Chapter 4: Dynamics of aircraft degradation
The dynamics of the number of failures is accumulated to help predications of mechanical failures especially basing on last repairs or periodic inspections. Factors are related to procedures and the time as well as extent of maintenance being the variable under control as the methodology is applied. The aircraft system is designed with an intended or expected life period, where period refers to time units (hours) of being used. Failed state, is reached due to gradual degeneration because of age as they become unable to perform functions designed for. A certain degree is instated after maintenance, or a system can be upgrade or replaced by repair.
Fig 4.1: probability of failure
Situation A: Increasing …show more content…
The above diagrams show failure occurrence patterns for a regularly maintained airplane. Situation A, aircraft has an increasing rate with age and reaches a threshold, and which replaced of airplane will be needed. With regular maintenance, failure rate declines, whereas improvements of maintenance diminish with time. Situation B, because of raising effort and maintenance costs the threshold will not be reached. Cost of maintenance to keep airplanes below threshold or airworthy is an important concern. Assumptions are that the through maintenance the airplane can surpass its intended lifespan, but costs are high. Manufacturers sent 20 years as the replacement age for many models, although it was extended.
Analysis made on US commercial airplanes shows that in 1997, 46% were over 17 years and 28% over 20years, whilst in 2001, 31% were over 15years of age and of them 66% of them accounted for the total per block hour maintenance. Nevertheless, degeneration occurs, it is polished by numerous factors; intensity use; quality and quantity of repair; environment; and scheduled maintenance. A point should be taken that roughly 60% of maintenance is …show more content…
The main deciders are the items being degenerated most on the aircraft. When the item is no longer functional it is termed to have implied failure, and a combination of them will render the plane not airworthy. Airline management goes over maintenance, with planned and unplanned preventive maintenance and replacements of failed parts and systems, addressing operations of failures.
Degradation
Considering operating conditions of an airplane are recorded by an unobserved health status index, derived from components and the aircraft systems. t will age of aircraft, defined by accumulated hours of use
Y (t)=health status at age t.
Change of any age is a random variable and status a dynamic stochastic process. Assuming average situation decreases with age, but variation in status based on atmospheric factors and operating traits, can occur at any point. Stochastic differential equation at a certain dynamic degeneration can be
d Y (t) = μt dt + σt dZt t (1) where μt < 0; degradation rate, σt > 0; scaling factor, dZt ;independent random
The dynamics of the number of failures is accumulated to help predications of mechanical failures especially basing on last repairs or periodic inspections. Factors are related to procedures and the time as well as extent of maintenance being the variable under control as the methodology is applied. The aircraft system is designed with an intended or expected life period, where period refers to time units (hours) of being used. Failed state, is reached due to gradual degeneration because of age as they become unable to perform functions designed for. A certain degree is instated after maintenance, or a system can be upgrade or replaced by repair.
Fig 4.1: probability of failure
Situation A: Increasing …show more content…
The above diagrams show failure occurrence patterns for a regularly maintained airplane. Situation A, aircraft has an increasing rate with age and reaches a threshold, and which replaced of airplane will be needed. With regular maintenance, failure rate declines, whereas improvements of maintenance diminish with time. Situation B, because of raising effort and maintenance costs the threshold will not be reached. Cost of maintenance to keep airplanes below threshold or airworthy is an important concern. Assumptions are that the through maintenance the airplane can surpass its intended lifespan, but costs are high. Manufacturers sent 20 years as the replacement age for many models, although it was extended.
Analysis made on US commercial airplanes shows that in 1997, 46% were over 17 years and 28% over 20years, whilst in 2001, 31% were over 15years of age and of them 66% of them accounted for the total per block hour maintenance. Nevertheless, degeneration occurs, it is polished by numerous factors; intensity use; quality and quantity of repair; environment; and scheduled maintenance. A point should be taken that roughly 60% of maintenance is …show more content…
The main deciders are the items being degenerated most on the aircraft. When the item is no longer functional it is termed to have implied failure, and a combination of them will render the plane not airworthy. Airline management goes over maintenance, with planned and unplanned preventive maintenance and replacements of failed parts and systems, addressing operations of failures.
Degradation
Considering operating conditions of an airplane are recorded by an unobserved health status index, derived from components and the aircraft systems. t will age of aircraft, defined by accumulated hours of use
Y (t)=health status at age t.
Change of any age is a random variable and status a dynamic stochastic process. Assuming average situation decreases with age, but variation in status based on atmospheric factors and operating traits, can occur at any point. Stochastic differential equation at a certain dynamic degeneration can be
d Y (t) = μt dt + σt dZt t (1) where μt < 0; degradation rate, σt > 0; scaling factor, dZt ;independent random