Effects of GBAS/SBAS Precision Approach Guidance on fuel Consumption and CO2 Emissions

In this paper we present the results of a study regarding potential fuel savings and associated reductions of CO2 emissions when using GNSS-based guidance instead of the Instrument Landing System. Previous studies have shown that GNSS-based guidance provides very stable guidance signal while the ILS can be prone to signal distortions by obstacles on the ground and surrounding terrain. In this study we use data from ILS calibration flights to model realistic vertical ILS guidance errors. These error models were then integrated into a full flight simulator of an Airbus A330-300 aircraft. A number of approaches were flown using the autopilot in order to obtain comparable data for different aircraft configurations and glide slope angles. Results show that only the improved guidance signal does not yield fuel savings. However, depending on the ILS guidance error at the point where aircraft intercept the glide path essentially change the flown glide path. This can have a systematic impact resulting in several kilograms of fuel savings on additional consumption depending if the errors result in lowering or increasing the effectively flown glide slope. Finally, GNSS-based guidance could have a significant impact in approaches with barometric vertical guidance if no temperature correction is made.