Subassemblies or components which cannot be repaired or overhauled at the Customer’s facilities and therefore have to be sent back to the Supplier (Level 3 maintenance) shall be highlighted accordingly. When agreed with BT that the Equipment can only be overhauled by the Supplier a detailed process instruction, the Equipment Overhaul Information – Level 3 as part of the Preventive and corrective maintenance instructions , will be required for Customer assurance purposes describing the: