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The bird -- a female red-tailed hawk that probably weighed about 3 pounds -- hit the top of the AH-1W Cobra attack helicopter and damaged the pitch change link around 1 p.m. Sept. 19, according to U-T San Diego.

Within seconds, vibrations from the impact caused the main rotor to separate from the aircraft, the newspaper reported.

The cause of the crash was determined by a Marine Corps investigation and released in a report from the 3rd Marine Aircraft Wing.

Sky10 pilot Dave Vargas was on scene shortly after the deadly crash.

"By the time we got there, everything had already burned pretty significantly to where we couldn't see any actual components of the helicopter." Vargas said, "We did see basically the charred remains and the emergency crews working."

Capt. Jeffrey Bland, 37, and 1st Lt. Thomas Heitmann, 27, of Marine Light Attack Helicopter Training Squadron 303 were killed instantly in the crash, which sparked a 120-acre-plus brush fire on the North County installation. Both Marines hailed from Illinois.

The breaking news hit home for Vargas. Before he worked with Sky10, Vargas was a Marine and in the same squadron as Bland and Heitmann.

"To be honest with you, it's sad," he said.

Investigators concluded that "the bird-aircraft strike event was likely unavoidable," because any drastic maneuver to avoid the bird also could have caused a crash, U-T San Diego reported.

Vargas said at more than one hundred miles an hour even a hawk weighing only a few pounds can destroy an attack aircraft.

"It comes with the territory; when you're out there flying, you never know what can happen," he added. "Anything can happen at any time, whether you're in the military or you're in the civilian side."

Investigators recommended that the Marine Corps work with Naval Air Systems Command to study the feasibility of redesigning the aircraft's transmission fairings and the pitch change links to make the AH-1W less vulnerable to bird strikes, according to the newspaper.

It was not clear whether the recommendation would be followed.

The pitch change links can be seen between the rotors and the body of the aircraft. They control how it tilts and how high it flies. Vargas said is one of the worst places to take a hit.

"When something like that is coming to the pitch links, yeah, it's definitely going to snap it off," Vargas said.

Vargas said military pilots often learn to fly on the Sky10 model, which is made by Bell Helicopters, the company that produced the Cobra.

Sky10 was involved in a bird strike in 2008 near Carlsbad. It hit a stabilizer wing on the tail of the aircraft. No one was hurt in the incident.