How to use Aircraft Maintenance Manual

Learn how to use Aircraft Maintenance Manual during Aircraft Maintenance. Understand the Structure, Content, Breakdown, and Numbering System of AMM, and Know how to locate information in AMM.

As I’m an Aircraft Maintenance Engineer, I have seen lots of Aircraft Maintenance Technicians who don’t know how to use the AMM for correct maintenance data. Many mechanics make this mistake during starting days in their aircraft maintenance career because they don’t understand the organization of AMM content.

Understanding the organization of AMM contents plays a vital role to find correct maintenance data for a specific type of aircraft.

Let’s get started,

• What is Aircraft Maintenance Manual
• AMM Regulatory Requirements
• AMM Revision
• Start with AMM Front Matter
• Locate information in AMM
• Content of AMM
• Standard ATA Chapters
• Special Attention
• Aircraft Maintenance Manual Features
• Standard Maintenance Practices and Procedures
• Aircraft Status for Maintenance
• Replacement of Equipment
• General Recommendations
• AMM for Powerplant
• Key Points To Note

What is Aircraft Maintenance Manual

Aircraft Maintenance Manual (AMM) is a manual developed by the manufacturer that provides detailed technical maintenance instructions for a specific type of Aircraft. The Aircraft Maintenance Engineer and/or Technician refer to the relevant AMM of the aircraft before they proceed further with the maintenance of the aircraft and its systems.

AMM Regulatory Requirements

The content of the Aircraft Maintenance Manual (AMM) is part of the Instructions for Continued Airworthiness (ICA) that the Type Certificate Holder is required to provide and maintain. Here Type Certificate Holder can be Airbus, Boeing, or any other aircraft manufacturer.

Organisation of Contents

The data contained in this AMM is in general compliance with ATA Specification 2200 (iSpec2200), Information Standards for Aviation Maintenance, and ASD-STE100 Simplified Technical English.

Publication Format

The AMM text is in Standard Generalized Markup Language (SGML) format. The standard illustrations are in Computer Graphics Metafile (CGM) format.

AMM Revision

The maintenance manual is kept current by the Revision Service. A list of effective pages (LEP) is provided with each revision.

There are two types of revisions –

1. Normal Revisions
2. Temporary Revisions

Normal Revisions – Normal revisions consist of a complete reissue with differential marking at the specified revision date.

Temporary Revisions (TR) – Temporary revisions are issued to introduce information that cannot wait until the next normal revision. Each temporary revision remains effective until it is incorporated in the next normal revision or it is superseded by another temporary revision (if additional changes are necessary, a replacement temporary revision will be issued). They must be incorporated as stated on the TR transmittal sheet.

Start with AMM Front Matter

The AMM Front Matter contains the following information –

1. Title section provides the name of the manual, the revision date, and the revision number.
2. Also provides the manufacturer’s contact address and legal notice.
3. Transmittal letter.
4. The Highlights section provides the reason for the revision of text and/or illustrations. They are sorted by ATA Chapter.
5. List of Effective Temporary Revisions – This list is always empty at the delivery of each normal revision. A list of Effective Temporary Revisions is dispatched with each Temporary Revision issued.
6. The Introduction provides general information on how to use the manual.
7. Effectivity Table that provides the correspondence between Fleet Serial Number (FSN) and Manufacturer Serial Number (MSN).
8. List of the Service Bulletins.
9. Customer Originated Changes (COC).

Locate Information in the AMM

All chapters of the Aircraft Maintenance Manual are grouped under five major headings. To locate information, identify the group of chapters related to the desired information, then identify the chapter within the group. With the chapter number identified, proceed to the chapter table of contents located at the beginning of each chapter.

• Reserved for AMM Owner Use: Chapters 1 – 4
• Aircraft General Group: Chapters 5 – 12
• Airframe Systems Group: Chapters 20 – 49
• Structure Group: Chapters 51 – 57
• Power Plant Group: Chapters 70 – 80

Standard ATA Chapters

The AMM is performed following the ATA standard. Each ATA reference corresponds to an aircraft system.

• Aircraft General: ATA 00 up to ATA 12
• Airframe Systems: ATA 20 up to ATA 50
• Structure: ATA 51 up to 57
• Power Plant: ATA 70 up to 80

Content of AMM

The AMM contains the instructions for the on-aircraft maintenance necessary to ensure the continued airworthiness of the aircraft.

The AMM contains information required to service, repair, replace, adjust, inspect and check equipment and systems on the aircraft. These tasks are normally performed on the ramp or in the maintenance hangar.

Information required for the maintenance of equipment off the aircraft (shop maintenance) is given in the Vendor or Manufacturer Component Maintenance Manuals (CMMV or CMMM). Where the AMM makes a cross-reference to a CMM, the cross-referenced information is related to off-aircraft maintenance and is not part of the Instructions for Continued Airworthiness, the Type Certificate Holder is required to provide.

However, in a very small number of cases, AMM tasks may refer to a CMM for on-aircraft maintenance. In these cases, the CMM is part of the Instructions for Continued Airworthiness (ICA).

The AMM also contains information about inspections and maintenance of aircraft structures. However, repair of structure is contained in the Structural Repair Manual (SRM) which also includes the Nacelle Structural Repair Manual (NSRM).

Information required for trouble shooting is contained in the Trouble Shooting Manual (TSM).

The AMM contains the necessary data to cover scheduled maintenance procedures prescribed by the Maintenance Review Board Report (MRBR), respectively the Maintenance Planning Document (MPD) and the deactivation/reactivation procedures relative to Master Minimum Equipment List (MMEL) respectively to the Configuration Deviation List (CDL).

The instructions and information contained in the AMM are applicable only to the aircraft listed in the Effectivity Table. So always refer or select the aircraft effectivity for proper instructions.

The information contained in the AMM has been divided into two main parts/categories:

1. Description and Operation
2. Maintenance Procedure

1. Description and Operation (D/O)

The purpose of the D/O is to familiarize maintenance personnel with the aircraft systems and give them sufficient information to understand how the systems operate.

• Component Location
• System/Component Description
• Power Supply (if applicable)
• Interface with other systems (if applicable)
• Operation/Control and Indicating
• System/BITE Test

2. Maintenance Procedure (MP)

A Maintenance Procedure is made up of Task(s) and Subtasks. Each Task is broken down into the following paragraphs:

• Procedure Title – The title of a maintenance procedure associated with an MPD task is generally identical to the MPD task description.
• Reason for the Job –  Explains the reason for the task.
• Job Set-Up Information – Equipment required for maintenance.
• Job Set-Up or Preparation – This includes Aircraft Maintenance Configuration, Circuit Breakers, and Safety Precautions.
• Procedure – Work steps and also includes sub-tasks.
• Close-Up – Work steps in order to put the aircraft back into its initial configuration.

Job Set-Up Information includes –

• Fixtures, Tools, Test, and Support Equipment – This table provides the fixtures, tools, and equipment that are required for maintenance operation and not part of the mechanic toolbox (standard hand-tool). Fixtures, tools, and equipment are classified into two types of items:
  • The non-specific items – also referred to as “NO-SPECIFIC” or “STANDARD”. These items are identified by their main features and should be purchased or manufactured freely on the market.
  • The specific items – These items are identified by a PNR (Part Number) and listed in the TEM (Tool and Equipment Manual).
• Consumable Materials – Gives a list of all the materials called up in the maintenance procedure.
• Work Zones and Access Panels – The zones are identified by a three-digit numerical code. This includes all location and access panel information required to perform the task.
• Expendable Parts – Use the Illustrated Parts Catalog (IPC) or the Power Plant Illustrated Parts Catalog (PIPC) to find the corresponding Part Numbers.
• Referenced Information – Any additional information which is necessary to perform a maintenance procedure (task).

Special Attention

An AMM Task can contain WARNING, CAUTION, and Note. Let’s understand the meaning of each.

WARNING: CALLS ATTENTION TO USE OF MATERIAL, PROCESSES, METHODS, PROCEDURES OR LIMITS WHICH MUST BE FOLLOWED PRECISELY TO AVOID INJURY OR DEATH TO PERSONS.

CAUTION: CALLS ATTENTION TO METHODS AND PROCEDURES WHICH MUST BE FOLLOWED TO AVOID DAMAGE TO EQUIPMENT.

NOTE: Calls attention to methods which make the job easier or provide supplementary or explanatory information.

Aircraft Maintenance Manual Features

• Servicing
• Removal and Installation
• Deactivation and Reactivation
• Test and Adjustment
  • Operational Test
  • Functional Test
  • System Test
  • BITE Test
• Inspection/Check
  • Detailed Inspection
  • General Visual Inspection
  • Special Detailed Inspection
• Cleaning and Painting
• Repairs

Servicing

AMM Chapter 12 is entitled SERVICING. This chapter contains instructions for the replenishment of items such as fuel, oil, hydraulic fluid, water, tire pressure, etc. The tanks and reservoir capacities are indicated, as well as the standard specification and grade of material to be used. The chapter contains scheduled and unscheduled servicing applicable to the whole aircraft.

Servicing information is also located within the other chapters of the manual. The information is provided as a result of the accomplishment of maintenance actions. It includes items such as the inflation or refilling of shock struts, the lubrication of control cables, the sterilization of potable water system, etc.

Removal and Installation

Removal and installation procedures include the instructions to remove or install a line replaceable component, assembly, subassembly, unit, combination of parts, etc. and interrelated part(s) from the aircraft. The procedures shall clearly describe the step-by-step operation in a logical workflow sequence as necessary to gain access to and subsequently remove the hardware or install the hardware and close access to.

Deactivation and Reactivation

The deactivation tasks give the procedures necessary to permit continued flight operations with the failure of a system or a part of a system, in compliance with the MMEL and CDL requirements. The deactivation task reference has Function Code 040 (CH-SE-SU-040-XXX).

The reactivation tasks give the procedures necessary to restore the system to the normal operating condition after the removal or deactivation of a faulty component or system. If it is necessary to do a troubleshooting procedure before the reactivation, the reactivation procedure includes a cross-reference to the TSM. The reactivation task reference has Function Code 440 (CH-SE-SU-440-XXX).

Note: Some Deactivation/Reactivation tasks do not include a reference to an MMEL/CDL item. This is because they are not related to the dispatch conditions quoted in these documents.

Test and Adjustment

Testing information is divided into following categories:

Operational Test

An operational test is required to ascertain only that a system or unit is operational. This test normally does not require special equipment or facilities other than that installed on the aircraft and is comparable to the test performed by the flight crews.

Functional Test

The functional test is the procedure required to ascertain that a system or unit is functioning in all aspects in accordance with a minimum acceptable system or unit design specifications. These tests may require supplemental ground support equipment and should be more specific and detailed than an operational test. It should contain all necessary information to perform proficiency tests to maintain system or unit reliability at an acceptable level, without reference to additional documents. A functional test usually occurs during minor maintenance.

System Test

The system test is the procedure containing all adjustment specifications and tolerances required to maintain the system and/or unit performance at maximum efficiency and design specifications. It shall be self-contained and may duplicate other tests. It is normally used during major maintenance.

BITE Test

There are two types of BITE Tests – Main BITE Test and Interactive BITE Test.

The operational and system tests are normally accomplished at the system level. The functional test relates to component performance after installation and is normally contained with the component maintenance practices. The recommendation to test or not test after a maintenance action is provided at the end of the appropriate maintenance practices subtopic.

If you cannot complete a test successfully, record the indication or problem, then refer to the Fault Isolation Manual section for that system.

Inspection/Check

Inspection/Check provides procedures to determine the serviceability of a part, assembly, system, specific interrelationship of parts that perform a functional operation, etc. Some procedures will give In-Service/Service Wear limits and will include specific procedures to evaluate and establish serviceability relative to design wear tolerances.

Inspection/Check are divided into two parts:

• Inspection/Check without removal of components from the aircraft.
• Inspection/Check further to the removal of components from the aircraft.

Inspection/Check without component removal, like:

• Visual Inspection/Check (cracks, damage, oxidation, paint, etc.)
• Measurements displacement, travel, overall clearances, leak measurements, etc.

Inspection/Check with component removal, like:

• Original manufacturers dimensions
• Maximum and minimum clearances and in-service wear limits (given in table form).

There are three types of inspections:

Detailed Inspection (DI)

An intensive examination of a specific item, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at an intensity deemed appropriate. Inspection aids such as mirrors, magnifying lenses, etc.. may be necessary. Surface cleaning and elaborate access procedures may be required.

General Visual Inspection (GVI)

A visual examination of an interior or exterior area, installation, or assembly to detect obvious damage, failure, or irregularity. This level of inspection is made from within touching distance unless otherwise specified. A mirror may be necessary to ensure visual access to all surfaces in the inspection area. This level of inspection is made under normally available lighting conditions such as daylight, hangar lighting, flashlight, or drop-light and may require removal or opening of access panels or doors. Stands, ladders, or platforms may be required to gain proximity to the area being checked.

Special Detailed Inspection (SDI)

An intensive examination of a specific item, installation, or assembly to detect damage, failure, or irregularity. The examination is likely to make extensive use of specialized Inspection Techniques and/or equipment. Intricate cleaning and substantial access or disassembly procedure may be required.

Cleaning and Painting

Cleaning or painting procedures contain the methods and processes required for cleaning or painting specific parts or areas. Materials will be identified by generic names and/or standard specification number.

Repairs

This section includes detailed step-by-step repair processes and specifications in a logical workflow sequence to restore a worn or damaged part to serviceable condition. This topic provides repair procedures with the exception of those covered by the CMMM/CMMV or by the SRM/NSRM. Repairs included in the Aircraft Maintenance Manual are non-structural repairs that can be performed on the aircraft. They are not submitted to the airworthiness authorities for approval but are technically approved by the aircraft manufacturer, for manufacturer components.

AMTOSS (Aircraft Maintenance Task Oriented Support System)

Maintenance practices are structured to incorporate features of AMTOSS. AMTOSS arranges maintenance practices to facilitate automated data retrieval by the airlines.

All tasks and sub-tasks are coded with an AMTOSS number. These numbers will show in the AMM.

The AMTOSS Task/Subtask number contains five, six or seven elements.

AMTOSS Element – Description

1. XX – ATA Chapter
2. XX – ATA Section
3. XX – ATA Subject
4. XXX – Function Code
5. XXX – Sequence Number
6. XXX – Configuration (alphnumeric code – A01)
7. XXX – COC (not part of AMTOSS)

The AMTOSS Sub-task numbers have the same elements as the AMTOSS task numbers.

1. ATA Chapter

The ATA chapters refers to the numbering system and referencing standards for commercial aircraft documentation.

2. ATA Section

Each chapter/system is broken down into sections/subsystems.

3. ATA Subject

Each sub-section/sub-subsystem is broken down into subjects.

4. Function Codes

The first two digits of the numbering system fourth element are in accordance with the ATA Specification, although in some instances a third digit has been added for a further breakdown of the basic function.

5. Sequence Number

The three-digit numeral used to give a unique identification number to each Task/Subtask similarly numbered throughout the preceding elements.

• To provide numerical separation between Task and Subtask, Task identification begins at 001 and rises, in sequence, to 049 (maximum) within the procedure.
• Subtask identification begins at 50 and rises, in sequence, to 800 (maximum) within the procedure.
• Illustrations and tables are considered as tasks.

6. Configuration

The three-digit alphanumeric indicator comprises of:

• First digit alpha to identify different Technical configurations (modification(s), service bulletin(s), etc..)
• Second and third digit numerals to identify alternative methods/techniques of maintenance.

7. COC (Not Part of AMTOSS)

A three-digit alphanumeric indicator that can be assigned by the airline to highlight specific airline data. This is not included in the TASK/Subtask number unless specifically requested by the airline in the COC dossier.

Standard Maintenance Practices and Procedure

Standard Maintenance Practices and procedures are described in chapters 20 and 70. Procedures applicable to one system only are described in the relevant ATA chapter of AMM.

Industry-standard maintenance practices are not given in the AMM. Thus, procedures related to simple components (including replacement/reinstallation) that do not require a specific aircraft configuration, safety precautions, and specific tests after installation, are not given in AMM.

When it is necessary to go on the surface of the aircraft (e.g. wing, THS) to do maintenance tasks, Aircraft Manufacturer recommends protection of the surface. This is to prevent a possible risk of damage to the surface from tools or parts that fall, objects below shoes, etc.

Aircraft Status for Maintenance

The following items shall be considered as the basic aircraft configuration, before you start a maintenance task:

• Aircraft on the ground resting on landing gear (the ground safety locks and the wheel chocks are in position on the landing gear).
• Engine shut down, thrust reversers closed and locked.
• Aircraft in clean configuration.
• Parking brake applied.
• Aircraft electrical network de-energized.
• Hydraulic systems depressurized.
• Access to the cockpit and cabin is available.
• All circuit breakers are in a closed position.
• All controls in NORM, AUTO or OFF position.

In case a specific aircraft configuration is required during a maintenance procedure, a specific paragraph “aircraft configuration” is provided at the task level in AMM.

Replacement of Equipment

The instructions for the replacement of equipment are given in the Removal/Installation topics. However, it is necessary to make sure that the replacement equipment has either the same PN as the removed equipment or an approved interchangeable PN.

HF General Recommendations

General recommendations related to the risk of human error during maintenance

If a maintenance team does the same task on different components of the same type during the same maintenance event and if the team makes a maintenance error, there is a risk that the same error and the same failure will occur on all these components at the same time.

It is recommended that operators do not do maintenance on different engines or redundant components installed on the same aircraft at the same time unless it is not possible to do differently.

If it is necessary to do maintenance on more than one engine or on redundant components at the same time, different maintenance teams do the work on each engine or component.

If an engine run is necessary to perform a maintenance task, make sure that only the related (one) engine is in operation at the time unless the task gives other specific instructions.

AMM for Powerplant

Engine maintenance in AMM covers the maintenance that can be performed while the engine is installed on the aircraft.

Powerplant Chapters – Shared ATA Chapters with AMM

Key Points To Note

Observe standard shop practice safety procedures and precautionary measures at all times to avoid damage to equipment or injury to personnel.

Do not weld engine components while they are installed on the airframe or engine because there is a risk of fire. All the weld repairs given by the engine manufacturer are for engines or components in a workshop.

It is recommended that the operators avoid performing maintenance on multiple engines installed on the same aircraft at the same time if at all possible. If it is not possible to avoid maintenance on more than one engine at the same time, it is recommended that –

• Different teams do the work on each engine.
• Operators make sure that the maintenance tasks are completed as specified.

NOTE: This recommendation is in agreement with Special Airworthiness Information Bulletin (SAIB) No. NE-00-12, issued by the Federal Aviation Administration (FAA). It is recommended to consult this FAA bulletin. For details and background information, refer to this FAA Bulletin.

Disclaimer : The above information is only for educational purposes.