By Sophie Lindqvist

A new concept called "predictable VFR" — visual flight rules applied through pre-agreed, three-dimensional blocks of low-altitude airspace — could open crowded airspace near the ground to drones and electric vertical take-off and landing (eVTOL) aircraft, according to research reported by Bioengineer.org. The mechanism at its core is the "operation volume": a bounded parcel of airspace, reserved in advance for a specific operator and time window.

That matters because low-altitude airspace is where demand is concentrated and where today's rules fit worst. Conventional air traffic control separates aircraft one by one, which does not scale to thousands of small, automated vehicles. Operation volumes replace that one-to-one separation with a reservation model closer to how airports allocate time slots.

What does the concept actually change?

For operators, the shift is from negotiation to planning. An operator requests a defined volume, receives it, and then flies predictably inside that volume rather than reacting to moment-by-moment instructions. Predictability is the whole point: the word "predictable" in the concept's name signals that other airspace users can know, in advance, where drone and eVTOL traffic will and will not be.

The research frames this as an extension of a familiar regime rather than a new one. VFR — the rule set under which pilots see and avoid each other without radar separation — is well understood. Adapting its logic to reservation-based volumes would let mixed traffic coexist without inventing an entirely fresh regulatory category.

Why low altitude is the bottleneck

The target zone is the crowded band of airspace close to the ground, where drones, eVTOLs, helicopters, and general aviation already compete for room. Advanced air mobility (AAM — the umbrella term for air taxi and cargo drone operations) depends on access to precisely this layer, particularly over cities.

The researchers' argument is structural: without a mechanism that parcels this layer into predictable, allocatable volumes, the number of concurrent operations stays capped by human oversight. With one, the ceiling on traffic density rises with computing capacity rather than controller workload.

Uncertainties remain

The source material describes a proposal, not a certified framework. It does not state which regulator has reviewed the concept, what testing has occurred, or any timeline for adoption. Whether operation volumes can handle dynamic conflicts — two operators wanting overlapping volumes at the same time, or off-nominal events such as vehicle failures inside a reserved block — is the question regulators will ask first.

Next for the concept is validation: proving, in trials, that predictable volumes hold up under real traffic densities before any authority can treat them as a rule set for the low-altitude layer.