Comparing Effectiveness of Measures That Improve Aircraft Structural Safety

Abstract

This paper aims to discover how the measures that improve aircraft structural safety compare with each other in terms of effectiveness. The safety measures included here are a load safety factor of 1.5, conservative material properties, redundancy, certification tests, error reduction, and variability reduction. A static point stress design with a simple redundancy model is considered, and individual errors in calculation (loads, stresses, failure) and in geometry and variability in loading, material properties, and geometry are modeled. A probabilistic model is used based on assumed uniform distribution for errors as often only upper limits on errors are available. For variabilities, some lognormal distributions are used. It is found that error reduction is more effective than certification testing, which is more effective than using an extra load safety factor. Variability reduction is found to be a very effective way of reducing the probability of failure (more effective than error reduction), but it should be accompanied by an increased B-basis value. In addition, certification testing is found to be effective when errors are large, whereas structural redundancy is found to be more effective when errors are low. It is also found that as safety measures are added and the probability of failure is reduced, the uncertainty in that probability of failure increases.