Development and evaluation of a speed guidance interface for trajectory-based dispatch towing

The implementation of trajectory-based air traffic operations, as proposed by the US-American and European programs NextGen and SESAR, requires fundamental changes of both inflight and ground procedures. This paper addresses an optimization of the taxi process by proposing trajectory-based dispatch towing operations. In the developed scenarios, an automated tractor shall tow the aircraft from gate to runway following prescribed speed profiles. After having shown an overview of the general concept, the development and evaluation of a human-machine interface (HMI) providing speed guidance to the pilots will be presented. In a mixed automation mode, the tractor shall be able to accelerate and decelerate the aircraft-tractor combination within specific limits. In order to allow for decelerations the tractor cannot apply, the pilot will need to conduct the aircraft's brakes when advised by the HMI running on an electronic flight bag (EFB). In a simulator study, commercial airline pilots evaluated different implementations of a speed guidance interface instructing the participants regarding needed brake inputs. The results reveal both advantages and disadvantages of the evaluated concepts. Participating pilots prefer a simple design like a digital advice or acoustic verbal instructions. An attention-grabbing design is especially important as the position of an EFB is usually located at the outer margin of the pilot's field of view and thus compromises the pilot's main task of monitoring the traffic situation. In contrast, concepts providing feedback regarding the actual and target ground speed were considered helpful in order to better interpret the brake advices in terms of the required pedal input. Consequently, the evaluation led to a redesign of the speed indicator by means of combining elements of the investigated concepts.