report seemed to indicate that problems with downwash caused a thrust deficit, which caused a 200 ft/min to 300 ft/min (61m/min to 91m/min) rate of descent seconds before the MV-22B Osprey’s left nacelle, which houses its turboshaft engine, hit the flight deck.
The aircraft mishap had similarities to another accident in 2015, when a MV-22B Osprey crash landed onto the deck of the amphibious transport ship USS New Orleans, according to the investigation. Both aircraft had similar gross weights and experienced recirculating downwash off the reflecting off the hull of the ship.
The MV-22B Osprey pilot in the USS New Orleans accident was faulted for underestimating how much weight his aircraft was carrying, according to a USMC investigation of that incident.
The USMC publicly placed no blame or pointed to any cause in the most recent MV-22B mishap, instead emphasizing that the peace-time training exercise was difficult to perform.
“The mission was complex, challenging, and included flying into and out of a highly congested operational area. Executing this mission required a detailed plan and superior technical performance,” Maj Gen Thomas Weidley, 1st Marine Aircraft Wing commanding general, wrote in an endorsement of the report. “The Marines manning the mishap aircraft were mission capable, fully-trained, and qualified. The mishap aircraft was mechanically sound.”
According to the report, the mishap occurred in daytime with light winds, and no pitch or roll in the USS Wisconsin. Prior to the accident, the aircraft crew reported nothing out of the ordinary, an account which was backed up by the recovered flight data.