Fluctuating weight in the helicopter's water bucket is believed to have been a factor in a fatal crash last month at the Gold Mountain Fire near Ouray.

The load in the K-MAX helicopter's water bucket jumped dramatically just before the crash, according to a NTSB preliminary report.

The pilot, Nicholas Dale, 56, of Sooke, BC, was killed in the July 12 crash in the Silver Jack Reservoir, The Daily Sentinel reported.

The helicopter was equipped with a 660-gallon water bucket suspended by a 150-foot line. During the first five drops, the loads were around 3,000 pounds each, investigators determined

A gallon of water weighs approximately eight pounds, so a full bucket is more than 5,000 pounds, they pointed out.

On the sixth trip to fill the bucket, the external load indicator showed a rapid increase from around 4,000 pounds to 7,700 pounds as the helicopter pitched up rapidly into an “extreme unusual attitude.”

“The helicopter pitch then decreased rapidly, and the trees, shoreline and water came back into the FOV (field of view). Based on external visual references and the attitude indicator … the helicopter was in an extreme right roll with the nose falling through the horizon toward the water,” investigators wrote after speaking with witnesses and examining data.

The bucket remained attached to the wire rigging from the helicopter with the valve in the closed position.

The NTSB noted that that the investigation is continuing. So, no cause was listed in the report.