This manual describes a programme for the management of human error in aviation operations known as Line Operations Safety Audit (LOSA). LOSA is proposed as a critical organizational strategy aimed at developing countermeasures to operational errors. It is an organizational tool used to identify threats to aviation safety, minimize the risks such threats may generate and implement measures to manage human error in operational contexts. LOSA enables operators to assess their level of resilience to systemic threats, operational risks and front-line personnel errors, thus providing a principled, data-driven approach to prioritize and implement actions to enhance safety.