Please share the full table definitions (including any NC indexes) and the execution plans. It would also be helpful if you prefixed each column with the table alias as you may know what table each column belongs to, but we have no way of knowing.

Without the information requested we can't be much help. For example if either CONV_CODE or AUTHORISTN_IN_PROGESS is a column in any table other than BD1_A_SALFLDG then you are essentially creating an INNER JOIN and if either is in that table, they are not in the clustered index so it would have to do a SCAN since those columns are not indexed.