English is a global language, learned worldwide as a native, first, and second language. In Azerbaijan, Received Pronunciation (RP) is considered the best accent for teaching English, but its model is outdated and requires revision. Since the 1980s, C. Upton has proposed updates reflecting phonetic changes, adopted in Oxford University dictionaries from the 1990s. Despite efforts to implement the new model, financial and educational challenges persist. Lexicographers, often unfamiliar with phonetics, maintain a conservative approach. This article examines the monophthongization of centering diphthongs in RP, analyzing changes in their quality and quantity. Research conducted at Azerbaijan University of Languages confirms that centering diphthongs are shifting into long monophthongs, a trend accepted across all age groups.