Using satellite-based altitude in cruise could burn more fuel, study finds

Simulations of more than 600 scheduled flights suggest geometric altitude could also require extra step descents.

Editorial illustration — not from the study.

Global navigation satellite systems can provide geometric altitude, based on an aircraft’s position relative to the Earth, while current cruise operations generally use barometric altitude measured from air pressure. The study examined how switching between the two would affect flight efficiency and altitude limits.

Researchers re-simulated more than 600 real scheduled flights under geometric-altitude conditions. On average, the simulated flights used more fuel during cruise, and many would risk exceeding their maximum barometric altitude, requiring additional step descents to avoid doing so.

What the simulations found

The simulations found that average cruise fuel consumption was higher when flights used geometric rather than barometric altitude. They also found a considerable risk that aircraft would exceed their maximum barometric altitude, which would require additional step descents. The study also assessed effects on flight time, although the abstract does not report a specific average change.

Why the altitude reference matters

Geometric altitude is often considered a way to support more efficient airspace design, but this study indicates that changing the altitude reference could have the opposite effect on cruise operations. If the simulated pattern applied in practice, flights could need more fuel and more level changes to remain below their maximum barometric altitude.

Evidence and caveats

The findings come from a fast-time simulation and comparison of more than 600 real scheduled flights, not from operating aircraft with geometric altimetry. The simulations required assumptions, including assumptions about aircraft take-off mass. The authors say the comparison design should reduce the effect of systematic errors because each flight was compared under both altitude systems, but the results remain a theoretical assessment rather than a direct flight demonstration.

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