FRESNO COUNTY (CBS SF) — A helicopter pilot called in to assist firefighting efforts near Fresno County died when the vehicle crashed Wednesday.

Cal Fire officials said the pilot was hired on a Call When Needed (CWN) basis and was assigned to a water-dropping mission on the Hills Fire, approximately nine miles south of Coalinga.

After the pilot’s Bell UH-1H helicopter crashed, ground crews responded immediately.

The pilot, who Cal Fire officials did not identify, was the only person in the helicopter during the crash.

Cal Fire said that the National Transportation Safety Board (NTSB) started an investigation into the crash Wednesday, with Cal Fire assisting.