Notwithstanding Articles 5(3 ) and 18(2 ) , in relation to engines of categories RLL or RLR and placed on the Union market on or before 31 December 2011 , Member States may authorise the placing on the market of replacement engines if the approval authority , upon examination , recognises and concludes that the installation of an engine that complies with the applicable emission limits set out in Tables II-7 and II-8 of Annex II will involve significant technical difficulties .