This is my first season watching the falcon cams. I've seen the larger Radisson chick trying to get up onto the ledge. My questions are: does a chick ever fall off the ledge? If it does, can a parent retrieve it and put it back or is it lost? 
Our peregrines (
Falco peregrinus anatum) have evolved to nest on cliff ledges, most of which are much smaller and narrower than the ledge they are currently occupying. As a result, the chicks are hard-wired not to fall. So to answer your question, no chicks don't, as a rule, fall from the nest boxes or nest ledges prior to fledging (taking their first flights). The longer they stay on the ledge, the more time they have to strengthen their wing muscles so that when they do take that first step off the building (either on purpose or by accident) then better their chance of surviving the first 24 hours after fledging and then the first 10 days of fledging.
The only time we have ever had a chick "fall" before fledging (first flight) age, was when one had a cerebral accident (like a stroke) and parts of its brain started to die. When the necrosis reached the chick's balance centre in the brain, the chick literally lost it's ability to keep itself upright (standing or sitting) and it's confusion, it got too close to the edge of the box and it toppled over the edge and fell to it's death. Sounds terrible but actually given what was happening its brain, it was probably a more human way to die than say waiting until the necrosis had reached the breathing centre at which point the chick would have lost the ability to breathe which would I figure would have been a much less humane way to die.
To answer the second part, no, at this age there is not much an adult can do to help the chick - as you can see on the webcams, the chicks are the size of their fathers and the female chicks are close to their mother's size already.
The closer the chicks get to fledging age, the safer they will be - in part because they will be larger and stronger, in part because they will be more comfortable sitting on the edge of the ledge and on the drain cover which will (hopefully) help them to be wiser and they will fledge when they are ready not because they got too excited and fledged earlier than they could have/should have. Not much we humans can do about it other than to keep our fingers crossed.
Hope that answers your questions Dagny
