Abstract
In this work, a maintenance float system is considered. Equipments in workstation are submitted to overhauls carried out at regular time intervals. A mathematical model has been constructed to find out the best combination of three parameters: the number of standby units, R, the number of maintenance crews in the maintenance centre, L and the time between overhauls, T. The strategy to construct the model involved: the development of differential equations in order to determine system state probabilities; the definition of an operating cycle; the calculation of the cycle duration and respective total maintenance system cost incurred; and the utilization of a search method to find out the combination of parameters that minimizes the total cost of a specific system.

Abstract
This work aims to determine the effect of performing age based preventive maintenance actions on a repairable system with a constant failure rate. Periodic overhauls are carried out every time the system reaches the end of a constant time interval without failures and the system is repaired whenever a failure occurs. Performing overhauls implies interventions such as: replacement of parts with increasing hazard rate, cleaning, oiling etc. In this work, the relationship between the initial failure rate (without periodic overhauls) and the failure rate with periodic overhauls is established. © 2008 ICQR.

Abstract
In industry, spare equipments are often shared by many workplaces with identical equipments to assure the production rate required to fulfill delivery dates. These types of systems arc called "Maintenance Float Systems". The main objective of managers that deal with these types of systems is to assure the required capacity to deliver orders on time and at minimum cost. Not delivering on time has often important consequences; it call cause loss of costumer goodwill, loss of sales and call damage organization's image. Maintenance cost is the indicator more frequently used to configure maintenance float systems and to invest in maintenance workers or spare equipments. Once the system is configured, other performance indicators must be used to characterize and measure the efficiency of the system. Different improvement initiatives call be performed to enhance the performance of maintenance float systems: performing preventive maintenance actions, implementation of autonomous maintenance, improvement of equipments maintainability, increase of maintenance crews' efficiency etc. "Carrying out improvement based on facts" is a principle of Total Quality Management (TQM) in order to step to business excellence. It requires monitoring processes through performance measures. This work aims to characterize and highlight the differences and relationships between three types of performance measures-equipment availability, equipment utilization and workplace occupation, in the context of maintenance float system. Definitions and expressions of these three indicators are developed for maintenance float systems. The relationship between maintenance float systems efficiency and the referred indicators is shown. Other indicators are also proposed and compared with the first ones (number of standby equipments, queue length etc.).

Abstract
Proportional hazards modelling is a powerful technique which can be used to investigate the effects of various explanatory variables on the life length of equipment. In this paper the analysis of aircraft cargo door complaints is considered, as this can cause serious delay problems. Particular attention is given to the assumptions supporting the application of the model. Consideration is given to problems in the choice of the appropriate basic metric time, definition of covariates and adapting the methodologies to this particular problem. Emphasis is placed upon the validation of the results by attempting several different structures of the dependent variables. Copyright © 1989 John Wiley & Sons, Ltd.

Abstract
The aim of this paper is to illustrate primarily the suitability and secondly the ability of both PHM and ‘two-sample’ tests in answering problems in the reliability field. The findings stress the fact that ‘two-sample’ tests should be preferred for comparison purposes and PHM for modelling the behaviour of the equipment in the presence of various factors. Copyright © 1991 John Wiley & Sons, Ltd.

Abstract
Purpose - The purpose of this paper is to determine the state probabilities for a float system when overhauls are performed periodically. Design/methodology/approach - First, a model is developed to express the relationship between the rate of occurrence of failure and time interval between overhauls. Then, a methodology is defined to develop differential equations for each system state in order to calculate corresponding system state probabilities. Findings - Since it is considered that units requiring an overhaul stay in operation until replacement, the possibility of failure of those units has to be included. Then, the determination of system state probabilities has to be done iteratively. Practical implications - The methodology proposed in this paper enables comparison of different designs for a float system submitted to periodic overhauls through some different performance measures. System state probabilities can also be used to determine the idle time of units, which is essential to obtain the cost of production loss and, therefore, the system maintenance cost. Originality/value - This paper considers simultaneously three different factors that influence maintenance float system performance: the number of spare units and the number of maintenance crews (which mean minimising the downtime effect) and the overhaul frequency (which means decreasing the number of failures). © Emerald Group Publishing Limited.