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.

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

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

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