## 4 Challenges for Ground Times and Respective Measures to Reduce Risks
### Operational and Technical Measures for Individual Stakeholders
#### 4.2.1 Efficient Planning and Operations  
Various challenges and measures arise in terms of efficient ground operational processes. As highlighted before, important objectives for all stakeholders are flexibility and predictability of TATs and taxi times. Thus, resilient procedures are of high importance to mitigate risks of long GTs. Flexibility means creating operational latitude in the case of disruptions to be able to still achieve the goals set. This is one key to success [14]. So, the right planning of ground support services is essential. [PERSON] and [PERSON] emphasize considering the risk of perturbation as a result of the inherent variability of ground processes by taking stochastic parameters into account [35]. E.g., GH providers should not plan all their GSE and labour to be in use the whole day and airlines should plan for buffer times, even though this is unfavourable in terms of high utilization rates [23]. Another important point for all stakeholders is the sufficient provision of personnel, especially at peak times. This is a priority of the planning task as it has a major impact on the fluidity and speed of operations. The business dynamics call for reliable quality of the service product at low cost. Shorter GTs should in no case compromise safety and quality. Therefore, process flow optimization (PFO) is crucial and favorable at any time. It implies an adjustment of the process that enables the change of specific parameters in conformance with procedural constraints. A preliminary analysis of the current operational level to identify system shortcomings is beneficial. There are the options of optimizing the equipment, improving the execution of control loops, or taking a look at operational procedures whether human behavior or technologies are the problems causing a bottleneck [36]. Here is a simple example of PFO for reduced GTs:Identification of a Bottleneck  
In general, aircraft ground damage including damage from GSE, other aircraft, or poorly connected cables can extend GTs. Where Is the Origin of the Problem? Ground damages often find their origin in human action. What Can Be Done to Mitigate or Eliminate the Problem? An appropriate measure to solve this problem is the proper training of personnel and employees. The IATA Airport Handling Manual suggests different training methods. It is essential to update the ground operations training to current rules and standards, especially in the interest of ramp safety for all involved parties [22]. For turnaround activities, parallelizing and shortening GH procedures are means to minimize the TAT. Further, refining process execution along the critical path is a possibility to increase robustness and efficiency. As mentioned above, fast cabin cleaning is essential. To assure cleaning does not become a critical activity, enough cleaners should be employed, however more workers induce higher costs for the airline [23]. Moreover, airport GH resources are scarce and they should be handled optimally. [PERSON] et al. found that the right placement of GSE can result in a significant reduction in GH times, so they propose a positioning for shorter delivery and GSE arrival times [37] These are only two exemplary measures that could be taken by GH service providers, and it is important to mention that the field of low-level options to reduce GTs reaches further. Still, stakeholders must observe the limits. Too short TAT could cause problems with aircraft brake cooling times or cockpit procedures [3]. Besides the options for GH procedures, there is also the taxi movement that defines the GT of aircraft. Ground routing is a fundamental aspect concerning safety requirements, conflict-free aircraft movements, and simultaneously short runway waiting times. The responsibility lies with ATC, which assigns passing times for specific taxiway intersections. Controllers must consider separation constraints, taxi speed, turning angles, runway occupancy, and origin and destination timing [30].