As airspace becomes increasingly congested with a diverse range of users—including drones, unmanned aircraft systems, vertical take-off and landing aircraft, as well as high-altitude operations—the need for a unified vertical navigation reference has never been greater. Current reliance on barometric altimetry and manual pressure reference adjustments complicates operations, reduces efficiency, and carries a risk of human error.

About the solution

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 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:

1. Defined lateral path with altitude constraints

• Aircraft construct and navigate vertical paths based on geometric height constraints at waypoints.

• Enhances 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.

• Airspace capacity increases by removing the Transition Layer and avoiding the loss of flight levels associated with it.

• Implementation requires minimal changes to current airspace or instrument flight procedures. Geometric height would be reported alongside barometric height.

2. Defined lateral and vertical path

• Aircraft construct geometric point-to-point vertical paths using geometric altimetry, based on defined geometric path flight procedures, as a form of Vertical Required Navigation Performance (V-RNP) to ensure procedural separation.

• Allows more efficient 3D Instrument Flight Procedure (IFP) design and optimisation of airspace use but constrains the aircraft’s vertical profile.

• Implementation requires updates to ATM tools, including surveillance and safety nets such as Mode-S cleared/selected flight level (CFL/SFL) checking and a barometric alerting tool (BAT).

• Greatly improves flight path management, enabling route planners to design more efficient routes in fully three-dimensional airspace.

Regulatory and standardisation aspects

• International standards would need to be updated to reflect vertical navigation by geometric altitude and barometric fallback procedures.

• EU regulations would likely need to mandate both ground system capability and airborne capability.

• For the second method, 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 technological improvements or mitigations and related new standards.

BENEFITS

• Safety: Eliminates the need for manual pressure datum changes, reducing pilot and controller workload and human error. Reduces risk of high glideslope capture.

• Environmental gains: Consistent altitudes allow better planning of individual flight profiles. Improved efficiency of airspace design may reduce fuel use and emissions, depending on the impact on individual flight profiles.

• Capacity increase: Enhanced containment and optimised route design in fully three-dimensional airspace. No loss of flight levels due to the Transition Layer, increasing available airspace.

• Cost efficiency: Potential savings through reduced engine wear due to thrust consistency.