Aircraft satellite navigation: A paradigm shift?

Despite delay, Nigeria’s satellite air navigation project is nearing completion. WOLE SHADARE writes of benefits to airlines and the aviation sector

Nigeria at the brink

Nigeria is at the verge of completing Performance Based Navigation (PBN) in 23 airports across the country, according to the Director-General of Nigerian Civil Aviation Authority (NCAA), Captain Usman Muhtar.

Although, Nigeria is two years behind the International Civil Aviation Organisation (ICAO) requirements for states to ensure full implementation of PBN, the Nigerian Airspace Management Agency (NAMA) is said to be leaving no stone in reaching the implementation stage.
PBN is the technology in air traffic services where aircraft receive advisory directives from satellite based equipment instead of ground based equipment. Traditional navigation techniques for aviation were developed using ground based navigation aids. There are various types of navigation facilities such as Non Directional Beacon (NDB) which is a radio transmitter at a known location which an aircraft can track to/from. VHF Omnidirectional Range (VOR) provides more accurate directional navigation information. Distance Measuring Equipment (DME) that provides distance information to/from the facility. Instrument Landing System (ILS) provides lateral and vertical guidance to aircraft approaching to land.

These facilities had to be located in positions where they were accessible for maintenance and in the most optimum position for its navigation purpose.

Conventional navigation aids limitation

The basic principle of all of these navigation facilities is the fact that aircraft in general navigate towards and away from the navigation aid itself, “point to point”. This means that the location of the navigation aid must be in an optimized location. This optimized position is, in many cases, not achievable (due to being situated in high terrain, open seas, politically unacceptable areas, etc). Therefore the route structure must be aligned with the position of the navigation aid and not aligned in the ideal position for its purpose. This results in additional distances being flown by aircraft which has a number of disadvantages including economic, environmental and efficiency disbenefits.

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Utilisation of the same arrival/departure tracks.

 As aircraft need to fly to and from the same navigation facility aircraft which are travelling in opposite directions can in many cases be following the same track over the ground while climbing and descending. While the safety implications of this can be mitigated against by introducing air traffic control separation procedures these are sometimes inadequate as occurred at Delhi Airport in 1996 where a Saudi Arabian Airlines B747 (SVA763) collided mid-air with a Kazakhstan Airlines (KZA1907).

High terrain
 
 At airports located in high terrain with difficult accessibility arrival procedures, based upon conventional ground based navigation aids, may result in aircraft being unable to land at the airport safely during periods of low visibility. An example of this is Juneau Airport Alaska whereAlaska Airlines Flight 1866 B727 crashed while attempting to land in 1971.

 Infrastructure cost

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 At airports with low numbers of flights the cost of equipping with navigation aids to support aircraft arrivals during reduced visibility can be prohibitively high. This results in no, or limited, arrival capability during bad weather.

 GNSS

The use of such satellite navigation systems by aircraft is known as Area Navigation (RNAV). In further stages, under the auspices of the International Civil Aviation Organisation (ICAO), the concept of Required Navigation Performance (RNP) was developed.  This introduced the requirement for on-board performance, monitoring and alerting of the RNAV system to allow the aircrew to detect if the navigation system is not achieving the performance required. During 2008 this was further refined with the launch of Performance Based Navigation (PBN). This concept specifies the aircraft RNAV system performance requirements be defined in terms of accuracy, integrity, availability, continuity and functionality required for any proposed aircraft operation.

Benefits

PBN has introduced the ability to design aircraft routes without reference the constraint of needing to fly “point to point” from one ground based navigation aid to another. It makes it possible to design routes which may be used in conjunction with the aircraft Flight Management System to fly complex tracks over the ground in a consistent and accurate manner. The main advantages of PBN are reduction of the need to maintain sensor-specific routes and the associated cost of installation and maintenance. It also leads to the avoidance for the need for development of sensor-specific operations with each new evolution of navigation systems.

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Experts told Woleshadarenews that the implementation of PBN was well underway as aircraft with necessary approval from NCAA can now fly into 23 airports in Nigeria without the use of ground navigational aids.

He listed the airports to include Benin, Calabar, Enugu, Ibadan, Ilorin, Owerri, Jos and Kaduna. Others are Lagos, Abuja, Maiduguri, Katsina, Minna, Sokoto, Zaria, Gombe.

He stated that because of the increased level of accuracy, reliability, continuity, integrity of information, overall enhanced safety and attendant benefits to airlines and the travelling public, it has become imperative for Nigerian operators to key in to PBN.

NAMA had in 2012 published PBN Area Navigation (RNAV) Approaches, Standard Instrument Departure Routes (SIDs) and Standard Arrival Routes (STARs) for the four major airports of Lagos, Port-Harcourt and Kano making them PBN compliant.

Last line

The introduction of satellite based RNAV operations and the subsequent development of RNP and PBN have significantly impacted the aviation industry. It has improved safety, efficiency capacity and reduced the impact upon the environment.

Wole Shadare