Atmospheric radiation produced during the interaction of cosmic rays with the atmosphere could be considerably high at typical flight altitudes and constitutes a risk factor for people and avionics onboard the plane. In this work, we present ACORDE, a Monte Carlo-based method to estimate the dose during a commercial flight by using state-of-the-art simulation codes and considering the course travelled, the real-time atmospheric and geomagnetic conditions, and a model of the plane and an anthropomorphic phantom to obtain the effective dose on a flight-by-flight basis.