RELIABILITY MONITORING

1. COSCAP - SA RELIABILITY MONITORING

2. LEGAL REQUIREMENT ICAO ICAO Annex 6 para. 8.9.1 requires an operator of large transport aircraft to ‘monitor and assess maintenance and operational experience with respect to airworthiness…..’

3. LEGAL REQUIREMENT FAA FAR 121.373(a) requires that the ‘operator’ shall establish and maintain a system for the continuing analysis and surveillance of the performance and effectiveness of its inspection program and the program covering (maintenance), and for the correction of any deficiency in those programs………...

4. LEGAL REQUIREMENT • JAR -OPS 1.035 Quality Systems. requires the establishment of a quality system to monitor compliance with an the adequacy of procedures required to ensure ……and airworthy aeroplanes. Compliance monitoring must include a feed-back system….. • 1.910(a) Operators maintenance Program. The program will be required to include a reliability program……(refer also AMC OPS 1.910a

5. Background • Early air carrier maintenance programs were based on the belief that each part of an aircraft required disassembly for inspection.

6. Background • Time limitations were established for maintenance and sometimes the entire aircraft was disassembled. • This process is known as ‘HARD TIME’ (HT)

7. MSG-1 • With the advent of the B747 more cost effective maintenance methods were needed.

8. MSG -2 • MSG 1 & 2 introduced the primary maintenance process called “ON-CONDITION” (OC) • OC classified components are component’s whose continued airworthiness can be determined by scheduled inspection/test; such as visual, measurement or other tests that does not require disassembly.

9. MSG - 2 • Regulatory control of ‘HT’ & ‘OC’ programs was, and is, not efficient. • To address this problem a method of program application and control was established that looked at “mechanical performance” rather than trying to predict a wear out point by inspection.

10. MSG- 2 • This new method was called “reliability control”. • “Reliability Control” is a system that monitors and maintains component “failure rates” below a predetermined value. • Components and systems that were not assigned a primary maintenance process (Continued)

11. MSG - 2 • .. Of either “Hard Time” (HT) or “On-Condition” (OC) were assigned a primary maintenance process called “Condition Monitoring” (CM) • A component or system maintained under CM does not respond to the ‘HT’ or ‘OC’ process and therefore has no scheduled servicing or inspection to determine the airworthiness of the item.

12. FAILURE PATTERNS • Before we go any further we should have an understanding of failure patterns. An appreciation of this concept is essential to understand the philosophy and background of Reliability schemes. • The study of numerous component life histories have shown that their behaviour is invariably as that shown in the familiar "bath tub" curve. Let us consider this curve section by section.

13. ‘BATH TUB CURVE’ Failure Rate Wear out period A B C D TIME IN SERVICE

14. FAILURE PATTERNS Section A - B • This portion is the "early failure or infant mortality" area. Failure rates are high and are caused by design and manufacturing problems. The remedy is redesign, and improved quality control. • After these problems have been overcome the problem remains although at a reduced failure rate level. In this case the failures are caused by faulty maintenance practices, errors during re-assembly of the component and installation into the system. A B

15. FAILURE PATTERNS - Section B - C B C • Having passed point B the failure rate becomes substantially constant, and lower than in the A - B area. Failures which occur in the B - C area are known as "chance or random failures", and do not exhibit any fixed pattern.

16. FAILURE PATTERNS - Section B - C (continued) • The almost constant failure rate in section B - C is of great importance in Reliability schemes. Failures which do occur in section B - C are brought about by random occurrences, such as unexpectedly high transient voltage, vibration etc. • Depending on the nature of the component, section B - C may be long or short.

17. FAILURE PATTERNS - Section C - D • This section shows a rapid increase in failure rates compared to B - C as the component is entering the "wear out" phase, and a fixed pattern of failures can be expected. Note that the "random failure" mechanism will still occur as it did in B - C and A - B, so there may be some failures which do not fit the emerging pattern. • The establishment of point C is extremely important in Reliability schemes. • This section shows a rapid increase in failure rates compared to B - C as the component is entering the "wear out" phase, and a fixed pattern of failures can be expected. Note that the "random failure" mechanism will still occur as it did in B - C and A - B, so there may be some failures which do not fit the emerging pattern. • The establishment of point C is extremely important in Reliability schemes. A B C D

18. FAILURE PATTERNS - Section C - D (continued) • It is now obvious that the optimum time for overhaul is just prior to point C. We may be familiar with a regulated escalation process using a method, whereby we inch our way along section B - C hoping to stumble on point C by inspecting samples. • The establishment of point C by other methods, for some classes of components is another important aspect of Reliability schemes.

19. MSG - 3 • The development of new aircraft types, (757/767, A310) and the recognition of problems with MSG-2, resulted in recommendations for a new set of guidelines be established to cope with these problems and changes. These proposals were eventually developed into MSG-3.

20. MSG - 3 (continued) • Scheduled Maintenance Program • MSG-3 has expanded the objectives of MSG-2. The objectives of MSG-3 still emphasize safety, reliability, and economy, but have gone beyond MSG-2 by: * Restoring equipment to specification once it has deteriorated * Collecting data to monitor equipment * Providing information that may be required for redesign in order to improve reliability

21. MSG - 3 (continued) • A Maintenance Program should ensure aircraft safety, operating efficiency, and minimize deterioration of the inherent reliability. Reliability is established by: • the design of each item and • the manufacturing processes

22. MSG - 3 (continued) • Scheduled maintenance can only minimize deterioration of the inherent reliability, but not improve upon it. • On-aircraft failures will be minimized through preventive maintenance techniques at a minimum cost.

23. MSG - 3 (continued) • The objectives of an efficient airline maintenance program are: * To ensure realization of the inherent safety and reliability levels of the equipment * To restore safety and reliability to their inherent levels when deterioration has occurred * To obtain the information necessary for design improvement of those items whose inherent reliability proves inadequate * To accomplish these goals at a minimum cost, including maintenance costs and of residual failures

24. MSG - 3 (continued) • MSG-3 improves upon MSG-2 in addressing these objectives in the following areas: *Maintenance Significant Items (MSIs) are derived using a "Top Down Approach” *Task decision logic questions are made more rigorous. The logic requires progressively more conservative maintenance tasks up to and including redesign; i.e., in the absence of information concerning the applicability and effectiveness of a task, the next most conservative task must be considered.

25. MSG - 3 (continued) * Servicing and lubrication is included as part of the logic diagram since this must be included to make a complete scheduled maintenance program * MSG-3 is task oriented and not maintenance process oriented. This eliminates the confusion associated with the various interpretations of CM, OC, and HT. Instead of classifying a maintenance requirement as an HT, OC, or CM task, the specific task is identified. MSG-3 has added several types of tasks to the MSG-2 maintenance program. These additions help to delineate tasks more accurately than before.

26. MSG - 3 (continued) An efficient maintenance program does not schedule additional tasks which will increase maintenance costs without a corresponding increase in reliability protection. The tasks in an MSG-3 scheduled maintenance program include: * Lubrication/Servicing * Operational/Visual Check * Inspection/Functional Check * Restoration * Discard * Combination tasks

27. MSG - 3 (continued) Applicability and Effectiveness. Every task selected must meet the criteria established for applicability and effectiveness. Selecting only those tasks which meet the applicability and effectiveness criteria prevents selecting task based on habit or tradition. If the answers to the task selection questions are justified based on applicability and effectiveness, only the appropriate tasks will be selected. (End)

28. RELIABILITY CONTROL Fundamentals

29. General • Each operator is different. • The operator’s operational environment will be reflected in his reliability program.

30. General cont...... • There are four (4) general categories of an operator’s maintenance program. • “Systems/components” • “Powerplants/components” • “Aircraft/engine checks and inspections” • “Structural inspection/overhaul”

31. General cont...... • All four groups can be controlled by a composite program or each may be handled separately.

32. General cont...... • For example: the basic engine may be maintained on “HT” and the engine accessories may be controlled by “OC” or the entire engine may be on “HT”

33. Primary Maintenance Processes

34. Primary Maintenance Processes • Hard - Time (HT) • On-Condition (OC) • Condition-Monitoring (CM)

35. A Preventive maintenance process It requires that a part be overhauled in accordance with a predetermined period of time, e.g. 2000 hours, flights or cycles. It may require that the unit be withdrawn from service and scrapped, e.g landing gear member with a fatigue life of 10 years or a turbine wheel with a life of 20,000 cycles. HARD TIME

36. A preventive maintenance process If requires that a part be periodically inspected or checked against a physical standard to determine whether it can stay in service. The purpose of the standard is to remove the part from service, before failure, during normal operation, occurs. ON- CONDITION

37. A primary maintenance process where the part or component is not being maintained by the HT or OC process. The part or component is allowed to fail. The failure rate is monitored by statistical analysis CONDITION-MONITORING

38. Multiple processes • Complex multicell units may be subject to control by two or three of the primary processes. • The predominant process will determine its classification. • E.g. the B747 Modular Package - Stab. Cont. has CM assigned as the primary maintenance process, but a leak check (OC task) is also scheduled.

39. Multiple processes (Engines) • The basic engine has characteristics that involve all three primary processes

40. Multiple processes (Engines) • Programs that control engine major overhauls consider the engine as a hard time unit. • Programs controlling shop maintenance to a ‘conditional’ standard may classify thee engine as ‘OC’ or ‘CM’

41. Assignment of an appropriate maintenance process requires strict adherence to the analysis method described in the MSG document. (Examples follow) Maintenance Process Assignment

42. Maintenance Process Assignment, MSG - 2

43. RELIABILITY CONTROL SYSTEMS SYSTEM DEVELOPMENT

44. Typical Systems • DATA COLLECTION • DATA ANALYSIS • CORRECTIVE ACTION • PERFORMANCE STANDARDS • DATA DISPLAY AND REPORT • MAINTENANCE INTERVAL AND PROCESS CHANGE • PROGRAM REVISION

45. Data Collection • The system must include a specific flow of information; identity of data sources, and procedures for the transmission of data. • Responsible persons must be identified in the organization for each step.

46. Pilot reports In flight engine performance data Sources of Data

47. Mechanical delays Engine shutdowns Unscheduled removals Confirmed failures Functional checks Bench checks Shop findings Sampling Input. Inspection info SDR Sources of Data

48. Reliability Control Systems BASICS OF ANALYSIS

49. Data analysis is the process of evaluating mechanical performance data to identify characteristics indicating a need for change: modifications, revision of maint. practices etc. The initial step is to compare the data to a standard representing acceptable performance. The standard may be a running average, graphs, charts etc. or any means of depicting a “norm” Data Analysis

50. Alert Chart