The airline industry is characterized by substantial operational uncertainty arising from demand fluctuations, weather disruptions, technical failures, labour constraints, fuel-price volatility, air-traffic congestion, and unexpected capacity shocks. In such an environment, excessive resource efficiency may reduce an airline’s ability to absorb operational disturbances, while strategically maintained operational slack may provide the flexibility required to preserve service continuity and financial stability. This study empirically investigates operational slack as a strategic capability and examines the mediating role of service reliability in strengthening financial resilience among airlines. Using a panel dataset of airlines covering multiple operating periods, the study develops quantitative measures of operational slack, service reliability, and financial resilience and applies descriptive statistics, correlation analysis, panel regression, robustness tests, and mediation analysis to evaluate the proposed relationships. Operational slack is measured through selected indicators of available capacity, workforce flexibility, fleet and maintenance resources, and other operational buffers, while service reliability is assessed using indicators such as flight completion, punctuality, schedule consistency, and disruption management. Financial resilience is evaluated through indicators reflecting profitability stability, liquidity, cash-flow strength, and the ability to withstand adverse operating conditions. The empirical framework tests whether operational slack directly improves service reliability and whether improved reliability subsequently enhances financial resilience. Particular attention is given to the indirect effect of operational slack through service reliability. The study is expected to demonstrate that appropriately calibrated operational slack can function as a strategic resource rather than merely representing excess cost. By empirically connecting operational resources, service outcomes, and financial resilience, the study contributes to airline operations and strategic management literature and provides evidence for resource-allocation decisions under uncertain operating conditions.