AC 120-79 

DATE 04/21/03 

INITIATED BY: AFS-300 

ADVISORY CIRCULAR 

DEVELOPING AND IMPLEMENTING A 

CONTINUING ANALYSIS AND SURVEILLANCE 

SYSTEM 

U.S. DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

Flight Standards Service 

Washington, D.C. 

04/21/03 AC 120-79 

PREFACE 

This advisory circular (AC) provides information on how to implement a continuing analysis and 

surveillance system (CASS), which is required for certain types of air carriers and commercial 

operators under Title 14 of the Code of Federal Regulations (14 CFR), §§ 121.373 and 135.431. 

A CASS is a quality management system for air carriers and commercial operators that monitors

and analyzes the performance and effectiveness of inspection and maintenance programs. 

This AC is one method of compliance with the requirements of 14 CFR. Instead of following

this method, the applicant may elect to follow an alternate method, provided that method is 

acceptable to the Federal Aviation Administration (FAA). Because the method of compliance 

presented in this AC is not mandatory, the term “should” used herein applies only to an applicant 

who chooses to follow this particular method without deviation. A CASS should be tailored to 

each specific operation; therefore, this AC cannot provide a single means of compliance that 

applies to all operators required to have a CASS. 

This AC and the FAA’s Continuing Analysis and Surveillance System (CASS) Description and 

Models Report (2002) provide information about the FAA’s expectations regarding industry

implementation of a CASS. As required by §§ 121.373 and 135.431, a CASS monitors an 

operator’s inspection and maintenance programs for compliance with applicable requirements, 

including FAA regulations and manufacturer instructions. The FAA encourages operators to 

also consider additional standards for use in a CASS, such as industry best practices or other 

government regulations and guidance relevant to inspection and maintenance activities. 

/s/ James J. Ballough 

Director, Flight Standards Service 

Page i (and ii)

04/21/03 AC 120-79 

CONTENTS 

Page

CHAPTER 1. INTRODUCTION .................................................................................................. 1 

100. Purpose of this AC..................................................................................................... 1 

101. Who should use this AC ............................................................................................ 1 

CHAPTER 2. BACKGROUND ON CASS .................................................................................. 3 

200. History of the CASS .................................................................................................. 3 

201. CASS regulations....................................................................................................... 3 

202. Purpose of a CASS..................................................................................................... 4 

203. Structure of a CASS................................................................................................... 4 

CHAPTER 3. USING THIS AC TO DESIGN A CASS............................................................... 9 

300. Types of operators this AC helps............................................................................... 9 

301. Approach of this AC.................................................................................................. 9 

CHAPTER 4. CASS IN THE OPERATOR ORGANIZATION................................................. 11 

400. CASS documentation............................................................................................... 11 

401. Written policy and procedures................................................................................. 11 

CHAPTER 5. MAJOR CASS ACTIVITIES............................................................................... 13 

500. Summary of a CASS................................................................................................ 13 

501. Verifying the performance of inspection and maintenance programs..................... 17 

502. Verifying the effectiveness of inspection and maintenance programs..................... 21 

503. Final root cause analysis and corrective action........................................................ 23 

504. Follow-up................................................................................................................. 30 

CHAPTER 6. PERSONNEL WHO PERFORM CASS FUNCTIONS....................................... 33 

600. Personnel managing CASS functions...................................................................... 33 

601. CASS personnel training and experience ................................................................ 33 

CHAPTER 7. COMMUNICATION BETWEEN CASS PERSONNEL AND OTHER

DEPARTMENTS ......................................................................................................................... 37 

700. Communicating specific CASS results and actions................................................. 37 

701. Educating personnel on CASS................................................................................. 37 

702. Communications with personnel outside the CASS................................................ 38 

 Page iii 
AC 120-79 04/21/03 

Page

CHAPTER 8. HOW THE CASS DIFFERS FROM AND RELATES TO OTHER

PROGRAMS................................................................................................................................. 41 

800. Summary of other programs .................................................................................... 41 

801. Discussion of individual programs .......................................................................... 41 

CHAPTER 9. HOW TO DETERMINE IF THE CASS IS WORKING PROPERLY................ 45 

900. Why a CASS should be evaluated ........................................................................... 45 

901. Steps to evaluate the CASS...................................................................................... 45 

CHAPTER 10. THE ROLE OF THE FAA IN RELATION TO AN OPERATOR’S CASS ..... 49 

1000. The FAA’s general role ......................................................................................... 49 

1001. The FAA principal inspector’s role ....................................................................... 49 

CHAPTER 11. ADMINISTRATIVE INFORMATION............................................................. 51 

1100. How to obtain FAA publications........................................................................... 51 

APPENDIX 1. SAMPLE CASS FOR A LARGE OPERATOR (6 pages) ............................. 1 

APPENDIX 2. SAMPLE CASS FOR A MEDIUM OPERATOR (6 pages).......................... 1 

APPENDIX 3. SAMPLE CASS FOR A SMALL OPERATOR (5 pages) ............................. 1 

APPENDIX 4. CASS MANUAL/DOCUMENT SAMPLE CONTENTS (2 pages)............... 1 

APPENDIX 5. INFORMATION RELATED TO THIS AC (3 pages) ................................... 1 

Page iv 
04/21/03 AC 120-79 

CHAPTER 1. INTRODUCTION 

100. Purpose of this AC. 

a. This advisory circular (AC) provides information on how to implement a continuing

analysis and surveillance system (CASS), which is required for certain types of air carriers and 

commercial operators under Title 14 of the Code of Federal Regulations (14 CFR), §§ 121.373 

and 135.431. A CASS is a quality management system for air carriers and commercial operators 

that monitors and analyzes the performance and effectiveness of inspection and maintenance 

programs. 

b. This AC is one method of compliance with the requirements of 14 CFR. Instead of 

following this method, the applicant may elect to follow an alternate method, provided that 

method is acceptable to the Federal Aviation Administration (FAA). Because the method of 

compliance presented in this AC is not mandatory, the term “should” used herein applies only to 

an applicant who chooses to follow this particular method without deviation. A CASS should be 

tailored to each specific operation; therefore, this AC cannot provide a single means of 

compliance that applies to all operators required to have a CASS. 

c. This AC and the FAA’s Continuing Analysis and Surveillance System (CASS)

Description and Models Report (2002) provide information about the FAA’s expectations 

regarding industry implementation of a CASS. As required by §§ 121.373 and 135.431, a CASS 

monitors an operator’s inspection and maintenance programs for compliance with applicable

requirements, including FAA regulations and manufacturer instructions. The FAA encourages 

operators to also consider additional standards for use in a CASS, such as industry best practices 

or other government regulations and guidance relevant to inspection and maintenance activities. 

101. Who should use this AC. 

a. This AC is directed toward any operator that develops a CASS, whether they are required 

to do so or not. The following table explains which operators must have a CASS and which 

operators may choose to have one. 

If you operate under... You... 

part 121 must have a CASS as required by § 121.373. 

part 129 with an approved maintenance 

program for U.S.-registered aircraft

should have a CASS, as addressed in AC 129–4, 

Maintenance Programs for U.S.-Registered 

Aircraft under FAR Part 129. 

part 135 and operate aircraft type-certificated 

for a passenger seating configuration, 

excluding any pilot seat, of 10 seats or more 

must have a CASS as required by § 135.431. 

part 91, 125, 133, 135, or 137 with aircraft 

having nine or fewer seats (§ 135.411(a)(1)) 

may be interested in developing a CASS because 

of the safety and other benefits it affords. 

b. This AC is useful for any personnel directly involved in implementing a CASS, as well as 

operator senior management with responsibility for inspection and maintenance activities. 

Par 100 Page 1 (and 2) 

04/21/03 AC 120-79 

CHAPTER 2. BACKGROUND ON CASS 

200. History of the CASS. 

The FAA implemented the requirement for a CASS in 1964 in response to safety concerns and 

discoveries of weaknesses in the airworthiness programs of some operators, as revealed during

accident investigations and FAA surveillance of operator maintenance activities. The FAA 

issued the requirement in conjunction with other regulations designed to strengthen requirements 

for air carriers’ inspection and maintenance organizations and activities.

201. CASS regulations. 

a. Requirement to have a CASS. This AC addresses certain key concepts in the CASS 

regulations, portions of which are italicized in the regulatory text quoted here for discussion later 

in this AC. Section 121.373(a) and (b) states: 

(1) Each certificate holder 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 other maintenance, preventive 

maintenance, and alterations and for the correction of any deficiency in those programs, 

regardless of whether those programs are carried out by the certificate holder or by

another person. 

(2) Whenever the Administrator finds that either or both of the programs

described in paragraph (a) of this section does not contain adequate procedures and 

standards to meet the requirements of this part, the certificate holder shall, after 

notification by the Administrator, make any changes in those programs that are necessary

to meet those requirements. 

NOTE: The wording of § 135.431(a) and (b) is substantively identical. 

b. Requirement to have inspection and maintenance programs. Except as otherwise 

provided in part 121, certificate holders under that part are required by § 121.367 to have an 

inspection program and a program covering other maintenance, preventive maintenance, and 

alterations. In accordance with § 135.425, the same requirement applies to operations under 

part 135 involving aircraft type-certificated for a passenger seating configuration, excluding any

pilot seat, of 10 seats or more. 

c. The elements of a maintenance program. An air carrier inspection/maintenance

program includes the following nine elements: 

(1) Accomplishment and approval of maintenance, including inspection; 

(2) Airworthiness responsibility; 

(3) A CASS; 

(4) Contract maintenance;

Par 200 Page 3 
AC 120-79 04/21/03 

(5) A maintenance manual; 

(6) A maintenance organization; 

(7) A maintenance recordkeeping system; 

(8) A maintenance schedule; and 

(9) Personnel training. 

202. Purpose of a CASS. 

a. If an operator fails to accomplish its inspection and maintenance programs according to its

manuals and applicable requirements, or if the manuals have deficiencies that result in flaws in 

the inspection and maintenance programs, an aircraft may be approved for return to service when 

it is not airworthy. The FAA views the CASS as a continuous, system safety-based, closed-loop 

cycle of surveillance, investigation, data collection, analysis, corrective action, monitoring, and 

feedback for operators to use to continually monitor and correct any deficiencies. 

b. The FAA expects that each operator designs its CASS to ensure it conducts its inspection 

and maintenance programs according to regulations and operator manuals, and that these 

programs are effective in achieving the desired result of consistently having only airworthy

aircraft approved for return to service. For the CASS to yield this safety benefit, the FAA 

expects the operator’s senior management to establish safety as its top organizational priority. 

To reach this goal, all personnel need to embrace organizational goals and act jointly to achieve 

them. 

203. Structure of a CASS. 

a. The intent of the regulations governing inspection and maintenance programs is to ensure

that at least the level of safety originally designed into an aircraft system is maintained and that

the aircraft is airworthy. Both inspection and maintenance program functions are included in 

what is called a continuous airworthiness maintenance program (CAMP). Within a CAMP, 

however, an operator must have separate programs and functions to conduct inspection tasks and 

maintenance tasks. 

b. There are two basic questions that the regulations require a CASS to address: 

(1) Are you following your inspection and maintenance manuals and procedures? 

The continuing analysis and surveillance of the performance of inspection and maintenance 

programs refers to the process of collecting and evaluating information to determine that the

inspection and maintenance programs are being executed according to regulations, operator 

manuals, and other applicable requirements. This portion of the CASS consists of conducting

and analyzing the results of audits and audit trends to verify that the operator is following its 

inspection and maintenance programs as written and is properly performing maintenance as

intended. The analysis conducted in this area of a CASS also identifies weaknesses, if any, in 

the systems and procedures used to carry out the inspection and maintenance programs. 

Page 4 Par 201 
04/21/03 AC 120-79 

(2) In following your manuals and procedures, are you producing consistently 

airworthy aircraft? The continuing analysis and surveillance of the effectiveness of the 

inspection and maintenance programs refers to the process of collecting and evaluating

operational data to verify the inspection and maintenance programs are not only being performed 

as written but also are producing the desired results. The desired result is that aircraft are always

airworthy when they are returned to service with a level of reliability consistent with the goals of

the inspection and maintenance programs. “Reliability” is used here as a broad term and is an

expression of dependability and the probability that an item—including an aircraft, engine, 

propeller, or component—will perform the required function under specified conditions without 

failure for a specified period of time. Testing for effectiveness consists of collecting and 

analyzing operational performance data such as:

Maintenance-related delays and cancellations; 

Failure rates of parts and components after they are approved for return to service; 

Discrepancy rates of aircraft after heavy maintenance; and 

Related trend analysis. 

c. The regulations require an operator to include, as part of its CASS, provisions to correct 

any deficiencies in its inspection and maintenance programs, regardless of whether the programs 

are actually conducted by the certificate holder or by another person (i.e., contracted services). 

The regulations also provide authority for the FAA to require the certificate holder to make 

changes in the inspection and maintenance programs if they do not meet the requirements of 

part 121 or part 135, as applicable. 

d. A well-structured CASS can assist an operator in taking a systems safety approach to its 

inspection and maintenance programs through recognition of the interaction of all the elements 

within an air carrier’s systems and subsystems. The systems consist of interrelated processes 

that comprise personnel, procedures, materials, tools, equipment, facilities, and software 

operating in a specific environment to perform a particular task or achieve a defined purpose, 

support, or mission requirement for an air carrier. 

e. An unairworthy aircraft can be the result of the actions of a wide variety of organizations 

and/or functions, in addition to those associated with inspection and maintenance. These

organizations and/or functions include senior management, flight operations, ground operations, 

and others. A good CASS would consider the potential role of these organizations and/or 

functions through effective surveillance and complete root cause analysis. These issues are

covered in greater detail in paragraphs 501 – 503 of this AC.

f. When performing its surveillance and analysis functions, persons responsible for a CASS 

are encouraged to use the system safety categories of safety attributes, safety culture, 

communication, accountability, training programs, and potential problem areas when identifying

hazards and managing risks. The FAA defines safety attributes as the following: 

(1) Authority. There is a clearly identifiable, qualified, and knowledgeable person with 

the authority to establish and modify a process. 

Par 203 Page 5 
AC 120-79 04/21/03 

(2) Responsibility. There is a clearly identifiable, qualified, and knowledgeable person 

who is accountable for the quality of a process. 

(3) Procedures. There are documented methods for accomplishing a process. The 

procedure description should answer the basic questions of who, what, when, where, and why, as 

appropriate. 

(4) Controls. There are checks and restraints designed into a process to ensure a desired 

result. 

(5) Process measurement. The air carrier measures and assesses its processes to

identify and correct problems or potential problems. 

(6) Interfaces. The air carrier identifies and manages the interactions between

processes. 

g. Systems safety and, therefore, CASS functions are built around principles of what is 

commonly referred to as risk management. This includes identifying hazards; evaluating how 

severe the hazards’ consequences would be and how likely they are to occur (risk assessment); 

and developing, implementing, and evaluating measures to address the identified risks and 

program deficiencies throughout a system’s life cycle to achieve an acceptable level of risk (risk 

management). Operators perform these functions on some level currently, although the degree 

of formality and sophistication depends on the size and scope of the operation as well as the level 

of training operator personnel have in risk management. In a CASS, the FAA expects a formal 

risk management process (system safety) with safety and compliance as the top priorities. A 

formal process is structured, but not necessarily complex or expensive. 

h. A CASS is intended to give operator management (and the FAA) a realistic picture of the 

frequency and nature of deficiencies occurring in the operator’s inspection and maintenance

programs, and the opportunity to correct them. If company personnel at any level perceive that 

their jobs are at risk by collaborating in this system, they are likely to withhold information or 

bias the analysis for self-protection. The FAA suggests that the operator design its CASS to 

emphasize the end goal of enhancing safety by evaluating and improving the inspection and 

maintenance programs. The analysis and surveillance should not be perceived or intended as a 

method of identifying individuals who have committed errors simply to take some sort of 

disciplinary action. Human error is inevitable, but the question for a CASS to answer is how to 

better design the inspection and maintenance programs to preclude errors from encroaching on 

system safety or resulting in noncompliance.

i. A particular challenge for any CASS is to overcome complacency that may be caused by

the high degree of redundancy and dependability in modern aircraft systems. Operators need to 

place high priority on the continuing analysis and surveillance of their inspection and 

maintenance programs because the potential consequences of deficiencies in those programs are 

very serious. 

j. Due to the wide range of affected operators, it would be unrealistic to set forth a single

means of compliance for all operators to follow. Just as each operator has its own inspection and 

Page 6 Par 203 
04/21/03 AC 120-79 

maintenance procedures manuals, each operator should have its own CASS. An operator should 

design a CASS appropriate to the size and sophistication of its operation.

Par 203 Page 7 (and 8) 

04/21/03 AC 120-79 

CHAPTER 3. USING THIS AC TO DESIGN A CASS 

300. Types of operators this AC helps. 

a. The CASS applies to many types of operators, ranging from small operators of one or two 

aircraft to operators with several hundred turbojet aircraft. The aircraft may include helicopters 

or airplanes. The operators may provide scheduled or unscheduled service, and may operate 

under part 121 or part 135. These functions affect the size and structure of an operator’s 

inspection and maintenance organizations. Additionally, an operator conducting operations 

under part 91, 125, 129, 133, 135 (nine or fewer seats), or 137, while not required to have a 

CASS, may also find this AC useful if it decides to implement a CASS. 

b. A primary difference among operators in regard to CASS design involves the personnel 

assigned to accomplish CASS-related duties. A smaller operator may have fewer assigned 

personnel, and it may have to draw upon personnel normally assigned to other functions to fulfill 

CASS functions part-time. The operator may even need to use outside resources such as contract

personnel to supply special expertise or independent review if its organization lacks the 

necessary special skills or training, or has an insufficient number of personnel to fulfill the CASS 

functions. A larger operator may have a significant number of personnel assigned full-time to 

CASS functions. 

301. Approach of this AC. 

a. This AC primarily addresses the functions of a CASS. The main text of the AC 

(chapter 5) presents the basic functions the FAA expects to see included in any CASS. 

b. In appendixes 1, 2, and 3, we present examples of how three different types of operators 

might accomplish these CASS functions and satisfy the intent of this AC. The examples are not

intended as a menu from which an operator may select a CASS. Rather, the examples are 

intended to demonstrate how an operator might design a CASS suitable for its operation. Each 

appendix contains descriptions of procedures based on likely available resources for a different

type and size of operator. The number and type of airplanes operated is not particularly

important. For example, the small on-demand air carrier operating under part 135 with two 

Saab 340B airplanes would probably meet the intent of this AC in essentially the same way as a 

small part 121 operator with one Boeing 727. The operator will need to develop its own 

procedures and use the terminology (for example, designating the personnel or organizations 

involved in different aspects of the CASS) that best fit its operation. For that reason, any job 

titles in this AC are for illustration; they are not requirements or even recommendations. 

Appendix 4 is a list of sample CASS manual/document contents. Appendix 5 lists related 

publications and the publications used to produce this AC.

Par 300 Page 9 (and 10) 

04/21/03 AC 120-79 

CHAPTER 4. CASS IN THE OPERATOR ORGANIZATION 

400. CASS documentation. 

The operator should describe its CASS policy and procedures in writing. They can be in a paper 

or electronic document, or other comparable record. For example, the operator may accomplish 

this in a detailed chapter or section within a general maintenance manual or in a separate CASS 

manual associated with the general maintenance manual. The intent is that policy and 

procedures not be simply oral understandings. 

401. Written policy and procedures. 

The CASS policy and procedures should: 

a. Recognize and treat the CASS as a coordinated system rather than as audit and data 

collection activities dispersed within the operator’s inspection and maintenance programs. 

CASS personnel do not necessarily have to be contained within a single department or office of 

the operator’s organization. However, the policy and procedures should identify all functions 

related to the CASS, rather than assume that because an audit or data collection function exists

somewhere within the organization, it automatically satisfies the CASS requirement with no 

further coordination necessary. 

b. Identify any programs, such as an optional FAA-approved reliability program, used to 

satisfy a major portion of the CASS. The CASS documentation may refer to the documentation 

for that other program rather than repeat the contents. The relationship/interfaces between the 

CASS and the other program should be clear and address responsibility and feedback issues to 

ensure CASS objectives are met. 

c. Be based on principles of systems safety analysis. 

d. Clearly identify the positions within the company with authority and responsibility for the 

CASS. The operator may use and define the terms as it sees fit, but these concepts (briefly

defined above in the discussion of systems safety, paragraph 203f) should be addressed. The 

definitions below would have meaning within the context of an air carrier’s organization and 

would not necessarily relate to the traditional concept of FAA regulatory authority. 

(1) Authority. For purposes of this AC, “authority” with regard to the CASS means the 

power to create or modify fundamental policy or procedures without higher level review or 

approval. The person with authority for the CASS may design or change the CASS without 

having to seek approval from a higher level of management. CASS procedures should include 

how to modify the CASS. 

(2) Responsibility. For purposes of this AC, “responsibility” with regard to CASS 

means the obligation, with attendant accountability, for ensuring tasks and functions are 

successfully accomplished in accordance with applicable policies, procedures, and standards. 

This work may be accomplished directly by the person with responsibility, or the work may be 

delegated. The person with responsibility for the CASS has the obligation to carry out the 

functions of the CASS, including overseeing and managing any personnel to whom CASS 

Par 400 Page 11 
AC 120-79 04/21/03 

functions and duties are delegated. Note that for smaller organizations where personnel share 

duties and may only carry out CASS functions part-time, this oversight and management 

responsibility relates only to those part-time tasks. 

A single person or position within the operator should have authority for the CASS, and a single 

person or position within the operator should have overall responsibility for managing and 

implementing the CASS. A single person may have both responsibility and authority for the 

CASS. That person might also have responsibility for other functions as well as the CASS. It

would be common for the person with responsibility for CASS functions to delegate some or 

much of this work to others within the operator, depending on the size and staffing of the 

operator. What the FAA expects is clear responsibility for the overall CASS so that there is not a 

fragmented system with high risk of confusion over who is responsible for a given task. 

Personnel with CASS responsibilities and duties should be as independent as possible from the 

day-to-day operations of the inspection and maintenance program. Ideally, the personnel 

conducting audits would work in separate departments from the departments performing the 

actual inspection and maintenance activities of the operator. However, this is not necessarily

feasible for small operators. At small operators, personnel performing CASS functions, 

particularly audits, may consist of one or more of the following: 

“Borrowed” personnel from certain other shops or departments. The operator’s 

procedures should include ways to avoid having these individuals assigned to audit areas 

where they normally work. 

The company owner or chief executive officer, particularly if there are no other 

employees and the CASS audits are focused on outside vendors and maintenance 

providers because all or most of the actual inspection and maintenance work is

accomplished through contracts. 

Outside resources contracted to perform audits and analysis for the company.

Others deemed qualified by the operator to provide the operator independent audit, 

operational data collection, and analysis services that fulfill the requirements of a CASS 

as described in this AC. 

e. Address the need for fluid communications and coordination among the persons with 

authority, responsibility, and duties related to the CASS.

Page 12 Par 401 
04/21/03 AC 120-79 

CHAPTER 5. MAJOR CASS ACTIVITIES 

500. Summary of a CASS. 

The regulations require that a CASS accomplish surveillance and analysis of the inspection and 

maintenance programs from two perspectives: verifying performance and verifying

effectiveness. The first two steps in the CASS process (surveillance and analysis) are carried out 

in two different ways. One is based on auditing, and the second is based on operational data 

collection and analysis. The results of the two types of surveillance and analysis feed into the

third and fourth basic CASS activities: corrective action and follow-up. The following table 

summarizes these four basic steps of a CASS within a system safety mode. 

Verify Performance of Inspection and 

Maintenance Programs 

Verify Effectiveness of Inspection and 

Maintenance Programs 

1. Surveillance: Audit process. 

Create a plan based on risk assessment.

Perform transaction audits. 

Perform systems evaluation. 

Identify hazards. 

1. Surveillance: Data collection process. 

Select data sets. 

Collect operational data. 

Collect equipment failure data. 

Note trends, anomalies, and potential 

hazards. 

2. Analysis: Accomplish risk assessment and 

preliminary root cause analysis. 

2. Analysis: Investigate adverse indicators; 

accomplish risk assessment and preliminary

root cause analysis. 

3. Corrective Action: Complete final root cause analysis, corrective action options, risk 

assessment, decisionmaking, and developing and implementing a corrective action plan. 

4. Follow-up (Performance Measurement): Monitor corrective action, verification, and 

follow-up surveillance planning. 

Par 500 Page 13 
AC 120-79 04/21/03 

Figure 5-1 summarizes the flow of the four basic steps of the CASS, which are described in 

further detail in paragraphs 501 – 504. 

Figure 5-1. The Four Basic CASS Activities: 

Surveillance, Analysis, Corrective Action, Follow-up 

CASS

Management and

Planning

Auditing Collecting Data

Initial Analysis

Setting Priorities

Completing

Root Cause Analysis 

Developing and Implementing

Corrective Action

Corrective Action Monitoring

FEEDBACK

Verification Surveillance Planning

SURVEILLANCE

ANALYSIS

CORRECTIVE

ACTION

FOLLOW-UP

Page 14 Par 500 
04/21/03 AC 120-79 

The following two figures expand on the “Auditing” and “Collecting Data” activities displayed 

in figure 5-1. Figures 5-2 and 5-3 show the variety of functions within an operation that may

affect the inspection and maintenance programs. An operator should consider these in its 

surveillance and root cause analysis process, as appropriate. 

Figure 5-2. Auditing Portion of the Surveillance Process 

Auditing

Training

Aircraft

Condition

Publications

Continuous

Airworthiness

Maintenance 

Program

Ground

Operations

Flight

Operations

Ground 

Operations

Maintenance Repairs

Conformity

Alterations

Government publications e.g., regulations, airworthiness directives

Industry documents e.g., ATA 100 index

Operator documents e.g., General Maintenance Manual

Manufacturer documents e.g., maintenance manual, service bulletins

Program description

Records

Reliability program

(optional)

Scheduling/Tracking

Aircraft loading

Deicing

Taxiing and towing

Fueling

Par 500 Page 15 
AC 120-79 04/21/03 

Figure 5-3. Data Collection Portion of the Surveillance Process 

Collecting Data

Operational Events

(Examples)

Equipment

Performance

(Examples)

Accidents/incidents

Cancelled/delayed flights

In-flight engine shutdowns

MIS Reports

MRRs

Chronic systems

CPCP findings

Engine performance monitoring

Logbook writeups

Reliability trends

Mean times between failure

Unscheduled landings

Nonroutine tasks from checks

Shop/vendor teardown reports

Rejected takeoffs

Unconfirmed removals

Page 16 Par 500 
04/21/03 AC 120-79 

501. Verifying the performance of inspection and maintenance programs. 

a. Surveillance of the performance of inspection and maintenance programs. 

(1) Definition of “audit” within a CASS. The main tool for surveying (assessing) 

whether the operator is properly performing (executing) its inspection and maintenance programs 

is audits. For purposes of a CASS, an audit is a formal examination of the activities of a

department or area of an operator’s inspection and maintenance programs based on an 

established standard such as the applicable manual. Audits are intended to ensure operator 

inspection and maintenance personnel and outside maintenance providers comply with the 

operator’s manual, program, and all applicable requirements. 

(2) Audit procedures. The operator should have written procedures to guide its 

auditing process, including the scheduling of audits. The CASS addresses both internal and 

external audits. Internal audits are audits the operator conducts within the company. External 

audits are audits the operator conducts of vendors supplying parts and services to the operator. 

CASS procedures should include a methodology for determining priorities and for establishing

and adjusting audit cycles (for example, 12-, 18-, 24-, 36-month cycles) so that resources are 

focused on the most pressing issues. This is a risk assessment and risk management process (see 

paragraph 501a(3) below for further explanation of risk assessment and risk management). 

Although the majority of the inputs to this process would be generated internally, one additional 

input may be the results of outside audits of the operator or its vendors conducted by entities 

other than the operator. For example, the results of audits or inspections conducted by the FAA 

or the Department of Defense (DoD) may be useful by providing an operator with: 

Specific findings requiring root cause analysis and possible corrective action 

(activities discussed later in this AC), and 

Information useful in focusing the operator’s own audits and operational data 

collection. 

The operator may approach this initial scheduling task in many different ways, ranging from 

resource allocation based on company experience and very basic analysis to use of a 

sophisticated, software-supported risk analysis process. Within this range of possible 

methodologies, the FAA expects the operator’s CASS procedures to contain a process to 

systematically make those decisions that are compatible with the size and complexity of the

operations. The FAA encourages operators to make this process as structured as possible. The 

operator should place priority first on safety and regulatory compliance, and second on issues of 

operational efficiency. However, an effective CASS meets all three of these objectives. 

(3) Prioritizing surveillance resources. Essentially, any methodology selected to 

prioritize surveillance resources (as well as to formulate corrective action decisions later in the

process) involves principles of risk assessment. Risk assessment is a concept applicable in many

aspects of an aviation operation (see Order 8040.4, Safety Risk Management, for additional 

information). This FAA order is an example and is not the only source of risk assessment 

Par 501 Page 17 
AC 120-79 04/21/03 

procedures; however, it provides insight into FAA expectations. The FAA encourages operators 

to incorporate the principles of this systematic process to: 

Establish a plan, including the scope of the process and priorities (for example,

detect and prevent noncompliance); 

Specify the areas of concern for surveillance and analysis (personnel, 

maintenance and inspection programs and organizations, operations, aircraft, 

facilities, systems); 

Identify hazards or potential threats to the operation; 

Determine how likely such hazards are to be realized and actually cause harm;

Determine the severity of the consequences if the hazard is realized; 

Express a combination of the likelihood and severity of harm as “risk”; and 

Evaluate the appropriate response to the identified risk. 

A CASS should take into account four principal potential sources of hazards: 

Personnel (hiring, capabilities, interaction); 

Equipment (design, maintenance, logistics, technology); 

Workplace (environment, sanitation); and 

Organization (standards, procedures, controls). 

A number of quantitative and graphical tools exist in the industry to help determine the 

gradations of a risk (high, medium, low) based on the likelihood of an unwanted event occurring

and the severity of the consequences if it does occur. In the initial steps of the CASS process, 

the appropriate response involves setting surveillance priorities based on risk assessments aimed 

at maintaining compliance and safety in inspection and maintenance. A CASS risk assessment, 

through the feedback loop, helps to set the audit and data collection priorities enhancing the 

focus of surveillance. The process is best accomplished by an interdisciplinary team, guided by

CASS management but involving representatives of the relevant technical areas. 

To identify the areas to audit and to set priorities, consider factors in outside reports. These

could include inspections, reports, special studies, or audits conducted by outside entities such as 

the FAA, (DoD), Department of Transportation, Office of the Inspector General, or National 

Transportation Safety Board. Outside reports may address: 

Information specific to the operator or its vendors; 

Information related to the industry as a whole and of interest to the operator; 

and/or 

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Information about an accident, incident, procedure/process, or equipment type 

that is relevant. 

(4) Audit materials. The operator should equip CASS auditors with checklists to ensure 

consistency and completeness of audits. The person responsible for the CASS should ensure the 

checklists are updated as needed. An auditor should also be permitted flexibility to ask questions 

not contained on the checklist if he or she finds an area that requires further investigation. 

(5) Areas to be audited. The operator’s procedures should include identification of all 

areas to be audited along with a process for updating this list. The following list presents 

examples of areas operators should consider for routine audit. A CASS audit should verify that: 

Manuals, publications, and forms (paper and electronic versions) are useable, 

up-to-date, accurate, and readily available to the user;

Maintenance and alterations are performed according to the methods, standards, 

and techniques specified in the operator’s manuals, including ensuring major 

repairs and alterations are properly classified and accomplished with approved 

data; 

Parts and components are properly stored, dispensed, identified, and handled; 

Airworthiness directives are appropriately evaluated, accomplished, and tracked;

Maintenance records are generated in accordance with manual procedures and are 

complete and correct; 

Required inspection items are identified and addressed according to the operator’s 

procedures; 

Airworthiness releases are executed by authorized persons according to the 

operator’s procedures; 

Shift turnover records, work interruptions, and deferred maintenance are 

accomplished according to applicable procedures;

Maintenance facilities and equipment, including base and line stations and 

contract maintenance providers’ facilities, are adequate; 

Personnel, including those of contract maintenance providers, are trained and 

qualified to accomplish their duties;

Tools and equipment are properly calibrated; 

Requirements for specialized tools or training are met, such as for nondestructive 

testing, category II/III operations, and run-up/taxi;

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Computer programs (software) for the inspection and maintenance programs are 

performed in accordance with specifications;

Vendors and suppliers provide services and products according to the operator’s 

policies and procedures; and 

Each aircraft released to service is airworthy.

(6) Objective of CASS audits. CASS audits should primarily be proactive, searching

out potential problem areas before they result in undesirable events. However, CASS procedures 

may also address how to direct audits in response to events or a series of events. For example, 

rejected takeoffs, unscheduled landings, in-flight shutdowns, accidents, or incidents may indicate

the need for special audits or surveillance under a CASS. The purpose of a CASS is to detect 

and analyze trends for indications of program weaknesses or deficiencies. For example, CASS 

auditors would not necessarily investigate a single maintenance-related rejected takeoff, although 

the maintenance program would. A CASS would, however, consider whether that instance 

indicated a need to focus audits on a particular issue. 

(7) Informal communications within CASS. Auditors and analysts should maintain 

informal lines of communication with personnel in the production departments so that inspection 

and maintenance personnel can discuss concerns they may have. Through this informal 

communications process, the operator can learn about potential hazards in the system. For 

example, the operator may learn about an event that might have occurred but, because of some 

intervention, did not. This event is known to shop personnel but is otherwise difficult or 

impossible to detect in routine audits. With informal lines of communication open to shop 

personnel, a CASS may detect this near-event. The FAA suggests that the operator’s CASS 

procedures address how to encourage this type of communication and interaction. 

b. Analysis of audits. 

(1) Root cause analysis. A risk assessment process tells operators where to allocate

resources and helps them understand what is found. Audit results should undergo risk 

assessment and preliminary root cause analysis to identify a deficiency, or potential deficiency, 

in any aspect of inspection and maintenance programs. This preliminary analysis helps CASS 

personnel determine the level of priority the issue merits and what type of additional technical 

expertise may be required to complete the root cause analysis and evaluate corrective action 

options. 

Root cause analysis treats errors as defects in the system rather than in a person. Root cause 

analysis looks beyond the symptom to find the organizational defect that permitted an error to 

occur to correct the fundamental problem, and to prevent recurrence. The more thorough the 

analysis, the greater the likelihood the operator will uncover why the system deficiency occurred 

and how the organization can respond definitively. The process starts during the audit itself, as 

auditors must collect information conducive to later analysis. If a CASS is to uncover a 

procedural weakness, for example, information about the procedure must be collected. This 

should be factual and objective information, not premature judgment about root cause. Root 

cause analysis is key to any complete CASS, even though procedures may vary in complexity

from operator to operator. 

Page 20 Par 501 
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(2) Objective of audit analysis. The objective of this analysis is to allow the operator to 

address the problem in such a way as to avoid recurrence of the deficiencies. To the extent

possible, the operator should set forth in the CASS documentation the analysis process. The 

analysis process should be as objective as possible to avoid any tendency to promote individual 

or commercial interests. The system should also place priority on finding the systemic or root 

cause of a program deficiency over seeking to assign personal blame, at any level of the 

organization, for an error. 

While audits are designed mainly to verify that an operator is performing inspection and 

maintenance in accordance with its manual, the regulations, and applicable requirements, 

auditors and analysts should also be alert for system deficiencies. That is, there may be 

procedures in the manual that are correctly followed, but that have become outdated, conflict 

with other manual procedures, or for some other reason are in need of change. Auditors and 

analysts should be encouraged to be inquisitive and think in terms of “what if?” so that the CASS 

functions proactively, detecting problem areas or trends before they lead to an accident, incident, 

or infraction of regulations. For example, what if event x occurred in conjunction with observed 

condition y? This approach is closely tied to the CASS analysis process but would require an 

analytical approach that permeates the CASS organization, from determining audit priorities and 

scheduling through auditing and analyzing, and including monitoring and evaluating corrective

actions. 

(3) Managing data from audit analysis. The audit analysis process is not typically as 

oriented toward quantitative analysis as the operational data analysis discussed below. However,

operators may find it useful to manage the data through database or quantitative applications. 

The FAA emphasizes that this is an approach that does not have to be complicated or costly. 

The level of formality and sophistication should match that of the operator. 

502. Verifying the effectiveness of inspection and maintenance programs. 

a. Surveillance of the effectiveness of inspection and maintenance programs. 

(1) Collecting operational data. The main tool for determining whether an operator’s 

inspection and maintenance programs are effective is collecting and analyzing operational data

focused on the equipment. Data should be collected that measures the output of the inspection 

and maintenance programs. The FAA does not intend to mandate the specific data an operator 

should collect. However, the FAA does expect an operator to have a process to ensure the data 

collected are adequate to meet the intent of the CASS requirement and are useful. The FAA 

expects an effective selection process and periodic review process, not specific data elements

that may not fit a given operator’s situation. 

(2) Types of operational data. Operational data can be divided into routine or 

unplanned (nonroutine). Examples of routine data are: 

Adjustment and/or calibration of equipment; 

Aircraft logbooks, including maintenance deferred in accordance with the 

minimum equipment list/configuration deviation list; 

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“Chronic” systems that alert for repeat writeups in a specified time period (for

example, 10 to 15 days); 

Corrosion prevention and control program findings; 

Engine condition monitoring information; 

Flight delays and cancellations related to mechanical issues; 

Results of fuel audits; 

Individual item failure rates; 

Mechanical reliability reports, mechanical interruption summaries, and similar

data; 

Nonroutine maintenance;

Teardown reports; 

Unscheduled parts replacement or unscheduled maintenance; and 

Vendor repair station information. 

Operational data also includes reactive data collection and analysis responding to emergency or 

other nonroutine events, such as: 

Accidents and incidents; 

In-flight engine and propeller separations and uncontained engine failures; 

In-flight engine shutdowns; 

Rejected takeoffs;

Unscheduled landings due to mechanical issues; 

Lightning strikes; and 

Hard landings. 

As with reactive audit surveillance, a CASS generally approaches problems from the analytical, 

systems perspective. For example, in response to one or more rejected takeoffs, a CASS might 

focus the operational data collection and analysis to determine if a pattern in rejected takeoffs

was evident, or if other types of data might be examined in relation to the rejected takeoff

situation. 

Page 22 Par 502 
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The above data sets are presented only as examples. Although the data sets are oriented toward 

equipment, this area of a CASS may also collect other types of data, such as information on 

types of maintenance errors experienced by the operator. 

(3) What to include in CASS documentation regarding collecting operational data. 

The operator’s CASS documentation should include a means of identifying data that is relevant 

and useful for that operator to use in monitoring the effectiveness of its specific inspection and 

maintenance programs. The operator should periodically review and reevaluate the usefulness of 

the data it collects and analyzes to accomplish this portion of the CASS.

b. Analysis of operational data. CASS procedures should:

(1) Provide analysts with an understanding of the potential significance of each data set 

and how to process the data to understand its significance. This may require: 

Statistical analysis, such as comparing the frequency of certain events or 

equipment failures with a determined norm, or 

Qualitative analysis, to evaluate reports of certain types of events. 

NOTE: This process is not necessarily the same as what would be used in an 

FAA-approved reliability program. 

(2) Emphasize that the analysis of operational data should consider root causes of 

negative trends or anomalies. This preliminary root cause analysis, including human factors, 

may require collaboration with technical personnel in the affected areas or specialists in 

engineering and reliability departments. 

(3) Delineate the roles of the CASS analysts as well as other departments or personnel in 

the analysis of operational data. 

Some operators select a system that uses alerts or warnings if results of the analysis exceed 

certain predetermined parameters. A CASS should not rely completely on such alerts to the 

exclusion of analysts’ judgment. The FAA’s expectation of a CASS in this regard is that the

operator have a complete, written procedure to review and analyze the operational data collected

and to determine when further review is necessary. 

503. Final root cause analysis and corrective action. 

While the surveillance and analysis steps differ for the verification of the performance of the 

inspection and maintenance programs versus verification of the effectiveness of those programs, 

the process merges when responding to CASS findings. The two types of analyses identify

potential deficiencies in the inspection and maintenance programs. In responding to these 

findings and analyses, the objective of a CASS is to determine the root causes of program 

deficiencies and address them appropriately, regardless of the perspective from which the

deficiencies are found. Note that the discussion is focused on a CASS function, not an 

organization. For a given operator, that function might be performed by more than one 

organization. 

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Generally, the area responsible for surveillance results will present these results to the technical 

or production area of the operator with a preliminary analysis of the collected information and, in 

some cases, possible underlying causes of the problem. Personnel in technical or production 

areas complete the root cause analysis (if necessary) and develop proposed corrective action 

alternatives. 

a. Final root cause analysis. 

(1) Preparing for root cause analysis. Analysis of audit findings or operational data 

requires evaluating mechanical and human performance, or other results generated by the CASS 

process, to determine the condition of a process, maintenance practices, or equipment. In the 

case of operational data, analysis begins with comparison of the data to a standard representing

acceptable performance. The standard may be in the form of an average or other means of 

calculating a reference. The standard may be set by the FAA, industry common practice, or the 

operator, as appropriate. 

The key is to have a CASS structure that addresses the basic disciplines and elements involved in 

finding and correcting program deficiencies. The CASS procedures should note that in 

performing root cause analysis, all relevant areas should be considered, including the role of 

senior management, policies, procedures, and communications. 

(2) Applicability of root cause analysis. Root cause analysis applies to both audit 

findings and analysis of results and trends in the operational data. For example, either audits or 

operational data analysis may point to maintenance errors being committed because of 

inadequate training. Analysis should not stop with simply determining which mechanics were 

inadequately trained and then training them. Rather, the analysis should determine why the 

training breach occurred and consider areas in management, communications, scheduling, or 

training program design that may be involved. 

(3) Principles and considerations of root cause analysis. Principles and 

considerations of root cause analysis are closely related to those of risk assessment, particularly

in terms of the thoroughness of the analysis. Both processes consider not simply the person 

involved in an issue (for example, the mechanic made a mistake), but all aspects of the 

organization in which that person works. This approach has the premise that human error is a 

consequence rather than a deliberate action, and that proactive measures and continuous reform 

of different aspects of the processes and organization can address “latent conditions” in the 

system and increase the system’s resistance to operational hazards. The term latent conditions 

refers to flawed procedures or organizational characteristics capable of creating hazards if the 

right conditions or actions occur. 

Root cause analysis should consider two major areas: 

Systems. Systems analysis plays an increasingly important role in a CASS

because of the increasing complexity and variety of operations, equipment, and 

organizations. Systems analysis emphasizes a coordinated approach to an 

enterprise, including specific written procedures and planning for all activities, 

clearly established authority and responsibilities, communications processes, and 

Page 24 Par 503 
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methods of measuring results, detecting system errors, and preventing recurrence. 

This approach recognizes the wide range of interrelated issues potentially

associated with a problem in the system, such as management policies, 

communications, and pilot technique, in addition to the inspection and 

maintenance activities themselves. 

Human factors. Human factors analysis looks at how humans communicate and 

perform in the work environment and then seeks to incorporate that knowledge 

into the design of equipment, processes, and organizations. This enhances safety

and maximizes the human contribution, partly by designing systems to anticipate 

the inevitability of human error. Human factors include basic issues that can be

addressed in audit checklists, such as whether there is adequate lighting for

mechanics and inspectors to perform their work, and whether schedules permit 

personnel to be properly rested. But the discipline addresses a wider range of 

issues affecting how people interface with technology and the operational system, 

including: 

Human physiology;

How people learn and perceive; 

Equipment, technology, and documentation; and 

Workplace. 

Operators should be aware that knowledge gained from human factors can help 

avoid maintenance and inspector errors, ensure that personnel initial skill sets 

match task requirements, ensure skills are maintained and improved, and enhance

the work environment. This knowledge can help CASS analysts perform root 

cause analysis. Continuing with the previous example of inadequate training, with 

insufficient awareness of human factors issues, operators may trace a maintenance 

error to a mechanic or technician who appears to be insufficiently trained for the 

task, and determine that the solution is more technical training. Further analysis 

may reveal, however, that there are contributing flaws in equipment design, job 

cards, manuals, the work environment, or organizational procedures such as shift

turnover that more training will not satisfactorily overcome. Or, it may turn out 

that a different kind of training, perhaps involving decisionmaking skills, is called 

for. 

The FAA is deeply involved in cooperative efforts with the industry and academia 

in promoting human factors in aviation. This field is rapidly evolving, particularly

in its application to aviation maintenance. According to a study conducted for the 

FAA, which cited Boeing research, maintenance error contributes to a significant

portion of air carrier accidents, with shift-turnover errors and work interruptions 

standing out as leading underlying causes. Based on the field’s growing

importance and the information available to industry, the FAA expects that 

Par 503 Page 25 
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operators will apply concepts of human factors to their CASS surveillance and 

analysis. 

CASS surveillance also should ensure root cause analysis, considering human 

factors, is part of the investigation of individual events by any personnel 

designated to respond to such events, such as rejected takeoffs. Otherwise, data 

reviewed in a CASS may be incomplete. 

One challenge presented by the increasing emphasis on human factors is how to 

balance two seemingly contradictory purposes. On the one hand, the FAA and 

industry need to encourage personnel to cooperate in addressing system 

organization and design issues without inhibitions caused by fear of discipline or 

enforcement. On the other hand, in some cases, individual employees or the 

operator may bear a degree of culpability (for example, in deliberately bypassing

important controls or committing a serious regulatory infraction in the commission 

of a maintenance error). In some instances, disciplinary action or even FAA 

administrative or legal enforcement may be indicated. This is a common issue in 

industry and FAA programs designed to promote the greater good of the system by

encouraging voluntary reporting of errors and infractions by aviation personnel 

and operators without threat of disciplinary action or penalty. A CASS, in any

event, is concerned specifically with identifying and correcting deficiencies in the 

inspection and maintenance programs and should be designed to that objective, 

rather than specific event resolution, even if CASS analysts research specific 

events. 

b. Analytical tools and processes. While it is not necessary for an operator to implement 

any specific externally developed system, analytical tools or processes are available to assist in 

the analysis process. Examples of these are:

(1) Maintenance Error Decision Aid. Developed by the Boeing Human Factors 

Engineering group in collaboration with the FAA, airlines, and the International Association of 

Machinists for analyzing human performance issues related to maintenance errors and trends. 

Operators use the Maintenance Error Decision Aid to track events, investigate and prevent

maintenance errors, and identify contributing factors, corrective actions, and prevention 

strategies. A software analysis package has been developed to work with this aid and facilitate

analysis of systemic issues. 

(2) Managing Engineering Safety Health. Developed by the University of Manchester 

in collaboration with British Airways Engineering. This system is geared toward researching the

workplace and organizational environment in aircraft maintenance to find the issues with the 

greatest potential to contribute to human factors problems. The system uses software, diagnostic, 

and sampling tools. Managing Engineering Safety Health conducts anonymous survey-like 

assessments among personnel at the work location, which are then analyzed. (This is a more 

structured, data-intensive approach toward determining and monitoring personnel attitudes 

toward the system than the interview process discussed earlier. The industry has far less 

practical experience with Managing Engineering Safety Health than with the Maintenance Error

Decision Aid.) 

Page 26 Par 503 
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(3) Human Factors Accident Classification System Maintenance Extension. 

Developed by the U.S. Naval Safety Center in collaboration with the FAA for use in the air

carrier industry as well as naval aviation. This comprehensive system incorporates a number of 

analytical tools and has profiled maintenance errors and contributing conditions, permitting

development of potential prevention measures. While the Human Factors Accident 

Classification System Maintenance Extension may be more sophisticated than many operators 

would need, it demonstrates principles and techniques of software-aided analysis that could be 

applied to a CASS. 

c. Corrective action options. 

(1) Determining whether or not to proceed with a corrective action. Once the CASS

auditors and analysts have identified a problem or deficiency, the operator must determine if a

corrective action is warranted and, if so, the details of the corrective action. 

(2) CASS procedures regarding determining whether to proceed with a corrective 

action. CASS procedures should outline: 

How such a determination will be made; 

Who will make the determination; and 

What levels of review, if any, will be performed. 

(3) Developing the proposed corrective action. Technical area personnel should have 

primary responsibility for developing the proposed corrective action, as they would be most 

familiar with the technical workings of the area in question and would be sensitive to the

possibility of creating new problems as a result of the corrective action. CASS procedures 

should emphasize a team approach. Team members should include the CASS auditors or 

analysts, technical area personnel in the affected maintenance and inspection disciplines, and 

perhaps other affected areas such as training or flight operations. 

(4) Types of corrective actions. There are several possible types of general corrective 

actions or responses, depending on the outcome of the risk assessment. 

Prevent recurrence through engineering or system changes designed to eliminate

the risk. 

Accept the underlying cause of a trend or discrepancy, but reduce the risk through 

implementing controls or countermeasures. Examples are training, policy or 

procedure revisions, or warning devices. Other countermeasures might be 

modifying or introducing new equipment or technology.

Accept that under certain conditions a discrepancy may occur, and be prepared to 

contain or mitigate the results of that situation. A CASS does not necessarily

have to implement corrective actions for every apparently negative trend or 

finding. Analysis of findings or trends may identify problem areas that do not 

present safety hazards and that the operator is willing to accept, in accordance 

Par 503 Page 27 
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with its risk assessment process. For example, the operator might find that a 

higher than average number of component removals with “no fault found” occurs 

at a particular location. The operator might determine that the reason for this 

situation is that the aircraft spends insufficient time on the ground for line 

maintenance to completely isolate the fault. The operator might prefer to 

continue the brief turn times and simply switch components. This would be a 

business decision for the operator to make. However, more comprehensive 

corrective actions would be mandatory if the CASS detects that the inspection and 

maintenance programs lack adequate procedures and standards to meet the 

requirements of part 121 or part 135, as applicable. 

d. Written procedures for developing and implementing corrective actions. A CASS 

should provide written procedures for developing and implementing corrective action based on 

the operator’s organizational structure and the training of its personnel. The procedures should:

(1) Result in a specific corrective action plan that addresses basic questions of: 

Development and proposal of the corrective action; 

Analysis and final approval level of the corrective action, including who is 

responsible for approval of the corrective action; 

Who will implement the corrective action; 

How the responsible person will implement the corrective action; 

When the corrective action should be completed; 

Who will evaluate the outcome, and how, including identification of data to be

collected, awareness of the possibility of unintended consequences, and events 

that should trigger a response; 

Who will monitor the status of the corrective action, and how; and 

Reporting the status of the corrective action (to whom, with what frequency). 

(2) Maintain the appropriate role of auditors in developing responses to findings so that 

they continue to remain independent from the corrective actions they may subsequently audit. 

(3) Distinguish clearly between the technical area personnel’s responsibility for 

developing and implementing corrective actions, and CASS personnel responsibility for 

producing the findings and analysis and making sure the technical area involved develops and 

implements appropriate corrective actions. 

(4) Designate the position or organization responsible for evaluating and approving

proposed corrective actions. The CASS director or other designated manager may appoint a 

corrective action team to design and propose a corrective action. The team—which typically

represents a cross section of the departments involved in audits, operational data collection, 

Page 28 Par 503 
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analysis, and production—oversees the implementation of the corrective action. Technical and 

reliability control boards are most often used in conjunction with FAA-approved reliability

programs; however, a similar concept applies to a CASS, even if no FAA-approved reliability

program exists. 

e. Corrective action risk assessment. 

(1) CASS procedures regarding risk assessment. CASS procedures should: 

Specify that personnel will analyze a proposed corrective action carefully before 

its selection and implementation to ensure corrective action is necessary and will 

actually fix the problem and not lead to unintended negative consequences. 

Remind both CASS and technical area personnel of the need to consider the 

impact of the proposed corrective action on other aspects of the operation. This 

would include other areas of the inspection and maintenance programs, such as 

manuals. The corrective action may require coordination with other areas, such as 

flight operations, that might be affected. 

(2) Personnel involved in risk assessment. Technical area personnel play the key role 

in risk assessment, but the process should include the CASS analysts, who will act as resources 

in support of the technical area managers and bring risk assessment and systems analysis 

techniques to the process. The auditor and analyst should be qualified (through training or 

experience) in systems analysis and can contribute to the evaluation of a proposed corrective 

action by determining if the basic system elements have been considered. However, the 

technical personnel have the expertise to actually develop and implement the corrective action, 

and to evaluate it in practical terms. Thus, the corrective action is a result of cooperation 

between the technical personnel and the CASS personnel. 

Personnel working on the proposed corrective actions should ensure they consider issues of a 

timetable for the corrective action implementation, as well as the safety attributes of authority, 

responsibility, procedures, controls, process measurement, and interfaces. 

f. Corrective action plan. 

(1) With the root cause analysis complete, corrective action options identified, and risk 

assessment performed as appropriate, a final decision can be made on the proposed corrective 

action plan. The corrective action plan should address all relevant issues, including a timetable 

for completion of the action, with milestones, if appropriate. The appropriate technical 

department (and other departments, such as flight operations, if the corrective action goes 

beyond the inspection and maintenance organizations) should then implement the plan. 

(2) The CASS procedures should identify:

How this plan will be approved and at what level of the company, and 

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The parties responsible for implementing, monitoring, and ensuring all affected 

parties are notified, both within inspection and maintenance and externally, if

necessary.

504. Follow-up. 

a. Monitoring corrective actions. The CASS procedures should: 

(1) Specify how implementation of corrective actions will be monitored and evaluated. 

This may require the following: 

Follow-up audits of a specific area;

Regular communication from the affected technical area as to the status of the 

corrective action; and/or 

Other forms of verification action by the auditors or analysts tracking the 

implementation. 

(2) Identify the person or entity (such as a CASS board) responsible for determining if 

any changes in the status of a corrective action are acceptable. The CASS auditors or analysts

have the duty of ensuring the corrective action has been implemented in accordance with the 

established timetable or, if not, determining why the timetable has changed. 

(3) Include responsibilities and guidelines for: 

Tracking the implementation of corrective actions in accordance with the 

timeline;

The role of auditors, managers, management committees, and senior management; 

How automation or computerized systems will be used; 

How risk assessment and/or systems analysis will be used to guard against 

unintended consequences; 

Measures to evaluate the effect of the corrective action; and 

The affected technical area to communicate the status of the corrective action to

the person responsible for monitoring implementation. 

b. Getting help from a manufacturer. In some cases, the operator may require data or 

assistance from a manufacturer in correcting a deficiency detected by the CASS. Manufacturers 

may not always assign these issues the same priority as the operator does. The operator should 

offer guidance in its CASS procedures, based on its particular experience, on how CASS and 

other personnel should address requested assistance or information from manufacturers, and how 

to proceed in case of unsatisfactory or slow responses. This may include developing a 

standardized letter citing the need for this information or assistance to satisfy the requirements of

Page 30 Par 503 
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§ 121.373, § 135.431, or other pertinent regulations. It may also include working with the FAA 

principal inspector to find solutions. 

c. Follow-up surveillance plan. CASS procedures should include how to determine the 

level of follow-up audits for verifying corrective action implementation. For example, based on 

the risk assessment or complexity of the corrective action, the designated CASS analyst or team 

may schedule special or more frequent audits. They may also change the data collection process 

or institute other means of verification. The FAA expects the operator to have a well-designed 

and logical process to design the follow-up actions. 

The information and analysis performed through the closed-loop, continuous cycle of 

surveillance, investigations, analysis, and corrective action permits the operator to refine its audit 

and data collection priorities through the risk assessment process.

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CHAPTER 6. PERSONNEL WHO PERFORM CASS FUNCTIONS 

600. Personnel managing CASS functions. 

a. A CASS should include a decisionmaking body at a relatively high management level to 

oversee or carry out CASS functions. These oversight groups could include: 

(1) Technical boards concerned with performance and other technical issues;

(2) Administrative boards that may have broader decisionmaking authority to act on 

technical recommendations; or 

(3) A single board combining both functions. 

The key concept is that there be a decisionmaking body at a relatively high management level to 

monitor the CASS and to make critical decisions in a timely manner. Typically, at a smaller

operator, this committee or board may be composed of the president of the company and the

directors of maintenance and flight operations. Typically, at a larger operator, participants may

be managers from several departments, such as maintenance and engineering, quality assurance,

and operations. 

b. If the operator uses committees or boards as major decisionmaking bodies for CASS 

issues, members of these bodies should: 

(1) Have an appropriate technical background, and 

(2) Be thoroughly familiar with the role and functioning of the CASS, systems analysis, 

and the evaluation of the root cause analysis and proposed corrective actions submitted for their 

review. 

The operator should consider requiring participants in such committees or boards to receive 

training or orientation on these issues to ensure they can provide critical evaluation. The 

membership of such boards and committees as well as the basic operating procedures and 

records should be described in the CASS document. 

601. CASS personnel training and experience. 

a. Maintenance. Each operator should determine the precise mix of training and experience 

needed by the operator’s auditors and analysts. In general, auditors and analysts should: 

(1) Have sufficient maintenance background applicable to the operator’s program to 

ensure they are familiar with inspection and maintenance procedures, technical documents, and 

aircraft systems. 

(2) Be able to understand and interpret the answers and data they see, as well as evaluate 

facilities, equipment, and processes they observe. While they are unlikely to have specialized

knowledge in all of the areas over which they conduct surveillance, a foundation of technical 

expertise is important. 

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b. Surveillance and analysis. Auditors and analysts need training and/or experience in the 

functions they are responsible for surveilling and analyzing. It is also essential that they have 

training and/or experience in the following areas:

Systems analysis;

Auditing techniques; 

Risk assessment and risk management; 

Root cause analysis; and 

Human factors. 

Additionally, operators may seek specialized training in specific quality processes or systems for

their CASS personnel, such as: 

(1) ISO 9000, a quality system set of standards developed by the International 

Organization for Standardization that seeks to standardize processes into organized and 

documented systems. 

(2) Six Sigma, which is process-oriented from an intensively data-oriented, statistical

approach. 

c. Technical. Persons who collect and analyze operational data may require specialized

technical backgrounds, such as engineering. This will depend on the complexity of the 

operational data the operator collects. These personnel may work in the unit conducting an 

FAA-approved reliability program or in an independent data collection and analysis system. 

d. Summary of experience and training for CASS personnel. The operator’s CASS 

document should reflect that the carrier has considered the type of experience and training, both 

initial and recurrent, appropriate to the auditors and analysts in its operation. Areas to consider 

include those listed in the table below: 

Page 34 Par 601 
04/21/03 AC 120-79 

Subject Area Auditors Audit Analysts Operational Data

Analysts

Part 121/135 (as 

applicable); 

Operations 

Specifications 

Initial and recurrent Initial and recurrent Initial and recurrent 

Systems Analysis 

Training 

General training in 

quality standards 

General training in 

quality standards, 

statistics, and/or 

widely used industry

courses such as 

ISO 9000 

General training in 

quality standards, 

statistics, and/or 

widely used industry

courses such as 

ISO 9000 

Audit Training Initial and recurrent; 

Coordinating

Agencies for 

Supplier’s Evaluation 

(C.A.S.E.) training, if 

applicable 

Experience or training

in conducting and 

reporting results of 

audits 

Statistical 

investigation 

experience or training

Risk Assessment 

Training 

Initial and recurrent Initial and recurrent Initial and recurrent 

Root Cause Analysis 

Training, Including 

Human Factors 

Initial and recurrent Initial and recurrent Initial and recurrent 

Technical 

Competence 

FAA mechanic 

certificate, 

engineering, or other 

maintenance 

background 

FAA mechanic 

certificate, 

engineering, or other 

maintenance 

background 

FAA mechanic 

certificate, 

engineering, or other 

maintenance 

background 

Educational

Background 

Related education or 

training may partially

fulfill similar 

qualification 

requirements set by

operator 

Related education or 

training may partially

fulfill similar 

qualification 

requirements set by

operator 

Related education or 

training may partially

fulfill similar 

qualification 

requirements set by

operator 

Par 601 Page 35 (and 36) 

04/21/03 AC 120-79 

CHAPTER 7. COMMUNICATION BETWEEN CASS PERSONNEL AND 

OTHER DEPARTMENTS 

The procedures for communicating CASS information and results internally to interested parties 

within the operator and, as applicable, externally (for example, vendors, the FAA) vary

depending on factors such as the size and nature of the operation, level of automation, and the 

CASS procedures themselves. The number and complexity of the standardized communications 

processes, such as forms or electronic mail messages with standard distribution, should be 

appropriate to the overall size and scope of the operator’s operation and CASS. 

700. Communicating specific CASS results and actions. 

a. The operator should develop appropriate standard communication processes for all 

aspects of the CASS to assist in standardizing procedures, including the following: 

(1) Audit checklists and results. 

(2) Analysis procedures and results. 

(3) Records of audit/analysis findings — internal. 

(4) Records of audit/analysis findings — external. 

(5) Corrective action forms and/or action plans. These forms should address system 

considerations to ensure there is a clear understanding of when the corrective action will be 

implemented, who is responsible, and what the impact will be on written procedures. 

(6) Information for monitoring and follow-up of corrective action. The processes should 

also assist in tracking the implementation of corrective actions once underway. 

(7) Periodic status reports to senior management and to the FAA. 

b. The CASS description should address such issues as the following: 

(1) Who is responsible for keeping these standard communication processes 

up-to-date and available;

(2) Who is responsible for completing the standard communication processes; 

(3) Where are communications sent, who must respond, and how are responses tracked; 

and 

(4) How, where, and for how long completed records are retained. 

701. Educating personnel on CASS. 

A CASS should include procedures and responsibility to create some form of communication 

between the area responsible for the CASS, other areas of the company, and the FAA. This may

Par 700 Page 37 
AC 120-79 04/21/03 

be accomplished through training, newsletters, bulletins, meetings, or other formats determined 

by the operator. One purpose of such communication is to educate mechanics and other 

departments that feed information and data into the CASS about why these data are necessary, 

what is done with the data, and how this process benefits the operation. 

702. Communications with personnel outside the CASS. 

The FAA expects a good communication system to meet the objectives in this section. Each 

operator must determine which system is best for its operation. 

a. A CASS should provide for regular, structured communications within the CASS 

structure and between the CASS and any other resources involved in decisionmaking for the 

operator. Examples of these would include: 

(1) Avionics and other shops; 

(2) Cabin safety organization; 

(3) Engineering department and FAA-approved reliability program organization; 

(4) FAA certificate management office or principal inspector; 

(5) Flight operations; 

(6) Ground operations; 

(7) Inspection department; 

(8) Internal evaluation program; 

(9) Maintenance control; 

(10) Maintenance operations; 

(11) Manufacturers’ technical representatives;

(12) Purchasing; 

(13) Quality assurance;

(14) Receiving inspection;

(15) Recordkeeping organization; 

(16) Safety program; 

(17) Senior management; 

(18) Stores department; and 

(19) Training departments. 

Page 38 Par 701 
04/21/03 AC 120-79 

b. The communications mechanisms should include a feedback loop designed to ensure that 

any changes implemented as a result of corrective actions are functioning as intended and are 

improving the process. This level of communication may be accomplished through a variety of 

means, including the following: 

(1) Periodic (weekly, monthly, quarterly) statistical and narrative CASS reports on 

trends, findings, and the status of corrective actions. 

(2) Periodic CASS meetings to discuss trends or specific problem areas. Such meetings

might be informal but frequent, such as at very small operators where the relevant managers 

work in close proximity, or more structured and formal, such as at larger operators where

specific boards or committees may be designated. 

(3) CASS board or committee meetings, including senior management, possibly on a

monthly or bimonthly basis. Even if meetings are somewhat informal, minutes should be kept. 

c. Typically, operators with programs incorporating statistical performance standards (alerttype programs) develop a periodic (monthly) report, with appropriate data displays, summarizing

the previous month’s activity. To help evaluate the effectiveness of the total maintenance

program, the report should cover all aircraft systems controlled by the FAA-approved reliability

program. An operator without an FAA-approved reliability program may find that using a 

similar report can enhance its CASS.

Par 702 Page 39 (and 40) 

04/21/03 AC 120-79 

CHAPTER 8. HOW THE CASS DIFFERS FROM AND RELATES TO

OTHER PROGRAMS 

800. Summary of other programs. 

The operator’s description of the CASS should identify other related programs in which the 

operator participates and explain how CASS relates to those programs and/or differs from them. 

Experience has shown that certain other programs are potential sources of information for the 

CASS, while other programs may be integrated into a CASS. Some programs have been 

mistakenly assumed to be so similar to a CASS that the operator might neglect an important 

aspect of the CASS. Therefore, the CASS documentation should describe the relationship 

between the CASS and programs such as the: 

a. FAA-approved Reliability Program; 

b. Internal Evaluation Program; 

c. Safety Program; 

d. Voluntary Disclosure Reporting Program; 

e. Coordinating Agencies for Supplier’s Evaluation; 

f. Aviation Safety Action Program; and 

g. Aviation Safety Reporting Program. 

801. Discussion of individual programs. 

a. FAA-approved reliability program. According to AC 120–17, Maintenance Control by

Reliability Methods, the concept of reliability control was developed to maintain an acceptable 

level of reliability and evolved based on FAA and airline efforts to develop more responsive 

methods of controlling maintenance without sacrificing safety or FAA regulatory responsibility. 

An FAA-approved reliability program includes systems for data collection and analysis, 

corrective action, statistical performance standards, data display and reporting, maintenance 

program adjustments, and process changes. AC 120–17 defines an acceptable level of reliability

as maintaining failure rates below a predetermined value. Under the program, the operator may

adjust maintenance, inspection, and overhaul intervals up to a specific limit without prior FAA 

approval. 

Typically, larger operators have an FAA-approved reliability program, but the operational data

collection and analysis requirements of such a program usually exceed the resources or 

requirements of smaller and even most medium-sized operators and generally are greater than 

what would be necessary for those operators’ CASS. However, if an operator does have an 

approved reliability program, this may be incorporated into the CASS as the means of

performing operational data collection and analysis to monitor the effectiveness of the inspection 

and maintenance programs. That operator’s CASS procedures should describe how the approved 

reliability program is integrated into the CASS. An FAA-approved reliability program cannot 

Par 800 Page 41 
AC 120-79 04/21/03 

substitute for a CASS because the reliability program does not include the broader auditing

surveillance and analysis of the full range of elements of the inspection and maintenance

programs, nor does it include the complete processes for developing and implementing

corrective actions. 

This AC is not intended to describe FAA-approved reliability programs. However, CASS 

operational data collection needs are typically similar to, if less extensive than, those of an

approved reliability program. An operator may, within its CASS, establish a program similar to 

an FAA-approved reliability program for the purpose of collecting and analyzing operational 

data. In such circumstances, the carrier would not be permitted to adjust its inspection or

maintenance program without FAA approval. Additionally, the operator must ensure its 

operational data collection program meets the needs of its CASS. 

It is common to use “reliability,” in a generic sense, in reference to dispatch availability of

equipment or in relation to equipment failure rates. If an operator’s CASS manual or document 

uses this terminology, it should distinguish whether the reference is to an FAA-approved 

reliability program or to generic reliability. 

b. Internal evaluation program. An internal evaluation program is a voluntary program to 

provide measurement of an operator’s internal processes and procedures to assess whether they

are adequate and functioning properly. An internal evaluation program should be independent of 

all other programs and systems and could be a useful tool to evaluate a CASS, as well as other 

systems or programs, such as the operator’s safety program. An internal evaluation program is a 

very high-level review to provide information to senior management as to how well critical

programs, such as a CASS, are working. It would not be a substitute for a CASS. An internal

evaluation program is a broader system evaluation program and is less “audit-oriented” than a 

CASS, although both use a system evaluation approach. An internal evaluation program poses 

questions necessary to determine if the operator’s systems, such as its CASS, are effective and 

efficient, and if the current program would support further growth. 

AC 120–59, Air Carrier Internal Evaluation Programs, describes the internal evaluation program. 

The internal evaluation program should not be misunderstood as a program that replaces existing

regulatory auditing requirements such as a CASS. Audits are a very minor part of an effective

internal evaluation program. 

c. Safety program. Certificate holders conducting operations under part 121 are required to 

have a director of safety or equivalent position unless the FAA permits a deviation in the

required management positions according to 14 CFR § 119.65. The director of safety should 

oversee a function that addresses the range of risks involved in commercial aviation, including

flight operations, maintenance, and ground operations. The director of safety should manage a 

comprehensive safety program with a variety of elements, such as investigations of and a 

reporting system for accidents and incidents, safety audits and inspections, operational risk 

assessment, and trend analysis. 

Page 42 Par 801 
04/21/03 AC 120-79 

Certificate holders conducting operations under part 135 are not required to have a director of 

safety position. Nevertheless, the FAA encourages these operators to designate a company

management official or manager to monitor and evaluate flight, maintenance, and ground safety

practices, procedures, and programs. 

d. Voluntary Disclosure Reporting Program. AC 00–58, Voluntary Disclosure Reporting

Program, provides guidance on procedures for certificate holders to use when voluntarily

disclosing to the FAA apparent violations of certain Federal Aviation Regulations. An 

operator’s participation in the program may reveal important information regarding maintenance

issues and lead to the development of comprehensive fixes relevant to the inspection and 

maintenance programs a CASS oversees. 

Under this program, the operator may voluntarily report violations of regulations that it discovers 

and avoid certain enforcement consequences. Some operators may be concerned about 

discussing regulatory infractions in widely disseminated CASS documents, even if they are 

addressed through the Voluntary Disclosure Reporting Program. 

It is not required that a CASS address disclosures made under the Voluntary Disclosure 

Reporting Program. However, the FAA recommends that the operator consider, in developing

its CASS procedures, whether to attempt to include information from voluntary disclosures in its 

CASS in any fashion. For example, CASS personnel may be the same personnel as those who 

handle voluntary disclosures. They may therefore be able to use “de-identified” information 

from voluntary disclosures to point to areas where additional auditing may be necessary. CASS 

personnel should be aware of comprehensive fixes developed in conjunction with the Voluntary

Disclosure Reporting Program. These are, after all, precisely the types of systems or procedural 

modifications that an effective CASS is seeking, to avoid adverse audit findings or unwanted 

operational performance. 

e. Coordinating Agencies for Supplier’s Evaluation. Coordinating Agencies for 

Supplier’s Evaluation (C.A.S.E.) is a cooperative effort within the airline industry to audit 

suppliers and vendors and to analyze, control, and determine the acceptability of vendors 

supplying parts and maintenance services to participating airlines. According to FAA Order 

8300.10, Airworthiness Inspector’s Handbook, the FAA has determined that use of C.A.S.E. 

audits can satisfy some of the requirements of §§ 121.373 and 135.431. The use of the C.A.S.E. 

program to satisfy these requirements must be authorized on operations specifications. 

If the operator participates in C.A.S.E., the CASS procedures should address whether or how the 

CASS will use C.A.S.E. audits and the basis for that decision. If the functions being audited 

depend on the specifics of the operator’s program, a C.A.S.E. audit would probably not suffice. 

The important point is that the operator have a written policy and procedures for when and how 

to use C.A.S.E. audit results in its CASS. 

f. Aviation Safety Action Programs. AC 120–66, Aviation Safety Action Programs, 

describes this program for the voluntary reporting of safety issues and events by employees, such 

as crewmembers and mechanics, of certain certificate holders. Aviation Safety Action Programs 

involve the collection, analysis, and retention of safety data that would otherwise be 

unobtainable. Such data can be important input to a CASS. 

Par 801 Page 43 
AC 120-79 04/21/03 

g. Aviation Safety Reporting Program. AC 00–46, Aviation Safety Reporting Program, 

describes this program which uses the National Aeronautics and Space Administration (NASA) 

as a third party to receive aviation safety reports. The Aviation Safety Reporting Program invites 

crewmembers, maintenance personnel, and others to report to NASA actual or potential 

discrepancies and deficiencies involving aviation safety. NASA designed and administers the 

Aviation Safety Reporting System to facilitate the program. These reports may help CASS 

personnel identify areas of potential concern within their own company based on industry-wide 

trends or experiences identified by NASA.

Page 44 Par 801 
04/21/03 AC 120-79 

CHAPTER 9. HOW TO DETERMINE IF THE CASS IS WORKING 

PROPERLY

900. Why a CASS should be evaluated. 

As with any system or program at the operator, the CASS itself should be evaluated (that is, a 

process measurement should be accomplished) so that any personnel responsible for overseeing

the CASS, such as the operator’s top management, may be confident that the CASS is 

accomplishing its function. Verifying that a CASS is working as intended is also a primary task 

of the FAA principal inspector. 

A common misconception is that an operator can evaluate its CASS based solely on the results of

the inspection and maintenance programs. That is, it is common to assume that if the aircraft are

consistently airworthy, the CASS must be doing its job. However, this favorable result may

occur for other reasons, such as the extraordinary diligence or memory of a few individuals. The

purpose of the CASS is to ensure, with a system-oriented, structured approach, that inspection 

and maintenance programs are properly executed and are effective consistently and by design

rather than by luck. The operator should not assume that good maintenance is synonymous with 

the CASS working properly. 

Thus, personnel with CASS oversight responsibilities (including the FAA) require a different 

approach to determine if the CASS is indeed working properly. They need to know that the 

operator has complete CASS policies and procedures to monitor and evaluate the inspection and 

maintenance programs, that these policies and procedures are being carried out, and that they

work. For example, to ensure the CASS is functioning properly, a senior operator manager 

would not analyze component removal rates, but rather verify that the CASS is analyzing

component removal rates, detecting trends as appropriate, and implementing corrective actions 

when necessary. The operator should have procedures, either in the CASS manual or referenced 

in the CASS manual but contained in another document (such as its internal evaluation program 

manual), for evaluating the CASS and informing top management of the effectiveness of the

CASS, separate from the effectiveness of the inspection and maintenance programs. The

regulations not only require inspection and maintenance programs that meet many specific

standards, they also separately require a system to monitor those programs. 

901. Steps to evaluate the CASS. 

The FAA expects an operator to develop its own methods of evaluating whether its CASS is 

working properly, including how the operator intends to measure whether it has allocated

sufficient staffing and resources to its CASS. 

a. System safety attributes. Determine that the CASS addresses applicable system safety

attributes (responsibility, authority, procedures, controls, process measurement, and interfaces). 

If the operator has an internal evaluation program that follows this format, it would provide the 

operator’s senior management with an appropriate means of evaluating the CASS. That would 

be one way, but not the only way, to evaluate a CASS.

Par 900 Page 45 
AC 120-79 04/21/03 

b. Indicators. The following questions may be useful in indicating whether the CASS is 

designed properly or working as intended, although the operator may identify other indicators: 

(1) Are CASS personnel sufficiently independent of the areas they audit? Are they

trained specifically in their CASS responsibilities?

(2) Are the resources allocated to the CASS sufficient to permit timely analysis of audits 

and data, as well as follow-up to corrective actions? Or are there delays in responding to 

findings and implementing corrective actions?

(3) Are CASS personnel able to perform their duties in accordance with reasonable 

schedules?

(4) How many findings are produced by the CASS, and what are the trends?

NOTE: CASS is supposed to produce findings, so absolute numbers, even

high numbers of findings, are not necessarily a negative outcome; if

combined with effective corrective actions and follow-up action, numerous

CASS findings could be a positive indicator that the CASS is doing its job of 

detecting deficiencies and yielding appropriate, well-analyzed corrective 

actions. Trends are important, however. The same types of findings should 

not recur often once the CASS has addressed them. 

(5) Have an unusually large number of unplanned maintenance events occurred within a 

specified time (for example, 21 days) after a substantial inspection or maintenance task? If so, 

does an investigation indicate there are deficiencies in the inspection and maintenance programs 

that should have been averted by the CASS, or can the anomaly be attributed to other factors?

(6) Does analysis indicate recurring problems in areas previously thought to have been 

addressed by corrective actions?

(7) Are new problem areas coming to light? (This would be indicative of the CASS 

working to detect new issues.) 

(8) Are CASS corrective actions resulting in new problem areas, reflecting insufficient 

risk or system analysis before the implementation of these corrective actions?

(9) How do CASS results compare with outside audit results, such as those conducted by

the DoD or the FAA?

(10) Have regulatory violations occurred that the CASS might have averted?

(11) Does operator senior management understand and support the CASS?

(12) Are CASS auditors and analysts encouraged to consider all possible aspects of an 

issue, including the role of senior management, when developing corrective actions?

Page 46 Par 901 
04/21/03 AC 120-79 

(13) Has the CASS evolved into a punitive process with the result of discouraging open 

participation of company personnel, or do personnel cooperate actively and offer input to the 

CASS?

(14) Are all areas of the inspection and maintenance programs undergoing CASS audits 

in accordance with a schedule based on a process of risk assessment and prioritization?

(15) Do the depth and quality of the audit reports and analysis reflect that personnel have 

sufficient time and resources?

c. Senior management review. Senior management should review CASS issues on a 

monthly or bimonthly basis. Meetings of this sort, possibly of CASS or maintenance 

management committees or boards, may be held to discuss findings, analysis, and the progress of

corrective actions. These meetings may address statistical data and trends, depending on the 

operator’s size and operation and their ability to produce comprehensive statistical reports.

Par 901 Page 47 (and 48) 

04/21/03 AC 120-79 

CHAPTER 10. THE ROLE OF THE FAA IN RELATION TO AN

OPERATOR’S CASS 

1000. The FAA’s general role. 

As with any applicable aviation regulation, an operator must understand that it holds the primary

responsibility for compliance, not the FAA. The FAA’s role is not to design the CASS for each 

operator, but to ensure the operator has satisfactory policies and procedures in place. For 

example, the FAA will not provide the industry with an exhaustive list of data to be collected and 

analyzed because of the wide variation in the nature and scope of their operations. However, the 

FAA expects each operator with a CASS to demonstrate that its CASS includes a process for 

selecting and periodically reevaluating data sets appropriate for its operation and for monitoring

the inspection and maintenance programs. The FAA also expects each operator to have a logical

and current reason for selecting the data sets it collects. 

1001. The FAA principal inspector’s role. 

The term FAA principal inspector, as used in this AC, is generally intended to mean the principal 

maintenance inspector (PMI). However, the principal avionics inspector (PAI) also plays an 

important role in the oversight of the operator’s CASS and shares many of the same 

responsibilities as the principal maintenance inspector (PMI). The FAA principal inspector: 

a. Works with the operator in developing the CASS, in providing guidance, and in ensuring

the operator’s CASS meets the intent of the regulation. 

b. Reviews the operator’s CASS records, such as results of audits and analysis, corrective 

action, and follow-up. Therefore, it would be useful for the operator and the principal inspector 

to have a common understanding of how long the operator will retain these records, not only in 

terms of usefulness to the CASS but also to help the inspector determine the operator is properly

executing its CASS. 

c. Meets on a regular basis with managers in the maintenance, inspection, and quality

assurance areas, particularly with the person responsible for the CASS. The operator’s CASS 

should provide one of the best barometers of the overall status of the inspection and maintenance 

programs, how they are being executed, whether they are effective, and whether change is being

implemented as necessary. 

d. Meets occasionally with senior management to determine how well they understand and 

support the CASS.

Par 1000 Page 49 (and 50) 

04/21/03 AC 120-79 

CHAPTER 11. ADMINISTRATIVE INFORMATION 

1100. How to obtain FAA publications. 

a. AC 00.2, Advisory Circular Checklist, as amended, contains a listing of all ACs. 

AC 00–44, Status of Federal Aviation Regulations, as amended, contains a listing of the CFR 

and current prices. You can also obtain a copy of current regulations online at 

http://www.access.gpo.gov/ecfr/. You can obtain the CFR and ACs, for which there is a fee, 

from the following address: 

Superintendent of Documents 

P.O. Box 371954 

Pittsburgh, PA 15250-7954 

b. To be placed on our mailing list of free ACs, contact: 

U.S. Department of Transportation 

Subsequent Distribution Office 

SVC-121.23 

Ardmore East Business Center 

3341 Q 75th Avenue 

Landover, MD 20785 

c. Our Web site is located at http://www.faa.gov. 

Par 1100 Page 51 (and 52) 

04/21/03 AC 120-79 

 Appendix 1 

APPENDIX 1 

SAMPLE CASS FOR A LARGE OPERATOR 

Type of Operator 

Fleet composition 150 turbojet airplanes; B–737, B–757, A–320.

Number of maintenance base 

and line stations 

Base station and 25 line stations.

Proportion of maintenance 

contracted to third parties 

All letter checks, overhauls, and major maintenance

performed in-house. Some line maintenance, parts 

work, and off-wing engine work is contracted.

Scheduled or on-demand Scheduled (part 121).

Size and structure of

inspection and maintenance

organizations 

Engineering and maintenance organizations include 

extensive engineering capability, quality assurance

department, full range of shops for support, 

components, electronics, engines, etc.

CASS Management and Planning 

General priority 

This operator prioritizes in the following manner:

(1) Safe operations (air and ground). 

(2) Detect and prevent noncompliance. 

(3) Improve operating efficiency. 

CASS written procedures (A System Safety Attribute — Procedures)

The CASS written procedures are located in a separate CASS manual. The CASS appendix is 

detailed, including specific procedures for root cause and systems analysis and discussion of how 

to address human factors. 

CASS in the operator organization 

The senior vice president of engineering and maintenance actively supports the CASS. The 

CASS specifically appears on the functional organizational flowchart. 

Authority for CASS (A System Safety Attribute — Authority) 

The director of quality assurance holds the authority for the CASS. 

Responsibility for CASS (A System Safety Attribute — Responsibility)

The CASS board is responsible for the CASS. The board is chaired by the manager of the 

CASS, who reports to the director of quality assurance.

Policy for CASS auditor/analyst independence from production (A System Safety

Attribute — Controls)

CASS auditors/analysts are in a separate department under quality assurance. Operational data 

collection and analyses are assigned to the reliability group (within the operator’s FAA-approved 

 Page 1 
AC 120-79 04/21/03 

Appendix 1 

reliability program) in the engineering department. The reliability group reports CASS 

information directly to the CASS board. 

Policy regarding personnel actions resulting from CASS findings/results

The operator’s policy is consistent with its participation in Aviation Safety Action Programs and 

the Voluntary Disclosure Reporting Program. Inadvertent errors do not lead to disciplinary

action or FAA enforcement action. Full reporting and disclosure is encouraged to facilitate 

system corrections. 

Surveillance and Analysis of Performance of Inspection and Maintenance 

Audits

Responsibility Manager of CASS.

Prioritization CASS board develops a surveillance plan based on risk assessment.

Cycles Each area is audited semiannually to every 3 years, depending on 

priority. Annual audit plan is updated quarterly.

Scope

CASS covers all internal and third-party areas of maintenance and 

inspection. Coordinating agencies for Supplier’s Evaluation audits 

may indicate the need for follow-up audits or may be integrated into 

the CASS.

Process

Full-time CASS auditors use checklists and conduct annual 

interviews of personnel at all levels of maintenance and inspection to 

uncover concerns or latent problems. The CASS department receives 

reports of all maintenance-related events, such as rejected takeoffs, 

for analysis and use in risk assessment for audits. Special audits may

be scheduled as needed. The CASS also reviews self-audits from all 

departments. Some vendor audits are conducted by document 

reviews, written questionnaires, telephone follow-up, or combinations 

of these. 

Follow-up is required if preliminary results raise concerns.

Flow 

Initial results are reported to the manager of the CASS. The CASS 

board reviews summaries of all findings/initial analyses and details of

issues as deemed necessary by the manager of CASS. 

Analysis 

Responsibility

Auditors conduct preliminary analysis based on specific experience 

and training and internally developed guidelines that channel analysis

to system root causes.

Perform 

preliminary 

root cause 

analysis 

Auditor/analyst.

Classify hazards/ 

perform risk 

assessment 

CASS board and analysts.

Flow

The CASS board transmits results to the affected department, which 

assigns personnel to participate on the corrective action team under 

direction of the CASS board.

Page 2
04/21/03 AC 120-79 

 Appendix 1 

Surveillance and Analysis of Effectiveness of Inspection and Maintenance 

Operational data collection

Responsibility Manager of CASS.

Prioritization The reliability group determines priority based on risk assessment.

Scope

Extensive. Ranges from pilot reports, engine condition monitoring, 

mechanical delays, and teardown reports to data from special 

authorizations such as Category II/III, extended range operation with

two-engine airplanes, and operations in reduced vertical separation 

minimum airspace and minimum navigation performance specifications 

airspace.

Process

In accordance with the operator’s FAA-approved reliability program. 

Data collection is oriented toward detecting trends, positive or negative,

before occurrence of events. However, data collection (and analysis) 

may vary based on maintenance-related events. The list of operational 

data sets collected is formally reviewed by the CASS board every

two years to determine if it needs to be adjusted. The initial list is based 

on AC 120–17 and CASS board determinations.

Flow The reliability group, although located within the engineering

department, has a direct reporting relationship to the manager of CASS.

Analysis of operational data 

Responsibility Reliability group.

Prioritization Reliability board.

Process Technical experts within the reliability group perform the analysis and 

make preliminary determination of possible root causes.

Flow Results are reported to the manager of the CASS and the CASS board.

Corrective Action 

Final root cause analysis 

Responsibility Manager(s) of technical area(s) affected.

Procedures

The director of CASS transmits preliminary analysis results to the

manager of the affected department, who designates technical personnel 

to coordinate final root cause analysis with the auditor/analyst. CASS

auditor/analyst oversees the process and ensures the formal root cause 

analysis process, including human factors and systems analysis, is

followed. 

Use of specific

analytical 

systems

Internally developed analytical process and industry tools.

Flow The auditor/analyst and technical department develop a joint final report 

and submit it to their respective managers.

 Page 3 
AC 120-79 04/21/03 

Appendix 1 

Determination of corrective action options 

Responsibility

The CASS board appoints a corrective action team, to include the CASS 

auditor/analyst, reliability group, technical area(s) affected, and related 

areas potentially affected (for example, flight operations).

Procedures

The team leader is from the technical area affected. Perform risk 

assessment of the problem and develop corrective action options. The 

CASS auditor/analyst or reliability group representative does not 

propose corrective actions but reviews options for systems 

considerations and relevance to root cause analysis.

Flow The manager(s) of the affected area(s), working with the team, transmits 

options to the CASS board.

Selection of corrective action and corrective action plan

Responsibility CASS board.

Procedures

Decision based on a priority for safety and regulatory compliance. Risk 

assessment is the basic tool to support the decision. CASS personnel do 

not participate in development of the corrective action but review for 

systems considerations and relevance to root cause analysis.

Flow

Depends on the level of the problem and the corrective action. Routine 

issues may be resolved at the team level with direct implementation by

the affected area manager; the CASS board is then advised of this 

action. More significant program changes may require prior review and 

concurrence from the CASS board. Highest-level decisions may be 

raised by the CASS board to the director of quality assurance or the

senior vice president of engineering and maintenance.

Follow-up 

Responsibility Manager of CASS.

Procedures

CASS auditor/analyst or reliability group, as applicable, assigned to 

develop follow-up plan based on seriousness of the problem. Follow-up 

may include communications from technical area verifying

implementation, follow-up audits or data collection, and/or follow-up 

evaluation.

Flow

Technical area reports implementation status to manager of the CASS, 

who informs the CASS board. The CASS board may inform the 

director of quality assurance if problem is sufficiently serious or

implementation plan is not followed.

NOTE: The above provide many examples of the system safety attributes — controls and

procedures. 

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04/21/03 AC 120-79 

 Appendix 1 

Communications Between CASS and Other Personnel (A System Safety

Attribute — Interfaces)

Communication of specific CASS results and actions 

Responsibility CASS board.

Procedures

Audits based on updated checklists. Operational data are collected and 

stored in computer systems; some analysis and alerting features are 

automated. Audit and analysis results communicated through company

electronic mail system, with acknowledgements. Corrective action 

tracking through computerized database system.

Flow

Electronic mail and standard electronic reports of information flow 

among CASS board, corrective action teams, technical areas, and 

director of quality assurance, when applicable.

Communications with inspection and maintenance personnel 

Responsibility CASS board.

Procedures

CASS initial and recurrent training included for all personnel, including

lectures from CASS personnel. Monthly newsletter summary to 

production areas regarding CASS activities.

Flow

CASS department works with training and company communications 

department, and receives feedback from managers and supervisors, 

particularly in the maintenance and inspection areas.

Interfaces (A System Safety Attribute — Interfaces)

Responsibility: CASS board. 

Flow: Communications channeled through manager of the CASS. 

Procedures: 

TO CASS Board FROM CASS Board 

Reliability group provides regular 

reports on analyses results, trends, and 

concerns. 

Feedback to technical areas regarding

findings, trends, concerns, and follow-up 

results. 

Auditors/analysts provide regular reports 

on findings, analyses, trends, and 

concerns. 

Feedback to Voluntary Disclosure 

Reporting Program manager regarding

proposed comprehensive fixes; 

coordination with manager of the CASS. 

Voluntary Disclosure Reporting

Program manager provides summaries 

of disclosures and proposed 

comprehensive fixes for CASS review 

and input. 

Monthly reliability analysis summaries

and other CASS summaries for 

distribution to the vice president of 

engineering and maintenance; director 

of quality assurance and other senior

management; department managers in 

maintenance, inspection, flight, and 

ground operations; internal evaluation 

program; safety office; and FAA 

principal inspector. 

 Page 5 
AC 120-79 04/21/03 

Appendix 1 

TO CASS Board FROM CASS Board 

Copies of Coordinating Agencies for 

Supplier’s Evaluation audit results. 

CASS reports reflect Voluntary

Disclosure Reporting Program 

comprehensive fixes without detailing

the initiating circumstances. 

CASS auditors review reports from 

company Aviation Safety Action 

Programs and at least annually review 

maintenance-related Aviation Safety

Reporting Program reports for 

consideration in setting audit and 

operational data collection priorities. 

Semiannual summary report to chief 

executive officer. 

Copies of reliability reports and CASS 

summaries to FAA principal inspector. 

The FAA principal inspector has online 

access to CASS reports and documents

such as summaries, analyses, trends, and 

corrective action tracking.

CASS board meeting minutes. 

Personnel Who Perform CASS Functions 

Full-time auditors and analysts; in some cases, an auditor may also be an analyst. 

All members of the CASS board who have not participated in specific CASS training receive a 

total of 16 hours initial training covering CASS, root cause and systems analysis, and human 

factors. 

Company has hired a human factors specialist to address issues across all departments and to 

participate on the CASS board. 

How the Operator Evaluates Its CASS (A System Safety Attribute — Process 

Measurement)

Responsibility Senior vice president of engineering and maintenance.

Procedures Internal evaluation program evaluates CASS annually. 

Flow

Internal evaluation program reports on CASS are transmitted directly to 

the chief executive officer and to the senior vice president of 

engineering and maintenance.

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 Appendix 2 

APPENDIX 2 

SAMPLE CASS FOR A MEDIUM OPERATOR 

Type of Operator 

Fleet composition 75 turboprop and turbojet airplanes; ATR–42, Canadair 

Regional Jets.

Number of maintenance base 

and line stations 

Base station and 5 line stations.

Proportion of maintenance 

contracted to third parties 

A, B, and C checks and most major inspections and 

maintenance in-house. Off-wing engine maintenance, 

avionics, and instrument overhauls contracted.

Scheduled or on-demand Scheduled (part 121).

Size and structure of

inspection and maintenance

organizations 

Engineering and maintenance organizations include 

small engineering capability, shops for support, 

components, electronics, engines, etc., and quality

assurance department.

CASS Management and Planning 

General priority 

This operator prioritizes in the following manner:

(1) Safe operations (air and ground). 

(2) Detect and prevent noncompliance. 

(3) Improve operating efficiency. 

CASS written procedures (A System Safety Attribute — Procedures)

The CASS is described in an appendix to the general maintenance manual. The CASS appendix

is detailed, including specific procedures for root cause and systems analyses, and discussion of 

awareness of human factors. 

CASS in the operator organization 

The chief executive officer supports the CASS. CASS specifically appears on the functional 

organizational flowchart. 

Authority for CASS (A System Safety Attribute — Authority) 

Vice president of engineering and maintenance. 

Responsibility for CASS (A System Safety Attribute — Responsibility)

The director of quality assurance heads the CASS board, which includes key department heads in 

engineering and maintenance, training, and flight operations. 

Policy for CASS auditor/analyst independence from production (A System Safety

Attribute — Controls)

CASS auditor/analysts are in a separate department under quality assurance. Operational data 

collection and analyses assigned to a “CASS reliability group” that is contained within the 

 Page 1 
AC 120-79 04/21/03 

Appendix 2 

engineering department but is not an approved reliability program and is unable to implement 

changes in the maintenance and inspection intervals without prior FAA approval. The CASS 

documentation is explicit that the operator’s reliability program is not FAA-approved. The

reliability group reports CASS information directly to the director of quality assurance. 

Policy regarding personnel actions resulting from CASS findings/results

Inadvertent errors will not lead to disciplinary action. Full reporting and disclosure is 

encouraged to facilitate system corrections. Operator participates in FAA Voluntary Disclosure

Reporting Program. 

Surveillance and Analysis of Performance of Inspection and Maintenance 

Audits

Responsibility Director of quality assurance.

Prioritization CASS board develops audit plan based on risk assessment.

Cycles Audit plan is established and reviewed annually. Audits are completed 

semiannually to biannually, depending on prioritization.

Scope All internal and third-party areas of maintenance and inspection.

Process

CASS board developed audit checklists for use by auditors. Audits are

conducted in accordance with the annual plan. CASS department 

receives reports of all maintenance-related events, such as rejected 

takeoffs, for analysis and use in risk assessment for audits. Special

audits may be scheduled as needed. Some vendor audits are conducted 

by document reviews, written questionnaires, telephone follow-up, or 

combinations of these. Follow-up is required if preliminary results raise

concerns.

Flow Initial reports and summaries to director of quality assurance. 

Analysis 

Responsibility Director of quality assurance.

Perform 

preliminary 

root cause 

analysis 

Auditor/analyst.

Classify

hazards/ 

perform risk 

assessment 

The CASS board and analysts classify hazards and perform risk 

assessment. 

Flow

Director of quality assurance reports summaries of all findings/initial 

analyses and details of issues to the CASS board for review and 

concurrence. CASS board transmits results to affected department, 

which forms corrective action team.

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 Appendix 2 

Surveillance and Analysis of Effectiveness of Inspection and Maintenance

Operational data collection

Responsibility Director of quality assurance.

Prioritization Reliability group.

Scope Includes pilot reports, engine condition monitoring, mechanical delays, 

teardown reports, and other data.

Process

Modeled after FAA-approved reliability programs. Data collection 

oriented toward detecting trends, positive or negative, before occurrence

of events. However, data collection (and analysis) may vary based on 

maintenance-related events. Operational data sets collected formally

reviewed by CASS board every 2 years; initial list based on 

AC 120–17, and CASS board determinations.

Flow Reliability group, although located within the engineering department, 

has a direct reporting relationship to the director of quality assurance.

Analysis of operational data 

Responsibility Director of quality assurance.

Prioritization Reliability group.

Process

Analysis performed by technical experts within the reliability group; 

includes preliminary determination of possible root causes or possible

procedural changes.

Flow Results are reported to CASS board.

Corrective Action 

Final root cause analysis 

Responsibility Director of quality assurance.

Procedures

CASS board transmits preliminary analysis results to the manager(s) of

the affected department(s), who designates technical personnel to 

conduct final root cause analysis with the CASS auditor/analyst. The 

CASS analyst oversees the process and ensures the root cause analysis

process, including human factors and systems analyses, is followed.

Use of specific

analytical 

systems

Internally developed formal analysis process or common industry tools.

Flow Technical department develops final report and submits it to the director

of quality assurance.

Determination of corrective action options 

Responsibility

Director of quality assurance designates corrective action team, led by

primary affected technical department(s), whose manager(s) designates 

a team leader.

Procedures

Risk assessment of the problem and the options. The CASS 

auditor/analyst or reliability group representative does not propose 

corrective actions but reviews possibilities for systems considerations 

and relevance to root cause analysis.

Flow Team presents recommendation to CASS board.

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Appendix 2 

Selection of corrective action and corrective action plan

Responsibility Director of quality assurance.

Procedures

Decision based on a priority for safety and regulatory compliance. Risk 

assessment is the basic tool to support the decision. CASS board 

verifies systems considerations and relevance to root cause analysis.

Flow

Depends on the level of the problem and the corrective action. Routine 

issues may be resolved at the team level with direct implementation by

the affected area manager; the CASS board is then advised of this 

action. More significant program changes may require prior review and 

concurrence from the CASS board or elevation to vice president of 

engineering and maintenance.

Follow-up

Responsibility CASS board.

Procedures

CASS auditor/analyst or reliability group, as applicable, assigned to 

develop follow-up plan based on seriousness of the problem. Follow-up 

may include communications from technical area verifying

implementation, follow-up audits or data collection, and/or follow-up 

evaluation.

Flow Technical area manager reports to director of quality assurance, who 

reports to CASS board.

NOTE: The above provide many examples of the system safety attributes — controls and

procedures. 

Communications Between CASS and Other Personnel (A System Safety

Attribute — Interfaces)

Communication of specific CASS results and actions 

Responsibility CASS board.

Procedures

Audits based on updated checklists. Operational data are collected and 

stored in computerized database systems; some analysis and alerting

features are automated. Audit and analysis results communicated 

through paper forms. Corrective action tracking through computerized 

database system.

Flow

Through electronic mail communications and standard paper reports, 

information flows among CASS board, corrective action teams, 

technical areas, and the director of quality assurance.

Communications with inspection and maintenance personnel 

Responsibility CASS board.

Procedures

CASS training included for all personnel; initial and recurrent training. 

The operator’s employee newsletter includes a brief monthly report on 

CASS results.

Flow

CASS board works with training and company communications 

department and receives feedback from managers and supervisors, 

particularly in the maintenance and inspection areas.

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 Appendix 2 

Interfaces (A System Safety Attribute — Interfaces)

Responsibility: CASS board. 

Flow: Communications channeled through director of quality assurance.

Procedures: 

TO CASS Board FROM CASS Board 

Reliability group provides regular reports 

on analyses results, trends, and concerns 

regarding operational data. 

Feedback to technical areas regarding

findings, trends, concerns, and 

follow-up results. 

Auditors/analysts provide regular reports 

on findings, analyses, trends, and 

concerns. 

Feedback to Voluntary Disclosure 

Reporting Program manager

regarding proposed comprehensive 

fixes; coordination with director of 

quality assurance.

Voluntary Disclosure Reporting Program 

manager provides summaries of 

disclosures and proposed comprehensive 

fixes for CASS review and input. 

Monthly reliability analyses

summaries and CASS summaries for 

distribution to vice president of 

engineering and maintenance, 

director of quality assurance, and 

other senior management; department 

managers in maintenance, inspection, 

flight, and ground operations; internal 

evaluation program; safety office; and 

FAA principal inspector. 

Designated CASS auditor/analyst

reviews reports and at least annually

reviews maintenance-related Aviation 

Safety Reporting Program reports for 

consideration in setting audit and 

operational data collection priorities. 

CASS reports reflect Voluntary

Disclosure Reporting Program 

comprehensive fixes without 

detailing the initiating circumstances. 

Copies of reliability reports and 

CASS summaries to FAA principal 

inspector. 

CASS board meeting minutes. 

Semiannual summary report to chief 

executive officer; copy to FAA 

principal inspector. 

Personnel Who Perform CASS Functions 

Full-time auditors and analysts; in some cases, an auditor may also be an analyst. 

All members of the CASS board who have not participated in specific CASS training receive a 

total of 12 hours initial training covering the CASS, root cause and systems analyses, and human 

factors. 

 Page 5 
AC 120-79 04/21/03 

Appendix 2 

How the Operator Evaluates Its CASS (A System Safety Attribute — Process 

Measurement)

Responsibility Vice president of engineering and maintenance.

Procedures Internal evaluation program evaluates CASS annually.

Flow

Internal evaluation program reports on CASS are transmitted directly to 

the chief executive officer and to the vice president of engineering and 

maintenance.

Page 6
04/21/03 AC 120-79 

 Appendix 3 

APPENDIX 3 

SAMPLE CASS FOR A SMALL OPERATOR 

Type of Operator 

Fleet composition Two turboprop airplanes; Saab 340B.

Number of maintenance base 

and line stations 

Base station only.

Proportion of maintenance 

contracted to third parties 

A checks in-house; B, C, and D checks, all off-wing

engine maintenance, and all overhauls of engines, 

instruments, and avionics contracted out.

Scheduled or on-demand On-demand (part 135).

Size and structure of

inspection and maintenance

organizations 

Maintenance structure comprises director of 

maintenance with chief inspector.

CASS Management and Planning 

General priority 

This operator prioritizes in the following manner:

(1) Safe operations (air and ground). 

(2) Detect and prevent noncompliance. 

(3) Improve operating efficiency. 

CASS written procedures (A System Safety Attribute — Procedures)

CASS chapter in general maintenance manual. The CASS chapter includes specific procedures 

for root cause and systems analyses, and discussion of awareness of human factors. 

CASS in the operator organization 

Chief executive officer actively participates in the CASS. CASS specifically appears on 

functional organizational flowchart. 

Authority for CASS (A System Safety Attribute — Authority) 

Chief executive officer. 

Responsibility for CASS (A System Safety Attribute — Responsibility)

Director of maintenance heads CASS committee, which includes the chief executive officer, 

chief inspector, and director of flight operations. 

Policy for CASS auditor/analyst independence from production (A System Safety

Attribute — Controls)

Director of maintenance “borrows” auditors within or outside the company based on auditor 

qualifications. Priorities are (1) independent from audited department and (2) experience or

familiarity with the area to be audited. Every 5 years the company contracts an independent firm

to conduct an outside evaluation of the CASS and other operator systems and programs to verify

sufficient objectivity in the audits. 

 Page 1 
AC 120-79 04/21/03 

Appendix 3 

Policy regarding personnel actions resulting from CASS findings/results

Inadvertent errors will not lead to disciplinary action. Full reporting and disclosure encouraged 

to facilitate system corrections. 

Surveillance and Analysis of Performance of Inspection and Maintenance 

Audits

Responsibility Director of maintenance.

Prioritization CASS committee assigns priorities based on risk assessment.

Cycles Audit plan is established and audits are accomplished annually.

Scope All internal and third-party areas of inspection and maintenance.

Process

CASS committee developed audit checklists for use by auditors, who 

may be committee members or personnel drawn from throughout the 

company. Director of maintenance receives reports of all

maintenance-related events, such as rejected takeoffs, for analysis and 

use in risk assessment for audits. Special audits may be scheduled as 

needed. Vendor audits are conducted by document reviews, written 

questionnaires, telephone follow-up, or combinations of these. 

Follow-up is required if preliminary results raise concerns.

Flow Initial results are reported to the director of maintenance.

Analysis 

Responsibility Director of maintenance (conducts preliminary analysis with the 

auditor).

Perform 

preliminary 

root cause 

analysis 

Auditor/analyst.

Classify

hazards/ 

perform risk 

assessment 

CASS committee.

Flow

CASS committee reviews all findings/initial analysis and details of

issues as deemed necessary by the director of maintenance. The CASS 

committee acts as the core corrective action team (may be supplemented 

with other personnel as required).

Page 2
04/21/03 AC 120-79 

 Appendix 3 

Surveillance and Analysis of Effectiveness of Inspection and Maintenance 

Operational data collection

Responsibility Director of maintenance.

Prioritization Director of maintenance.

Scope Basic. Includes pilot reports, engine condition monitoring, mechanical 

delays, cancellations, teardown reports, and other data.

Process

Data collection oriented toward detecting trends, positive or negative,

before occurrence of events. The list of operational data sets collected is

formally reviewed by the CASS committee every 2 years to determine if

it needs to be adjusted. The initial list is based on the CASS 

committee’s experience at other operations and with this fleet.

Flow Flight operations and director of maintenance transmit reports to CASS 

committee.

Analysis of operational data 

Responsibility Director of maintenance.

Prioritization CASS committee.

Process

Analysis performed by director of maintenance or chief inspector. 

Preliminary determination of possible root causes or possible procedural

changes.

Flow Results are reported to the CASS committee.

Corrective Action 

Final root cause analysis and determination of corrective action options 

Responsibility Director of maintenance.

Procedures

Designates technical personnel to perform final root cause analysis and 

identify corrective action options. Director of maintenance oversees the 

process and ensures the root cause analysis process, including human 

factors and systems analysis, is followed. 

Use of specific

analytical 

systems

Based on director of maintenance’s training and internally developed 

procedures.

Flow Director of maintenance presents corrective action options to the CASS 

committee.

Selection of corrective action and corrective action plan

Responsibility CASS committee.

Procedures

Decision based on a priority for safety and regulatory compliance. Risk 

assessment is the basic tool to support the decision. The CASS 

committee verifies systems considerations and relevance to root cause

analysis.

Flow CASS committee makes selection.

 Page 3 
AC 120-79 04/21/03 

Appendix 3 

Follow-up 

Responsibility CASS committee.

Procedures

Affected technical personnel report to the CASS committee on 

implementation of corrective action. Director of maintenance may

independently verify. Follow-up audit planned for following year cycle 

of audits.

Flow Technical area reports to director of maintenance, who informs the 

CASS committee.

NOTE: The above tables provide many examples of the system safety attributes — 

controls and procedures. 

Communications Between CASS and Other Personnel (A System Safety

Attribute — Interfaces)

Communication of specific CASS results and actions 

Responsibility CASS committee.

Procedures

Audits based on updated checklists. Operational data are collected and 

stored in files. Audit and analyses results communicated through 

electronic mail.

Flow Electronic mail communications to all company management.

Communications with inspection and maintenance personnel 

Responsibility CASS committee.

Procedures Director of maintenance conducts initial briefing for all personnel to 

orient them on CASS.

Flow Director of maintenance to all affected personnel.

Interfaces (A System Safety Attribute — Interfaces)

Responsibility: CASS committee.

Flow: Communications channeled through director of maintenance. 

Procedures: 

TO CASS Committee FROM CASS Committee:

Director of maintenance provides regular 

reports on analyses results, trends, and 

concerns regarding operational data. 

Feedback to technical areas regarding

findings, trends, concerns, and followup results. 

Chief inspector reviews reports at least 

annually and reviews maintenancerelated Aviation Safety Reporting

Program reports for consideration in 

setting audit and operational data

collection priorities. 

CASS committee meeting minutes. 

Page 4
04/21/03 AC 120-79 

 Appendix 3 

Personnel Who Perform CASS Functions 

Auditors and analysts are only part-time in these functions. They receive some specific CASS 

training, including on-the-job and formal training. 

How the Operator Evaluates Its CASS (A System Safety Attribute — Process 

Measurement)

Responsibility Chief executive officer.

Procedures

Chief executive officer reviews indicators of a properly designed and 

functioning CASS, including quality of analysis, independence of the

audits, and sufficiency of third-party audit procedures. 

Flow The chief executive officer’s review is documented and shared with

CASS committee members and the FAA principal inspector.

Page 5 (and 6) 

04/21/03 AC 120-79 

 Appendix 4 

APPENDIX 4 

CASS MANUAL/DOCUMENT SAMPLE CONTENTS 

A. General Information. 

(1) Definition of terms. 

(2) Purpose of the CASS. 

B. System Organization and Personnel. 

(1) CASS organizational chart. 

(2) Person/position with authority, including how to determine whether a CASS is 

functioning properly and policies/procedures for modifying the CASS. 

(3) Person/position with responsibility. 

(4) Duties and responsibilities of CASS personnel (supervisors, auditors, analysts). 

C. Elements Basic to a CASS. 

(1) Policies/procedures for scheduling and conducting internal/external audits. 

(2) Policies/procedures for identifying and updating the list of operational data sets to be 

collected, and for collecting data. 

(3) Policies/procedures for analyzing audit results. 

(4) Policies/procedures for analyzing operational data. 

(5) Policies/procedures for developing and analyzing proposed corrective actions. 

(6) Policies/procedures for approving and implementing corrective actions, including

changes to the maintenance and inspection programs. 

(7) Policies/procedures for monitoring and follow-up of corrective actions. 

D. Critical CASS Interfaces. 

(1) Policies/procedures for communications within the CASS and between the CASS and 

other areas of the operation. 

(2) Interface documents (audit forms and checklists, corrective action notices, statistical

and periodic reports, etc., including, as applicable, control, storage, and retrieval of CASS 

records and communications). 

 Page 1 
AC 120-79 04/21/03 

Appendix 4 

E. Relationship of the CASS to Other Programs. 

Policies/procedures to integrate or relate other operator programs to the CASS. 

F. Personnel Qualifications. 

(1) Policies/procedures regarding qualifications and training of CASS personnel. 

(2) Training records. 

Page 2
04/21/03 AC 120-79 

 Appendix 5 

APPENDIX 5 

INFORMATION RELATED TO THIS AC

Related FAA Documents 

AC 00-46, Aviation Safety Reporting Program. 

AC 00–58, Voluntary Disclosure Reporting Program. 

AC 120–16D, Air Carrier Maintenance Programs. 

AC 120–17, Maintenance Control by Reliability Methods. 

AC 120–59, Air Carrier Internal Evaluation Programs. 

AC 120-66, Aviation Safety Action Programs (ASAP). 

AC 120–72, Maintenance Resource Management Training. 

AC 129–4, Maintenance Programs for U.S.-Registered Aircraft Under FAR Part 129. 

FAA Order 8040.4, Safety Risk Management. 

FAA Order 8300.10, Airworthiness Inspector’s Handbook, volume 2, chapter 65, and volume 3, 

chapter 37. 

FAA Order 8400.10, Air Transportation Operations Inspector’s Handbook, appendix 6, 

chapter 10, figure 10-5. 

Flight Standards Handbook Bulletin for Airworthiness (HBAW) 95-06, Maintenance Programs 

for Aircraft Engines, Including Leased Engines, Used by Operators of Transport Category

Aircraft. 

HBAW 96-05, Air Carrier Operations Specifications Authorization to Make Arrangements with 

Other Organizations to Perform Substantial Maintenance.

Joint Flight Standards Handbook for Air Transportation (HBAT) 99-19 and HBAW 99-16, 

14 CFR Part 121 and 135 Air Carrier Safety Departments, Programs, and the Director of Safety. 

Information on the World Wide Web 

A Practical Approach to: Conducting a Cost-Effective Root Cause Analysis. Medical Risk 

Management Associates, LLC. (See http://www.rootcauseanalyst.com/costeffective.htm). 

Establishing A Value Criterion (1999). (See http://rootcause.com/criteria.htm). 

Page 1 (and 4) 
AC 120-79 04/21/03 

Appendix 5 

Human Factors Guide for Aviation Maintenance (February 1998), Michael Maddox, editor. 

Prepared by Galaxy Scientific Corporation, Advanced Information Technology Division, 

Atlanta, GA. Prepared for Jean Watson, Washington, D.C.: FAA Office of Aviation Medicine. 

(see http://hfskyway.faa.gov). 

Learning from Our Mistakes: A Review of Maintenance Error Investigation and Analysis 

Systems (1998), by David A. Marx. Washington, D.C.: FAA Office of Aviation Medicine. 

(See http://hfskyway.faa.gov). 

Root Cause Analysis. What is RCA? Solve Tomorrow’s Problems Today. A Management 

Perspective (1999). Decision Systems, Inc. (See http://rootcause.com/whatsrca.htm). 

System Safety Process Steps. (See http://www.asy.faa.gov/Risk/SSProcess/SSProcess.htm). 

Human Factors Accident Classification System Analysis of Selected National Transportation 

Safety Board Maintenance-Related Mishaps, by CDR John K. Schmidt and Jean Watson. 

(See http://hfskyway.faa.gov). 

Other Documents and Information Related to This AC

In addition to the references cited above, this AC was prepared using the following documents 

and information: 

Beyond Aviation Human Factors (1995), by Daniel E. Maurino, James Reason, Neil Johnston, 

and Rob B. Lee. Hants, England: Ashgate Publishing Limited. 

Continuing Analysis and Surveillance System (CASS) Description and Models

(September 30, 2002). Prepared for Risk Analysis Branch, AAR–490, Federal Aviation 

Administration, William J. Hughes Technical Center. Prepared by FJ Leonelli Group, Inc., 

Aviation Systems Consultants. Contract No. DTFA01-98-C00069, Project Code 3011-241. 

Handbook of Airline Operations (2000), Gail F. Butler and Martin R. Keller, executive editors. 

New York: The McGraw-Hill Companies, Inc.

Handbook of Aviation Human Factors (1999), Daniel J. Garland, John A. Wise, and 

V. David Hopkin, editors. Mahwah, NJ: Lawrence Erlbaum Associates, Inc. 

Human Factors and Maintenance Resource Management (March 7, 2002). Presented by

Yosef Morgan, Applications Manager, Maricopa County Community College. 

Phoenix, Arizona. 

Human Factors in Aviation (1989), by Elwyn Edwards. Earl L. Wiener and David C. Nagel, 

editors. San Diego: Academic Press. 

Managing the Risks of Organizational Accidents (1997), by James Reason. Hants, England: 

Ashgate Publishing Limited. 

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04/21/03 AC 120-79 

 Appendix 5 

Page 3 (and 4) 

Risk Management in Aviation (March 7, 2002). Presented by Jim Hein, Federal Aviation 

Administration Safety Inspector, Honolulu Flight Standards District Office. Phoenix, Arizona.

The Continuing Analysis and Surveillance System, Consolidation of FAA Interview Findings and 

Recommendations (May 29, 2002). Prepared for Volpe National Transportation Systems Center. 

Prepared by Phaneuf Associates Incorporated. Contract No. DTRS57-99-D-00055, Task 

Order No. 19. 

The Limits of Safety: Organizations, Accidents, and Nuclear Weapons (1993), by 

Scott D. Sagan. Princeton, NJ: Princeton University Press.