We were solidly in the clag with a student flying a Sikorsky S-58 on an ATC clearance for a block of airspace over an NDB holding pattern from 4000 to 6000 feet MSL. The windshield was turning opaque and ice built upon the two massive main gear struts. My student added power to maintain our 80-knot holding speed, and the vibration level increased. I knew that our main rotor blades were icing up. After adding approximately five inches of manifold pressure the helicopter shook and then the vibrations diminished. We reduced power back to normal, as the entire process repeated itself.
展开▼
