• ILS: Guidance can be affected by local signal perturbations (e.g., multipath, terrain effects) and requires regular monitoring and flight inspection.

• GBAS: Delivers steadier GNSS‑based guidance with airborne computation of protection levels using broadcast integrity data; flight inspection frequency is generally reduced compared with multiple separate ILS installations.

• ILS: Typically requires one tuned frequency per installation (one localizer/glideslope pair per runway end).

• GBAS: A single VHF channel assignment can support many individual approach procedures (up to 48), reducing VHF spectrum demand and the number of separate ground transmitters.

• ILS: Coverage is effectively limited to the runway served and its immediate vicinity.

• GBAS: Service volume extends outward from the airport, enabling precision guidance within the GBAS service area and supporting multiple approach paths to the same or different runway ends and, in some cases, to other nearby aerodromes within the service volume.

• ILS: Primarily supports straight‑in approaches aligned to the localizer; curved or segmented final trajectories are not supported directly.

• GBAS: Supports straight, curved and segmented approach trajectories and allows optimized, tailored final approach paths (for example, to avoid obstacles or noise‑sensitive areas).

• ILS: Requires specific siting and protected critical areas for the localizer and glideslope; these protected zones can constrain surface and flight operations.

• GBAS: Typically has more flexible siting and reduces the extent of critical ground areas, easing taxiing and surface movements and reducing some operational constraints.

• ILS: Guidance can be affected by local signal perturbations (e.g., multipath, terrain effects) and requires regular monitoring and flight inspection.

• GBAS: Delivers steadier GNSS‑based guidance with airborne computation of protection levels using broadcast integrity data; flight inspection frequency is generally reduced compared with multiple separate ILS installations.

• ILS: Demands maintenance and flight inspection for each installed system, with associated lifecycle costs for multiple runway ends.

• GBAS: Consolidates approach capability into a single ground facility that serves multiple procedures, lowering the number of installations to maintain and potentially reducing overall lifecycle costs.

• ILS: Proven for CAT I/II/III autoland operations where installed and certified, with well‑understood local failure modes tied to runway transmitters.

• GBAS: Provides integrity through real‑time corrections and ground monitoring; evolving GAST classes (for example, GAST‑D and multi‑frequency variants) aim to deliver CAT II/III capability. GBAS availability depends on GNSS constellations, ground monitoring robustness, and mitigations for threats such as ionospheric gradients and interference.

• ILS: Vulnerable to local RF multipath and signal distortion but does not depend on satellites.

• GBAS: Dependent on GNSS signals and therefore exposed to satellite‑related threats (ionospheric effects, spoofing, jamming). Mitigations for GBAS include multi‑constellation/multi‑frequency processing, multiple reference receivers, robust Fault Detection and Exclusion (FDE) and continuous interference monitoring.

• ILS: Each runway end requires discrete approaches and separate infrastructure; publishing or modifying procedures typically involve separate installations.

• GBAS: Facilitates publication of multiple, airport‑tailored procedures from a single ground installation, simplifying procedural design, reducing ground navaid footprint and enabling more flexible airspace procedures.

Both systems have proven roles. ILS remains a mature, well‑understood technology for precision autoland where it is deployed. GBAS offers greater procedural flexibility, infrastructure consolidation and scalability with multi‑frequency/multi‑constellation GNSS, but it requires robust GNSS threat mitigation and appropriate certification to support higher CAT operations.