# Through-Life Maintenance Cost of Digital Avionics
## Abbreviations
### Nomenclature
\begin{tabular}{l l} \(t_{M}^{O-level}\) & mean time of O-level maintenance \\ \(ER(T_{W})\) & average number of unscheduled removals of LRU due to permanent failures, \\  & intermittent faults, and in-flight false-positives for time \(T_{W}\) \\ \(PS\) & planned quantity of spare LRU in the warehouse \\ \(US\) & unplanned quantity of spare LRU that will need to be supplied from the \\  & manufacturer to ensure regularity of flights \\ \(C_{LRU}\) & cost of a spare LRU \\ \(N_{W}\) & quantity of airplanes under the supplier's warranty \\ \(EC_{W,2}\) & expected cost for the second WM option \\ \(t_{TE}^{I-level}\) & average LRU testing time using the ground test equipment at the I-level maintenance \\ \(F_{TE}^{I-level}\) & quantity of different LRU types that the ground test equipment can test at the \\  & maintenance on the I-level \\ \(C_{TE}^{I-level}\) & ground test equipment cost on the I-level \\ \(t_{spare}\) & average time of waiting for spare LRU from the warehouse in the situation \\  & \"aircraft on the ground\" \\ \(t_{stop}\) & average time of the scheduled stop of the aircraft at the airport of the airline's base \\ \(E(T_{repair})\) & mean time of LRU repair \\ \(P_{PF}\) & a posterior probability that the LRU dismounted from the aircraft due to \\  & permanent failure \\ \(P_{FP}\) & a posterior probability that the LRU dismounted from the aircraft due to a \\  & false-positive error of BITE \\ \(P_{IF}\) & a posterior probability that the LRU dismounted from the aircraft due to \\  & intermittent fault \\ \(t_{testing}^{PF}\) & time of testing the LRU removed from aircraft due to permanent failure \\ \(t_{testing}^{PP}\) & time of testing the LRU removed from aircraft due to a false-positive error of BITE \\ \(t_{testing}^{PP}\) & time of testing the LRU removed from aircraft due to intermittent fault \\ \(EC_{CW}^{OP}\) & minimal EMCW corresponding to the optimal WM option \\ \(C_{TR}\) & mean cost of LRU shipping to manufacturer and back to the airline \\ \(C_{IF}\) & mean cost of the LRU repair due to intermittent fault at the manufacturer \\ \(C_{PF}\) & mean cost of the LRU repair due to permanent failure at the manufacturer \\ \(T_{PW}\) & post-warranty period measured in flight hours \\ \(ER(T_{PW})\) & average number of unscheduled removals of LRU due to permanent failures, \\  & intermittent faults, and in-flight false-positives for time \(T_{PW}\) \\ \(N_{PW}\) & quantity of aircraft operated in the airline without a warranty \\ \(EC_{PW,1}\) & expected cost for the first PWM option \\ \(EC_{PW,2}\) & expected cost for the second PWM option \\ \(EC_{PW,3}\) & expected cost for the third PWM option \\ \(EC_{PW,4}\) & expected cost for the fourth PWM option \\ \(EC_{PW,5}\) & expected cost for the fifth PWM option \\ \(t_{ATE}^{I-level}\) & mean time of checking the LRU with help of ATE at the I-level \\ \(C_{PF,R}\) & mean cost of SRU repair with permanent failure at the outsourcing company \\  & or manufacturer \\ \(t_{PF,D}^{I-level}\) & mean time to detect the place of a permanent failure in the failed LRU with depth \\  & to SRU using ATE \\ \(C_{TR,SRU}\) & mean cost of delivering the faulty SRU to the outsourcing company or manufacturer \\  & and back to the airline's warehouse \\ \(C_{ATE}^{I-level}\) & cost of ATE that serves the I-level \\ \(F_{ATE}^{I-level}\) & quantity of LRU types that ATE can check \\ \(C_{j}\) & \(j\)-th type SRU cost \\ \(n\) & quantity of SRU types in the examined LRU \\ \(SRU_{j}\) & quantity of spare \(j\)-th type SRU \\ \(\mathrm{H}_{j}\) & aggregated quantity of the \(j\)-th type SRU that installed in all aircraft' LRU of the airline fleet and spare LRU located in the warehouse \\ \(P(\mathrm{H}_{j})\) & probability that the total number of LRU will be provided with SRU type \(j\) \\ \(\lambda_{j}\) & rate of permanent failures of \(j\)-th type SRU \\ \(t_{RS,j}\) & average repair time of the \(j\)-th type SRU at the manufacturer \\ \end{tabular}   
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