exact answer would depend on applications it is used for.
The R&TTE Directive would apply, unless the equipment is exempt.
To determine that you need to look at Annex I, specifically:
ANNEX I
EQUIPMENT NOT COVERED BY THIS DIRECTIVE AS REFERRED TO IN ARTICLE 1(4)
5. Products, appliances and components within the meaning of Article 2 of Council Regulation (EEC) No
3922/91 of 16 December 1991 on the harmonisation of technical requirements and administrative procedures
in the field of civil aviation (2).
Then check the definitions in 3922/91.