) the advice given was to throttle back... keep the wings level, and by adjusting pitch, keep the speed between (IIRC) 40 and 60 knots (something like that anyway). Our pilots said if you manage that, the impact should be completely survivable. Now we were operating over a very large, flat area (sheep paddocks mainly) so no real obstructions to worry about...AND the aircraft was a Cessna 172 Skyhawk. Not exactly large OR heavy. I am certain NONE of that advice is applicable to a large aircraft that needs a proper runway!!! 
These are always somewhat hilarious, but the number who think they could is surprising. I’d put the figure at a just a couple of percent, and they’d be young gamers.
I once took a friend, who was a very avid MS Flight Sim gamer to the 747-400 sim. I’ll admit that he did better than I expected, ‘cos at least he knew where most of the buttons were, and what they did, but manually flying..he did far worse than he expected. He, at least, knew how to set up an autoland.
Looking back at basic flying training at Pt Cook, the only students who would manage a landing on their first attempt (and this is with an instructor right next to them, and having learnt all of the numbers, etc) were the ones who had already flown. And even if they had a licence it wasn’t guaranteed. It’s always amusing when people talk about getting ATC’s help. Firstly they’re unlikely to have any knowledge of flying or the aircraft, and secondly, and perhaps most importantly, how do you actually talk to them?
It would be a better outcome than other possibilities, but it’s still going to be a 120 kph accident, in a structure that is nowhere near as rigid as even a cheap car, and without things like airbags. Just keeping wings level is something many have immense difficulty with.
Hmm, and I thought I greased it. Deflated.....
So have you ever thought how you would approach the situation where you were on the other end of a radio to someone who ended up sitting up-front trying to land (say for example a 767) aircraft with incapacitated pilots?
I once asked a CSM, who shared the strange belief that he could land the aircraft, just how he'd start off. So, got him to look around, and pick any button that he though would be useful, and when he was ready, we'd push it. So, dutifully pushed it, and he was rewarded with the extremely loud sound of the autopilot disconnect wailer. So, now there's two problem, manual flying, and needing to get rid of the noise before he can hear anything.
If they're in a light aircraft, I won't be any help at all.
And there lies the rub. How can I start will telling them how to locate the PTT button, without them already knowing how to use the PTT button?
I was suggesting the passenger may have some light experience, and now captive in an aircraft type of which you are familiar.
Again, a big assumption, but perhaps somehow the message has gone to ATC that the aircraft is in distress (inflight internet access perhaps?) and passenger in row-0 manages to don the pilots comms headset so can hear, but does not touch anything until instructed by experienced pilot. Or perhaps the instructions are via Skype call over in-flight internet service?
I wonder how far they’ve tested that. Some aircraft will ultimately disconnect the autopilot if not correctly configured for landing and at a very low level. Be a bit sad to be looking good, but then at 100’ have the autopilot dump it back into your hands, and very likely with a strong nose up out of trim situation as well (because some aircraft put in quite lot of nose up trim, as a safety measure in case of accidental disconnect). I see no reason not to put the gear down. The autothrottle will handle the drag change, and if you’re worried about the braking side of it, then many have some form of autobrake, which is a very simple dial selection.
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