Originally Posted by Anno_Domini
When he saved Rachel, the cape helped the fall by surrounding itself around himself and Rachel as well as Batman also landing while wrapped in the cape. When he saved Gordon's son, he dropped down with no support from the cape and got up limping.
That still would have done nothing to slow them down enough to avoid at the very least a number of broken bones. (if not outright death, considereing it looked like the party was held in the penthouse of a high-rise building) There is nothing in that scene to indicate that's why they survived the fall.