IMPERIAL COUNTY, Calif. (NewsNation) — Two branches of the U.S. military are investigating after two aircraft crashes in as many days occurred in Southern California.

The latest crash on Friday involved an MH-60S Seahawk helicopter. The Navy said all four crew members survived.

One crew member received an injury that was non-life-threatening and was taken to a hospital, according to Naval Air Facility El Centro.

A crash involving an MV-22B Osprey on Thursday — also in Imperial County, California — killed five Marines during a training exercise.

Despite the proximity of the crashes, military aviation expert Richard Martindell said they are not related.

“It’s totally coincidental; there’s no relationship between the two,” he told NewsNation.

More than 40 people have died while flying on Ospreys since 1991. Most recently, in March, one crashed in Norway, killing four American service members participating in a NATO exercise.

The Seahawk is in widespread use by the U.S. Navy and Martindell said the Marines have worked to address the aircraft’s problematic history.

“It will take 30 to 60 days to investigate both of these aircraft,” he said. “It will take up to a year for the Navy and the Marines to review the results and decide if they want to make any changes to operational procedures or design changes.”

The Marines have not released the identities of those killed.

On June 3, a Navy pilot was killed in an F18 Super Hornet crash about 300 miles north of the two incidents this week.