Four airmen were injured in a mishap involving an E-8C Joint Surveillance Target Attack Radar System at the 116th Air Control Wing at Robins Air Force Base in Georgia Tuesday morning.

In a statement to Air Force Times, the 116th said the ground operations mishap involved the JSTARS’ engine. The four airmen were evaluated for their injuries and released.

2nd Lt. Dustin Cole, a spokesman for the 116th, said the incident is under investigation and would not describe the nature of the damage, say whether other aircraft were damaged, or if JSTARS aircraft are grounded.

The incident was first reported on the unofficial Air Force amn/nco/snco Facebook page.

JSTARS is a modified Boeing 707-300 that serves as an airborne battle management, command and control, and intelligence, surveillance and reconnaissance platform. It has a 27-foot-long, canoe-shaped radome under its forward fuselage that contains an antenna to gather battlefield information on ground forces. That information is quickly relayed to Army and and Marine Corps stations and other ground command, control, communications, computers and intelligence nodes.

The Air Force does not have many JSTARS. In 2016, readiness figures showed 16 in the Air Force’s inventory, but only 11 or 12 were mission-capable at any given time.

The 116th is a Georgia Air National Guard unit that operates JSTARS aircraft, Guard and active-duty airmen were blended into a single unit when it was stood up in 2002.