In the last 12 months, the Marine Corps has sustained a troubling nine major aircraft crashes, resulting in 14 fatalities — most of which occurred in a tragic January 2016 helicopter collision — and 11 lost aircraft.

While many of these incidents remain under investigation, the head of Marine Corps aviation said findings so far reveal human components to the mishaps.

“I look at them all in great detail,” Lt. Gen. Jon Davis told reporters in Washington, D.C., on Wednesday. “We are not seeing a material failure component to those aviation mishaps. It’s mainly human error.”

The January 14, 2016, collision of two CH-53E Super Stallion helicopters that resulted in the deaths of all 12 Marines aboard was the result of failure to maintain adequate distance during the night training flight, according to an investigation released in October.

The findings of other mishap investigations have yet to be released, but Davis said it appears they involved aircraft that were in fine flying condition.

In December, two crashes occurred within days of each other in the Pacific. On Dec. 7, an F/A-18C Hornet crashed off the coast of Iwakuni, Japan. Its pilot, Capt. Jake Frederick, ejected but did not survive. On Dec. 13, an MV-22 Osprey disintegrated off the coast of Okinawa after crash landing in shallow water. The five-Marine crew survived with varying injuries.

“They’re still being investigated, but there was nothing wrong with those airplanes, mechanically,” Davis said. “These were — they were qualified, they were proficient — these were crews that had been flying a fair bit, flying in some pretty challenging conditions.”

Davis acknowledged that the wreckage of the crashed Hornet had yet to be recovered, adding complexity to the investigation and making it difficult to rule out a mechanical cause.

In an earlier mishap that occurred Sept. 22, an AV-8B Harrier went into a spin during a combat training exercise and crashed off the coast of Okinawa, the pilot ejecting successfully. The crash prompted Lt. Gen. Larry Nicholson, the commander of III Marine Expeditionary Force, to briefly ground all Harriers in the Pacific.

In that case, Davis said, the aircraft had been “perfectly serviceable” and the incident had prompted him to instruct Harrier pilots not to fly with heavy drop tanks during air combat training.

“The airplane’s supposed to be very spin-resistant,” Davis said. “I’ve never spun a Harrier, and I’ve got 3,300-some hours flying a Harrier.”

These crashes in October and December, along with a mid-air collision of two F/A-18A Hornets off the coast of San Diego in November, all came after Marine Corps officials said they had made changes to increase pilot flight hours and proficiency.

“We’re about three hours per pilot per month better than we were [in May 2015], but that’s not good enough,” Davis said. “We’re still shy of our target. [But] I was surprised with the mishaps we had in October.”

Davis said the Corps has taken steps to be more structured and provide better supervision for sortie planning and execution, among other changes.

In addition to efforts to produce more ready basic aircraft for pilots to train on to meet their flight hour targets, he said, he has stressed to commanding officers that “we have a group of aviators who have not flown as much as we did when we were growing up, and we just have to be more structured and more pedantic about how we fly.”

— Hope Hodge Seck can be reached at hope.seck@military.com. Follow her on Twitter at@HopeSeck.