SAN FRANCISCO (CBS SF) — A man died Sunday afternoon in a hang gliding accident in San Francisco, according to the San Francisco Fire Department.

Fire dispatchers got the first report of the incident at about 3:50 p.m. at Fort Funston, Battalion Chief Jeff Barden said.

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Witnesses said the man flew the hang glider directly into a hill without trying to steer away from it, Barden said.

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He said that first responders are not sure whether the man suffered a heart attack or whether he got caught in an updraft of wind.

Barden estimated the man was in his 50s. He was hang gliding by himself, Barden said.

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