Why airborne and shipborne ASW work together

If airborne ASW is best, why do navies still invest heavily in expensive shipborne sonar?

Aircraft are faster and mobile, but ships supply persistence and area defense; combining their sensors and weapons produces the strongest ASW system.

Aircraft can move quickly between sensor positions and provide extra bearings to help locate a submarine. A frigate supplies persistence and can defend a point, while its towed array may provide the first indication that a submarine is present. Both ships and aircraft can pursue and attack a contact, but combining their positions and capabilities makes the task more effective. A helicopter can carry the torpedo toward the submarine while the larger ship and its crew remain farther away. That separation avoids bringing the frigate unnecessarily close to a submarine's firing range.