ENERGY-OPTIMIZED APPROACHES: A CHALLENGE FROM THE PERSPECTIVES OF PILOTS AND AIR TRAFFIC CONTROLLERS

Abstract

Carrying out an approach that is as economical and safe as possible remains a challenge for flight crews with a multitude of requirements to meet simultaneously. For an aircraft to descend from cruise to touchdown with the lowest possible fuel consumption and noise signature, an approach is required that is both at idle thrust in the ideal speed and follows an ideal vertical profile. This must be done with as low drag as possible without using speed brakes, extending the landing gear too early, or flying unnecessary horizontal segments with high thrust settings. In practice, approach profiles are subject to numerous limitations due to airspace structure and air traffic density. Even with strict ATC restrictions, there are often possibilities for pilots to fine-tune the timing of changes in the airspeed profile, the strategy in the descent profile, and, derived from this, the timing of configuration changes such as deploying flaps and landing gear. In September 2019, a total of 90 test approaches were carried out at Zurich Airport on DLR's Airbus A320 ATRA using the LNAS pilot assistance system for the most economical and quiet approaches possible. To manage these challenges, pilots and air traffic controllers need a good understanding of flight mechanics, an awareness of safety margins, continuous workload management, compliance with standard operating procedures and consciousness of environmental considerations. The assistance system reduces the crew's workload and provides support for all these tasks. In traffic situations where no minimum separation between aircraft is required, ATC instructions with margins allow approaches at idle thrust with a speed profile that is convenient for both the flight crew and air traffic control. The optimization potential within the scope of influence of pilots and air traffic controllers for energy-optimal approaches has been demonstrated during flight trials in Zurich, within the bandwidths permitted by current regulations and flight procedures. The approaches carried out with the assistance system were significantly more economical and quieter on average than the approaches performed by a pilot group tasked with conducting low-fuel and low-noise approaches without the assistance system. The pilots rated the recommendations of the assistance system positively. It will be some time before an energy-management pilot assistance system is fully integrated into an airborne Flight Management System (FMS) that communicates directly with air traffic control. Nevertheless, the flight trials in Zurich indicate that significant fuel savings and reduction of noise emissions are already achievable with specific training of pilots and air traffic controllers.