OAKLEY -- A crop duster pilot killed last week may not have seen the weather tower that his plane clipped, causing him to crash on a remote island in the Delta, according to a preliminary report by the National Transportation Safety Board.

Stephen Allen, 58, died in the crash reported about 11 a.m. Jan. 10 on Webb Tract Island, located about two miles north of Bethel Island. Allen was a resident of Courtland, a town about 20 miles south of Sacramento.

Allen was the only person on board the Rockwell International S-2R Thrush Commander crop duster, which according to Federal Aviation Administration records was built in 1975 and registered to Walnut Grove-based Alexander Ag Flying Service.

According to the NTSB, Allen was applying seed when he crashed. He appears to have struck a 200-foot meteorological tower -- constructed of galvanized tubing and designed to collect wind information -- that was installed on the island in 2009.

The NTSB wrote in its report that "the fact that these towers are narrow, unmarked and gray in color makes for a structure that is nearly invisible under some atmospheric conditions."

A final report about the crash is not expected to be completed for several months.