The Air Force cited pilot error as the cause of the CV-22B Osprey crash on June 13 at Eglin AFB, Fla.

The service said Thursday in a statement the accident investigation board president found “clear and convincing” evidence that the cause of crash was the “crew’s failure to keep the aircraft clear of the lead aircraft’s wake,” which resulted in an “uncommanded” roll to the left and rapid loss of altitude. The CV-22B was flying in a two-ship formation when it crashed at approximately 6:45 p.m. EST during a routine training mission.

All five crew members survived, though the aircraft was destroyed upon impact. The Air Force estimates the loss at approximately $78 million.

The Marine Corps also cited pilot error for an April V-22 crash in Morocco that killed two crew members (Defense Daily, Aug. 20).

The results of the accidents come as the Pentagon seeks to persuade the Japanese government that the V-22s are safe to operate. The Marines deployed 12 V-22s in Iwakuni, Japan, on July 23, which are eventually to be stored at Marine Corps Air Base Futenma, which lies in a densely populated area of Okinawa. The V-22s are slated to replace legacy CH-46 Sea Knight helicopters in Japan.

The potential presence of the V-22s on the base has alarmed local residents concerned about their safety. The Japanese government has insisted on reviewing the results of investigations into the two accidents.

Pentagon officials said the Ospreys, built by a partnership between Boeing [BA] and Textron [TXT] unit Bell Helicopter, have come a long way since being plagued by development problems in the 1990s that produced several fatal accidents and caused the program to be put on hold.

The CV-22 Osprey, the Air Force’s variant for U.S. Special Operations Command (USSOCOM), is a tiltrotor aircraft that combines the vertical takeoff, hover and vertical landing qualities of a helicopter with the long-range, fuel efficiency and speed characteristics of a turboprop aircraft. Its mission is to conduct long-range infiltration, exfiltration and resupply missions for special operations forces.