Adeptus-B said:

You can't "un-assign" a marine's power armour. A marine's armour is a part of his body, it belongs to him as much as his second heart belongs to him. I can understand some missions necessitating scout armour. Give your players a choice which armour to use, recommended scout or power armour. When they choose their power armour for power-gaming reasons have them get found out pretty early, the target beats feet, they get surrounded by infinite enemies and a large number of elites, almost (or some of them killed), and the mission fails. At the recap make it obvious the power armour gave you away and maybe next time when a mission calls for scout armour they'll take it.

Though I will be honest the above is pretty harsh. I wouldn't be amiss to making the mission an auto-fail unless the PA equipped marines pass numerous -40 to -60 tests.

It is mentioned in normal 40k background and in FFG DW background descriptions space marines wearing scout armour will bring visors and the like to replicate some of the functions of their normal helmets. I believe such visors (or the guidelines for them) are in RoB.

 It's possible to get jump packs for non powered armored troops, there's one listed in Dark Heresy, but this isn't going to be the same as the ones that Assault Marines (as previous people have said), due to the power required, the weight and the power supply.

BUT I can't see that they are likely to be available generally in DW, there is a bit of a clash of specifications, giving some one the much lighter easier to stealth armor and then putting a super obvious rockets on the back of them.

 That being said, I can imagine some chapters that are willing to blast their neophrite scouts into melee on the jump packs (perhaps the Doom Eagles) but that would only be because the scouts are not yet worthy of wearing Astartes Power Armour. Not that we'll ever see that on TT.

And as has been said, if it's just to land on a planet from altitude then the much quieter and darker Grav Chutes seems much a much better choice. So much so that I can see that working in TT and the Raven Guard (as well as others) would be screaming for it as an option.

Decessor said:

Sure, power armour helmets won't work with unpowered scout armour- but why no carapace helmet? I'm pretty sure my players will ask for them…

Thebigjul said:

If it's irrelevant for the head, it would be irrelevant for every other location, too.

So, I'm guessing that I should just let them have carapace helmets if they opt for scout armour (I suppose I could glue extra helmets from the Cadian frame to their belts on the miniatures) and just chock it up to "Not everything in the RPG works like it does in the Tabletop game"…?

I had another thought. The power armour helmets include autosenses. One of the lesser noted features of autosenses is that it compensates for the loss of vision and hearing that wearing a fully enclosed helmet would normally entail. So, a scout wearing a fully enclosed helmet that isn't powered and lacks autosenses would be hard pressed to do their job of scouting as their senses would be impaired.

 There are times when even space marine scouts are going to need enclosed helmets. I've seen people use the Forgeworlds Elysian drop troops helmets.