Analyzing Aircraft Reliability with the Application of Weibull Distribution Theory

Diploma Thesis from the year 1992 in the subject Engineering - Aerospace Technology, grade: 95, , language: English, abstract: Determining an aircraft component's reliability often involves estimating its mean life, although to do this, the appropriate statistical distribution must be applied. The exponential model is often used because of its simple application. However, this distribution has its limitations. To overcome the shortcomings of the exponential model, this thesis examines how Weibull Distribution Theory can be utilized to produce appropriate component reliability estimators with a degree of certainty. The Weibull distribution is a flexible distribution in that it has the ability to approximate other distributions such as "e;Normal"e; and "e;Exponential . Subsequently, appropriate mean life estimators can be determined for various types of life data. The versatility offered by the Weibull Distribution model makes it ideal for selectively supplementing current methods of field reliability monitoring, especially when the onset of component wear out is suspected or the success of a modification is sought. The type of field data encountered when monitoring aircraft reliability dictated that a Weibull model be developed for Type 1, multiply censored data. To determine whether data fitted a Weibull distribution, the Rank Regression method was used to produce median ranks for plotting on Weibull probability paper. To analytically determine Weibull parameter estimators and approximate confidence limits, the Maximum Likelihood method was utilized. Automation of both these methods was achieved using Fortran programming. As the number of failures increase, Weibull parameters stabilize and the degree of certainty provided by Weibull confidence limits improves. This results in the Weibull model being able to produce mean life estimates in a timely manner. With the aid of Weibull shape parameters, field problems may be relatively quickly identified and/or confirmed, allowing for faster corrective action response.