The sightseeing helicopter that crashed into the Hudson River last month, killing all six people aboard, suddenly broke into three pieces before dropping into the water, according to a preliminary report released by federal investigators on Wednesday.

The report, from the National Transportation Safety Board, provided no explanation for the helicopter’s midair destruction. It simply laid out some of the facts that investigators gathered immediately after the tragedy on April 10 that left the pilot and a family of five Spanish tourists dead.

The helicopter, a Bell 206L-4 LongRanger operated by New York Helicopter Tours, had been flying at about 110 miles an hour over the river that afternoon, at an altitude of 625 feet to 650 feet, before it rose to about 675 and then descended rapidly, the report said. In the next seven seconds, it fell more than 550 feet before it splashed into the water without its rotor blades or tail at about 3:15 p.m.