Borrowing from the International Civil Aviation Organisation (ICAO) the No Country Left Behind (NCLB) initiative, Nigeria has joined the satellite navigation concept which is relatively new in Africa. WOLE SHADARE who was at the test-run and implementation of the Satellite-Based Augmentation System (SBAS) writes on its cost-effectiveness to airlines and other users
Over time, navigation has always relied on ground-based 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.
NAMA test runs implements SBAS
The Nigerian Airspace Management Agency (NAMA) moved further in augmenting all the satellite navigation systems. The three-day event brought together experts in digital communication, representatives of the African Civil Aviation Commission (AFCAC), the International Civil Aviation Organisation (ICAO), Agency for Aerial Navigation Safety in Africa and Madagascar (ASECNA) among other global and regional aviation bodies to Abuja a day after NAMA successfully carried out the demonstration flight to improve on the accuracy, integrity, and availability of the signal through augmentation of the satellite systems with its $8.5 million Beechcraft King Air 350i aircraft. The use of satellites for navigation (GNSS) is not new in Nigeria as NAMA had already implemented Area Navigation General (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.
According to experts, the country’s 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 the moment done in 32 airports including military airports and private and state government and federal airports is the performance-based navigation. It provides users with large guidance, for improvement on the accuracy, integrity, and availability of the signal. The satellite-based navigation system covers all phases of flight. What NAMA implemented moment that had been done in 32 airports including military airports and private and state government and federal airports is what is called performance-based navigation. It, however, does not mean that the ground-based navigation system would be de-commission as a result of the implementation of satellite-based navigation.
MA, Mr. Lawrence Mathew Pwajok, told Aviation Metric that in aviation, it is required that every service must have redundancy, stressing that for the agency, it was an improvement in terms of availability of service.
His words: “When we have the ground-based navigational facilities, we still went ahead to implement performance-based navigation. The ground equipment is susceptible to power fluctuations, weather changes and also technical errors, and maintenance issues. It is a system that can go off and it should have an alternative. An aircraft that is approaching landing, if the equipment suddenly goes off because of power fluctuation, or an animal crosses it and affects the signal, it should have an alternative.”
“You can’t close the airport because the ground equipment has gone off because of power or some environmental factors that are affecting it. We must have a contingency and that is required even by the NCAA regulation that for every service that you provide, you must have a backup.
“For the power system that you provide, you normally have about two or three redundancies. If any fails, you can’t have all of them failing, so now if we have an instrument landing system, yes we are investing heavily in it. Some airlines might decide to remain using the normal system and they might be comfortable and it might be okay for them as long as it gives them access to the airport for landing and takeoff.
“It is going to be at the discretion of airlines, we are not going to force any airline to have to fit it in. If you are comfortable with instrument landing equipment, we are going to deploy it and we do that as a requirement to have a backup for every service we provide.
“For us, it is not that we are going to decommission the instrument landing system; we want to provide an alternative for our airspace users knowing the technicality of the service that they provide. “We won’t want to deny anybody assess to an airport because one piece of equipment is not working. We have satellite means of communication, we have terrestrial communication systems. For our surveillance, we have ground surveillance radar and satellite surveillance. We are providing adequate backups.”
Director, of Engineering Services, NAMA, Farouk Ahmed Umar, explained that the SBAS was 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, according to Umar, will be everywhere within the region unlike the ground base that has defined service volumes outside which there is no coverage, that is, there is continuity of service and reference point and computing the errors.
“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,” he added.
When an airline discloses the quantum of their fuel consumption, one would understand what they go through. If one multiply that by five minutes of reduction in flight time, it would be easier to appreciate the savings in fuel burns. The use of SBAS by airlines leads to fuel saving, time-saving, and the reduction of CO2 emission which is very critical. Environmental sustainability is very key in this satellite navigation. That is one of the driving forces when it reduces flight time, fuel consumption, and CO2 emission.