This study aims to analyze the derivation of weak active participles (APs) from triconsonantal imperfective verbs within the X-slot model of autosegmental phonology. The first stage of the research involves building a corpus of APs from a well-established corpus-based dictionary, namely [characters omitted] 'Dictionary of Modern Arabic Language'. The corpus contains 620 APs which are categorized, in accordance with the position of the glide in their stems, into initially, medially, finally and doubly weak APs. The analysis reveals that despite having irregular surface representations, the underlying representations of weak APs are parallel to those of their strong counterparts. The surface irregularities of these APs are attributable to the inherent instability of the glides which causes them to be susceptible to diverse phonological rules. These phonological rules are given accurate and simple representations in autosegmental phonology due to the autonomy that elements on different tiers have in this approach.