## 3 Framework of Forecasting AOG Models in Aviation
### Challenges in Troubleshooting and AOG Management  
**Inventory Management and Supplier Coordination**  
Another complicating factor for AOG management is the management of the spare parts inventory. Aircraft fleets differ because one model may have part requirements different from a different airplane model [25]. An essential factor is that airlines could easily be on the extremes of a \"part supply versus demand\" continuum, with either overstocking or understocking parts as problematic. The demand forecasting models are instrumental in helping the airlines identify which part is likely to be used and when. Nonetheless, defective evolution because of limited quality inputs or volatile customer demand patterns can lead to stockouts or the wrong part being stocked in the wrong place [33]. This factor is made worse by the fact that many items have different service lives, ranging from items that have a short service life while others are stable and once installed, they can be periodically removed for maintenance and then put back.  
Suppliers and MRO are crucial to AOG processes, and communication is vital, but it is replete with problems [34]. Even suppliers have their problems, such as manufacturing problems, that make it hard to supply spare parts on time. In addition, the globalization of the aviation system also indicates that the suppliers with whom the airlines must work include many companies across different continents, different time zones, different sets of regulations, and different supply chain systems. Most of the time, airlines must also outsource their MRO to third-party providers. Despite the potential for such providers to bring considerable experience to a firm, the coordination between the airline and an MRO or suppliers when many players are involved can be challenging. Discrepancies in communication, contract disputes, and time-consuming approval procedures can lead to the extension of AOG downtime.  
**Impact on AOG Downtime**  
Logistical factors such as lead time, inventory build-up, and managing relationships with suppliers can significantly increase the time an organization experiences AOG downtime [35], ultimately leading to higher operations costs and customer complaints. An aircraft that has been on the ground for an extended period causes disruptions in arrival and departure schedules and thus results in the cancelation of flights or delayed operations, which can be damaging to the image of the airline in question. Further, AOG events can be costly in terms of equipment repair costs, spare replacement costs, and revenue loss, especially for long and high-yield flights. The \"Impact of Logistical Factors on AOG Downtime (2020-2024), (Table 2)\" highlights trends in lead time, inventory issues, and supplier delays among key players in the aviation industry, showing their impact on AOG downtime. These metrics reflect the efficiency of aviation maintenance supply chains. Lead time, measuring the time from ordering to part delivery, decreased from 25 days in 2020 to 12 days in 2024, indicating improved procurement processes and predictive analytics.  
Inventory issues, representing delays caused by stock inefficiencies, dropped from 48 h in 2020 to 30 h in 2024, though challenges in inventory management persist. Supplier delays, the time lost due to late deliveries, fell from 30 to 18 days over the same period,reflecting better supplier coordination and logistics improvements. Despite progress, supplier delays and inventory inefficiencies remain significant contributors to AOG downtime, emphasizing the need for further optimization in these areas.