NTSB: Helo Crash That Killed Four Was Preceded by Attempted Warnings From the Ground

The hose for the device that sucks water up from the surface, often referred to as a "snorkel," started swinging wildly as the helicopter maneuvered and accelerated, something that employees of Firehawk Helicopters, the company that pioneered the use of Blackhawks for firefighting, noticed from the ground but about which the pilot was apparently unaware. One employee on the ground called the control tower to have a controller alert the pilot to the danger and tell him to slow down immediately. Another employee waved her arms in warning to the pilot.

But neither attempt to alert the pilot got there in time, and the hose hit the main rotor blades, causing them to break off, severing the tail rotor as they were shed. The helicopter then spun into the ground, exploding upon impact and killing all four aboard.