Aircraft Maintenance Procedures
Fermina Enge
No aircraft is so tolerant of neglect that it is safe in the absence of an effective inspection and maintenance programme. The processes that affect an aircraft are deterioration with age (e.g. fatigue, wear, and corrosion) as well as chance failures (e.g. tyre burst, excess structural loads).
Those actions required for restoring or maintaining an item in a serviceable condition including servicing, repair, modification, overhaul, inspection, and determination of condition." [World Airlines Technical Operations Glossary]
Aircraft maintenance is that part of the process of aircraft technical activity which is conducted on aircraft whilst it remains in the line maintenance or base maintenance environment. Aircraft maintenance is intended to keep the aircraft in a state which will or has enabled a certificate of release to service to be issued. A hangar environment may be available but is often not necessary. The reasons for carrying out maintenance are neatly summarised by [Lam 2002]:
Maintenance will consist of a mixture of preventive and corrective work, including precautionary work to ensure that there have been no undetected chance failures. There will be inspection to monitor the progress of wear-out processes, in addition to:
Base maintenance may be referred to as heavy (or depth) maintenance, and consists of tasks that are generally more in-depth and long-lasting than those above, but are performed less frequently. An MRO (maintenance, repair and overhaul) company will need large facilities and specialised equipment and staff to undertake base maintenance, and many operators contract-out this function. The different activities may include:
The intervals of maintenance are parameters set within the Approved Maintenance Schedule (AMS), which is in turn based on the Maintenance Planning Document (MPD). These will be set according to different criteria, mostly depending on how well damage can be detected and failure predicted [CAA, 2017]:
The formal document which details the way in which all maintenance tasks carried out on an aircraft shall be accomplished. This includes items such as lubrication system functional checks and servicing of the airplane but usually excludes structural repairs and modifications.
Maintenance is at the core of the operations in any industry, but no one could argue that this is especially true for the aviation industry. In the end, aircraft maintenance is a top priority to guarantee the safety of the passengers and the crew at all times. Moreover, maintenance is required to comply with regulations and meet the requirements to keep aircraft airworthiness.
However, an official definition provided by Part 145 regulation states that line maintenance is any maintenance task that can be performed outside of a hangar (under open skies) except for situations in which the weather deteriorates to such conditions, that a hangar becomes mandatory.
Line maintenance is different from scheduled maintenance in a few key ways. First, scheduled maintenance is generally performed at regular intervals regardless of whether an aircraft is experiencing any issues. Second, scheduled maintenance is typically more comprehensive and can involve more complex procedures than line maintenance. Finally, scheduled maintenance is usually performed by the original equipment manufacturer or an independent airworthiness management organization, while line maintenance is also performed by airline or airport personnel.
Line maintenance is performed on a daily basis and involves checking and correcting any minor defects or malfunctions that may have occurred during the previous flight. This type of maintenance can be carried out at the airport where the aircraft is stationed or at any other location where it may land during its operation.
Base maintenance, on the other hand, is performed on a regular schedule and includes more extensive inspections and repairs. This type of maintenance typically takes place at a designated base or facility, where the aircraft is taken out of service for a period of time until all necessary checks and repairs are completed.
Unlike base maintenance, line maintenance focuses on immediate problems and keeping the aircraft safe for operation in the short term instead of addressing long-term issues, but still aims to maintain the overall airworthiness of the aircraft. Both types of maintenance are crucial for ensuring safe flight operations and complying with regulatory requirements provided by the local aviation authority listed by ICAO or other sizeable aviation organizations.
Maintenance activities are usually defined by the maintenance department of the airline. The department will create maintenance programs with activities that are considered line maintenance and those considered base maintenance.
Given the complexity of each aircraft, there is usually a specific maintenance program for each type of aircraft which is why some aircraft operators look for external maintenance engineering services.
The scope of aircraft maintenance can vary depending on the size and type of aircraft, as well as the specific issue that needs to be addressed. However, there are certain types of maintenance tasks that are commonly performed on most aircraft. These tasks include:
Cabin checks are performed to ensure that all emergency equipment is in working order and that all passenger seat belts are functional. In addition, the cabin crew may use this time to perform routine cleaning and restocking activities.
Engine checks are performed to ensure that all engine systems are functioning properly. This includes checking oil levels, fuel system components, and engine performance data. In some cases, engine checks may also involve visual inspections of engine components for signs of wear or damage.
Aircraft systems checks are performed to ensure that all onboard systems are functioning properly. This includes checking the status of flight controls, navigation systems, communications systems, and electrical systems. In some cases, aircraft systems checks may also involve testing individual components to ensure proper function.
One of the benefits of line maintenance in aviation is cost savings. Through regular line maintenance, airlines can avoid more costly and time-consuming repairs and replacements down the road. Additionally, line maintenance allows for quicker identification and resolution of potential problems before they become larger issues.
Line maintenance also helps ensure the safety of passengers and crew on board aircraft by regularly checking and maintaining critical components such as engines, flight control systems, and navigation equipment.
Furthermore, regular line maintenance helps maintain compliance with regulatory requirements for airworthiness. This not only ensures safety but also allows airlines to continue operating without interruption or delay.
Line maintenance is a vital part of keeping an aircraft in good working conditions. By performing routine checks and repairs, licensed mechanics can ensure that an aircraft remains safe and airworthy. Not only is it required by regulations, but it also helps to prevent potential accidents and malfunctions.
In addition, line maintenance can help improve efficiency and reduce downtime for aircraft operators, ultimately leading to better overall profitability for them. It is important for airline companies to have a comprehensive line maintenance program in place and to properly train their staff on proper maintenance procedures. The responsibilities of line maintenance personnel should not be taken lightly as they play a crucial role in ensuring safe flights for all passengers.
Fortunately, advancements in technology have allowed for improved methods of line maintenance, such as predictive maintenance and digitization of processes. With these new tools, both engineers and technicians can have better results from any inspection or repair.
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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.
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.
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.
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.
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