Aircraft models and variants that are not presently covered by the ANP database must be represented by substitutes (often referred to as ‘proxy’ aircraft), i.e. aeroplanes with similar noise and performance characteristics that are included in the database that can be adequately scaled (in terms of “equivalent number of movements”) to represent the missing aeroplanes. To facilitate the substitution process, the ANP database includes a table that maps currently operating commercial aeroplanes with detailed airframe-engine combinations, which is compared to the aeroplanes listed in the actual database. The substitutions table provides a list of suggested aircraft substitutions