1. Institutions and any parent undertaking and its subsidiaries shall implement the IRB Approach for all exposures, unless they have received the permission of the competent authorities to permanently use the Standardised Approach in accordance with Article 150.
Subject to the prior permission of the competent authorities, implementation may be carried out sequentially across the different exposure classes referred to in Article 147 within the same business unit, across different business units in the same group or for the use of own estimates of LGDs or conversion factors for the calculation of risk weights for exposures to corporates, institutions, and central governments and central banks.
In the case of the retail exposure class referred to in Article 147(5), implementation may be carried out sequentially across the categories of exposures to which the different correlations in Article 154 correspond.
2. Competent authorities shall determine the time period over which an institutio
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