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TECHNICAL TERMS

Accident

Advisory Circular

Aircraft

Aircraft Communications Addressing and Reporting System (ACARS)

Aircraft, Large

Aircraft, Small

Aircraft Maintenance Manual (AMM)

Airplane

Airworthiness

Airworthiness Certificate

Airworthiness Directive (AD)

Assembly

Burden, Maintenance

Cargo

Component

Cost, Direct and Indirect

Cycle, Aircraft Operating

Damage, Foreign Object (FOD)

Engine

Engine Shop Visit

Expendable

Extended Overwater Operations

Extended-Range Operations (EROPS)

Extended-Range Twin-Engine Operations (ETOPS)

Fail-Safe

Flight

Hot Section Inspection (HSI)

Hours, Block/Flight

Inspection, Detailed

Inspection, External Surveillance (Structural)

Inspection, General Visual

Inspection, Internal Surveillance (Structural)

Inspection, Walk-Around Check

Item, Expendable

Item, Life-Limited

Item, Repairable

Item, Rotable

Item, Time-Limited

Life, Economic Useful

List, Minimum Equipment (MEL)

Maintenance

Maintenance, Condition-Monitored

Maintenance, Hard Time

Maintenance, On-Condition

Maintenance, Scheduled

Mean Time Between Failure (MTBF)

Mean Time Between Removals (MTBR)

Mid-Time, Mid-Life

Non-Destructive Testing (NDT)

Overhaul

Pool, Parts

Program, Maintenance

Quick Engine Change (QEC)

Rebuild

Registration Certificate

Repair

Repairable

Rotable

Rotorcraft

Service Bulletin (SB)

Supplemental Type Certificate (STC)

Time, Block

Time, Flight

Time, Total

Time Between Overhauls (TBO)

Traffic Alert and Collision Avoidance System (TCAS)

Type Certificate

Type Certificate Data Sheet

Utilization, Aircraft

 

ACCIDENT

        An occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight, until such time as all such persons have disembarked, in which:

ADVISORY CIRCULAR

        A publication of the FAA to inform the aviation public of non-regulatory material of interest.  Unless incorporated into a regulation by reference, the contents of an AC are not binding.  An AC is issued to provide guidance and information in its designated subject area or to show a method acceptable for complying with a related Federal Aviation Regulation.

 

AIRCRAFT

        A device that is used or intended to be used for flight in the air.

 

AIRCRAFT COMMUNICATIONS ADDRESSING AND REPORTING SYSTEM (ACARS)

        A communications system that automatically reports via radio when and aircraft is out of the gate, off the ground, back on the ground, and at the gate again, thus automatically collecting data on flight cycles, flight time and block time.  During flight the system may also monitor and report on aircraft and engine performance.

 

AIRCRAFT, LARGE

        A defined category used by the US FAA for aircraft having a maximum certificated takeoff weight more than 12,5000 pounds.

 

AIRCRAFT, SMALL

        A defined category used by the US FAA for aircraft having a maximum certificated takeoff weight of 12,5000 pounds or less.

 

AIRCRAFT MAINTENANCE MANUAL (AMM)

        A manual that describes the methods, techniques and practices to be used by persons performing maintenance, alterations or preventive maintenance on an aircraft (see FAR 43.13)

 

AIRPLANE

        An engine-driven fixed-wing aircraft, heavier than air, that is supported in flight by the dynamic reaction of the air against its wings.

 

AIRWORTHINESS

        The condition of an item (aircraft, aircraft system or part) in which that item is capable of operating in a safe manner to accomplish its intended purpose.  Two key factors are: the aircraft (or device) must conform to its type design and it must be in a condition for safe operation.

 

AIRWORTHINESS CERTIFICATE

        An Airworthiness Certificate is issued by the FAA for an individual aircraft when it is satisfied that the aircraft conforms to the Type Certificate and is in a condition for safe operation.  The Airworthiness Certificate is issued to the registered owner, and is transferred with the aircraft.  It remains in effect as long as the aircraft is maintained (or altered) according to the appropriate FAA regulations and continues to be registered in the United States. (See FAR 21).

 

AIRWORTHINESS DIRECTIVE (AD)

        A mandatory order issued by the FAA, usually applying to specific types of aircraft, engines or appliances, when an unsafe condition exists and that condition is likely to exist or develop in other aircraft, engines or appliances of the same design.  An AD usually requires some maintenance action (possibly only an inspection), within some specific time in order to ensure continued safety and airworthiness, and no aircraft may be operated in contravention of the requirements or limitations of an AD.

 

ASSEMBLY

        A number of parts, subassemblies, or any combination thereof joined together to perform a specific function and which can be disassembled without destruction of designed use.  (The distinction between an assembly and a subassembly is not always exact.  An assembly in one instance may be a subassembly in another where it forms a portion of an assembly.)

 

BURDEN, MAINTENANCE 

         (Also referred to as INDIRECT MAINTENANCE COST)  Those maintenance labor and material costs not considered to be direct maintenance costs, but which contribute to overall maintenance program costs through overhead operations, administration, record-keeping, scheduling, controlling, planning, supervision, tooling, test equipment, facilities, etc.

 

CARGO

        All traffic other than passengers.  Cargo included freight, mail and excess baggage shipments.

 

COMPONENT

        Any self-contained part, combination of parts, sub-assemblies or units, which perform a distinctive function necessary to the operation of a system.

 

COST, DIRECT AND INDIRECT

        Although there is not an "official" definition from any regulatory body, aircraft direct operating costs (DOCs) are customarily categorized as follows:

                                Flying Operations

                                            Crew Salaries & Expenses

                                            Fuel & Oil

                                            Insurance

                                Maintenance

                                            Direct Labor & Materials

                                            Maintenance Burden

                                Depreciation & Rentals

                                Landing Fees & Airport Handling Charges (sometimes)

 

The major categories of indirect operating costs include:

                                Aircraft Services

                                Traffic Services

                                Servicing Administration

                                Reservations & Sales

                                Advertising & Publicity

                                General & Administration

 

CYCLE, AIRCRAFT OPERATING

        A complete flight sequence including taxi, takeoff, flight en route, and landing.  In the case of engines, a cycle includes starting, acceleration, to maximum rated power, deceleration and stopping (FAR 33.14).

 

DAMAGE, FOREIGN OBJECT (FOD)

        Damage to any portion of the aircraft (most commonly engines) caused by the impact or ingestion of birds, stones, hail or other debris.

 

ENGINE

        The basic engine assembly plus its essential accessories as supplied by the engine manufacturer.  These included those units and components which are used to induce and convert fuel/air mixture into thrust/power; to transmit power to the propeller shaft, if any, and accessory drives; to supplement the function of other defined systems external to the engine; and to control and direct the flow of internal lubrication.  The nacelle and reverser are excluded.  See also definition of QEC.

 

ENGINE SHOP VISIT

        An engine removal is classified as a "shop visit" whenever the subsequent engine maintenance performed prior to reinstallation entails one of the following:

Sometimes the definition is specifically tailored, as in some Airworthiness Directives that say, for example, "for the purpose of this AD, an engine shop visit is defined as input to an engine repair shop where the low pressure turbine module is removed"...or "the front and rear flanges of the combustion case are separated"... or "any major module is separated"... or "the inlet gearbox is exposed."

       

EXPENDABLE

        See ITEMS, EXPENDABLE

 

EXTENDED OVERWATER OPERATIONS

        Flight operations over water at a horizontal distance of more the 50 nautical miles from the nearest shoreline.  These are operations for which the regulations require certain communications equipment, as well as various items of emergency and water survival equipment (life rafts and emergency flotation devices, for example).  Note that the distance is specified from the shoreline, not necessarily from an airport.

 

EXTENDED-RANGE OPERATIONS (EROPS)

        Generally, flight operations at a distance more then 60 minutes flying time with one engine inoperative from a suitable airport.  "EROPS" now has virtually no official standing except within Canada where certain communication, navigation and emergency requirements pertain to all aircraft in extended -range operations, regardless of the number of engines.  In the US and many other countries, the requirements have evolved into "ETOPS" (listed separately below) with rules that apply only to twin-engine aircraft operating beyond the 60-minute distance.

 

EXTENDED-RANGE TWIN-ENGINE OPERATIONS (ETOPS)

        ETOPS applies specifically to twin-engine aircraft operated at a distance more than 60 minutes flying time with one engine inoperative from a suitable airport.  In the US there are approvals for ETOPS at distances from suitable airports, varying from 75 minutes up to 180 minutes at the engine-out cruising speed.  In general, aircraft used in ETOPS must have an ETOPS type design approval which may require the incorporation of a substantial number of equipment operations and Service Bulletins, and the national air authorities may approve specific operators, aircraft and routes based upon various qualifications, demonstrated reliability and competence.  See Advisory Circular 120-42A for a discussion of the US requires of ETOPS.  See also EROPS above.

 

FAIL-SAFE

        A design criterion which requires that predictable failure of an item will not place the aircraft into an uncontrollable condition.  The intent is that a partial failure of a structured element, for example, will not lead to the catastrophic failure of the entire structure.

 

FLIGHT

        The entire passage consisting of one or more flight legs, from leaving the airport of origin to arrival at the airport of final destination and operated under one flight number.

 

HOT SECTION INSPECTION (HSI)

        The inspection and restoration of the hot section items of an engine (principally the combustion and turbine sections), usually at a predetermined time/cycle limit.  A hot section inspection is not necessarily considered an "ENGINE SHOP VISIT" (see separate listing) if no major disassembly or repairs are required.

 

HOURS, BLOCK/FLIGHT

        See TIME

 

INSPECTION, DETAILED

        An intensive visual examination of a specified detail, assembly or installation.  It searches for evidence of irregularity using adequate lighting and, where necessary, inspection aids such as mirrors, hand lends, etc.  Surface cleaning and elaborate access procedures may be required.

 

INSPECTION, EXTERNAL SURVEILLANCE (STRUCTURAL)

        A visual check that will detect obvious unsatisfactory conditions/discrepancies in externally visible structures.  It may also include internal structure which is visible through quick opening access panels/doors.  Workstands, ladders, etc. may be required to gain proximity.

 

INSPECTION, GENERAL VISUAL

        A collective term which includes the External Surveillance Inspection, the Internal Surveillance Inspection and the Walk-Around Check.

 

INSPECTION, INTERNAL SURVEILLANCE (STRUCTURAL)

        A visual check that will detect obvious unsatisfactory conditions/discrepancies in internal structures.  This type of inspection applies to obscured structures and installations which require removal of fillets, fairing, access panels/doors, floor-boards, liners, insulation blankets, etc.

 

INSPECTION, WALK-AROUND CHECK

        A visual check conducted from ground level to detect obvious discrepancies.

 

ITEM, EXPENDABLE

        Items for which no authorized repair procedures exists, and for which cost of repair would normally exceed that of replacement.  Expendable items include nuts, bolds, rivets, sheet metal, wire, light bulbs, cable and hose.  For financial accounting purposes, expendable items are normally considered to be consumed when they are issued, so they are then not carried as inventory assets.

 

ITEM, LIFE-LIMITED

        An item which, when listed on the aircraft, engine or propeller type certificate data sheet or the manufacturer's instructions for continued airworthiness, must be permanently removed from service and discarded before a specified time (e.g. hours, cycles or calendar limit) is achieved.  Among the most significant life-limited items for appraisal purposes are engine disks and shafts.

 

ITEM, REPAIRABLE

        A replacement part or component, commonly economical to repair, and subject to being rehabilitated to a fully serviceable condition over a period of time less than the life of the flight equipment to which it is related.  Examples include many engine blades and vanes, some tires, seats and galleys.

 

ITEM, ROTABLE

        An item that can be economically restored to a serviceable condition and, in the normal course of operations, can be repeatedly rehabilitated to a fully serviceable condition over a period of time approximating the life of the flight equipment to which it is related.  Examples include avionics units, landing gears, auxiliary power units and major engine accessories.

 

ITEM, TIME-LIMITED

        An item which must be inspected, tested or reconditioned at specified intervals of time (hours, cycles or calendar) in order to ensure continued airworthiness.  Not the same as ITEM, LIFE-LIMITED listed separately.

 

LIFE, ECONOMIC USEFUL

        As it pertains to an aircraft or engine, the economic useful life is the period of time over which it is (or is expected to be) physically and economically feasible to operate it in its intended role.  Periodic maintenance and repair will usually be required in order to preserve safety and efficiency during the economic useful life.

 

LIST, MINIMUM EQUIPMENT (MEL)

        An approved list of items which may be inoperative for flight under specified conditions and/or specific limited periods of time.  For example, an aircraft with triple-redundant navigation systems might be permitted to depart with one system inoperative, or certain lights may be inoperative for daylight flights.  An MEL is not transferable between operators of the same equipment.

 

MAINTENANCE

        Those actions required for restoring or maintaining an item in serviceable conditions, including servicing, repair, modification, overhaul, inspection, determination of condition, preservation and storage.

 

MAINTENANCE, CONDITION-MONITORED

        A primary maintenance process under which data on the whole population of specified items in service is analyzed to indicate whether some allocation of technical resources is required.  Not a preventive maintenance process, condition monitored maintenance allows failures to occur, and relies upon analysis of operating experience information to indicate the need for appropriate action.

 

        Note:  Failure modes of condition-monitored items do not have a direct adverse effect on operating safety.

 

MAINTENANCE, HARD TIME

        A primary maintenance process under which an item must be removed from service at or before a previously specified time in order to perform some required actions such as inspection or refurbishment.

 

MAINTENANCE, ON-CONDITION

        A primary maintenance process having repetitive inspections or tests to determine the condition of units, systems, or portions of structure with regard to continued serviceability.  Corrective action is taken when required by the item's condition.  For example, a hydraulic component may be tested regularly to determine its internal leakage rate, but refurbishment is required only when the rate exceeds a specified limit.

 

MAINTENANCE, SCHEDULED

        The maintenance performed at defined intervals to retain an item in a serviceable condition by systematic inspection, detection, replacement of worn out items, adjustment, calibration, cleaning, etc.

 

MEAN TIME BETWEEN FAILURE (MTBF)

        A performance figure calculated by dividing the total unit time or cycles accrued in a period by the number of unit failures that occurred during the same period.

 

MEAN TIME BETWEEN REMOVALS (MTBR)

        A performance figure calculated by dividing the total unit time or cycles accrued in a period by the number of unit removals (scheduled plus unscheduled) that occurred during the same period.

 

MID-TIME, MID-LIFE

        (Sometimes known as HALF-TIME, HALF-LIFE)  These are two terms commonly used by appraisers to describe the maintenance time status of an aircraft or engine.

 

NON-DESTRUCTIVE TESTING (NDT)

        A maintenance procedure to determine the condition of an area or part of an aircraft or component by means of tests that do not affect the function or serviceability of the item being tested.  Some commonly used NDT methods include visual, radiographic, magnetic particle, ulta-sonic, dye penetrant and eddy-current inspections.

 

OVERHAUL

        The disassembly, inspection and/or check of an aircraft, component, engine or appliance to an extent necessary to determine, as substantiated by service experience and accepted practices, that it is in satisfactory condition to operate one complete overhaul period.  It shall include the replacement, repair, adjustment or refinishing of such parts as required, which, if improperly accomplished would adversely affect the structural strength, performance, flight characteristics or safety of the aircraft involved.  See FAR 43.2 and also "REBUILD" defined below.

 

POOL, PARTS

        An arrangement whereby participants are entitled to withdraw items from the agreed stock held by any participant.

 

PROGRAM, MAINTENANCE

        A program, either acceptable or approved by airworthiness authorities, which defines a logical sequence of maintenance actions to be performed as events or pieces of a whole which, when performed collectively, result in achievement of the desired maintenance standards.  The program may be originated by the manufacturer or the operator.

 

QUICK ENGINE CHANGE (QEC)

        A QEC kit is a collection of components and accessories such as pumps, generators, thrust reverser, nose cowl, wiring harnesses and fluid lines installed onto a bare engine to speed the eventual installation of the entire power plant onto an aircraft.  See also ENGINE.  The actual make-up of the QEC kit will usually depend on the type of aircraft that the engine will be used on, and may also be different for different engine positions on the same aircraft.  With the QEC kit installed, the power plant is sometimes then called a QEC UNIT.

 

REBUILD

        A maintenance process whereby an aircraft, engine, propeller, appliance or component part is disassembled, cleaned, inspected, repaired as necessary, reassembled and tested to the same tolerances and limits as a new item, using either new parts or used parts that either confirm to new part tolerances or limits or to approved oversized or undersized dimensions.  See FAR 43.2.

 

REGISTRATION CERTIFICATE

        With certain exceptions for foreign aircraft, aircraft with temporary authorizations, or aircraft of the armed forces, no aircraft may be operated without a Registration Certificate that is issued to its owner by the FAA.  The Registration Certificate is also the basis for assigning a US Identification number (N-NUMBER).  Generally, the Registration Certificate remains effective until the aircraft is sold, exported, destroyed or scrapped.  

 

Note:  This definition pertains specifically to the US, but comparable regulations apply in most other jurisdictions.

 

REPAIR

        The restoration of an airframe, power plant or appliance to a condition for safe operation after damage or deterioration.  A "Major" repair is one that, if improperly done, might appreciably affect weight, balance, structural strength, performance, power plant operation, flight characteristics or other qualities affecting airworthiness.\

 

REPAIRABLE

        See ITEM, REPAIRABLE

 

ROTABLE

        See ITEM, ROTABLE

 

ROTORCRAFT 

        (Sometimes ROTOCRAFT)  A heavier-than-air aircraft that depends principally for its support in flight on the lift generated by one or more rotors.

 

SERVICE BULLETIN (SB)

        A document issued by the manufacturer to notify the owner or operator of an aircraft (or engine or other device) of recommended (or required by Airworthiness Directives) modifications, substitute parts, special inspections/checks, reduction of existing life limits or establishment of first-time life limits and conversions from one engine model to another.  Service Bulletins may or may not be FAA-approved.

 

SUPPLEMENTAL TYPE CERTIFICATE (STC)

        See also TYPE CERTIFICATE.  An STC is issued by the FAA to grant approval for an alteration of a product by a major change in the type design, where such a change is not great enough to require a new application for a Type Certificate.  The STC is kept by the applicant and is then the basis for issuing or retaining airworthiness certificates to all aircraft (or engines or propellers) subsequently modified in the same way.  In the case of alterations by the original manufacturer, approval is normally in the form of an amendment to the original Type Certificate, rather than an STC. (See FAR 21).

 

TIME, BLOCK

        Block time is the time from the moment an aircraft first moves for the purpose of flight until the moment is comes to rest at the destination; sometimes called block-to-block time.  Push-back time is considered as part of Block Time.

 

TIME, FLIGHT

        Flight time is the duration of the airborne portion of the flight, sometimes called the wheels-off to wheels-on time.  It is always less than block time (see above).

 

Note:  FAR1 appears to equate Block Time and Flight Time, but this is not generally accepted.

 

TIME, TOTAL

        The operating time that an aircraft, engine or component has accumulated since new.  Unless otherwise stated, this is usually total flight time, rather than total block time.

 

TIME BETWEEN OVERHAULS (TBO)

        The maximum time that an item is permitted to operate between overhauls.  TOBs are usually expressed in flight hours, cycles or calendar increments.

 

TRAFFIC ALERT AND COLLISION AVOIDANCE SYSTEM (TCAS)

        A system intended to alert flight crews of the existence of nearby aircraft and to provide warning of imminent collisions.  There are three categories of TCAS; TCAS I is a proximity warning system that advises pilots of the presence of nearby aircraft.  TCAS II is intended to warn pilots of an impending collision and it commands vertical avoidance maneuvers.  TCAS III warns of the impending collision and commands both vertical and horizontal avoidance maneuvers.

 

TYPE CERTIFICATE

        A Type Certificate pertains to aircraft, aircraft engines, and propellers.  The FAA issues a Type Certificate when the applicant (normally the manufacturer) submits the type design, test reports and computations and proves to the FAA's satisfaction that the product meets the applicable requirements of the FARs regarding airworthiness, noise and emissions.  The Type Certificate is kept at the manufacturer's facility and is the basis for issuing airworthiness certificates to all aircraft (or engines or propellers) subsequently manufactured according to the same type design. (See FAR 21).

 

        Type Certificates may also be issued for products manufactured in foreign counties with which the United States has an agreement for the acceptance of these products if the country of origin certifies that the product meets airworthiness, noise and emission standard equivalent to the US standards, and the manufacturer submits the appropriate supporting technical data.

 

TYPE CERTIFICATE DATA SHEET

        The Type Certificate Data Sheet is the part of the Type Certificate setting forth the limitations prescribed by the applicable airworthiness regulations and any other limitations and information found necessary for type certification.

 

UTILIZATION, AIRCRAFT

        The average daily flying hours for an aircraft or a fleet of aircraft.  May also be expressed in hours per year or hours per month.

 


Reproduced with permission from the ISTAT Appraiser's Handbook.

        

 

 

       



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Fleet Data Source: Aviation Week Intelligence Network Fleets Database and AVITAS research.