Definition

A Certificate of Release to Service (CRS) is a declaration made by appropriately authorised personnel once it has been verified that the task being signed for has been properly carried out. Such a declaration is NOT a statement of airworthiness of the aircraft – the obligation for airworthiness sits with the owner/operator.

Summary

A CRS must be issued upon the completion of any maintenance carried out on an aircraft and its components once it has been verified that the ordered maintenance has been properly carried out in accordance with appropriate organisational procedures and Part 145 requirements. 

It is important to note that a CRS is only related to the scope of work being signed for; it is not a declaration of airworthiness of an aircraft.

In essence, properly performed maintenance restores the aircraft/component to the standards required by the design requirements that themselves have been derived to establish an inherent level of safety and reliability of the aircraft/component.