## 4 Challenges for Ground Times and Respective Measures to Reduce Risks
### Operational and Technical Measures for Individual Stakeholders
#### 4.2.2 Advanced Technologies and Infrastructure  
Hereafter, this section gives a brief overview of technological and infrastructural difficulties and opportunities for reduced GTs. Note that each airport has its individual conditions including geography and weather that can be challenging and influence the applicability of measures. Figure 4 depicts a selection of concepts addressed. Infrastructure changes are inauspicious for all stakeholders. In fact, they are not only costly and often not possible for special and regulatory reasons, but their implementation process disrupts operations. Yet, terminal layout, apron, taxiway, and runway configurations can only be changed in the long-term. However, they are a straightforward way for airports to reduce surface delays. One example are parallel taxiway systems for reduced surface conflicts [18; 30]. Furthermore, the 2050+ Airport consortium proposes future technical measures for invariant processes at airports that might increase time efficiency, but also require infrastructure adjustments. Promising future concepts are the use of robot arms to support container loading [41], biometric boarder control [42], and electric engine taxiing, which shortens pushback times as aircraft can move backward on their own. Further, an underground supply system for electrical power or underground (de)loading devices could fasten the particular processes and minimize the number of required vehicles and GSE present at the apron. This reduces the surface traffic, which allows for a straight taxi-out [43; 44]. The future of air traffic is characterized by ongoing digitalization. The most promising area for efficient ground processes are new technologies coming along with what is referred to as Industry 4.0 or Aviation 4.0. Smarter production processes shall be enabled by artificial intelligence, machine learning, data science, and the Internet of Things. Reduced GTs could result from the automation of GH at airports. Further, airlines and airport operators could implement a sensor network in aircraft and at the airport, which would allow for enhanced predictability [45]. In the upcoming years, next-generation aircraft types characterized by electric systems and advanced wing layouts will challenge airports. The better the suitability between aircraft and airport, the more efficient operations can be. The introduction of new aircraft types and configurations comes along with new GH characteristics. Recent studies concentrated on an autarkic turnaround that does not demand the use of GSE, as aircraft are furnished with appropriate tools and equipment. Those novel aircraft configurations require less airport resources and a lower number of GSE in place. This would allow airlines to operate more independently. Moreover, GSE positions are predefined by the respective aircraft interfaces. Even though there is a trend towards commonality, new aircraft design options for faster GH include a rearrangement in the form of clustering of those interfaces. This change will again require adaption in form of GSE positioning [3; 7]. Since the TAT serves as an important KPI already, the development phase of new aircraft designs contains discussions about GH operations. Design choices should drive shorter TATs to improve economic performance. However, there are operations where the duration does not depend on the aircraft architecture--such as refuelling times, which depend on the fuel flow [27]. GH service providers could investigate more into the direction of deploying new and advanced GSE. [PERSON] briefly touched upon the option of a multi-functional towing vehicle [3]. It should allow an embarkation process during taxiing. The concept already integrates the idea of autonomous driving and electric propulsion power. The vehicle combines multiple functions. It serves as a jet bridge, towing truck, and shuttle bus at the same time. Towing aircraft after arrival towards their parking position is also one of its envisioned functions.