Application Of SBAS For Approach Navigation In Nigeria by Farouk Umar, Director, NAMA

A presentation by the Director of Safety Electronics and Engineering Services (DSEES) on the SBAS Flight Demonstration at Nnamdi Azikiwe International Airport, Abuja on February 1^st,  2023.

Overview

Over time navigation has always relied on ground-based navigational aids. But with the advent of satellite navigation adopted by ICAO (GNSS), the scenario began to change. Due to errors inherent in the GPS constellations, the raw navigation signal from the satellites was not accurate enough to provide precision approaches. The satellite errors were due to various factors, including SA (selective availability) which was a deliberate introduction of errors to downgrade the quality of signals. However, with the removal of the SA errors, there was a significant improvement in the accuracy of the satellite guidance signals.

This nonetheless, could not meet the requirements for precision approaches. To further improve the accuracies of the navigational satellite signals a number of measures were adopted, such as Satellite Based Augmentation Systems (SBAS) and Ground Based Augmentation Systems (GBAS), which are ways of detecting and correcting satellite errors by comparison of received satellite signals from a known reference point and computing the errors.

The error-corrected signal was then transmitted to users as augmentation signals to improve the accuracies of the raw satellite signals being received by users.

If the error-corrected signals are transmitted at each localized area from the ground directly to users it is called GBAS, and if the error-corrected signals are relayed and transmitted to users through geostationary satellites to the users, it is called SBAS.

Nigerian Perspective

The use of satellites for navigation (GNSS) is not new in Nigeria as we have implemented RNAV approaches using satellite signals. However, these approaches are non-precision approaches as the accuracies do not meet up to precision categories. The RNAV provides only lateral guidance with no vertical guidance signals. It then still means that the ground-based navigational aids provide better accuracies. Our ground-based instrument landing systems provide navigation guidance from Category I to Category III approaches, which means airport or traffic capacities are still better with the existing ground-based instrument landing system during bad weather. However, the cost of acquisition and maintenance of ground-based navigational aids is high and therefore, alternative means of navigation that are cost-effective is a welcome development.

The Introduction of Space-Based Augmentation System (SBAS)

As earlier mentioned, augmentation of the satellite signals improves its accuracy which enables its application for near-precision approaches. That means the SBAS enhances the received satellite signal accuracies such that both lateral and vertical guidance signals are more accurate and reliable than the RNAV counterpart. This is really a significant milestone in the area of navigation. Our area of interest in this concept is the application of the SBAS for approach purposes. The traditional ground-based instrument landing systems have been the sole means of instrument approaches before now. It is expected that the SBAS (LPV) when implemented will be available for use in addition to the existing ground-based navigational aids and the already applicable RNAV. The choice of which to use will be at the discretion of the airspace users.

Advantages of the SBAS Application

The SBAS is seen to provide a cost-effective solution for navigation within the country and beyond where the deployment of ground-based equipment is not cost-effective, especially at smaller airports and private aerodromes.

The availability of the SBAS services will be everywhere within the region unlike the ground-based that has defined service volumes outside which there is no coverage, that is, there is continuity of service and availability is much higher compared to the conventional ground-based system.

Private and other smaller airports that cannot afford the deployment of ground-based navigational aids can derive benefits from the application of the SBAS.

Any Disadvantages?

The application of the SBAS for a Category I like approaches, for now, still limits the weather minima of use to Category I or less, whereas, our existing ground-based navigational aids provide Category II and more approaches thereby reducing flight delays and/or cancellations that will have occurred due to bad weather.

Are the airlines/users ready to invest in aircraft equipment to key in and derive the benefits offered by the new services? These are points of note rather than disadvantages.

Remarks

In ensuring that the introduction of the above SBAS is beneficial to industry users the following points should be noted;

• Collaboration with intended users should be encouraged and they should be properly briefed and carried along on all aspects of the implementation of the SBAS and its benefits.
• Collaboration with international partners, relevant authorities, and key providers of all services, to develop the governance, institutional frameworks, and financial models, including the provision of necessary codes for the deployment of the SBAS should be explored in the implementation drive of the SBAS.
• Costs or charges related to the services should be clearly spelled out to airspace users and all stakeholders on time to enable them to plan implementation strategies.
• It should be noted that the above services will operate alongside the existing ground-based navigational systems to provide a seamless transition into the future navigational systems as it is not all users that may have the capacity to implement them immediately.

Conclusion

The introduction of the SBAS for approaches is no doubt a welcome development for the industry, particularly NAMA which is saddled with the responsibility of deployment and maintenance of navigational aids within the country, which is capital intensive. With the above development, NAMA can reduce dependence on ground-based navigational aids in remote and private areas thereby making savings for other critical areas of need.

I, therefore, seize this opportunity to thank all our partners, particularly ASECNA and other foreign stakeholders for their time and efforts to ensure that this implementation plan is given the desired attention through this SBAS flight demonstration.

I will not end this brief without special thanks to NIGCOMSAT Ltd for the efforts they put in to make sure that the country and the sub-region benefits from our very vital and essential satellite services that they are offering as the backbone for the SBAS.

Engr. Farouk Ahmed Umar (FNSE) Is Director, Engineering Services Nigerian Airspace Management Agency (NAMA)

Wole Shadare