Optimized Profile Descent
An Optimized Profile Descent (OPD) is a procedure in which equipment onboard the aircraft chooses the optimum point to begin the aircraft's descent to landing. During the descent, the aircraft's flight computers select the lowest possible thrust setting (often flight idle) to keep the aircraft on the desired descent profile, adjusting for wind, temperature and other flight variables throughout the descent. In this way, CO2 emissions are reduced and the aircraft burns less fuel.
For the OPD to be most effective, the aircraft must be allowed to continue its descent, without interruption, from beginning to end. In order to accomplish this, especially around busy airports, controllers must coordinate the OPD flight path with the flight paths of other traffic. In this way, controllers can sequence aircraft to avoid conflicts that would cause an OPD to be interrupted.
Aircraft following RNP flight paths are highly predictable, with minimal deviations, if any, from the desired track, even in poor visibility or adverse wind conditions. The precision, accuracy and reliability of PBN flight paths (especially RNP) gives air traffic control the tool it needs to sequence air traffic, so that arriving aircraft can be cleared for OPDs without interrupting other operations.
By combining RNP curved final approach flight paths that are shorter than conventional straight-in final approach paths, with the advantages of OPDs, airlines and aircraft operated can dramatically reduce both fuel burn and CO2 emissions.