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ACCESSORY GEARBOX – a gearbox mounted on the engine of an aircraft, which transmits the shaft power to numerous mechanical devices, such as engine driven pumps. The gearbox reduces (or increases) the rotational speed of shafts needed to power such external devices.

AIRCRAFT MAINTENANCE MANUAL – the main maintenance manual issued by the aircraft manufacturer. It describes in practical detail and in steps all maintenance tasks which are required by the MPD and also others, related to defect rectification.

AIRCRAFT ON GROUND – an acronym used to describe any situation in which the aircraft cannot return to commercial service thereby causing large financial losses to the operator and problems for passengers. This term is almost like an “SOS” in aircraft maintenance. It is being used to expedite deliveries of parts, assure prompt reaction from the aircraft manufacturer, etc. It is very bad practice to misuse the term AOG for situation which are not critical.

BILL OF MATERIAL – a document listing required material for a given maintenance task. Often used during major task, such as a large aircraft modification. A BOM shows exactly what part numbers and in what quantities are required to complete a modification.

COMPONENT MAINTENANCE MANUAL – a maintenance manual for aircraft components. Under a typical Part 145 aircraft approval, CMM procedures may not be used. The CMM is used by specialized shops having a Part 145 approval for specific aircraft components. Therefore, the CMM contains maintenance tasks which must be done off wing. On wing maintenance procedures would be described in the AMM.

EUROPEAN AVIATION SAFETY AGENCY – a European international body, which regulates aviation issues. EASA prepares drafts of new regulations, which are then passed by the European Commission.

EXHAUST GAS TEMPERATURE – the temperature of the gases leaving the engine. This is a very basic parameter to determine the deterioration state of an engine.

ENGINE SERIAL NUMBER – the serial number of a given engine, the only way to distinguish between different engines of the same type.

ENGINE SERVICE MANUAL – a publication, created by the Engine Manufacturer, which describes how to maintain the engine.

FEDERAL AVIATION ADMINISTRATION – the US national aviation authority.

FULL AUTHORITY DIGITAL ENGINE CONTROL – this is a digital device (a “computer” as some would say) which controls the operation of an engine. The FADEC is responsible that a simple input from the pilot or autopilot (such as a movement of the Throughst lever) corresponds to appropriate engine behavior. In particular, the FADEC must adjust the engine fuel injection to current temperature, pressure and other environmental factors. It is very important and also very expensive aircraft component.

GROUND SUPPORT EQUIPMENT – equipment which is used on the ground to assist in handling and maintenance actions on the aircraft. This can be a set of stairs, a crane, a jack or just about anything else.

HIGH PRESSURE COMPRESSOR – this is the compressor in a turbine engine, which takes in air already compressed by the previous, low pressure, compressor and compresses it even further. When looking at the cross section of an engine, this would be the compressor closest to the combustion chamber.

HIGH PRESSURE TURBINE – the high pressure turbine is located directly behind the combustion chamber of a turbine engine. It is driven by high pressure gas created from the combustion of fuel in the engine and powers the high pressure compressor

INTERNATIONAL AIR TRANSPORT ASSOCIATION – an international body, which derives standards for the aviation industry worldwide. IATA aims more at commercial, rather than technical, aspects of the air transport business.

INTERNATIONAL CIVIL AVIATION ORGANIZATION – an international aviation organization, which works under the cover of the United Nations. ICAO was established in 1944 and its goal is to pursue unified aviation regulations, in particular concerned with aviation safety, throughout the world. ICAO publishes its Annexes, which are a set of guidelines (similar in form and matter to national regulations) for several aspects of air transport. The regulations from national aviation authorities, such as the FAA and EASA, are based largely on ICAO standards.

ILLUSTRATED PARTS CATALOGUE – a publication, created by the aircraft manufacturer, which lists all the parts which can be found on the aircraft. The listing is divided into ATA chapters and provides part numbers for every part and component which may be replaced during regular aircraft maintenance. In most cases, the IPC will also list the data of the component vendor, so that airlines can easily source a given part.

LIFE LIMITED PART – a part or component, for which a life limit has been set by the manufacturer. A life limit, unlike a hard time requirement, means the necessity to scrap (destroy) a given part. In modern aircraft, there are only a few life limited parts installed – mainly in the engines and the landing gear. However, the life limits are sacred and may not be, in any circumstance, overflown.

LOW PRESSURE COMPRESSOR – a part of a turbine engine, the low pressure compressor takes in air at outside air pressure and compresses it to an initial value. This value i
s normally too small for a turbine engine to operate efficiently and is then passed into the high pressure compressor. The low pressure compressor is located at the very front of a turbine engine (in case of a turbofan engine, just behind the fan).

LOW PRESSURE TURBINE – a part of a turbine engine, the low pressure turbine is located at the very end of the gas path of an engine. It is being run by the exhaust gas, and is placed after the high pressure turbine. The low pressure turbine transmits its torque via a shaft to the low pressure compressor.

LINE REPLACEABLE UNIT – any component of an aircraft or engine which can be replaced during line maintenance. This constitutes complete components, like avionic units, whole engines or engine components like the FADEC.

MINIMUM EQUIPMENT LIST – a list of aircraft components or systems which may be inoperative during flight. The list shows what may be defective and also a set of limitations which are imposed on a flight due to the defect. The list is derived from a master minimum equipment list, which is published by the aircraft manufacturer, but it can and should be updated by an airline and must be approved by the national aviation authority.

MANUFACTURE DATE – the date an aircraft, engine or component has been manufactured. Typically, the date of the C of A or the export C of A is used to determine the actual manufacture date of an aircraft.

MAINTENANCE PLANNING DOCUMENT – a document issued by the aircraft manufacturer, outlining all maintenance tasks and maintenance intervals applicable to a given aircraft. The MPD is a basis for an airline’s approved maintenance program (AMP), although airlines can change some of the MPD requirements based on their own user experience and own operating conditions. Such changes must be approved by the local aviation authority.

MAINTENANCE REVIEW BOARD – a board of experts which works on approving and creating methodologies for the creation of MPDs (Maintenance Planning Documents). Those groups define intervals for maintenance tasks based on their experience and research data provided by the manufacturers.

MAINTENANCE AND REPAIR ORGANIZATION – an organization which is certified to perform maintenance and repair on an aircraft, engine or aircraft component. In Europe, such organizations must be approved in accordance with Part 145.

ORIGINAL EQUIPMENT MANUFACTURER – the original manufacturer of an aircraft, engine or component. The OEM in aviation will be a company which holds the type certificate (TC) for the aircraft or engine. An OEM has several responsibilities, including the publication and updating of all required manuals, approving repair designs, issuing service bulletins, etc.

OUTLET GUIDE VANES are an essential element of the engine’s compressor that is responsible for the efficient delivery of air.

QUALITY ASSURANCE – a set of tasks performed to ensure that all processes within an organizations are carried out in accordance with the aviation regulations and internal company procedures. Today, quality assurance or quality monitoring is often referred to as compliance monitoring.

RETURN TO SERVICE – the process of returning an aircraft back to service after maintenance activities. During a heavy check this includes completing the check work package, ensuring that all tasks have been completed and properly signed off and issuing the final certificate of release to service (CRS).

SERVICE BULLETIN – a technical document issued by the manufacturer (type certificate holder) of an aircraft or by a Part 21 design organization. An SB contains information on how to modify an aircraft or aircraft maintenance schedule.

SERIAL NUMBER – self-explanatory. The serial number serializes (defines) specific components of a given part number.

SHOP VISIT – a maintenance event on an aircraft component, such as an engine, landing gear or any other, less complex part. After a shop visit, the component is released back to service by means of a release certificate such as an EASA Form One.

SHOP VISIT REPORT – a report issued after a shop visit by the maintenance facility. The shop report details all work performed on a component. It is not mandatory to issue a shop visit report, although they are to be expected especially after work performed on complex components such as engines or landing gear.

TURN AROUND TIME – the number of days it takes to MRO a tool before it is returned to service.