Jump pack troops fight in close combat just like other troops, using the troops' characteristics for WS, S, A and so on. Because of their great speed jump pack troops can advance 3D6" after an assault and fall back 3D6".
Jump Pack Troops In Assaults
Source: Core Rulebook 3E, p. 92
Jump pack troops fight in close combat using their own characteristics, and can advance or fall back 3D6" thanks to their speed.