3D-Precision Curved Approaches: A Cockpit View on ATM

Pre-defined curved approach procedures represent an essential for noise abatement and may reduce the risk of controlled flight into terrain (CFIT) for today’s aviation considerably. In addition, a Ground Based Augmentation System (GBAS) supports accuracy and precision of the desired flight path. While the lateral guidance during current curved approach procedures is usually based on a position solution provided by satellite navigation systems in conjunction with inertial navigation systems, the vertical guidance is still based on measurements of a barometric altimeter. This type of approach with vertical guidance is supposed to enhance the situational awareness for pilots compared to non-precision approach procedures and reduce the risk for controlled flight into terrain. However, the accuracy of the barometric vertical guidance is inferior compared to precision approach procedures, temperature dependent and require the correct pressure setting for each approach in the aircraft. Therefore, novel curved approach procedures are supposed to rely solely on satellite navigation augmented by either a ground based or satellite based system and only optionally by inertial measurement systems. Such coupled (hybrid INS and GNSS) systems are usually highly integrated and monitored by a flight management system. Therefore, the requirements for the equipment of aircraft that are conducting such approach procedures are very stringent. Using only GBAS could relax those requirements. In this work, an option for precision curved approach procedures was investigated and tested in flight trials. This option is based on a GBAS. In general, different possibilities are imaginable to enable GBAS based curved approaches. For instance, GBAS could only serve as means to enhance the navigation performance to achieve stringent RNP requirements. Or GBAS could serve as the sole means to enable a curved approach. This option is described in this paper. Others include the Microwave Landing System or are conducted as a visual approach. The option which utilizes the GBAS functionality to broadcast desired (curved) flight paths, the Terminal Area Path (TAP) functionality was investigated in this work. For this, simulator trials were performed to evaluate different means of flying these procedures in terms of guidance displacement sensitivity and means of displaying deviation information. Based on the results of the simulator trials flight trials were conducted. Results from flight trials are presented in this manuscript to show how this method for conducting curved approaches can be applied.