Jump pack troops can move up to 12" during their movement phase. A unit of jump pack troops can charge 6" in the assault phase if it is within 6" of the enemy. In other words they move at twice the speed of troops on foot, but assault the normal distance.
As jump packers fly through the air they ignore the effects of terrain unless they move in it. Jump pack troops are affected by terrain differently to infantry because they won't be delayed by it – they will either land safely or not. If jump pack troops enter difficult terrain roll a D6 for each model in the unit. On a 2-6 the model lands without incident, on a 1 the model crashes into the trees, rocks or whatever and is removed as a casualty. No armour saves are allowed.
Errata — Chapter Approved: Main Rules Clarifications (v2.0): Troops with jump packs may not move over enemy troops.
Errata — Chapter Approved: Main Rules Clarifications (v2.0): Space Marines, Chaos Space Marines, Sisters of Battle, Tau, Orks, Dark Eldar and Eldar with jump packs but who also have legs, do not have to use the jump packs when they move, they can simply walk instead. This means they can enter difficult terrain like normal infantry without making dangerous terrain tests.