Since the early days of aviation, barometric pressure measurements have been a simple and robust method for altimetry. Two drawbacks exist though: there is no direct reference to terrain, and the constant variations in pressure caused by the weather lead to increased vertical profile variability restricting capacity and flight efficiency in today’s high traffic density. One goal of Green-GEAR thus is to investigate the environmental potential of geometric altimetry enabled by satellite navigation, increasing safety and eliminating waste of airspace by removal of the transition layer and supporting more environmentally friendly climb and descent operations. With the safety case for the change of separation definition already open, not only integration of manned aviation with drones (that are already using geometric altimetry in current operations) can be addressed but Green-GEAR will also look at the potential for increasing capacity through reduced vertical separations enabled by geometric altimetry. Last but not least the project, will investigate the potential of environmentally driven route charging, with new mechanisms for charging airspace users to incentivise minimum climate impact. Route charging will reward those who avoid volumes of airspace with a high climate impact and disincentivise flight planning through high demand sectors / flight altitudes except where it optimises environmental benefit overall, while being cost neutral to airspace users and passengers on average. Added capacity in the “greener” volumes of airspace enabled by reduced vertical separations limits necessary flight plan modifications, furthering acceptance of the approach. The combination of these three topics in Green-GEAR not only raises substantial synergies and ensures a harmonised approach; it also allows to identify and solve possible interoperability issues quickly and to mature the interdependent solutions in sync, reducing time to market for any and all of them.