# Through-Life Maintenance Cost of Digital Avionics
## 4 Warranty Maintenance Models of Avionics Systems  
Correct regulation of the relationship between the supplier (manufacturer) of the aircraft and the buyer (airline) primarily determines its efficiency in operation. The most acute problem faced in this relationship arises during the warranty period when the supplier bears the main costs of repairing the aircraft systems. The supplier fixes the system's defect by free charge and can either replace or repair the failed system within a reasonable time. However, the buyer must acquire sufficient spare LRU to guarantee the absence of flight delays. The quantity of spare LRU is dependent on the chosen option of warranty maintenance (WM). For avionics systems, the selection of the optimal WM option is dependent on the following: (a) supplier's warranty obligations; (b) operational reliability indexes; (c) whether the buyer has ground test equipment [33] (p. 86). Manufacturers and suppliers of avionics systems typically use the following warranty time-related indicators: warranty period (\(T_{W}\)), guaranteed repair time (\(T_{RS}\)), and guaranteed expedited delivery time of a spare LRU (\(T_{ED}\)). Warranty time-related indicators have specific units of measurement. The warranty period is expressed in a calendar period (years, months) from the beginning of the warranty. The guaranteed turnaround time on a repair is computed in a calendar duration (days) from the beginning of repair. The guaranteed expedited delivery time of a spare LRU is expressed in a calendar duration (days) from the claim date. Any contract for the supply of avionics systems specifies the values of \(T_{W}\), \(T_{RS}\), and \(T_{ED}\). The supplier's time-related indicators of the warranty may be presented in different measurement units. For instance, assume that \(T_{W}\) = 2 years and the yearly aircraft flight time is 2500 h; then, if necessary, we can measure the warranty period in hours, e.g., \(T_{W}\) = 2 \(\times\) 2500 = 5000 h. Sometimes, the warranty period's length is specified separately in the calendar duration and flight hours. In such cases, the \(T_{W}\) indicator equals the value that is reached first. The aircraft buyer does not pay for repairing the failed LRU during the warranty period. However, it pays for spare units needed to guarantee flight regularity. Consequently, the aircraft buyer should select a WM option corresponding to the minimum total operating costs. Various WM options may depend on whether the airline has ground test equipment and \(T_{RS}\) and \(T_{ED}\) values. The existence of ground test equipment at the airline base allows testing the operability of the dismounted LRU and shipping only those LRU to the manufacturer that have confirmed failures. Airline sends the LRU whose failures were not confirmed to the warehouse. Such LRU are included in the exchange fund and can be installed onboard upon request. The first WM option includes only O-level maintenance. Here, all LRU, rejected by BITE, the airline ships to the manufacturer for repair. The most significant cost indicator for the airline during the warranty period is the total expected maintenance cost, which we denote by EMCW. It is clear that during warranty, EMCW comprises the cost of dismounting and installing the LRU on the aircraft board and the cost of LRU in the warehouse recalculated per one aircraft. We denote the average costs associated with the first WM option as \(EC_{W,1}\). Evident that the cost of spare LRU has a significant impact on \(EC_{W,1}\).