AIRCRAFT RELIABILITY Y.K.Sinha Rajalakshmi Engineering College AIR TRANSPORTAION AND AIRCRAFT MAINTENANCE (AE1012)

Topics to be covered Aircraft reliability The maintenance schedule & its determinations Condition monitoring maintenance Extended range operations (EROPS) & ETOPS Ageing aircraft maintenance production

What is reliability ? Reliability is a broad term that focuses on the ability of a part, assembly or system to perform its intended function Mathematically speaking, assuming that the part, assembly or system is performing its intended function at time equals zero (T 0 ), reliability can be defined as the probability that an item will continue to perform its intended function without failure for a specified period of time (T 0 + T S ) under stated conditions.

RELIABLE T0T0 TSTS

T0T0 TSTS UNRELIABLE

Definition of Reliability Reliability is the probability that a part, assembly, or system will perform its intended function in a stated condition or environment for a predetermined length of time without failure.

What is Reliability ? Reliability is performance over time. Why is reliability needed ? It is the key design parameter over the aircraft life cycle that shows effectiveness, affordability and operator’s satisfaction. How is the airplane reliability established ? By continuous recording, analysis and monitoring data pertaining to operation of aircraft systems, sub-systems and components.

Equipment failure Most equipment failures have no relationship to length of time in-service. Most failures are unpredictable. But if you detect a future failure early, you can handle it most cost effectively before it becomes a breakdown

Equipment degradation

Condition Monitoring

Reliability Programme A Reliability Programme is an event reporting system based on performance values experienced under actual conditions. It provides a means of measuring the performance of aircraft systems and components and comparing the performance to predetermined levels of acceptable performance. An event reporting system and data analysis permits the rapid identification of adverse trends. If the systems and components do not meet established levels, an alert is issued and an investigation is initiated to assess the problem and initiate a programme of corrective actions.

COLLECTION Pilot Reports Delays & Cancellations Component Removals Inspection Findings Shop Findings Power Plant Data Structural Data Flight Statistics OMT / QAR Data DATA DISPLAY,REPORTS ANDANALYSIS Statistical Reports Trend Monitoring Fleet Campaign Validation Study Historical Data CORRECTIVE ACTION AND ANALYSIS Modify Maintenance Process Modify Maintenance Tasks Service Bulletin Modifications Correct Maintenance Procedures Modify/Correct Shop Procedures Escalate/Reduce Intervals Adjust Inventory Levels

Reliability Programme Advantages Improved management of airworthiness Effectiveness of maintenance programmes Provides visibility for cost control Optimizes management of fleet performance Timely database sustains the fleet vital statistics Supports technical efficiency of the Operations Control Center It provides the tools for reliability analysis of aircraft structures.

Reliability Programme Disadvantages Lack of data discipline provides mis-information The larger the fleet operation the larger the computing resources required Data must be consistent and accurate to be meaningful.

Reliability theory Reliability is the probability that a device continues to perform a particular function over a particular period of time and under stated conditions. Let R denote the reliability of a component, and let F be the rate of failure, then R + F = 1 R dependent on the failure-free operation.

Reliability (ctd) In reliability theory it is customary to assume a constant failure rate. Then we typically express reliability R, the probability of survival to time t, in the form: R = e - t = e -t/T where T = mean time between failures, or mean time to failure whichever is most appropriate in the circumstances.

Reliability formulae Consider the situation where a system is composed of several subsystems whose reliability is known, the terms being compatible. There may be parallelism, interconnections of various kinds, etc. Two common methods of interconnection are important - in series and in parallel.

Connection in series Let R 1, R 2, R 3,..., R n denote the reliability of components, and F 1, F 2, F 3,..., F n denote the corresponding failure rates. Then the system operates only if all the components themselves operate. The overall reliability of the system is R where R = R 1 x R 2 x R 3 x... x R n

Connection in parallel In this case the system operates if at least one of the components operates. The relevant formula is then: F = F 1 x F 2 x F 3 x... x F n or (1 - R) = (1 - R 1 ) x (1 - R 2 ) x (1 - R 3 ) x... x (1 - R n )

Combination