A helicopter pilot on routine inspection patrol of oil pipelines crashed and died in northern Wisconsin, authorities said Tuesday.

Enbridge employee Dean M. Bass, 64, of Sarnia, Ont., was heading to Duluth on Monday when his helicopter went down in a remote spot on the Bad River Tribal Reservation, according to the Ashland County Sheriff’s Office.

Searchers with law enforcement, other emergency agencies and Enbridge reached the crash site about 6 a.m. Tuesday, roughly 4½ hours after the helicopter was spotted by the Civil Air Patrol, the Sheriff’s Office added.

Bass had been heading west from the Upper Peninsula of Michigan for a brief stop at the Duluth International Airport before continuing on to Madison, Wis., in his Eurocopter AS350.

“Our prayers and thoughts go out to the family of our helicopter pilot and to his many friends and co-workers,” a statement from Enbridge read.

The cause of the crash is being investigated by the Federal Aviation Administration and the National Transportation Safety Board.