# Accession Number:

## ADA159571

# Title:

## The Relationship between Material Failures and Flight Hours: Statistical Considerations.

# Descriptive Note:

## Professional paper,

# Corporate Author:

## CENTER FOR NAVAL ANALYSES ALEXANDRIA VA NAVAL PLANNING MANPOWER AND LOGISTICS DIV

# Personal Author(s):

# Report Date:

## 1985-01-01

# Pagination or Media Count:

## 22.0

# Abstract:

This paper attempts to clarify the relationships among the following four hypotheses 1 The number of material failures across intervals of calender time containing equal accumulated flight hours follows a Poisson distribution 2 the number of elapsed flight hours between successive independent material failures follows an exponential distribution 3 the expected number of monthly material failures is strongly correlated with monthly flight hours. By a well-known result, hypotheses 1 and 2 are equivalent. By a second well-known result, hypotheses 1 and 3 are also equivalent. However, hypotheses 1 and 4 are not equivalent. That is, while the expected number of failures is exactly proportional to flight hours under a Poisson distribution, this relationship is not revealed by a linear regression between failures and flight hours. For example, we demonstrate that if the mean and variance of flight hours across months are equal and if the failure rate per flight hour equals .01, then the correlation between failures and flight hours will equal .10. Additional keywords Goodness of fit tests A-7 aircraft Naval aircraft.

# Descriptors:

# Subject Categories:

- Attack and Fighter Aircraft
- Statistics and Probability