Mixing layers between air and liquid are ubiquitous in nature and extremely common in industrial applications. Among the latest, air-assisted atomization is one of the predominant forcing used to induce breakup in liquid jets. In these flows, a low-momentum liquid jet and a high-momentum air stream are injected simultaneously along the same direction, separated only by a thin solid plate. The interaction between the two phases generates an instability that manifests in the form of flapping events, during which most of the droplets are created owing to the breakup of these liquid sheets. In this study, we discuss the statistical relevance of flapping events and how they contribute to determine the final droplet-size-distribution. We present an algorithm to isolate each event in Direct Numerical Simulations and discuss the dispersion between each event. Finally, we demonstrate the importance of performing this type of analysis to reveal of statistical properties of the droplet size distribution.