The move came a day after Defense Minister Song Young-moo pledged to reflect the families' opinions in the formation of the probe team, which currently consists of military and public officials from the Marine Corps, Navy, Army and Air Force.
The MUH-1 Marineone, the Marine variant of the KUH-1 Surion helicopter, crashed at a military airport in the southeastern city of Pohang on Tuesday, killing five of the six Marines aboard and injuring the other.
"The bereaved families have demanded that civilian experts, whom the National Assembly and the families recommend, must participate in the investigation team," the source said on condition of anonymity. "We plan to accept the families' demand."
The Marine Corps will hold discussions with the families to thrash out details about the civilian experts' participation in the probe Friday.
The investigators are said to be putting more weight on technical defects, rather than human error, as the more likely cause of the crash because the chopper's rotor blades were separated from the fuselage just four to five seconds after takeoff.
The Marines received the helicopters in January for transporting its service members and equipment. The MUH-1s are the first major aircraft in the possession of the 28,000-strong troops since they were integrated into the Navy in 1973.
The Marines had planned to introduce a total of 28 Marineones by 2023. Following the accident, the Marine Corps and Army have grounded all Marineones and Surions. (Yonhap)