Systematic altitude errors in Baro-VNAV approaches : an analysis across Europe

The aviation sector is moving from ground-based navigation aids to Performance Based Navigation (PBN), primarily using satellite-based systems. Although modern aircraft can perform fully guided lateral and vertical Global Navigation Satellite System (GNSS) navigation, many older or non-upgraded aircraft still depend on barometric altimeters for vertical guidance. This dependency makes them prone to systematic altitude errors due to temperature deviations from the International Standard Atmosphere (ISA), particularly during Barometric Vertical Navigation (Baro- VNAV) approaches. This thesis investigates these temperature-related errors at the Final Approach Points (FAP) of 27 European airports, using ADS-B data from 2024. Geometric and barometric altitude differences were analysed to estimate deviations in flight path angles and subsequently the change in fuel consumption via a simplified fuel model. The findings show a clear correlation between annual mean temperature and altitude error: in colder airports such as Helsinki, aircraft flew on average 165 ft lower, causing a yearly estimated 326 tonnes of excess fuel consumption; in warmer regions like Madrid, a similar deviation to the positive side resulted in over 952 tonnes of fuel savings. Looking at Europe and the Swiss International Air Lines case study, the results show that for every airline, the fuel difference depends on the location of their hubs and main destinations. Overall, the upcoming PBN mandate in the EU is not expected to have a drastic fuel impact regarding this systematic error. However, some airlines, especially those operating in the north, may take those results into account when deciding on a fleet-wide SBAS/GBAS upgrade.