LAS VEGAS (AP) — A rented helicopter that crashed near Las Vegas, killing two Connecticut men, was found to have sediment in its fuel tanks just hours before the fatal flight, a preliminary report shows.

However, the cause of the crash last month of the private sightseeing aircraft has not yet been determined, according to the National Transportation Safety Administration report released Tuesday.

The investigation is continuing and could take more than a year, NTSB spokesman Terry Williams said.

The report says a flight instructor had canceled a plan to use the Robinson R44 helicopter on the morning of Oct. 23 to allow time for the fuel problem to be repaired.

Later in the day, the report states, the instructor called the helicopter rental office at North Las Vegas Airport and told officials the “maintenance was done and the helicopter was ready to fly.”

The flight instructor, who was not identified, has not spoken with investigators.

“It is not known what he did to the helicopter before the (fatal) flight, (or) the fuel in the helicopter,” the preliminary report said.

The crash happened less than 20 minutes after takeoff, near scenic Red Rock Canyon National Conservation Area less than 12 miles (19 kilometers) from the airport.

Passers-by on a highway saw the crash and pulled pilot Scott Socquet, 53, of Milford, Connecticut, and passenger Howard Jameson, 27, of New Fairfield, Connecticut, from the wreckage. They died at a hospital.

The NTSB report noted that Socquet was a certified air transport and helicopter pilot.

Investigators found no evidence of a catastrophic engine failure, according to the report.

But they did discover that a main rotor tachometer magnet had separated from its housing, which a manufacturer’s representative said would have led to a faulty revolutions-per-minute reading, the report states.