States will be required to perform maintenance activities on a routine basis to verify the GBAS is operating within the required standards. The maintenance plan, defining the timings, should be defined. ICAO DOC 8071, Volume 2, presents guidelines on recommended ground and airborne testing practices. Examples of maintenance activities may include:

• Verifying whether the VDB transmitter frequency, VDB receiver Frequency, and VDB transmitter output Power are within tolerance limit
• Verifying whether any spurious emissions emanating from the VDB transmitter are within tolerance limit
• Verifying whether power in adjacent channels is within tolerance limit
• Verifying whether the antenna Voltage Standing Wave Ratio is within tolerance limit
• Verifying whether the ionospheric variation is within the ionospheric threat model
• Checking the functionality of any GBAS monitoring systems to Air Traffic Control or Maintenance Centres
• Reviewing Event Logs for any new fault conditions
• Verifying functionality of any redundant power systems
• Checking for any signs of damage or corrosion to the supporting infrastructure
• Routine Flight Inspections to verify VDB coverage (at the discretion of the State)

Additionally, States should continuously monitor for changes to the satellite constellation (e.g. satellite maintenance activities) and assess the impact of constellation changes on the performance of the GBAS, specifically on availability. Furthermore, States should continuously monitor for changes to the environment surrounding the GBAS, including new developments and vegetation growth, to ensure that impacts to GBAS performance are minimised.

States should assess the performance of the GBAS against the Performance Indicators established in regular basis during the implementation and post‐implementation phases. States may also regularly review the effectiveness of performance indicators established in evaluating the performance of GBAS.

Examples of Performance Indicators may include:

• Operational Availability of the GBAS
• Reliability (Mean Time Between Outage) of the GBAS
• Mean Time to Repair
• Number of GBAS approaches performed intothe aerodrome
• Operation and Maintenance costs
• Status of GBAS based navigation services
• Enhancement in airport capacity
• Fuel saving and environmental performance
• Optimization of ATC procedures and reduction of workload

Since performance indicators are associated with the evaluation on the performance or progress towardsthe intended result(s), each State may focus on different aspects with benefitsfrom GBAS to serve their own purpose and set up their own set of performance indicators against the performance of GBAS.

States should continuously monitor for changes to the satellite constellation and assess the impact of constellation changes on the performance of the GBAS, specifically on availability. Moreover, State ANSP have the responsibility to monitor and report the status of navigation services. To support this requirement, navigation service providers should provide status information to ATS. If the status of a navigation service changes, pilots should be advised via direct communications and/or via a NOTAM system.