Passive: Ashe's attacks grant a stack for 6 seconds. At 4 stacks, she may activate this ability.
Active: Ashe gains 25 / 32.5 / 40 / 47.5 / 55% attack speed and her attacks deal 21 / 22 / 23 / 24 / 25% attack damage as physical damage instead for 4 seconds.
Taken from league of legends wiki:
"The multi-attack effect is similar to Lightslinger and Double Strike, except that on-hit effects aren't applied by the extra attacks.
Triggering Runaan's Hurricane five times is intentional behavior. [2]
On-hit effects are disabled on the latter four attacks and will not be triggered even by Wind's Fury. Each flurry only applies on-hit damage from Runaan's Hurricane once.
Wind's Fury's splash damage is affected by the damage modifier - dealing 「 15 (+5.75 / 6 / 6.25 / 6.5 / 6.75% AD) damage per arrow 」「 15 (+28.75 / 30 / 31.25 / 32.5 / 33.75% AD) damage per flurry 」 to each secondary target."