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This paper presents a model for determining stock levels of repairable items supporting a fleet of commercial aircraft operated by a transportation company in the Philippines. The items are characterised by infrequent demand, high cost and a hierarchical (or indentured) structure. The system has three re-supply sources of serviceable parts, namely, the in-house repair shop, the out-house repair shops, and the suppliers. Non-repairable items are scrapped and replaced with new items on a one-for-one basis. The model considers two levels of indenture represented by modules and components. The objective is to minimise the total expected steady-state annual cost of holding inventories and of aircraft delays. A minimum requirement on module availability is also applied. The formulation is such that the regular discrete optimisers available could not be readily used to solve it. The model is implemented on an illustrative problem, employing an integer search for the item stock levels within a limited range.

This review includes papers found in the literature for repairable item inventory systems since 1997. The idea is to complement related earlier reviews until 1997, which are mentioned in the paper for the benefit of the interested reader. The papers are classified into two groups, based broadly on the types of inventory systems: single echelon and multi-echelon systems. A number of modeling approaches found in the papers in both groups are noted.

This paper presents a two-stage approach to solving the timetabling problem for an academic department. The first stage seeks to find the best faculty assignment to courses and sections where these courses are offered. The assignment is based on faculty specializations. The second stage finds an appropriate weekly schedule for the faculty-course-section assignment obtained in the first stage. The problems in both stages are modeled as 0-1 integer linear programming problems. The models are solved using LINGO 14, courtesy of Lindo Systems, Inc., with run times practically negligible.

This paper presents an integer quadratic programming model for solving the air cargo allocation problem of a digital logistics company. The objective is to minimize the average annual cost of booking air cargo space, which the subject company pays while also getting the optimal space to be reserved by the company monthly in a year. The model includes constraints on satisfying the demand in terms of gross weight, and the required order multiples. Results for the three destinations selected for the present study by the Operations Department of the company indicate a significant reduction in the average annual air cargo booking cost.