# Through-Life Maintenance Cost of Digital Avionics
## 5 Post-Warranty Maintenance Models of Avionics Systems  
Low-cost airlines with few aircraft may not have enough money to perform all maintenance levels. Accordingly, these airlines may remove the second and third maintenance levels and use only O-level. In this case, the airline transfers to specialized companies heavy maintenance checks and routines. Such companies are usually called repair stations. According to [34], U.S. airlines outsourced 71% of heavy maintenance in 2008. Therefore, we consider only the organizational level maintenance (O-level) for the first post-warranty maintenance (PWM) option. The first PWM option is simple for airlines but may turn to be very expensive. All LRU that rejected by BITE in-flight the airline should ship to the manufacturer for repair. In this case, for ensuring the flights' regularity, the airline should buy a comparably large quantity of spare LRU. The first PWM option implies that LRU shipped to the manufacturer will include not only LRU with permanent failures but also LRU removed from airplanes due to intermittent faults and in-flight false-positives. Thus, the airline will have to pay for repairing all LRU dismounted from the aircraft fleet due to permanent failures, intermittent faults and BITE false-positives. Upon expiration of the warranty period, the airline is obliged to pay the cost of repairing the LRU, transportation costs, labor costs, and the cost of the spare LRU. Therefore, the integral maintenance cost indicator for the airline is the total expected maintenance cost during the post-warranty service life of the avionics system, which we denote as EMCPW. This cost comprises the following components for the first PWM option: the cost of dismounting and mounting LRU in the aircraft during the post-warranty period, the cost of delivering LRU to the manufacturer and back to the airline, the cost of LRU repairs, and the cost of spare LRU per aircraft. We determine EMCPW for the first option as follows:\[EC_{PW,1}=q\Big{[}LC\times t_{M}^{O-level}+C_{TR}+C_{IF}P_{IF}+C_{PF}P_{PF}+C_{FP}P _{FP}\Big{]}ER(T_{PW})+C_{LRU}(PS+US)/N_{PW}, \tag{33}\]  
where \(C_{TR}\) is the mean cost of LRU shipping to manufacturer and back to the airline, \(C_{PF}\), \(C_{IF}\), and \(C_{FP}\) are the mean cost of the LRU repair due to permanent failure, intermittent fault, and in-flight false-positive at the manufacturer, respectively, \(T_{PW}\) is the post-warranty period measured in-flight hours, \(ER(T_{PW})\) is the average number of unscheduled removals of LRU due to permanent failures, intermittent faults, and in-flight false-positives for time \(T_{PW}\), and \(N_{PW}\) is the quantity of aircraft operated in the airline without a warranty. For the first PWM option the average LRU repair time \(E(T_{repair})\) is calculated by Equation (23). Let's consider three different PWM options of the maintenance system with two levels (O- and I-level). For rechecking the dismounted LRU in the first option, the airline uses ground test equipment at the I-level of maintenance. After rechecking, the airline ships the LRU with confirmed failures to the manufacturer or to the outsourcing company for repair. The units with unconfirmed failures are shipped to the warehouse where spare LRU are stored. For this maintenance option, EMCPW includes the following cost components: the cost of O-level maintenance during the time \(T_{W}\), the cost of checking LRU with ground test equipment, the cost of shipping failed LRU to the manufacturer and back, the repair cost of LRU having a permanent failure at the facilities of the manufacturer, the cost of ground test equipment recalculated per one aircraft, and the spare LRU quantity cost recalculated per one aircraft.