Line Replaceable Units (LRUs) are modular units that considerably enhance equipment maintainability. LRUs, designed to make components replaceable in the field, i.e., at the operating location instead of having to be brought into a workshop, were first used for designing parts and components in the aeronautics industry.

The so-called “LRU definition problem” is the problem of deciding which item to replace upon each type of failure: when a replacement action is required in the field, service engineers can either replace the failed item itself or replace a parent assembly that holds the failed item, in this case the LRU. Replacement of the LRU may be quick, but costly in comparison with the price of the single component. The other option might be cheaper but also more time-consuming; it might not even be possible on the spot. The objective of the LRU-definition problem is to minimize the total cost of item replacement and the investment in additional assets, given a constraint on the availability of the fleet of assets.

Key concepts in any LRU-based design are availability and maintainability. Availability is the probability of any equipment being operational when required; maintainability is the probability that any equipment can be repaired in the required time. In the case of ITS equipment both factors are crucial; they might even dictate whether the scheduled transport service is even practicable. It is especially important here to ensure availability in ticketing equipment, for example, which is a sine qua non of being able to carry out the service.

GMV has plumped firmly for LRU-based ITS equipment design amongst all the latest options. In the case of the latest onboard ticket vending and validating machines (DTD100), for example, a modular design has been devised with various LRUs such as touch screen, communication modules, power source, printer, card reader, etc. The overriding idea is to bring down LRU replacement time to a maximum of 10 minutes, thereby guaranteeing equipment availability. Maintainability is ensured too; each LRU can be individually tested and the machine can communicate the fault to the user or maintainer by means of an unequivocal error code for each LRU.

GMV is thus working on the cutting edge of LRU application, traditionally reserved for sectors like aeronautics, in order to offer its clients robust and affordably maintainable equipment with guaranteed availability.

Author: Isidro Prieto Valderrey.