## 4 Application Analysis and Results
### Application Results
#### 4.2.1 Effectiveness Analysis  
To evaluate the effectiveness of the SAA approach, we considered the following three strategies:  
1. The ideal situation of applying the MTO strategy. 2. An empirical method in real production. 3. The GCA strategy obtained by the SAA approach. The MTO strategy is the best way to organize aircraft manufacturing and assembly. However, MTO realization is not straightforward, due to the uncertainty of customer orders. An empirical method, which is a substitute used in real production now, can construct GCA by choosing the most popular options of the option groups. According to empirical methods, option units for navigation, communication, and related functions that affect basic flight safety must be installed in the GCA, while highly customized functions of customers, such as cabin layout and interior, are not required. Taking a certain type of aircraft as an example, among the 55 option units of the 32 systems in the aircraft, functions such as cockpit door monitoring, music playback system, life raft, life jacket, etc., are not installed in the GCA. In addition, the following three types of customer options may not be installed:  
(1) Option units for additional functions, such as a second set of high-frequency and satellite communication systems;  
(2) Option units for cabin decoration, such as cabin layout, door curtains, carpets, seats, portable oxygen cylinders, and passenger oxygen units;  
(3) Option units for cabin function, such as kitchen plug-ins, second-attendant seats, dog kennels, and a dressing room. The GCA must ultimately meet specific customer requirements and must not be repaired before delivery (e.g., repairing holes after large openings). Therefore, determining its configuration requires consideration of the following constraints:  
(1) The drawings in enclosed areas, such as the aircraft head and at the front of the production process, need to be installed in advance, such as certain cables;  
(2) The mandatory customized functional structure and equipment must be easy to disassemble in the future, without causing any structural damage;  
(3) Necessary structures and equipment that depend on customized option units, such as kitchens, bathrooms, passenger-announcement systems, etc., which are affected by cabin layout, must be identified. From this, the basic configuration of the GCA can be determined, and the decision-making process is shown in Figure 4.  
Figure 5 shows the production time according to the three strategies. Each pillar represents the production time of a specific strategy, and it consists of the assembly time, disassembly time, and re-assembly time. The gap between the total production time and the reworking time is marked in the figure. Figure 4: GCA decision model. Figure 5: Comparison of objectives for the three considered strategies. Figure 5 indicates the following:  
1. The MTO strategy had a production time of 2011.77 h with no reworking time, which was the least of the three modes. Aircraft OEMs usually hope for a proper and fixed pace of aircraft production. However, due to changes in the airline's product business strategy, operational status, etc., the aircraft delivery time to the airline is highly uncertain. The MTO strategy is inapplicable under uncertainty conditions because the MTO production is usually idealized for each order. 2. When the aircraft order is highly uncertain and the MTO strategy is no longer applicable, OEMs adopt a GCA approach for aircraft production. OEMs apply the SAA approach solution with the total production time reduced by 33.08% compared to the empirical method solution for the same orders, as demonstrated in Figure 5. The reason is that the empirical method generates the configuration by individually optimizing each option group; thus, it cannot optimize the configuration from a global perspective or considering the uncertainty of orders. 3. Additional work has to be conducted after planning; a rework workstation is set to take pro-active actions to convert the GCA into an order-specific configuration.