Résumé : Conflicts between airports and inhabitants around aircraft noise have increased across the world. In several cases, they have become critical for the expansion of the airport business and thus possibly for the regional and/or national economy. These conflicts have also urged public authorities to pay more attention to aircraft noise through regular assessments imposed to the airports. In the EU for instance, large airports have to produce annual noise reports that notably include noise contours and the number of inhabitants who live within them.Surprisingly, scholars have paid little attention to noise indicators imposed by public authorities. However, by-law assessment of noise is by nature the result of political decisions at the crossroad of diverging interests expressed by various lobbies. As a result, noise indicators are not necessarily neutral and may be conservative to save the airport/airline business. Considering Brussels Airport, Belgium, as a case study, this is investigated through a comparative cartography of official noise indicators (especially LDEN with 55 dB as a lower threshold) versus citizen protests (complaints to the ombudsman; petitioners; complainants against the Federal State). Diverging geographies suggest that LDEN with 55 dB as a lower threshold is conservative. This calls for a critical assessment of how it was adopted by the EU. This will be conducted going through the EU’s records, notably to assess first drafts of the regulation and how lobbies reacted at the time.