The announcement comes four days after the Dec. 13 incident that caused some local furor.
The 17-pound window fell near where about 60 children were participating in physical education on the sports field of Daini Futenma Elementary School, according to reports.
"A thorough inquiry determined that the incident was caused by human error," 1st Marine Aircraft Wing officials said in a statement released Sunday. "The window in question is designed to be removed in order to assist pilot egress in an emergency situation. The appropriate procedures for ensuring the window was secured were not correctly followed."
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Following the incident, the Corps is conducting a full-court press on training, according to the announcement. All Okinawa-based CH-53E aircraft have been inspected, with a focus on the windows, to ensure there are no mechanical or structural problems.
Aviation personnel have gotten retraining on proper window installation procedures, and maintenance crews have reviewed aircraft maintenance procedures, including those specific to the helicopter windows.
Routine maintenance days and safety meetings, as well as regular inspections and upkeep, will continue to ensure the aircraft remain safe for flight, according to the release.
"1st MAW has taken comprehensive actions to ensure the safety of all Okinawa-based CH-53 aircraft, the aircrew that fly in them, and our broader community," officials said.
The safety of Marine Corps aircraft, which operate around and over Okinawan communities, has long been a concern for some on the island. Okinawa Gov. Takeshi Onaga, an outspoken critic of the Marine presence, called the recent incident "unforgivable."
It's particularly bad timing for the Marine Corps, coming just three months after another Super Stallion had to put down in a private field near Okinawa's Northern Training Area after catching fire in flight. The cause has not been made public.
"This incident is regrettable, and we again apologize for the anxiety it has caused the community," 1st MAW officials said of the window incident. "We strive to be good members of the Okinawan community and to ensure the safety of both our personnel and our community in which we live and serve."