I think it's a DC 15 Ref save to catch the lip...

Achkby, Flying Halfling Sorcerer

With his new, increased speed, Achkby underestimates his jumping aptitude and flings himself quite a bit more vigorously horizontally than vertically.
In fact, he flings himself forward with such alacrity that he goes hurtling by those party members who came down just on the far side of the chasm ("Waaaa!"), and crashes to a sliding, skidding landing nearly twenty feet past them.

Panicking as he sails into the duskiness further down the tunnel, he quickly hops to his feet and backpedals up the tunnel to the group.
"Wagh," he pants to the group over his shoulder. "Did we lose it?"