Estimation of Massey Ferguson Tractors Life and Repair Distribution Functions and Required Number of Repairmen

In order obtain suitable and effective farm machinery performance besides higher crop yield, on time farm machinery field operations are essential. Farm tractors are important machines that used for soil tillage, crop planting and protection. It is even used for harvesting crops in some areas. Thus, any failure in farm tractors influences the series of field operations. Farm managers are usually looking for high reliable farm machineries to complete necessary operation in the pre-determined time Hunt [1]. However, farm tractors stop due to break downs and it is desired that they repaired on a minimum time and back to farms. Farm machinery costs are divided into two categories, i.e. owning or fixed costs and operating or variable costs Morris [2]. The cost of farm machinery repair and maintenance can contribute to most of farm machinery operational costs (after fuel) which can be reached to 15-60% of total crop production costs Mobley [3]. Having an effective repair and maintenance program, the costs of machinery maintenance and failures will be reduced to an optimum point Lips & Burose [4] by gathering machinery failures data on the farms, the failures distribution function can be estimated well and then some important issues such as machinery reliability and energy failures can be predicted as well Barabadi & Kumar[5]; Billinton & Allan [6]. In addition, the required number of repair-mans can be predicted by simulation of data in such a way that farm machines imposes minimum waiting time for repair. The common life distribution functions for continuous data are Normal, Exponential, Logarithmic and Weibull Haj Shirmohammadi [7]. Weibull functions with wider applications can be descending, ascending or constant based on the function parameters Bartkute & Sakalauskas [8].