The Modular Engine Arisings, Repair and Overhaul Simulation - MEAROS

Rolls Royce; London, England and CACI Advanced Simulation Lab

MEAROS, the Modular Engine Arisings, Repair and Overhaul Simulation, simulates the operation, maintenance and supply of gas turbine aircraft engines. The model is primarily designed around the special requirements of the aero-engine industry although it is equally applicable to ships, land vehicles, and indeed to electric power generation. It models the four indenture levels within the engine and five levels of maintenance. The model will be used to evaluate the efficiency and cost effectiveness of proposed maintenance plans for both military and civilian aircraft fleets. MEAROS considers age related failure characteristics and utilizes non-engine failure aircraft downtimes as opportunities for engine preventative maintenance.

The removal of an aircraft engine and its subsequent recovery is expensive. It represents a significant fraction of the overall cost of operating a fleet of aircraft. In many cases the cost of spare parts is roughly equal to the primary acquisition costs. It is therefore important to accurately forecast which components will be needed and when.

Aircraft engines, especially gas turbine engines, require frequently scheduled maintenance and inspection to ensure that the probability of an installed failure is kept to a minimum. There is also a considerable amount of unscheduled maintenance, particularly with military aircraft. It is essential to predict the maintenance requirements of the engine in terms of costs and resources.

MEAROS can be used to compare alternative support postures in terms of resources and maintenance capability. First an established scenario and support posture would be analyzed. Then more analyses would be performed while varying one or more factors.

For example, the number of flights could be successively increased while keeping resources fixed to determine the limits of supportability. The flying schedule would become so hectic that the operational availability of the aircraft would not be acceptable. Conversely, the number of flights may be fixed and the support resources varied until specified aircraft availability is obtained.

In addition to making comparisons between support policies that may be used within an operator's own organization, MEAROS analyses may form the basis of contractual negotiation between an operator and an external maintenance contractor. For example, the model may be used to generate a forecast of arisings, which could form the basis for discussion of the appropriate level of repair and overhaul cover to be provided by the contractor.

Alternatives Considered: MEAROS was designed to replace two FORTRAN simulations that had been written in the late 60's and early 70's.

Benefits of SIMSCRIPT II.5: The model will be used by the Ministry of Defence and at a number of different locations within Rolls Royce. Some of the users will run it on IBM mainframes, some on SUN workstations and others on Gould minicomputers. All of the users need to be certain that they are running the same model. It is therefore essential that the code is truly portable. Some of the users will be running relatively small and simple fleets. The developers will generally only have access to desktop PCs. These two factors make it desirable, if not essential; to have dynamic storage to minimize the memory requirements, which has proved to be a significant, factor in determining the run times of the model. The model will be developed over a period of many years to meet the ever-changing environment of aircraft operation and engine design. It is intended that the MoD and Rolls Royce do these developments jointly. The model must therefore be easy to maintain, validate, and test. It must also, to a certain extent, be self-documenting, although adequate documentation has been written to support the model. It makes the task much easier if the programmer/analyst can read and immediately understand the code.

Customer Quote: "As someone who has spent the past 16 years trying desperately to maintain and develop the predecessor to MEAROS, the biggest benefit to me is that I can now get on with other things, safe in the knowledge that this model is well documented, professionally written, and easy to maintain."