The project NARROW PATH delivered a feasibility study for the definition of new techniques aiming at increasing the navigation performance of small drones (<25 Kg) flying in LL (Low Level) and VLL (Very Low Level) airspaces.

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NARROW PATH has received funding from European Union and Regione Campania within the program POR CAMPANIA FESR 2014-2020.

The study took place from January 2018 to June 2018.



Drones’ (UAS) navigation is affected by several parameters:  an analysis can allow to set the margins for the safety of operations.

In case of a drone flying place in pre-defined airspaces, it is  necessary to define a buffer area, such as a “corridor” around the aircraft’s flight path.


This area can be defined as the sum the following error contributions:

> Path Definition Error (PDE): the difference between the defined path and the desired path at a given place and time;

> Navigation System Error (NSE): the difference between the true aircraft location and the aircraft location indicated by the navigation system;

> Flight Technical Error (FTE): the difference between the aircraft location indicated by the navigation system and the defined flight path.


Therefore, the Total System Error is the sum of these three and affects the width of the buffer area.

project objectives


The research performed in Narrow Path focused on the FTE and the NSE to explore the possibility to reduce the protection “buffer value” applied to a specific route.

The main objective was to allow a small drone flying as close as possible to ground obstacles and being able to keep its separation from other drones with acceptable margin for safe operations.

The project aimed also at increasing the capacity of VLL and LL airspaces, with a view to the growing presence of drones in everydays life.

Our results


Narrow Path study assessed the feasibility of a significant reduction of the buffer area under most conditions for different commercial drone models.

In fact, it has been confirmed that an agreed buffer value can be less than 50 meters even under strong winds.

Therefore, the introduction of technical improvements has highlighted constraints for keeping the safety of operations and has allowed to reduce the TSE value.

The research activity focused mainly on FTE containment and less on NSE, while the PDE was found to be negligible for defining the value of the buffer area.

In particular, the study has explored the possibilities to:

> Install advanced satellite navigation systems (i.e. GNSS – Galileo/GPS, EGNOS) on board of a small drone, in the form of a “GNSS UTM transponder” to reduce the NSE;

> Evaluate the FTE by means of a drone simulator (especially developed in-house for the study) able to estimate the aircraft response to different types of in-flight solicitations

> Measure the autopilot error affecting the capability to maintain the trajectory of the flight path.



  • Narrow Path project showed the possibility to achieve the Required Navigation Performance RNP 0.02 (2/100 of NM, approximately 37 m) in many operational conditions, but also RNP 0.01 (approximately 18 m) with some additional limitations.

  • The risk assessment conducted with SORA (Specific Operations Risk Assessment) methodology for the scenarios proposed confirmed that the operations can be still done under the conditions of Specific category (and not certified category).


The FESR/ERDF aims to strengthen economic and social cohesion in the European Union by correcting imbalances between its regions.

The fund focuses its investments on several key priority areas. This is known as ‘thematic concentration’:

Innovation and research;

The digital agenda;

Support for small and medium-sized enterprises (SMEs);

The low-carbon economy.