The tourism sector has been one of the hardest hit during the COVID-19 pandemic, facing a shortage of available official data which further complicates the elaboration of appropriate measures to palliate the effects of the pandemic. Economists and policymakers have been increasingly relying on so-called high-frequency data to provide a more up-to-date view of the economic effects on tourism, which may persist to some extent in 2021 and beyond. In this work we contribute to the cause by making use of high-frequency flight data to discern passenger capacity and estimate a Passenger Capacity Index.