Overview of Aircraft Maintenance

The aircraft cannot fly with faults, it must be fixed before takeoff. You may think that this is such a complex and time-consuming task, but let me tell you that with the help of easy and simple regulation it does not create any burden for the engineer. All faults must be repaired before the departure of the aircraft, except those specified in MEL or CDL.

Jump To

• Maintenance Definition
• Maintenance Documents
• Line Maintenance
• Base Maintenance
• Maintenance Certification
• Error Capturing Method
• Critical Maintenance Tasks
• Independent inspection
• Re-inspection
• AMP
• AMP Source Docs
• MEL
• CDL
• NOGO

Maintenance can be defined in a number of ways, Aircraft Maintenance includes so many things. Let’s see the exact definition of maintenance, as per ICAO.

Definition of maintenance

The performance of tasks on an aircraft, engine, propeller, or associated part required to ensure the continuing airworthiness of an aircraft, engine, propeller, or associated part including any one or combination of overhaul, inspection, replacement, defect rectification, and the embodiment of a modification or repair.

Modification – Modification means, A change to the type design of an aircraft, engine, or propeller.
Repair – Repair means, The restoration of an aircraft, engine, propeller, or associated part to an airworthy condition, in accordance with the appropriate airworthiness requirements, after it has been damaged or subjected to wear.

According to Part-M, Aircraft Maintenance doesn’t include pre-flight inspections. Pre-flight inspection is a type of inspection carried out before flight to ensure that the aircraft is fit for the intended flight.

Documents used for Aircraft Maintenance

Documents used for Aircraft Maintenance are a part of instructions for continued airworthiness. The following documents are used to maintain the airworthiness of aircraft.

• Aircraft Maintenance Manual (AMM) – This manual contains the information required to service, repair, replace, adjust, do an inspection, and check of equipment and systems of the aircraft normally done on the ramp or in the maintenance hangar.
• Illustrated parts Catalog (IPC) – This Illustrated Parts Catalog (IPC) is intended only for use in identifying, provisioning, requisitioning, storing, and issuing line replaceable aircraft parts and units.
• Trouble Shooting Manual (TSM) – This manual gives the information required for troubleshooting.
• Structure Repair Manual (SRM) – The SRM contains information about the Allowable Damage Limits, material Identification for structure subjects to field Repair, typical Repairs which are generally applicable to structural components of the airplane, that are most likely to be damaged.
• Aircraft Wiring Manual (AWM) – This manual gives wiring diagrams of the electrical installations.
• Aircraft Schematics Manual (ASM) – This manual gives schematic diagrams of the electrical installations with sufficient data for aircraft fault isolation.
• Aircraft Wiring List (AWL) – This manual gives the status of the items of equipment, semi-equipment, and related wiring. It gives the P/N related to a given FIN and the cable type for a given cable number.
• Component Maintenance Manual (CMM) – The manual contains data about maintenance on the component in a workshop. It does not contain data about maintenance on the component when it is installed in the aircraft.

Instructions for Continued Airworthiness

• List of ICA Manuals/Data by manufacturer
• List of ICA Documents by Supplier

Manual/Data

• ALS – Airworthiness Limitation Section
• AMM – Aircraft Maintenance Manual
• AWL – Aircraft Wiring List
• ASM – Aircraft Schematics Manual
• AWM – Aircraft Wiring Manual
• CML – Consumable Material List
• ESPM – Electrical Standard Practices Manual
• ETOPS CMP Document – ETOPS Configuration Maintenance and Procedure Document
• EWIS ICA CSD – Electrical Wiring Interconnection System ICA Compliance Source Document
• IPC – Illustrated Parts Catalog
• MRBR – Maintenance Review Board Report
• NTM – Nondestructive Testing Manual
• TEM – Tool and Equipment Manual
• TSM – Trouble Shooting Manual
• SRM – Structural Repair Manual
• In case of SRM – Only a part of these manuals/data is ICA.

Maintenance of Aircraft is intended to keep the aircraft airworthy. Aircraft maintenance activity is divided into two categories i.e. line maintenance and base maintenance.

What is Line Maintenance

According to EASA Part 145, Line maintenance is any maintenance that is carried out before flight to ensure that the aircraft is fit for the intended flight.

What types of activities included in Line Maintenance

Line Maintenance activities include troubleshooting, defect rectification, component replacement with the use of external test equipment if required. Line Maintenance also includes the replacement of components such as engines and propellers.

Scheduled maintenance checks are part of line maintenance. It also includes visual inspections that will detect obvious unsatisfactory conditions/discrepancies but do not require extensive in-depth inspection. Inspection of structure, systems, and power plant items are through quick opening access panels/doors that are allowed during line maintenance.

Minor repairs and modifications can be done during line maintenance which does not require extensive disassembly. This can be accomplished by simple means.

What is Base Maintenance

Maintenance tasks falling outside the criteria of line maintenance are considered as Base Maintenance.

Maintenance Certification

Certification of maintenance can be done by an appropriately qualified and authorized person in an organization.

The maintenance certificate is a maintenance release document which contains a certification confirming that the maintenance work to which it relates has been completed in a satisfactory manner in accordance with appropriate airworthiness requirements.

Certificate of Release to Service (CRS)
No aircraft can be released to service without a certificate of release to service (CRS) issued by a certifying engineer on behalf of the Maintenance Organisation, on completion of any maintenance work.

Authorized Release Certificate (CA Form 1)
CA form 1 declare the airworthiness of maintenance work undertaken on products, parts, and appliances.
Equivalent to a CA Form 1 may be EASA Form ONE and FAA Form 8130-3.

Error Capturing Method

Error-capturing methods are those actions defined by the organization to detect maintenance errors made when performing maintenance.

Error capturing methods need to be adequate for the specific task and the disturbance of the system.

A combination of several actions  (visual inspection, operational check, functional test, rigging check) may be necessary in some cases. In that condition, the Error-capturing method should always be implemented to avoid errors during maintenance.

An error capturing method is implemented after the performance of any critical maintenance task.

Critical Maintenance Tasks

• Tasks that may affect the control of the aircraft flight path and attitudes, such as installation, rigging, and adjustments of flight controls;
• Aircraft stability control systems (autopilot, fuel transfer);
• Tasks that may affect the propulsive force of the aircraft, including installation of aircraft engines, propellers, and rotors; and
• Overhaul, calibration, or rigging of engines, propellers, transmissions, and gearboxes.

Critical tasks shall be highlighted in the Check Schedules and work orders, as follows; “Critical Task”.

Independent inspection

Independent inspection is one possible error-capturing method. An independent inspection should ensure correct assembly, locking, and a sense of operation.

An independent inspection is an inspection performed by an ‘independent qualified person’ of a task carried out by an ‘authorized person’.

The ‘independent qualified person’ does not issue a certificate of release to service, therefore they are not required to hold certification privileges.

What to do in unforeseen cases when only one person is available. In such a condition reinspection must be carried out.

Re-inspection

A reinspection is an error-capturing method subject to the same conditions as an independent inspection is, except that the ‘authorized person’ performing the maintenance task is also acting as an ‘independent qualified person’ and performs the inspection.

Reinspection, as an error-capturing method, should only be performed in unforeseen circumstances when only one person is available to carry out the task and perform the independent inspection.

The certificate of release to service is issued after the task has been performed by the ‘authorized person’ and the reinspection has been carried out satisfactorily.

When we talk about the continuing airworthiness of aircraft, the first thing that comes in our mind is the maintenance of aircraft. However appropriate maintenance of aircraft is not possible without Approved Aircraft Maintenance Program.

Aircraft Maintenance Program (AMP)

AMP is aircraft specific and this document is the basis for airworthiness management. An approved aircraft maintenance program is a list of all maintenance tasks and inspections that are required to be performed by an aircraft maintenance engineer (certifying staff) on an aircraft at a given interval. The intervals quoted in units of flight hours, flight cycles, or calendar time.

The maintenance of each aircraft shall be organized in accordance with an aircraft maintenance program.

Each AMP and its revision needs to be approved by the competent aviation authority.

An owner or operator’s aircraft maintenance program is normally based upon the maintenance review board (MRB) report, the maintenance planning document (MPD), the relevant chapters of the maintenance manual, or any other maintenance data containing information on scheduling. Furthermore, an owner or operator’s maintenance program also takes into account any maintenance data containing information on scheduling for components.

Source Documents for Aircraft Maintenance Program

1. Manufacturer’s Maintenance Planning Document (MPD)
2. Maintenance Review Board Reports (MRBR)
3. Airworthiness Limitation Sections (ALS)
4. Relevant chapters of the maintenance manual (ATA 05) or any other maintenance data containing information on scheduling.
5. Any additional requirements as specified by the competent authority (DGCA/EASA/FAA).
6. Continuing airworthiness documents issued by the manufacturer, such as SBs/AOTs, etc.
7. ICAs (Instructions for Continuing Airworthiness) or other maintenance-related documents issued by STC holder / Design Approval Holders / Component OEMs. 
8. Operator requirements including recommendations of reliability program, Delay / Defect / Incident Investigation.
9. EDTO CMP Documents.

The design and application of the AMP shall observe human factors principles wherever applicable.

The maintenance program shall also include continuing structural integrity program,  condition monitoring, and reliability program as applicable for the fleet aircraft.

The purpose of a reliability program is to ensure that the aircraft maintenance program tasks are effective and their periodicity is adequate.

The program is event-driven and allows for the early detection and correction of problems before they become a potential fleet and safety issue.

The Reliability Program is an integral part of the Approved Maintenance Program.

The AMP shall be reviewed by the CAM, verified by QM, and submitted to the office of civil aviation authority of the state for approval.

AMP composition  – The AMP shall contain the following sections:

• Section 1 – General Introduction.
• Section 2 – Schedule  Maintenance Checks
• Section 3 – CAA Requirements.
• Section 4 – COSL & LLP
• Section 5 – Reliability  Control Program
• Section 6 – Maintenance  Inspection Programme
• Section 7 – Out Of Phase  Tasks
• Section 8 – Maintenance  Inspection Schedules.

MEL (Minimum Equipment List)

Minimum Equipment List (including the preamble), is an approved document by the state of registry of aircraft, which authorizes to dispatch an aircraft with aircraft equipment inoperative under the conditions specified therein. MEL also complies with EDTO CMP Requirements.

An operator uses the latest applicable MMEL provisions released by the Type Certificate Holder.

CDL (Configuration Deviation List)

Configuration Deviation List (CDL) is a part of the Airplane Flight Manual. Always follow current and approved AFM.

The operation of the aircraft without certain secondary airframe and engine parts is possible as indicated in the Master Configuration Deviation List of the Flight Manual.

Whenever any part of the aircraft is found cracked and the same can go under CDL, then the certifying engineer must ensure that the cracked part is completely removed and the CDL guideline followed.

NOGO items

All items related to the airworthiness of the aircraft and not included in the MEL or CDL are automatically required to be operative.