The pilot reported that, while back-taxiing for departure, on a snow-and-ice-covered runway in a strong crosswind, the airplane began to slide towards the left side of the runway. He corrected for the slide back towards the runway center line, but the airplane encountered a “violent gust of wind” and began to slide again. He applied right brake and right rudder while leaving in full right aileron, but the airplane had zero braking action. As the airplane continued to slide, he applied engine power in an attempt to increase the rudder authority and “correct the direction back towards the runway” to no avail. Subsequently, the airplane slid off the left side of the runway, the left wheel impacted a snowbank, and the airplane “tipped” to the left. The airplane came to rest in a nose down attitude, banked to the left at about a 40° angle, and sustained substantial damage to the left wing and aileron. The pilot reported no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. The pilot added that the weather at the accident airport, about the time of the accident, was wind from 120° at 20 knots. The pilot was back taxiing on runway 20.