Aircraft systems are designed with reliability, safety and cost effectiveness in mind. The certification of the aircraft is based on tests and results of theoretical analyses that show the compliance with the FAR/JAR requirements.
Monitoring for safety for in-service aircraft is an important, critical and extremely complex process. The ultimate objective is to assure that the safety level is equal to the original estimate or better. The manufacturer of the aircraft is particularly responsible for overall monitoring and assessment of all safety related events and corrective actions.
Many different philosophies were adopted for this purpose. The safety monitoring and audit strategy is generally based on experience, engineering judgment, event analysis and numerical quantification by using probability theory and statistical tools. The aircraft sequential entry in the service and the aging of their components lead to the non-homogeneity of the fleet. Safety assessment based on the qualitative methods becomes difficult. Utilization of the quantitative methods could lead to wrong conclusions, such as the dilution effect where magnitude is related to the fleet age, which could be very detrimental in a safety assessment. Specific failure modes associated with a relatively small portion of the fleet could be easily overlooked when the analysis is based on the standard statistical tools that are commonly used by the industry.
Our ignorance could be the root cause of hazardous events leading to the decline of overall safety.