Overview
The objective of the RNP trials at Brussels airport was twofold:
- Familiarise ATC/flight crews with RNP approaches (on-going PBN transition).
- improve environmental performance for arriving flights, by enhancing predictability for the flight crews.
The standard mode of operations in Brussels is radar vectoring because of the density and complexity of the airspace and traffic, with a lot of military areas around Brussels Airport (EBBR), and traffic that needs to be merged and sequenced from various directions. This means that crews get radar vectors as from 30 to 40 NM from the airport and have no view of the actual Distance To Go (DTG) before landing, implying that crews cannot fully optimise their descent.
The trial was conducted in two phases (in summer 2022 and in winter 2023-2024). For both phases, it was taking place with all airlines, during night (low traffic), for RWY 25R-25L, workload & weather permitting and using ATC and airline input as part of the Collaborative Environmental Management (CEM) framework in place at EBBR. The main airlines contributing to the project were Brussels Airlines, DHL and TUI.
The evaluation of both phases of the trial was done based on the following monitoring areas, supported by insightful tables using boxplots providing comparisons between RNP and non-RNP approaches:
- General statistics using cumulative numbers between RNP flown/not flown.
- RNP eligibility: How often could the RNP approach be flown? (Put as primary approach in ATIS.)
- RNP acceptance: How often is the RNP approach effectively flown?
- Horizontal flight efficiency in terms of track DTG. One of the assumptions to check is if radar vectoring is sometimes not more efficient than published approaches since vectoring also allows for shorter routings.
- Vertical flight efficiency looking at average level-off time =< FL100, FL75 and 3000 ft.
- Noise assessment by means of mobile noise monitoring stations installed in the approach path.
- Fuel assessment using data from AOs. For specific airlines, fuel data has also been correlated with skeyes’ data (correlation study level-off times and fuel usage).
- ATC/Flight Crew feedback.
Observations were conducted by allocating arrivals to a flow (N, E, SE, SW, W) and setting up an intersection gate for each of those flows. Those gates were established within a circle with a radius of 35NM centered around a point situated 6NM E of RWY 25L/R between the axes.
For each arrival, the track DTG and altitude/FL intersection was recorded.
In the second phase of the trial, adjustments from the first phase were applied and validation of the expected improvements was conducted. The set-up was similar to the first phase. The adjustments consisted among others in:
- The addition of speed constraints in the RNP procedures aiming at improving sequencing and environmental performance (notably noise) by reducing level-offs at low altitude, the addition of a waypoint in the procedure to improve turn anticipation in case of a shortcut would be given by the ATCO.
- The refinement of the meteorological scope:
- Minimum temperature of -5°C (since performed in the winter). With temperatures below -10°C, approaches could not have been flown in LNAV/VNAV (only LNAV), meaning that aircraft would have had to fly them as a 2D approach.
- Visibility and ceiling criteria were relaxed since considered too restrictive in trial period 1.
After the completion of the second trial, a comparison was made between the two trial periods.
Some findings were discovered that are further investigated in cooperation with participating airlines. The results of the trials are issued by the Stargate project consortium but are not publicly available at the time of completing the work of Pillar 2.