It is currently drilling a 17.5-inch diameter hole -- smaller than the 28 inches required to rescue the miners -- in an effort to realign after veering off course over the weekend.
The weather service said thunderstorms and winds in excess of 60 mph in Vermont produced 1-inch-diameter hail and knocked down numerous trees and wires.
The addition of the Fan Drive Gear System added only seven moving parts, but the 18-inch-diameter gearbox had to be engineered to withstand thousands of high-stress takeoffs and landings without maintenance.