The fact that PBN (Performance Based Navigation) outperforms conventional navigation in all phases of flight is well known by the aviation industry. Among its many advantages, the more efficient use of airspace, the increase of the airspace capacity, and the reduction of the pilot’s and ATCO’s workload stand out above the rest.

By reducing and removing the aircraft’s navigation dependency on obsolete ground stations, PBN is currently enabling more precise positioning and guidance. Thus, increasing the global flight efficiency by reducing the total flight path distance. Which in the end, translates into numerous benefits for airlines, ATC service units, and passengers such as the reduction of fuel consumption, flight time, and CO2 emissions among many other factors.

Within the PBN concept are enclosed different levels of performance (accuracy, integrity, and continuity of the operations), functionalities, enabled navigation sensors and requirements in what are called navigation specifications (Nav Specs). Currently, most of the airports and air navigation service providers have focused their efforts on the implementation of the standard PBN Nav Specs (RNAV 1, RNP 1), which are flyable by the majority of airline companies. And despite this being the most suitable strategy on PBN deployment, it eventually implies that there is still important room for improvement as navigation specifications with better performance are not being exploited. Nowadays, making the most out of the available technology in air navigation terms, means implementing the so-called RNP-AR (RNP Authorization Required) Nav Spec, during the approach phase of a flight.

RNP-AR Nav Spec enables reduced obstacle limitation and the design of curved legs along the final approach segment (last segment prior touchdown), which has proven very useful in airports with challenging terrain or heavily constricted airspace scenarios. Moreover, it also provides an immediate cutback of the flight distance, time, fuel, and emissions. Let’s put those improvements into numbers!

With the implementation of RNP-AR procedures, the total approach flight distance can be reduced from 5 to 12NM respect to the average standard ILS or any other RNP approach. For a medium airport with an annual traffic around 100k ATM, assuming only 20% of their arrival operations are able to fly the advanced approaches (RNP-AR), at the end of the year savings could surpass the 1 690 metric tons of CO2, thanks to the saving of 540 tons of fuel. Certainly, all these benefits may vary depending on the airspace design and on how close to the limits defined by ICAO the procedure is set.

Nevertheless, it is true that in very complex environments with high traffic demand, the coexistence of advanced procedures together with standard PBN procedures could be challenging to manage. A good solution to that could be the implementation of a hybrid operation system, where the availability of the advanced procedures would depend on the weather and the traffic situation at each moment in time.

 

Also, the fact that RNP AR procedures require expensive avionics and certification, additional training sessions for the flight crews and ATCOs, and the development of extensive safety material among others, is indeed discouraging airlines, airport operators, and ANSPs to invest in such procedures.

Even so, seeking operations optimization should always be the aviation industry’s main driver. Moreover, global trends are moving towards finding greener solutions and it is no secret that aviation is always on the spotlight of the polluting industries. A time will come when regulatory green policies destined to cut its emissions will be enforced, and RNP AR will definitely play a key role in that matter.

RNP AR advantages have been clearly demonstrated and the technology to implement this procedures is ready. The current challenge facing is bringing into the CBA the environmental and time-saving benefits associated with this state-of-the-art procedures.

 

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About the authors
ALG IFPD Team. vcoca@alg-global.com
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