Development of a Maintenance Man Hours Estimating Relationship during preliminary design of More and All Electric Aircraft

Evaluating operating costs is a key step in the successful development of an aerospace project. In particular, maintenance costs represent a very important cost voice for aircraft and many tools for estimating them since the preliminary design phase are publicly available. Since new aviation tendencies and technological improvement are pushing towards the developing of More Electric Aircraft (MEA), new cost estimating relationships need be built up in order to replace the conventional ones, that can no longer be exploited in these cases. The objective of the present work is to provide an estimation relationship which is able to evaluate the amount of scheduled Maintenance Man Hours (MMH) that are saved or added, when going from a conventional On-Board System (OBS) architecture to a more or all electric one. This goal has been accomplished through two approaches. The first one is literature based and consists of analysing the A320 Maintenance Planning Document (MPD) to identify the tasks that have to be removed, replace or added when the electrification of the systems takes place. By identifying those tasks, it has been possible to evaluate the MMH variation for three MEA and one All Electric Aircraft (AEA) reference architectures of the A320. The second approach that has been followed is experience based and consists of a series of interviews to maintenance and OBS experts. The goal of the interview is to get a second estimate of the MMH variation that occurs in the electrification process of each on-board system. By doing so, it has been possible to compare the results coming from the two methods and adjust the results basing on the strength and weaknesses of each approach, hence resulting at the end with a more accurate estimate. The estimated values for the OBS MMH variations have then be used to build up the Maintenance Man Hours Estimating Relationship (MMHER), which has been subsequently verified and applied to a use case. Finally, the MMHER has been integrated into an architecture generating software, ADORE, framework. This unlocked the possibility to perform an iterative optimization loop where random architectures are generated by the software and then evaluated by the MMHER. The evaluation then, serves as a feedback for ADORE, which guides the design towards the most time saving architecture. This study clearly shows the advantages of going from conventional to MEA and AEA architectures in terms of saved scheduled MMH. In particular, the removal of the hydraulic secondary power is expected to allow major savings, while instead the introduction of Li-Ion batteries and an electrified environmental control system is expected to lead to a greater amount of MMH needed for scheduled maintenance. Lastly, the use of ADORE has allowed to determine the scheduled MMH optimum architecture.