A Two-Way Controlled Sample for Collecting Tanker Aircraft Base Maintenance Information
A description from the statistical viewpoint of the sampling design, selection of estimators, and preliminary analysis of maintenance data on KC-135 tanker aircraft of the Strategic Air Command, collected in June-July 1967. The aim was to study (1) the effect of aircraft aging on maintenance needs, (2) the relationships between man-hours and other maintenance costs, and (3) sources of error in recording materials consumed. Thirty-three aircraft were selected by a two-stage process so that the sample was stratified by airbase and controlled by age group, while giving all aircraft approximately equal selection probabilities. This necessitated sampling with unequal probabilities, making sample variance difficult to estimate. Engine maintenance was excluded because engines move from airframe to airframe.