Human in the Loop: Predicted Likelihood of Vehicular Mission Success and Safety

Abstract

A double-exponential probability distribution function of the extreme value distribution type is introduced to quantify the likelihood of the failure of a human to perform his/her duties when operating a vehicle: an aircraft, a spacecraft, a boat, a helicopter, a railroad vehicle, etc. Such a failure, if any, is attributed to the insufficient human capacity factor when there is a need to cope with a high-level (extraordinary and offnormal) mental workload. The suggested probability distribution function is applied to a situation when an imperfect human, imperfect equipment/ instrumentation, and an uncertain and possibly harsh environment contribute jointly to the likelihood of a vehicular mission failure and/or insufficient safety.While the human’s performance is characterizedby thedouble-exponential probability distribution function, the performance of the equipment/instrumentation (which includes, in the analysis, the performance of both the hardware and the software) is characterized by the Weibull distribution, and the role of the uncertain environment is considered by the probability of the occurrence of harsh environmental conditions of an anticipated level of severity. It is believed that the suggested mental-workload/human-capacityfactor model and its possible modifications and generalizations can be helpful, after appropriate sensitivity analyses are carried out, when developing guidelines for personnel selection and training, when choosing the appropriate simulation conditions, and/or when there is a need to decide if the existing level of automation and the employed equipment/instrumentation are adequate in offnormal, but not impossible, situations. If not, additional and/or more advanced, and perhaps more expensive, equipment or instrumentation should be developed and installed.