14 CFR § 121.123
Servicing maintenance facilities
July 13, 2020
Each certificate holder conducting supplemental operations must show that competent personnel and adequate facilities and equipment (including spare parts, supplies, and materials) are available for the proper servicing, maintenance, and preventive maintenance of aircraft and auxiliary equipment.
[Doc. No. 28154, 61 FR 2611, Jan. 26, 1996]