Inside CARS: why a common altitude reference matters for U-space
1 April 2026
One of the core enablers of the DAEDALUS concept is the Common Altitude Reference System (CARS). But what is it, and why does it matter?
The problem
Aircraft today measure altitude in two fundamentally different ways:
- Geometric altitude — height above the WGS84 ellipsoid, measured by GNSS
- Barometric altitude — height above a pressure reference level, measured by an altimeter
Two drones flying at the same "barometric altitude" could be metres apart vertically if they are operating in different pressure conditions, or if one switches reference mid-flight.
The transition layer — where aircraft switch between barometric and geometric references — wastes significant vertical airspace. In dense U-space environments, every metre counts.
How CARS solves this
CARS defines a unified vertical reference based on geometric altitude (GNSS), with integrity monitoring to ensure the reported altitude is trustworthy. This allows:
- Tighter vertical separation between drones
- Predictable altitude deconfliction across different operators
- Simplified airspace design with well-defined altitude layers
DAEDALUS and CARS
In the DAEDALUS framework, CARS is the foundation on which the Dynamic Airspace Layering engine operates. Without a common, trusted altitude reference, dynamic layering cannot guarantee safe separation.
The project will develop and validate the CARS concept through simulations and real-world flight tests.
