The BT part number is a BT unique number generated automatically in the TCUA system. The BT part numbering follows the Form, Fit, Function rule (see Change Management Directive 000450, rev.7). The supplier is obliged to follow the same rule in order to ensure traceability at all times. A new supplier´s (or sub-supplier´s) part number shall trigger a new part number in BT and reciprocally.