Running Out of Torque, Altitude, Airspeed and Ideas
CHIEF WARRANT OFFICER 4 JOSEPH PIKAL
Headquarters, U.S. Army Europe and Africa Safety Office
It was winter and my unit was tasked with providing medevac coverage to the implementation forces that would oversee the adoption of the Dayton Peace Agreements recently signed by the warring factions of the former Yugoslavia. Our flight of three UH-60A Black Hawks would depart Landstuhl Army Heliport, fly to Munich and stop for fuel, and then continue to Linz, Austria. The next morning, we would depart with a refuel at Graz, Austria, then to Taszár, Hungary, to stage before going south into Bosnia to perform our mission.
All legs of the flight would be conducted in instrument flight rules (IFR), as winter clouds had set in over Europe and low ceilings in the Alps made visual flight rules (VFR) flight impossible. Freezing temperatures and light rime icing was forecasted for the entire flight. Because we flew in the ice every winter, all of the pilots had experience in these conditions. Our crew chiefs and maintenance personnel also put in extra effort to keep the blade de-ice systems fully operational, so I felt at ease with a flight into icing conditions.
My Black Hawk weighed about 19,800 pounds, and our hover torque was around 91%. I was a little concerned because this was the heaviest helicopter I’d flown outside of sling load training; however, temperatures were close to freezing, and the two 1.0 ETF engines we had would produce more than enough torque for hover and cruise. We’d also be burning fuel during flight.
The flight to Munich was uneventful, except that one aircraft was grounded due to electrical problems. The two remaining aircraft continued to Linz and landed with no problems. The following morning, we prepared for the next leg of the flight. The weather was the same as the previous day, and we completed our pre-flights and run-ups. During run-up, however, our sister ship experienced a maintenance issue and was unable to continue. Since we could not assist, we completed our HIT check, asked for IFR clearance and departed for Graz.
We climbed to our cruise altitude of flight level (FL) 90 and leveled off. During our climb, we noted that the temperature was minus 4 C and there was visible moisture in the air. We turned on the pitot heat, engine inlet anti-ice and windshield anti-ice. Shortly afterward, the “ice detected” caution light illuminated, so we turned on the blade deice power. I looked at the FM homing antenna out my door and the wire strike protection system (WSPS) deflector to monitor ice accumulation. After about 15 minutes, there was nearly an inch of white rime ice on each surface. I had seen this many times before, so I was not concerned.
We were about three-quarters of the way through the flight when I noticed the clouds had turned from light to dark gray. I didn’t know if we had more clouds above us or if they were getting thicker. I glanced at the ice rate meter. It quickly swung over to “heavy” and stayed there for a short time before slowly moving back to “light.” I then looked at the FM homing antenna and WSPS to confirm what I‘d just seen on the ice rate meter. The fluffy white rime ice was now covered in a coating of clear ice.
After a few minutes, another layer of rime ice started to build on the clear ice, causing the ice rate meter to swing to “heavy,” stay there a minute or two, and then return to “light.” This cycle continued until we had 3 inches of mixed ice on the antenna and WSPS. About this time I noticed the aircraft was starting a descent, so I alerted the co-pilot, who added additional power to maintain altitude and airspeed. I also noticed we would develop a horizontal shimmy as the weight of the ice built on the blades before shedding off.
As the ice continued to build on the blades and airframe, we required more power to maintain our flight profile. I now knew that the forecasted icing conditions were incorrect and we could no longer let ice accumulate on the aircraft. I informed the controller we were picking up too much ice and requested to descend to FL 70. I knew that the temperature would not change much, but hoped we could get out of the clear ice.
At FL 70, the mixed ice continued to accumulate until we had another 2 inches on the aircraft. We were now using max torque available to maintain altitude and airspeed and had started keeping time for the 30-minute TGT window. I informed the controller that ice was still accumulating and that we would like to descend to the lowest altitude for radar vectors to the airfield. He said we were already as low as we could be and still remain at minimum safe altitude for IFR flight. So we continued to fly as the ice continued to build.
To maintain RPMR and altitude, we slowed our airspeed in 10-knot increments when required. We went from 120 to 90 knots indicated airspeed over the next 20 minutes of flight time. I told the controller that I didn’t think we could maintain altitude for much longer and asked when he could let us descend. He said we were still over mountainous terrain and that, “You must not descend!” The fear in his voice made me realize that descending on our own accord to exit the icing was not an option.
As we slowed the aircraft to 80 knots, the controller gave us our clearance to 2,000 feet mean sea level (MSL). We came out of the clouds at 4,000 feet MSL with about 6 inches of mixed ice on the aircraft. The ice started to shed as we warmed up, and by the time we landed at Graz, there was not a single bit left on the aircraft.
As we finished our shutdown and prepared for refuel, I was relieved to be on the ground. The mixed ice, the rate of accumulation, and its weight and effect on the aircraft was a new experience — one I hope never to experience again. Although the weather forecast had been inaccurate, I felt my crew, the aircraft, and the anti-ice and blade de-ice systems did their jobs quite well. We had to trade airspeed to maintain our altitude, but that bought us enough time to get away from the mountains to make a safe descent.