System Safety and System Safety Application

Exploring and Evaluating Airline System Safety:
Aircraft Maintenance-related Indicators
Abstract 
This paper explores how system safety concepts are being applied in aircraft or airline accident. The main objective of this paper is to demonstrate the relevance and usefulness of precursors in safety analysis, and not to develop exact and detailed predictive models. The paper discussed various causal factors of airline accidents and directed our attention to those related to aircraft maintenance. Firstly, the paper discussed a theoretical framework for modeling the possible escalation of small equipment problems into more severe incidents and, further on, into accidents. The Service Difficulty Reports (SDRs), with their different severity ratings, are analogous to the incidents described in the risk models presented in this paper. However, only the framework for such a model was discussed without attempting to develop an operational model. Finally, the paper concluded that our knowledge of and experience with small maintenance problems could be used to predict the occurrence of more serious problems in the future.
Introduction
Accident and fatality rates are the most widely accepted measures of overall airline system safety. These rates represent the risk associated with air travel in terms of the probability of an accident or fatality. However, accidents and fatalities are not necessarily the best indicators of the safety of airline operations. Equipment related factors are being considered as the leading indicators of accidents or incidents. Hence, the airline or aircraft may be positioned with a greater risk of accidents if it experiences a high incidence of equipment related difficulties during service.
A theoretical framework for relating equipment (maintenance) related problems to accidents are presented in this research that would seek to identify factors that possibly influence the safety posture of airlines and aircraft. Risk models are presented to demonstrate the possible linkages and to demonstrate the relevance and usefulness of precursors in safety analysis, and not to develop exact and detailed predictive models.
Airline System Safety and Its Evaluation
In recent years there has been great concern about the safety of the commercial aviation system. It has been observed that there are almost always insufficient maintenance personnel and inventory at most "spoke" airports and, therefore, necessary maintenance work must be deferred until the aircraft returns to one of the carrier hubs or maintenance bases. Another reason for the increased number of items on the deferred maintenance list is the inability of the airlines, once again due to the hub and spoke scheduling systems, to devote as much time during quick turnaround to fix items. Thus, deferral of maintenance is encouraged by the hub and spoke system. Pilots have voiced their concern over the pressures of deregulation leading to the Minimum Equipment List (MEL) abuse resulting from such extended deferred maintenance practices (Donoghue, 1987). The absolute minimum equipment required to be in working order is spelled out in the MEL for each aircraft.
Carrying a large number of deferred maintenance may not be a violation as such, but it means operating the aircraft with reduced system redundancies. This could be reducing the safety margin. There has also been a concern that, since deregulation, preventive maintenance practices - i.e., analysis of systems and parts for flaws before they manifest themselves in a failure of some sort - have suffered.
In response to concerns about the safety of the commercial aviation system worldwide, industry executives have all recognized the need for improving the measurement of safety in commercial aviation. This measurement is generally seen as a means of quantifying safety (Barnett & Wang, 1998). But, prior to trying to measure safety it is useful to look at the meanings attached to the word "system safety."
Defining System Safety
Stephans (2004) says that: "safety is freedom from harm and is achieved by doing things right the first time, every time". Also, according to Stephans (2004), “system is composite of people, procedures, and plant and hardware working within a given environment to perform a given task”. As a whole, Stephans (2004) defined “system safety” as the discipline that uses systematic management and engineering techniques to aid in making systems safe throughout their life cycles.
The goal, then, of system safety is for improvement in safety and the reduction of risk. It is clear that everybody is for “safe” transportation. But what does that mean? Nothing is totally safe and there is a degree of risk associated with any activity. Hence, by “safe” one could be referring to the level of risk that is acceptable. Clearly, society imposes a much higher safety standard on aviation than it does on highways (Stephans, 2004).
Realizing that absolute safety is the ultimate destination, there is a need to identify the direction in which to travel to move along towards this destination. Appropriate measures to serve as milestone markers along the way are also necessary. These markers will serve to quantify the "acceptable level of risk" and will also serve as indicators of the "margin of safety." (Chérif, 2005). Thus, there is a need to explore and evaluate what is meant by aviation safety so as to be able to relate performance with respect to safety.
Safety Culture in the Aviation Industry
In order to measure, assess and compare airline and aircraft performance in areas important to safety, indicators that are objective and comparable are necessary. As mentioned, the traditional approach to measuring safety has been, and remains primarily, the analysis of accident and fatality rates, hence are reactive indicators. The accident rate is the most widely accepted measure of overall aviation safety. It is an objective measure and provides a basis for comparing the performance across a cross-section and across time periods. Accidents provide little more than after-the-fact evidence that safety in the aviation industry was inadequate. The number of accidents and fatalities each year is so small that the occurrence of one or two random events - major crashes or the lack thereof - skews data (Barnett & Wang, 1998). Thus, in terms of statistics, it is better to use the accident rate methodology. The accident rate methodology reflects what has happened, and its relevance to accident prevention is limited. The occurrence of major airline accidents, like that of the core-melt of nuclear reactors, can be termed a "low-probability, high-consequence risk.” Due to the extreme undesirability of such events and the disastrous consequences of their occurrence, it is not possible to analyze them by carrying out experiments. As a result, one must resort to other means of trying to learn about these events in order to prevent their occurrences. Also, recognizing that accident, fatalities and their rates may lack predictive power, it has been suggested that other indicators be developed for assessing safety (Chérif, 2005).
Perhaps the information about the events preceding accidents can be used of in an intelligent manner to learn about the possibility or risk of accidents themselves. Thus, the researcher realize that there are two different ways of looking at the evaluation of safety in the aviation industry - one is to look at the final outcomes of unsafe operating procedures or environments, and the other is to look at the "foretellers" of these final outcomes.
Safety Performance and Safety Posture
"Safety performance" is used to refer the occurrence of accidents or incidents amongst the airlines and aircraft. Generally, accidents and fatalities are used as measures of safety performance. On the other hand, the term "safety posture" is used to refer to the unsafe conditions that are precursors to accidents and incidents. These can be thought of as being "leading safety indicators" or "foretellers" of safety performance. Safety posture provides an indication of how airlines and aircraft are posed with respect to future safety performance. Safety posture thus represents the risk of future accidents and i...