Many of the descriptions of the magical forms of transport in the Eberron (v3.5) campaign setting (e.g. airships, galleons, lightning rails) speak of bound elementals as the source of propulsion for the transport. My question is two-fold. First, what spells (specifically) would be used to bind these elementals? Second, would it be possible to free/destroy/dismiss these elementals, and if so, which counterspell would be used?
According to the Eberron Campaign Setting p267, airships, galleons and the lightning rail require the spell greater planar binding, along with the feat Bind Elemental (Eberron Campaign Setting p51).
The spells dismissal and banishment can dismiss an extraplanar elemental. Both spells have a range of Close and target the elemental itself, so you'd need line of sight to the Khyber dragonshard that contains the elemental—you can't just hit an airship from the ground.
As airships, etc., are essentially giant magic items, dispel magic would only suppress the vehicle for 1d4 rounds, but would not free the elemental, as the spell greater planar binding is instantaneous and not itself subject to dispel magic or antimagic field.
It's not stated anywhere what happens if the dragonshard is broken, but a reasonable ruling would be that it works like trap the soul, which frees the creature if the gem is broken.