Federal investigators are continuing a probe into the crash of a private plane on Oct. 3 near Gary, Ind., that killed two Florida-based veteran rail construction executives, one of them the pilot. But a preliminary report offers few clues as to the cause.

Killed were Patsy J. “PJ” Crisafi, 48, co-founder and executive vice president of Roadway Worker Training Inc. and Vincent “Vinnie” Vaccarello, 45, co-founder and co-president of All Railroad Services Corp., both in St. Augustine.

Crisafi was piloting the plane, a Cirrus SR-22 aircraft, from Smyrna, Tenn., to Gary, Ind.

The Oct. 11 report by the National Transportation Safety Board does not pinpoint what may have caused the crash. NTSB’s report says the Gary airport control tower cleared Crisafi to land but that he did not respond on a changed frequency.

Chuck Baker, president of the National Rail Construction and Maintenance Association, of which both were board members, said witnesses reported either a small explosion or engine failure while the plane was still in the air.

Crisafi’s firm specializes in railroad consulting, employee training and track safety and support; Vaccarello’s provides pole-line removal, tree trimming and vegetation maintenance at rail crossings, among other services, say company websites.

Crisafi was an 18-year management veteran of CSX Transportation, while Vaccarello is a former operations vice president for Balfour Beatty Rail.

“Vinnie and Patsy were both well-known and respected in the industry,” says John August, executive vice president of RailWorks Corp., for which they had worked as subcontractors. He says the executives were headed to Chicago to meet Canadian rail engineering officials.