CHAPTER 2. RELIABILITY CONTROL FUNDAMENTALS 13• GENERAL•
a. It is intended that characteristics of each operator, i.e., philosophy, consideration of operational and environmental factors, recordkeeping systems, etc., be reilected in his own program. The extent and scope oi each operator's application of reliability control is defined in his reliability program document.
b. There are four general categories of an operator's maintenance program.
(1) Systems/components.
(2) Powerplants/components.
(3) Aircraft/engine checks and inspections.
(4) Structural inspection/overhaul.
All four may be controlled by a composite program, or each may be handled individually. The program can encompass a select group of items from a category without affecting other controls for the remaining items of that category. for example, the basic engine might be maintained by a program that does not include its accessories. The accessories could be on another program or they could be under traditional operations specifications control.
d. Statistical analysis is most effective in its application to systems and components because the occurrence of failures can be readily reduced to meaningful statistics. When alert rates are used in the analysis, graphic charts (or equivalent displays) show areas in need of corrective action.
Conversely, statistical analysis of inspection findings or other abnormalities related to aircraft/engine check and inspection periods requires judgmental analysis. Therefore, programs encompassing aircraft/engine check or inspection intervals might consider numerical indicators, but sampling inspection and discrepancy analysis would be of more benefit.
PRIMARY MAINTENANCE PROCESSES. The three primary maintenance processes utilized by maintenance programs are (1) hard-time, (2) on-condition, and
(3) condition-monitoring.
a. Following are general descriptions of the three maintenance Each program should include specific definitions of the processes it uses and how they are applied. Refer to appendix 1 (MSG-2) and Advisory Circular 121-1A for further definition of maintenance processes.
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(1) Hard-Time (HT). This is a preventive primary maintenance process. It requires that an appliance or part be periodically overhauled in accordance with the carrier's maintenance manual or that it be removed from service.
(2) In-Condition (OC). This is a preventive primary maintenance process. It requires that an appliance or part be periodically inspected or checked against some appropriate physical standard to determine whether it can contime in service. The purpose of the standard is to remove the unit from service before failure during normal operation occurs.
(3) Condition-Monitoring (CM). This is a maintenance process for items that have neither "Hard-Time" nor "On-Condition" maintenance as their primary maintenance process. CM is accomplished by appropriate means available to an operator for finding and solving problem areas. The detalled requirements for the condition-monitoring process are included as appendix 1 to this circular.
b. Complex (multicell) units may be subject to control by two or even all three of the primary processes. The predominant process will determine its classification. For example, the B-747 Modular Package - Stabilizer Control has CM assigned as its primary maintenance process by the MRB report, but a leakage check, which is a conventional O task, is also specified.
c. The basic engine has characteristics that involve all three primary maintenance processes.
(1) Programs that control engine major overhaul intervals consider the engine as a hard-time unit. The overhaul standards are specified by overhaul manuals or other publications that do not identify individual processes as such.
(2) Programs controlling shop maintenance to a "conditional" standard (restoration, etc.,) may classity the engine as on-condition or as condition-monitoring depending on the characteristics of the program. The applicable maintenance processes and their intervals should be designated in (or referenced by) the program document. MSG-2 (ref: appendix 1), discusses the analysis method for assigning maintenance processes. This method was used in the maintenance review board activity for the engines of the widebodied jets. This analytical method, in conjunction with service experience, can be applied to earlier engines.
15. RELTABILIIY CONTROL SYSTEMS. Typical systems used in reliability control are: (1) data collection, (2) data analysis, (3) corrective action,
(4) performance standards, (5) data display and report, (6) maintenance interval adjustment and process change, and (7) program revision. The intent of this section is not to provide a rigid specification but rather to explain the purpose of the systems which the operator can use as a framework for his particular program. The following paragraphs discuss these systems:
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a. Data collection system. This system should include a specific flow of information, identity of data sources, and procedures for transmission of data, including use of forms, computer runs, etc. Responsibilities within the operator's organization must be established for each step of data development and processing. Typical sources of performance information are as follows, however, it is not implied that all of these sources need be included in the program nor does this listing prohibit the use of other sources of information:
(1) Pilot reports.
(2) In-flight engine performance data.
(3) Mechanical interruptions/delays.
(4) Engine shutdowns.
(5) Unscheduled removals.
(6) Confirmed failures.
(7) Functional checks.
(8) Bench checks.
(9) Shop findings.
(10) Sampling inspections.
(11) Inspection writeups.
(12) Service difficulty reports (MRR).
b. Data analysis system. Data analysis is the process of evaluating mechanical performance data to identify characteristics indicating a need for program adjustment, revision of maintenance practices, hardware improvement (modification), etc. The initial step in analysis is the comparison of the data to a standard representing acceptable periormance. The standard may be a running average, tabulations of removal rates for past periods, graphs, charts, or any means of depicting a "norm."
Programs incorporating statistical performance standards alert type programs). Reliability programs developed under Advisory Circular 120-17 and earlier criteria utilize parameters for reliability analysis such as delays per 100 departures for an aircraft system. They incorporate performance standards as described in paragraph (d) of this section. These standards define acceptable performance. When compared with a running graphical or tabular display of current performance they depict trends as well as show out-of-limits conditions. The system performance data is usually reinforced by component removal or confirmed failure data. The conditionmonitoring process can be readily accommodated by this type program.
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(2) Programs using other analysis standards (nonalert type programs). Data that is compiled to assist in the day-to-day operation of the maintenance program may be effectively used as a basis for continuous mechanical performance analysis. Mechanical interruption summaries, flight log review, engine monitoring reports, incident reports, engine and component analysis reports are examples of the types of information suitable for this monitoring method. For this arrangement to be effective, the number and range of inputs must be sufficient to provide a basis for analysis equivalent to the statistical standard programs. The operator's organization must have the capability of summarizing the data to arrive at meaningful conclusions. Also, actuarial analysis should be periodically conducted to ensure that current process classifications are correct.
(3) Summary. The objective of data analysis is to (1) recognize the need for corrective action, (2) establish what corrective action is needed, and (3) determine the effectiveness of that action.
c. Corrective action system. The actions to be taken are a reflection of the analysis and should be positive enough to effectively restore performance to an acceptable level within a reasonable time. The system must include notification to the organizational element responsible for taking the action.
The system should provide periodic feedback until such time as performance has reached an acceptable level. The mechanics of the corrective action system normally encompass methods that have been established for the overall maintenance program such as work forms, special inspection procedures, engineering orders, technical standards, etc. Special provisions should be included for critical failures; i.e., failures in which loss of the functior or secondary effects of the failure impair the airworthiness of the aircraft.
d. Statistical performance standards system. A performance measurement expressed numerically in terms of system or component failures, pilot reports, delays or some other event (bracketed by hours of aircraft operation, number of landings, operating cycles, or other exposure measurement) serves as the basis for the standard. The development of control limits or alert values is usually based on accepted statistical methods such as standard deviation or the poisson distribution. However, some appiications use the average or base line method. The standard should be adjustable with reference to the operator's experience and should reflect seasonal and environmental considerations. The program should include procedures for periodic review of, and either upward or downward adjustment of, the standards as indicated. It should also include monitoring procedures for new aircraft until sufficient operating experience is available for computing performance standards.
e • Data display and report system.
(1) Operators with programs incorporating statistical performance priate data displays, summarizing the previous month's activity. The report Chap 2 Page 16 Par 15
effectiveness of the total maintenance program. It should highlight systems which have exceeded the established performance standards and discuss what action has been taken or planned. The report should explain changes which have been made or are planned in the aircraft maintenance program, including changes in maintenance and inspection intervals and changes from one maintenance process to another. It should discuss continuing over-alert conditions carried forward from previous reports and should report the progress of corrective action programs.
(2) Programs using other analytical standards (nonalert type programs) should consolidate or summarize significant reports used in controlling their program to provide for evaluation of its effectiveness.
These reports may be in the form of computer printouts, summaries, or any intelligible form. A typical program of this type reports the following information:
(a) Mechanical Interruption Summary (MIS).
(b) Mechanical Reliability Reports (MRR).
(c) Listing of all maintenance process and interval assignment. (Master specification)
(d) Weekly update to letter (c) above.
(e) Daily Repetitive Item Listing (by aircraft).
(f) Monthly Component Premature Removal Report (includes removal rate).
(g) Monthly Engine Shutdown and Removal Report.
(h) Quarterly Engine Reliability Analysis Report.
(1) Engine Threshold Adjustment Report.
(J) Worksheets for maintenance process and interval changes (not provided to FAA, but FAA approves process changes).
f. Maintenance interval adjustment and process change system. A major characteristic of reliability control programs is they afford the operator a formal means of adjusting maintenance/inspection/overhaul intervals without prior FAA approval. This does not relieve the operator or FAA of their responsibility for the effects of the program on safety. Procedures for adjusting maintenance intervals should be included in the program.
(1) Maintenance interval adjustments should not interfere with an ongoing corrective action. Special procedures for escalating systems or components whose current performance exceeds control limits should be provided.
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Typical considerations for adjusting hard-time and on-condition intervals are as follows; however, it is not implied that all of these factors be considered for each case:
(a) Sampling.
(b) Actuarial studies.
(c) Unit performance.
(d) Inspector or shop findings.
(e) Pilot reports Methods for adjusting aircraft/engine check intervals should be included if the program controls these intervals and sampling criteria should be specified.
(2) The system should include procedures for initial classification of maintenance processes (HT - OC - CM) and for changes from one process to another. It should also include authority and procedures for changing maintenance specifications and related documents to reflect the interval adjustment or primary process change.
g. Program revision system. The program should include a procedure for revision which is compatible with FAA approvals discussed in chapter 4 of this circular. The procedure should identify organizational elements involved in the revision process and their authority. The program areas requiring formal FAA approval include any changes to the program that involve:
(1) Procedures relating to reliability measurement/performance standards.
(2) Data collection system.
(3) Data analysis methods and application to the total maintenance program.
(4) Process changes:
(a) For programs incorporating statistical performance standards (alert type programs) procedures for transferring components of systems from one primary maintenance process to another.
(b) For programs using other analysis standards (nonalert type programs) changing systems or components from one primary maintenance process to another.
(5) Adding or deleting components/systems.
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(6) Adding or deleting aircraft types.
(7) All procedural and organizational changes concerning administration of the program.
16.-24. RESERVED.
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CHAPTER 3. PROGRAM AIMINISTRATION
25. GENERAL• Administration of reliability programs (as discussed in this circular) requires a specific organizational structure within the operator's maintenance organization. Participants should be drawn from appropriate elements of the organization and should be authorized to act on behalf of their elements. The highest maintenance official or his designee should participate in the administration of the program. He should serve as the final authority for major activities and for program changes requiring FAA approval.
b. The makeup of the administration group may vary considerably from one operator to another. It may have a technical board that analyzes performance deteriorations and shop findings to make determinations that may be acted on by an administrative board. The two boards can be combined if this better serves the needs of the particular operator. The board type of administration should entail meetings scheduled for some specified interval and should
c. In lieu of a formal board, operators with sufficient organizational capability which should include a strong engineering function may administer their program by assigning appropriate responsibilities to each organizational element. In this type arrangement, responsibility for operation of the program should be assigned to a specific element of the operator's organization.
Procedures for operating each of the systems described in chapter 2 of this publication are essential to the success of the program. These procedures should be incorporated in appropriate sections of the operator's manual system. This will provide each organizational element, and individuals therein, instructions as to their part in the program. Forms should be used, as necessary, to facilitate and document recurring transactions that involve several elements such as (1) changes from one maintenance process to another,
(2) analysis of substandard system or component mechanical performance, (3) shop disassembly analysis for condition-monitoring purposes or overhau frequency adjustment, etc., and (4) sampling inspection for aircraft check or inspection adjustment.
26. RELIABILITY PROGRAM DOCUMENT. The operator should develop a document describing the application of reliability control methods.
a. This document should include at least the following:
(1) General description of the program.
(2) Organizational structure, duties and responsibilities.
(3) Description of the individual systems.
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(4) Derivation of performance standards (if used).
(5) Changes to the program including designation of changes requiring FAA approval.
(6) Copy and explanation of all forms peculiar to the system.
(7) Revision control and certification of revisions to the document.
b. The document should describe the workings of all systems in sufficient detail to provide for proper operation of the program. It should include in detail how the three maintenance processes are applied. The document should describe the monthly report and any other reports relative to the program, and include samples of these reports with instructions for their use.
organizational element (s) responsible for publishing reports should be identified and the distribution should be stated. Copies of pertinent reports should be provided to FAA.
C. The document should also include definitions of significant terms used in the program with particular emphasis on definitions of the three maintenance processes.
27.-34. RESERVED.
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CHAPTER 4. PROGRAM APPROVAL INITIAL APPROVAL. FAA Form 1014, Operations Specifications, (OMB 04-R0075) is used for initial approval of reliability programs. This form, along with the program document and related data should be submitted to the FAA district office assigned responsibility for that operator.
Guidance on the preparation of FAA Form 1014 is available from the FAA district office. Approval will be certified in the program docunent in addition to the operations specifications.
36. REVISION APPROVAL. Revisions requiring formal approval (ref: chapter 2, paragraph 15.g. of this circular) will be subject to the same consideration as initial approval. The mechanics of the approval certification will be as defined in the document. If the revision concerns items listed in the operations specifications, the effected page(s) will be amended to reflect the revision.
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Appendix 1 AIRLINE/MANUFACTURER MAINTENANCE PROGRAM PLANNING DOCUMENT - MSG-2 (Prepared by: R & M Subcommittee, Air Transport Association) (Date: March 25, 1970)
1.O GENERAL Introduction. Airline and manufacturer experience in developing scheduled maintenance programs for new aircraft has shown that more efficient programs can be developed through the use of logical decision processes. In July, 1968 representatives oi various airlines developed Handbook #MSG-1, "Maintenance Evaluation and Program Development,' which included decision logic and interairline/manufacturer procedures for developing a maintenance decided that experience gained on this project should be applied to update the decision logic and to delete certain 747 detail procedural information so that a universal document could be made applicable for later new type aircraft. This has been done and has resulted in this document, #MSG-2.
Objective. It is the objective of this document to present a means for developing a maintenance program which will be acceptable to the Regulatory Authorities, the Operators, and the Manufacturers.
The maintenance program data will be developed by coordination with specialists from the operators, manufacturers, and when feasible, the regulatory authority of the country of manufacture.
Specifically it is the objective of this document to outline the general organization and decision processes for determining the essential scheduled maintenance requirements for new airplanes.
Historically, the initial scheduled maintenance program has been specified in Maintenance Review Board Documents. This document is intended to facilitate the development of initial scheduled maintenance programs. The remaining maintenance, that is nonscheduled or nonroutine maintenance, is directed by the findings of the scheduled maintenance program and the normal operation of the aircraft. The remaining maintenance consists of maintenance actions to correct discrepancies noted during scheduled maintenance tasks, nonscheduled maintenance, normal operation, or condition monitoring.
1•3 Scope. The scope of this document shall encompass the maintenance program for the entire airplane.
1•4 Organization. The organization to carry out the maintenance program development pertinent to a specific type aircraft shall be staffed by representatives of the Airline Operators purchasing the equipment, the Prime Manufacturers of the airframe and powerplant and when feasible the Regulatory Authority.
Appendix l 10401 The management of the maintenance program development activities shall be accomplished by a Steering Group composed of members from a representative number of Operators and a representative of the Prime Airframe and Engine Manufacturers. It shall be the responsibility of this group to establish policy, direct the activities of Working Groups or other working activity, carry out liaison with the manufacturer and other operators, prepare the final program recommendations and represent the operators in contacts with the Regulatory Authority.
1.4.2 A number of Working Groups, consisting of specialist representatives from the participating Operators, the Prime Manufacturer, and when feasible the Regulatory Authority, may be constituted. The Steering Group, alternatively, may arrange some other means for obtaining the detailed technical information necessary to develop recommendations for maintenance programs in each area. Irrespective of the organization of the working activity, it must provide written technical data that support its recommendations to the Steering Group. After approval by the Steering Group, these analyses and recommendations shall be consolidated into a final report for presentation to the Regulatory Authority.
200 DEVELOPMENT OF MAINTENANCE PROGRAMS 201 Program Requirement. It is necessary to develop a maintenance program for each new type of airplane prior to its introduction into airline service.
20101 The primary purpose of this document is to develop a proposal to assist the Regulatory Authority to establish an initial maintenance program for new types of airplanes.
The purpose of this program is to maintain the inherent design ievels of operating safety.* This program becomes the basis for the first issue of each airline's Operations Specifications-Maintenance to govern its initial maintenance policy. These are subject, upon application by individual airlines, to revisions which may be unique to those airlines as operating experience is accumulated.
2.1.2 It is desirable, therefore, to define in some detail:
(a) The objectives of an efficient maintenance program,
(b) The content of an efficient maintenance program, and
(c) The process by which an efficient maintenance program can be developed.
* See Glossary.