the loss of power in both engines due to the ingestion of ice and snow. Also causal was the pilot's preflight and in-flight decisions to fly into areas of known and forecast moderate icing conditions in contravention to the prohibitions contained in the helicopter's Federal Aviation Administration approved Type Certificate Data sheet. A factor in the accident was the failure of the company maintenance organization to install the optional ice/snow deflector shields in front of the engine inlets that are designed to prevent the ingestion of ice and snow. An additional factor was the inaccurate and inappropriate weather briefing provided by the second AFSS specialist.