Date: 202011
Local time of day: 1201-1800
Location: ZZZ.TRACON, US
Flight conditions: IMC
Weather elements / visibility: Icing; Cloudy; 0
Light: Dusk
Aircraft: S-70/UH-60 Blackhawk/Seahawk/Pavehawk/Knighthawk
Operator: Military
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Aerofoil Ice System
Component problem: Improperly Operated
Reporter organization: Government
Reporter function: Pilot Flying; ARMY H-60 CREW
Reporter qualification: Flight Crew Commercial; Flight Crew Rotorcraft; Flight Crew Multiengine; Flight Crew Instrument; Other Rotorcraft-Helicopter
Human factors: Time Pressure; Training / Qualification; Troubleshooting
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Regained Aircraft Control; Flight Crew Took Evasive Action
Contributing factors: Human Factors; Manuals; Weather
Primary problem: Manuals

Narrative: On [Date]; I was acting as Pilot in Command (PIC) of a UH-60 L Army National Guard Helicopter conducting a round-trip air movement of crew and passengers from ZZZ1 to ZZZ. I was sitting left seat; my Co-pilot (PI) sat right seat. I had two crewmembers in the gunner's seats (Row 2); and one passenger in Row 3. Total: 5 souls on board.Earlier in the day; we had flown IFR from ZZZ1 to ZZZ2 for a fuel stop before heading to ZZZ. We had received a military weather briefing and were aware of an AIRMET Zulu for moderate icing along the route. We monitored PIREPS and determined as a crew that the risk of anything beyond moderate icing was minimal; as the few PIREPS observed were for light rime ice at flight levels above our planned flight altitude.The conditions observed on the flight from ZZZ2 to ZZZ were very stable. There was a stratiform cloud layer; approximately 1;000 to 2;000 ft. thick; that we either flew below or above the cloud layer the entire way to ZZZ. We observed no icing.We were on the ground for approximately two hours after landing at ZZZ. I continued to monitor weather conditions; and it appeared they had not changed from the time we landed. I observed the same AIRMET Zulu and a couple of PIREPS reporting light rime above our planned flight level.Prior to departure; my crew and I conducted de-ice checks in accordance with our aircraft's technical manual; which all passed.After an uneventful climb to our requested flight level of 7;000 ft. MSL; we leveled off. At this time the annunciator panel gave us a warning of 'MR ICE DETECTED'. We had discussed this as an expected possibility; acknowledged the caution; and monitored our ice rate meter; which read 'Light Icing Detected'.At this time; I asked ATC if they knew where the cloud tops were. We were informed that they were at approximately 8;000 ft. MSL. Faced with the decision to climb approximately 1;000 ft. through visible moisture; or descend approximately 4;000 ft. through visible moisture; I requested to climb to 10;000 ft. MSL. ATC gave a clearance to 9;000 ft. MSL. We began our climb.In approximately 1.5 minutes; our icing condition worsened. Our ice rate meter pegged out at its maximum indication of severe icing. The helicopter began to shake; and we lost a dangerous amount of our main rotor RPM (a true [anomaly]). I immediately pressed down on the collective to preserve our rotor RPM; took the controls from my co-pilot; [advised ATC] by announcing 'PAN PAN PAN' on ZZZ Approach frequency. I asked the controller to help me get out of the icing situation and was ultimately cleared down to 2;500 ft. MSL.My crew and I flew the helicopter well; in a level attitude at approximately 2;500 ft. per minute. We maintained 100% rotor RPM during our decent and exited the cloud layer at approximately 3;000 ft. MSL. I tested the controls as we got closer to the surface to ensure I would be able to arrest the helicopter's rate of decent. Upon exiting the clouds; the icing condition improved; and the rest of the flight home was uneventful and under VFR conditions.Chain Of Events:How the problem arose: The problem arose from the unexpected encounter into severe icing.How it was discovered: The severe icing was detected by on the on-board ice detection system; severe vibrations were felt by the crew; and the low rotor warning alarm sounded.Corrective actions: The Good: The crew responded to the [situation] well by manipulating the flight controls to preserve rotor RPM; communicating the [anomaly] to ATC; and flying the aircraft out of the icing conditions.The Bad: The crew did not respond correctly to the initial 'ICE DETECTED' caution. In accordance with the UH-60 Operators Manual; 'The ice rate meter activates the ICE DETECTED caution when the BLADE DE-ICE POWER switch is turned off; informing the pilot of the requirement to turn on the system'. Contributing Factors:Neither the UH-60 Operating Manual or checklist clearly emphasizes the immediatememory item actions required in the event of an icing [situation].An updated -1 weather brief was not obtained from the Air Force Operational Weather Squadron by the Pilot in Command.Human Performance Considerations:The perception of the Pilot in Command that the 'AUTO' function on the ice rate meter meant that the system will 'automatically operate upon detection of ice' was incorrect.The perception of the Pilot in Command that the weather conditions would be the same on the return flight as they were on the first portion was incorrect.The actions of both the Pilot in Command and Co-pilot ultimately saved the lives of the crew; however their inaction to turn the de-ice system on was detrimental to the safe operation of the aircraft.Factors affecting the quality of human performance:Neither the Pilot or Co-pilot complained of fatigue or other exogenous factors prior the flight. Both had a good night's rest and were well within the confines of their duty day at the time of the incident.Recommendations:Ensure aircrew are intimately familiar with the de-ice equipment and capabilities on their aircraft. Recommend that changes be made to the UH-60 Operator's Manual and checklist to emphasize the seriousness of an icing [situation] and the immediate response required. This should be an underlined step. Once the ICE DETECTED caution appears; the immediate action required is for the blade de-ice switch to be turned ON.




Synopsis: UH-60 Pilot reported encountered icing; received accumulation warning; but failed to understand and activate the rotor ice protection system. Pilot reference UH-60 Operator's Manual suggestion.