While bent over your model tweaking with the needle valve, too often you hear "I ain't got it.....," followed by a low frequency thump. Usually, several expletives will be inserted, some used imaginatively.
A hand-crafted masterpiece of airframe miniaturisation crammed with state of the art electronic equipment and powered by an exquisitely machined engine is no more.
The pilot, who is frequently the builder/owner, has made an unscheduled landing or has discovered the radio in his hands has a greater range than the eyes in his head.
Your immediate problem is how to react. Generally, it is considered bad form to immediately ask if you may borrow the pilot's glo plug battery. Similarly, you probably shouldn't ask if he's finished with the peg.
Any equipment related reasons for the crash you hear are by definition reasonable. Pilot error is too rare and sensitive to suggest, so don't say, "That's odd, I haven't had any problems on that frequency today," until at least an hour after the crash.
Offer to help go look. Don't say, "It sounded like it hit something solid." Note that most lost models are found and returned. Don't ask if he had his name and phone number in the model or wonder out loud if the model hit a house or car.
If it looks like more than enough people have "volunteered" to help with the search, try to weasel out of going. There are nettles and poison ivy out there, and seeing a grown man cry isn't pleasant. If the pilot takes a plastic bag with him or comes back empty handed to get one, assume the worst.
Actually, in a really bad crash, two hands and a pocket are enough space for everything worth salvaging.
Whatever you do, don't hold a post-mortem on the spot. The pilot probably doesn't want to discuss: Battery condition, poor construction, pilot error, used rubber bands, fuel tank capacity, light blue covering, model selection vs. pilot skill, As best you can, avoid specifics, sound supportive, and look appropriately grave.
You'll want the same consideration some day. Dave P