Improvements of Aircraft Availability

Improvements in aircraft availability allow better assignment of aircrafts to specific missions. Aircraft Availability is important to reach the organisational goals like ‘air power’ and mission availability. The performance indicator Aircraft Availability gives insight of the contribution to the mission capability of the fleet. Depending on the goal, there are different ways to calculate Aircraft Availability. In one definition of Availability the performance parameter depends on the Mean Time Between Failures and the Mean Time To Repair (corrective maintenance after a failure has occurred). Improvements of Aircraft Availability are not always performed on the same level of the performance indicator itself, but on a more detailed level. In the above mentioned definition of Availability, a higher availability is reached by increasing the MTBF and/or decreasing the MTTR. Within the RNLAF, Aircraft Availability is not monitored stand alone but in conjunction with other logistic indicators. All is embedded in the business policy “Integral Weapon System Management”. Defining the right indicators to control the availability is not easy; the indicators must be carefully tuned between business goals on the one hand and (maintenance and supply) processes on the other hand. Additionally, also norms, measurement band width and organisational requirements must be defined. In this report an oversight is given of the used indicators of Aircraft Availability, and a start of the discussion of “What is a right indicator” is made. 1.0 INTRODUCTION Aircraft Availability (AA) is a global performance indicator that is useful for management to control the fleet and the MOB. The RNLAF has incorporated a managerial control concept: Integral Weapon System Management (IWSM). The purpose of IWSM is to guarantee availability and exploitation of the system during the whole life cycle of the system. The intention is to seamlessly integrate supporting processes of the (weapon) system, by introducing standards and norms for logistics. The implementation of these logistics processes should be cost-efficient and minimising life cycle cost. This, however, may not influence airworthiness. Improvements of Aircraft Availability Within the Royal Netherlands Air Force 4 2 RTO-MP-AVT-144 IWSM comprises the following function scopes: • Product Management: determines the requirements of a weapon system, to during the whole life cycle meets the operational needs. • Configuration management: identifies and controls configurations and changes in configurations. • Integrated Logistics Support management: integrated logistics support of a weapon system, during the whole life cycle appropriate logistics support against controllable costs. • Contract Management: set up of agreements with suppliers of products and services. • Financial management: planning and realisation of cash flow. • Quality management: organising and guaranteeing of quality, by a quality system according determined requirements of products, services, and processes. • Administration: facilitates managerial information for IWSM. The responsibility for each weapon system, such as F-16, Chinook, and Apache, is dedicated to the weapon system manager, who reports long term enhancements and periodically evaluation of the performance indicators. The weapon system manager is responsible for the managerial process of norms, requirements, and directives to control the underlying executing process. In this IWSM management concept the emphasis is the realisation of employability of the weapon system. This employability or system effectiveness is divided into: • Operational availability: System reliability. Maintainability. • Mission reliability. • Conformity of design. These are the roots/fundamentals of the interest of the RNLAF in availability. In the next section different kinds of availability will be explained, including their goal and definition. In section 3 some of the basic routines of working with indicators are described, supported with daily practices. Since aircraft availability is a too broad indicator to manage solutions of logistic processes, is section 4 looking for more appropriate indicators. The implementation of new performance indicators is pointed out in section 5. Finally in section 6 the conclusions are given. 2.0 AIRCRAFT AVAILABILITY Availability is defined (according to NATO ARMP-7): “the ability of an item to be in a state to perform a required function under given conditions at a given instant of time or over a given time interval, assuming that the required external resources are provided.” Improvements of Aircraft Availability Within the Royal Netherlands Air Force RTO-MP-AVT-144 4 3 In the broadest sense, Aircraft Availability (AA) is defined as the portion of time the weapon system can fulfil the dedicated function. Availability is also dependent of reliability and maintainability of the system. RNLAF divides AA into: • Inherent. • Operational. • Scheduled. • Unscheduled. All four indicators are used by the RNLAF and have their own formula. 2.1 Inherent Availability Inherent availability is a performance parameter that depends on the Mean Time Between Failures and the Mean Time To Repair (corrective maintenance after a failure has occurred). In mathematical terms, it can be defined as: MTBF MTTR + MTBF Ai = Inherent Availability (Ai) is defined as the availability that does not take delay times into account like: • Waiting for support capacity. • Internal transport. • Waiting time on spares. Given the formula, it is obvious that a higher availability is reached by increasing the MTBF and/or decreasing the MTTR. The latter applies to corrective maintenance, whereas the first can be done by using high-reliability parts or by implementing preventive maintenance. The Ai generates the highest possible upper limit of the availability of the system. The amount and the influence of any delays in the processes are depending on the way the logistic support has been implemented and is recognisable in operational availability (see Section 2.2). Ai is a good indicator to evaluate the influence of the values of MTBF and MTTR of each of the (sub) components on the system as a whole. 2.2 Operational Availability Operational Availability (Ao) in the contrary does include delay times, corrective and preventive maintenance. This is a more ‘realistic’ approach, since losses in processes are hard to prevent. MTBMA MTBMA + MMT + MLDT Ao = Legend: MTBMA= Mean Time Between Maintenance Actions MMT= Mean Maintenance Time MLDT= Mean Logistic Delay Time Legend: MTBF= Mean Time Between Failure MTTR= Mean Time To Repair Improvements of Aircraft Availability Within the Royal Netherlands Air Force 4 4 RTO-MP-AVT-144 The difference between MTTR (in Ai) and MMT is that MTTR only calculates an average of corrective maintenance activities and MMT involves both preventive and corrective maintenance actions. The Ao is the indicator for employability and is dependent on the ratio of preventive and corrective maintenance and the accompanying delays, against the total active time of the system. This quantitative indicator gives insight in the areas (for example delivery delays or lead time of a maintenance example) in which the most successful improvements could be made. Also Ao can be expressed as a ratio of the time in which the weapon system is available, over the total time that is to be taken into account. 2.3 Scheduled Availability Next implementation of AA is scheduled availability, which calculates availability in a slightly different way. It is based on the time the aircraft is ready (fully or partially) for a mission and the time spent on scheduled maintenance. The formula for Scheduled Availability (As) is: As is defined as the portion of time, in which a weapon system fulfils the needed function. In this definition only scheduled maintenance is ‘planned’. Pre condition is that unscheduled maintenance is not calculated. The availability is calculated only to take into account preventive maintenance action. 2.4 Unscheduled Availability Unscheduled Availability (Au) is defined as the portion of time that a weapon system fulfils the required function, assuming there is no scheduled maintenance. The availability is calculated by corrective maintenance. The RNLAF is interested in the availability of the F-16 minus time spent on scheduled and unscheduled maintenance. The goal is to reduce the unscheduled maintenance part. The causes of a high value of Au is investigated. 2.5 Results Monthly, management is reported on availability of the total fleet and per unit. The units are the MOBs of the Netherlands, the training, and out of area locations. The reports give insight in NMCM due to modification, preventive and corrective maintenance. Legend: FMC= Full Mission Capable PMC= Partly Mission Capable NMC= Not Mission Capable due to unscheduled maintenance Legend: FMC= Full Mission Capable PMC= Partly Mission Capable NMC= Not Mission Capable due to scheduled maintenance FMC + PMC FMC + PMC + NMCscheduled As = FMC + PMC FMC + PMC + NMCunscheduled Au = Improvements of Aircraft Availability Within the Royal Netherlands Air Force RTO-MP-AVT-144 4 5 Table 1: Figures of Aircraft Availability. Aircraft Availability