| This dissertation uses aircraft maintenance related indicators to study the safety posture of airlines. Safety posture is measured by the incidence of service difficulties, as indicated by Service Difficulty Reports (SDRs), which are reports on equipment related problems encountered with aircraft while in service, and by the incidence of engine shutdowns and removals. An aircraft that experiences a high incidence of equipment related problems is considered to have a high risk of accidents.;A theoretical framework is proposed to model the escalation of relatively minor equipment problems into more severe incidents and, eventually, into accidents. Safety posture is then analyzed using statistical techniques. Key variables, such as fleet mix, average aircraft age, engine type, scale of operations, rate of aircraft utilization, equipment exposure measures, and maintenance expenditures, are used to explain safety posture.;The evidence suggests that there are significant differences among aircraft types and among airlines. Narrow-body aircraft and their engines have better safety postures than their wide-bodied counterparts. The engine shutdown and removal rates are higher for wide-bodied aircraft. Furthermore, the rate of serious SDRs increases faster with age for wide-bodied aircraft than for narrow-bodied aircraft.;Aircraft age alone does not explain the incidence of serious SDRs. The effects of age appear to be partially masked by the other factors. But, there appears to be a rapid "learning process" for the reliability and maintenance of new engine models, as indicated by the substantial decline in the rates of engine failure after their first three years in service. The effects of exposure, measured by the hours of operations, are more significant for engine shutdowns and removals than for SDRs. Also, the rate of engine shutdowns appears to decrease with increased daily utilization. Finally, the safety posture of the established airlines does not appear to be any better than that of the new entrants. If airline deregulation has encouraged the introduction of new entrants, then it has not, by doing so, adversely affected safety. Airline safety has never been better, and there is no indication that it is worsening. However, further research is needed to ascertain the implications of aging and maintenance on the safety posture of specific types of aircraft. |
