**Kyriakos I. Kourousis**

School of Engineering, University of Limerick, V94 T9PX Limerick, Ireland; kyriakos.kourousis@ul.ie Received: 30 August 2020; Accepted: 2 September 2020; Published: 2 September 2020

**Abstract:** This article aims to present and discuss a set of technical matters a ffecting the maintenance and sustainment cost of military transport aircraft (airlifters). An overview of the military aviation technical support system is provided, in conjunction with a high level discussion on the life cycle cost. Four technical support pillars are defined as part of this analysis: supply, restoration and upgrade, engineering and regulatory compliance. A focused discussion on airlift sustainment factors, based on past experience, is used to identify technical considerations that can be used for the evaluation of new aircraft. A number of technical considerations which are key for cost purposes are identified and mapped against the defined technical support pillars, related to engineering and technical support and airworthiness managemen<sup>t</sup> aspects. Important practical technical considerations are identified, discussed and critiqued under an independent lens. This article can stimulate discussion of the maintenance and sustainment costs of airlifters, both within military aviation operators and the defence industry community but also within the civil aircraft maintenance industry.

**Keywords:** aircraft maintenance; airworthiness; military aviation; airlift; cost

### **1. Technical Support in Military Aviation**

The technical support system in the United States and European military aviation is typically structured as organisational (squadron level), intermediate (base level) and depot level maintenance. Looking at the di fferent functions within these segments, one can identify technical activities broadly covering:


These technical support pillars (supply, restoration and upgrade, engineering and regulatory compliance) are intended to sustain the airworthiness and the operational capability of a military aircraft fleet. Operational readiness and utilisation (including training) interact with all facets of maintenance at all levels (I, O and D), since the objective of technical support is to supply mission ready aircraft. In turn, operational readiness has an impact and it is a ffected by grounding time. This simplified view of the military aircraft maintenance and sustainment system is illustrated in Figure 1.

**Figure 1.** The different elements of a maintenance and sustainment (technical support) system for military aircraft and their interactions with operational readiness and utilisation.
