Since triangles ABC and BAD are congruent, their corresponding sides are equal. This means that the lengths of the sides AC and AD must be equal.
Given:
- AC = 8 m
- AB = 17 m
Since triangle ABC is congruent to triangle BAD, it follows that:
\[ AD = AC = 8 \text{ m} \]
Therefore, \( AD \) is 8 m long.