I thought they did through the use of daemonicly possessed hardware.
There is some old lore about Chaos Navigators that Navigate via another signal. I can find second hand references on the internet; not on in any books though.
Perhaps the chaos navigators are themselves possessed.
Ehh, not exactly "successfully". When I read about CSM warp travel it is very random as to where they will appear in real space, very unpredictable.
They could be. But they don't have to be. As Malus points out, the Night Lords of 10th Company are directed by a non-possessed navigator who has little trouble navigating without the Astronomicon.
At the very least it's no less successful than the Imperium's use of the Astronomicon. But even then, it's far less likely to result in their deaths and has been repeatedly used to slip Imperial blockades so I'd call it pretty successful.
The problem is the warp isn't populated by the 4 gods' demons it's populated by multiple forms, many unaligned. That being said I imagine the gods do protect their followers, but why would you entrust your self 100% into the hands a demonic beings prone to forgetting about their followers?
