Two people were killed Saturday when their homemade plane crashed in Arizona, officials said.

Glen Tenniswood, 68, and Ron Walker, 78, were flying their experimental “Air Camper” when it crashed southeast of Montezuma Castle National Park, located about 5 miles from Camp Verde, Yavapai County Sheriff’s Office said Sunday.

Family members told police Tenniswood, the pilot, was taking Walker on a short flight around the area. Family members contacted police after they failed to reach the duo for several hours. The plane was located around 8:30 p.m. after authorities tracked it using a cellphone belonging to one of the men.

It’s unclear how long the plane was in the air or what caused the crash.

Air campers are home built. The plans and wood for the craft are available online, but the buyer has to obtain the hardware, engine and covering separately.

Tenniswood’s air camper was a fixed wing single-engine plane. Records show he had two air camper-style planes, AZCentral reported.