What is the GeoAlt Solution About?

The Green-GEAR Project aims to revolutionise vertical navigation by exploring the feasibility of adopting Geometric altimetry across all flight phases. This system uses a single common reference point for aircraft altitude, enabling a means for seamless integration between traditional and emerging airspace users, without the complication of local pressure settings and Transition Layers. The project examines two main methods for implementing Geometric altimetry:

Defined Lateral Path with Altitude Constraints: For this method, aircraft would construct and navigate vertical paths based on geometric height constraints at waypoints. This would enhance safety by eliminating the need for manual pressure setting changes when crossing the Transition Layer. Environmental benefits include more consistent altitudes, which at lower levels can improve performance and reduce noise. Additionally, airspace capacity would increase by removing the Transition Layer and avoiding the loss of flight levels associated with it. This method could be implemented with minimal changes to current airspace or instrument flight procedures. Geometric height would be reported alongside barometric height.

Defined Lateral and Vertical Path: For this approach, aircraft would construct geometric point-to-point vertical paths using Geometric altimetry, based on defined geometric path flight procedures, using as a form of Vertical Required Navigation Performance (V-RNP) to ensure procedural separation. It allows for more efficient 3D Instrument Flight Procedure (IFP) design and optimisation of airspace use but constrains the aircraft’s vertical profile. Implementation of this method would require updates to Air Traffic Management tools, including surveillance and safety nets like Mode-S cleared/selected flight level (CFL/SFL) checking and a Barometric Alerting Tool (BAT).

This method greatly improves how flight paths are managed, allowing route planners to design more efficient routes using a fully three-dimensional airspace.

Regulation / Standardisation Aspects

To enable this concept, international standards would need to be updated to reflect vertical navigation by geometric altitude and barometric fallback procedures. It is highly likely that EU regulations would need to be created to mandate both ground system capability and airborne capability.

For the second of the two methods, V-RNP would need to be defined, with FMS capabilities standardised through EUROCAE and RTCA.

Geometric Altimetry is dependent on improved resilience to GNSS jamming and spoofing through technology improvements or mitigations and related new standards.

Benefits:

The adoption of Geometric altimetry promises numerous advantages:

• Safety: Eliminates the need for manual pressure datum changes, reducing pilot & controller workload and reduces human error. Reduces risk of high glideslope capture.
• Environmental Gains: Consistent altitudes allow better planning of the individual flight profile. The improved efficiency of airspace design enabled by Geometric altimetry may reduce fuel and emissions overall, depending on the impact to individual flight profiles.
• Capacity Increase: Enhanced containment and optimised route design in a truly three-dimensional airspace. No loss of Flight Levels due to Transition Layer, increasing the amount of airspace available.
• Cost Efficiency: Potential cost savings through engine wear reduction due to thrust consistency, reduced fuel costs.