# Through-Life Maintenance Cost of Digital Avionics
## 8 Conclusions  
This article has proposed a new mathematical model for assessing the through-life maintenance cost of digital avionics. For the first time, we proposed mathematical equations for evaluating the MTBUR of in-flight monitored avionics systems considering permanent failures, intermittent faults, and false-positives of BITE. It has been shown that the dependence of MTBUR on the conditional probability of in-flight false-positive has a different pattern. At used data, on the interval from 0 to \(10^{-4}\), MTBUR weakly depends on the conditional probability of false-positive during flight and falls maximum by 10%. On the interval from \(10^{-4}\) to \(10^{-2}\), MTBUR strongly depends on this probability and decreases by eight times. Therefore, the conditional probability of in-flight false-positive should be at least no more than \(10^{-4}\). It has also been shown that to provide the in-flight conditional probability of a false-positive in the interval \(10^{-5}\)-\(10^{-4}\), the number of in-flight test checks should be 10 to 100.  
Generalized expected maintenance cost equations during the warranty and post-warranty period of operation of avionics systems, seeing the characteristics of permanent failures, intermittent faults, and in-flight false-positives of BITE, have been developed for various maintenance options that differentiate by the number of maintenance levels, allowing to choose the most effective maintenance option for each maintenance period. Numerical analysis has shown that ATE's use at the I-level maintenance virtually eliminates the harmful effect of intermittent faults and in-flight false-positives on the quantity of spare LRU. We show that the third PWM option is less sensitive to changes in the conditional probability of in-flight false-positive and the rate of intermittent faults than the fourth and fifth PWM options concerning the number of spare LRU, which is because the mean repair time is longer for the fourth and fifth than for the third PWM option. Considering as an example the avionics system ADIRS installed on A380 (Emirates Airline), we have demonstrated that the maintenance option with three levels provided the use of IFD on the levels I and D is the best. Because it decreases the full expected cost of maintenance by eleven-fold as compared to only I-level maintenance, by nine-fold compared to a two-level choice without IFD, by 1.45 fold in comparison with three-level maintenance without using IFD, and by 1.71 fold compared to the three-level option with IFD only at the I-level.  
In future research, we hope to develop the cost models for post-warranty maintenance options involving only outsourcing service companies.  
This article presents the collective work of two authors. The authors ([PERSON] and [PERSON]) jointly participated in conceptualizing the problem, formal analysis, development of mathematical models, data curation, numerical calculations, and writing the article. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Data Availability StatementData sharing not applicable. No new data were created or analyzed in this study. Data sharing is not applicable to this study.  
The authors declare no conflict of interest.