Marine Corps apologizes after aircraft part falls on 2nd Japanese school in a week, injuring a student A student was injured this time.

 -- For the second time in less than a week, a part from a U.S. military aircraft has fallen on a school in Okinawa, Japan.

A Marine CH-53E helicopter window fell onto the sports field of Daini Futenma Elementary School near the Marine Corps Air Station Futenma at about 10:09 this morning, 1st Lt. Karoline Foote, a spokeswoman from the First Marine Aircraft Wing, confirmed to ABC News.

The Japanese school is located in the southern prefecture of Okinawa. The helicopter crew immediately returned to MCAS Futenma and reported the incident, Foote said.

About 50 students were on the field when the aircraft’s window fell, city education board officials told NHK News, a Japanese public broadcaster. One boy sustained minor injuries after being hit by some gravel that was stirred up when the window hit the field, The Associated Press reported.

Police said the helicopter’s window is about 35 inches wide, 33 inches long and weighs about 17 pounds, NHK News reported.

The window reportedly landed about 10 yards from where the students were playing.

“We take this report extremely seriously and are investigating the cause of this incident in close coordination with local authorities,” Foote said. “For safety purposes and to preserve the site for an investigation, we ask the community remain clear from the object's landing site. This is a regrettable incident and we apologize for any anxiety it has caused the community.”

The incident is “inexcusable,” Japanese Chief Cabinet Secretary Yoshihide Suga said at a news conference today.

The mishap has angered Okinawans, coming six days after a cylindrical object fell on the roof of a nursery school from a U.S. military aircraft passing overhead. There were no injuries and the Marine Corps is also investigating that incident.