Four more Marines were killed in a December 11 crash in North Carolina. Both crashes happened during night training missions. The pilots were said to have descended too steeply, leading the second aircraft into a condition that caused it to stall. They had their certification to be an aircraft commander pulled for six months. The December crash is still under investigation, but sources said there was a failure of hydraulic systems that are believed to have at least contributed to the accident.
Hydraulic pressure is used by pilots to maintain control of aircraft in flight.
The Marine Corps owns eight of the aircraft, the Air Force owns two, and there are two developmental versions of the aircraft operated by the flight test unit at the Navy's Patuxent River base. An experimental version of the Osprey crashed in 1991, resulting in no fatalities, but a 1992 crash killed seven Marines while the aircraft was still in the early development phase. The Marine Corps has invested heavily in the Osprey. CNN National Security Producer Chris Plante, The Associated Press and Reuters contributed to this report. An AOL Time Warner Company.