AN APPLICATION OF THE BIRTH AND DEATH PROCESS TO THE PROVISION OF SPARE MACHINES

IN any progressive organization there must be, as the source of its progressiveness, a continuing generation of new ideas and unremitting effort to do things more efficiently and therefore more economically. However, if the success of a business organization lies, as it undoubtedly does in part, in its ability to organize its employees to work together in a harmonious team, then it must follow that some ideas, although good in themselves, may not necessarily be acceptable to the corporate body. This is not to say that such ideas should not be aired but rather to lead up to the usual statement that the authors of this paper are not necessarily expressing the official views of B.O.A.C. Nevertheless, they have to recognize the opportunities and encouragement given to suchperhaps academic might be the word at this stage-work as they have been able to do. Before describing some of the technicalities of our work on the application of queue theory to the provisioning of spare engines, it will be advisable to put the work into its context within B.O.A.C. While it is true to say that safety must condition all the thinking of aircraft maintenance engineers, one of their main day-to-day problems is how to plan the work in the hangar so that unscheduled removals of unserviceable items cause as little disturbance to routine operations as possible. Unfortunately, failures are nasty creatures, whichever way they are looked at, and although some allowance for their incidence can be made in routine planning of work, they tend to be very will o' the wisp in their behaviour. In scientific or statistical circles this type of behaviour is known as random, and randomness is the bane of the "practical" engineer who likes to have things working according to plan. Now except for trying to improve the reliability of an item by progressive modifications, different overhaul techniques and standards, nothing can be done about this randomness. But the disruptive