Former commander believes pilot error ruled out in KC-130T deadly crash in Miss.

Marine Corps KC-130

(CNN) - A former C-130 commander has told NewsChannel 12 he believes pilot error has been ruled out in the KC-130T aircraft crash that killed 15 Marines -- six from Camp Lejeune -- and a sailor -- also from Camp Lejeune -- in Mississippi.

Lt. Col Bill Franchi told NewsChannel 12 of the grounding "It appears to me that they have ruled out pilot error and are narrowing the focus of the investigation to a mechanical component or structural failure. In an abundance of caution it is standard practice to ground all models of aircraft until they can all be inspected."

The Marine Corps grounded all its KC-130T aircraft Thursday.

"Out of an abundance of caution, the Marine Corps took the prudent action not to fly our KC-130T aircraft in the wake of the mishap on July 10 until further notice," the Corps said in a statement Thursday.

The plane is often used for airborne refueling, and can also deliver cargo, troops and equipment.

The transport plane, which was carrying 15 Marines and a Navy corpsman, was moving personnel and equipment from North Carolina to a western base to train before deploying, the Marine Corps said. It has 12 of the aircraft in its fleet.

The crash remains under investigation. The Federal Aviation Administration reported it lost contact with the plane when it was flying at an estimated altitude of 20,000 feet.

Andy Jones, a witness to the crash, described the moments before the plane struck the ground.

"At first it looked like an acrobatic plane, like a stunt plane, blowing the smoke out the back," Jones said. "Then all of a sudden you realized that the smoke was coming off one of the sides of the wing."