STOCKTON, Tooele County — Low clouds and restricted visibility may have contributed to a plane crash that killed three people.

In a preliminary report made available Monday, the National Transportation Safety Board said the April 25 crash occurred as the plane was flying from Missoula, Mont., to Alamorgodo, N.M., when it crashed about 1 1/2 miles north of Stockton. All three people onboard — pilot Tom Risk, 66, of Littleton, Colo., and crew members Mike Flynn, 59, of Alamogordo, N.M., and Brian Buss, 32, Alberton, Mont. — were killed. The crew members for Neptune Aviation of Missoula, Mont., were bound for southern New Mexico to help fight a 19,000-acre wildfire.

"According to two individuals who were near the crash site, the airplane could be heard proceeding in a southeasterly direction, and although to them it sounded low, it could not be seen because of the low clouds," the NTSB's preliminary report said. "In a matter of seconds after the airplane passed their location, they heard what sounded like the airplane impacting the terrain."

The NTSB investigation continues. A final cause on the crash is not likely to be determined for at least a year.

— Ben Winslow