An A licence is a line maintenance mechanic! Not an Engineer, they can not issue a CRS for other peoples work or do trouble shooting they can only do minor scheduled maintenance i.e transit/daily/weekly and approved tasks that only they have carried out.
PART-66 /JAR-66.A.20 Privileges
(a) Subject to compliance with paragraph (b), the following privileges shall apply:
1. A category A PART-66 /JAR-66 Aircraft Maintenance License permits the holder to issue certificates of release to service following minor scheduled line maintenance and simple defect rectification within the limits of tasks specifically endorsed on the authorization. The certification privileges shall be restricted to work that the Licence holder has personally performed in a Part-145 organization.
2. A category B1 PART-66 /JAR-66 Aircraft Maintenance License shall permit the holder to issue certificates of release to service following maintenance, including aircraft structure, powerplant and mechanical and electrical systems. Replacement of avionic line replaceable units, requiring simple tests to prove their serviceability, shall also be included in the privileges. Category B1 shall automatically include the appropriate A subcategory.
3. A category B2 PART-66 /JAR-66 Aircraft Maintenance License shall permit the holder to issue certificates of release to service following maintenance on avionic and electrical systems.
4. A category C PART-66 /JAR-66 Aircraft Maintenance Licence shall permit the holder to issue certificates of release to service following base maintenance on aircraft. The privileges apply to the aircraft in its entirety in a Part-145 organization.