COPPER MOUNTAIN — In the perilous world of ski racing, downhill is the most dangerous event. Speeds can exceed 80 mph and jumps routinely hurl racers airborne, flinging them more than 100 feet down the slope. A French downhiller was killed this month in Canada while training for the upcoming World Cup season. Downhillers tend to have a cheaters-of-death, “Top Gun” swagger, but last summer the U.S.