The helicopter was deformed and destroyed in the __?___ collision.

The helicopter was deformed and destroyed in the inelastic collision.

Explanation:

When two object collide there exist two way of colliding: elastic collision and inelastic collision. Two terms are considered during the collision: kinetic energy and momentum. If both of these terms are conserved in any collision then there is no significant loss of property, this is called as elastic collision. If only momentum is conserved but kinetic energy is converted into other forms then it is inelastic collision. In inelastic collision, the energy is lost in the form of vibration, sound etc. causing the damage to colliding object. Hence the deformation of helicopter was due to inelastic collision.