ADIRS-1 inoperative
Primary ADIRS channel 1 failed; aircraft relying on remaining or standby navigation sources in accordance with MEL.
View termCategories
MEL and CDL MEL and CDL
Browse MEL and CDL MEL and CDL terms for pilots, air traffic controllers, cabin crew and aviation learners.
Languages
Air-Conditioning Pack Inoperative
Indicates a failure of an air-conditioning pack, possibly affecting cabin pressurization and requiring MEL compliance before dispatch.
View termAirworthiness directive logged
Mandatory compliance record entered in technical log documenting completion of authority-issued safety directive.
View termAlternate procedure required
Standard operating sequence unavailable; crew must follow officially published alternate or contingency checklist.
View termAnti-ice valve failure
Malfunction of wing or engine anti-ice valve preventing hot-air flow, compromising ice protection and requiring flight profile adjustment.
View termAntiskid System Inoperative
A condition where the antiskid braking system is not operational, requiring alternate braking procedures and possible performance penalties.
View termATA chapter reference
Standardized reference number identifying aircraft system/component according to the ATA 100/2200 maintenance coding system.
View termAuxiliary generator inoperative
Aircraft auxiliary power unit (APU) generator not providing electrical power, requiring external source for ground operations and start.
View termAuxiliary Power Unit Dispatch
Authorization for a flight to dispatch with the Auxiliary Power Unit (APU) operating or required, usually due to ground power limitations or MEL stipulations.
View termBleed-Off Take-off
A take-off performed with engine bleed air turned off to optimize thrust, typically when performance-limited.
View termBrake Wear
The condition in which the aircraft’s brake components have undergone material loss due to repeated use, requiring monitoring and possible replacement if limits are exceeded.
View termCabin Log Defect
A discrepancy, malfunction, or abnormality reported by crew and recorded in the aircraft cabin log for maintenance attention, typically affecting passenger or crew services and requiring rectification before or after flight.
View termCabin pressure controller 1 inoperative
Primary automatic pressurization channel failed; crew managing cabin differential in manual mode per QRH procedures.
View termcategory A
A Minimum Equipment List category requiring rectification of an inoperative item within a time period specified in the MEL, usually before next flight.
View termcategory B
A Minimum Equipment List category requiring rectification of an inoperative item within three consecutive calendar days, excluding the day of discovery.
View termcategory C
A Minimum Equipment List category requiring rectification of an inoperative item within ten consecutive calendar days, excluding the day of discovery.
View termcategory D
A Minimum Equipment List category requiring rectification of an inoperative item within 120 consecutive calendar days, excluding the day of discovery.
View termCertified release to service
Formal written declaration by licensed engineer that aircraft or component is airworthy and fit for return to operation.
View termCompass deviation
Error between magnetic compass indication and actual magnetic heading exceeding permissible limits; requires calibration swing.
View termCondition monitoring
Ongoing process of assessing system or component health through data and trend analysis to guide maintenance decisions.
View termConfiguration Deviation
A formally approved variation from the aircraft’s standard configuration as specified in the Configuration Deviation List (CDL), which may permit flight with certain external parts missing or inoperative.
View termconfiguration deviation list
An official document specifying permissible aircraft configuration deviations that do not affect safe flight, used for dispatch with non-standard configurations.
View termConfiguration Deviation List Item
An entry in the Configuration Deviation List authorizing dispatch with specific external or configuration deviations, within specified limitations.
View termConfiguration Deviation List Item
An authorized deviation from aircraft configuration detailed in the Configuration Deviation List, permitting dispatch with specific missing or inoperative external parts.
View termconsecutive flights
A sequence of successive flights where certain MEL/CDL items may remain deferred or require repeated checks as specified.
View termConsumable replenished
A maintenance log entry confirming replenishment of expendable items such as oil, hydraulic fluid, or oxygen.
View termcontrol number
A unique identifier assigned to a deferred defect, MEL/CDL item, or maintenance entry for tracking and compliance.
View termcorrective action
The specific maintenance or operational step taken to resolve a defect, discrepancy, or deferred item as documented in the logbook or MEL.
View termCrew seat inoperative
Flight-deck seat fails to lock, adjust, or retract, potentially compromising crew safety and requiring MEL evaluation.
View termdeferral
A formal process allowing a non-essential inoperative item to be left unrepaired for a specified time under MEL/CDL limits.
View termDeferred action control
Cockpit switch or placard indicating an MEL-approved deferred maintenance item that must not be activated in flight.
View termdeferred defect report
A formal record noting a defect which has been deferred under MEL/CDL procedures, including details of rectification plan and interval.
View termdispatch deviation
An authorized variation from standard aircraft configuration or equipment status, documented for legal dispatch of a flight.
View termDispatch limitation
Restrictive condition under which an aircraft may be dispatched due to system defect or MEL, affecting allowable operation.
View termEngineering order applied
Formal modification or repair directive implemented and documented by engineering, referenced in aircraft technical records.
View termETOPS Minimum Equipment List
The Minimum Equipment List applicable to extended-range (ETOPS) flights, specifying the minimum required equipment for oceanic and remote area operations.
View termEvacuation slide inoperative
Inflatable escape slide at an aircraft door unserviceable, precluding passenger carriage until rectified or deferred per MEL.
View termFerry flight permission
Authority granted to reposition an aircraft without revenue passengers, often under MEL limitations, to maintenance or delivery point.
View termFleet campaign directive
Mandatory maintenance or modification order issued by the operator or manufacturer, applicable to an entire fleet.
View termFlight crew defect report
Written logbook entry by flight crew describing observed technical defect or malfunction requiring maintenance action.
View termFunctional test needed
Indicates requirement for an operational or systems test to confirm correct function of a repaired or replaced item.
View termHydraulic Quantity Low
Indicates that the fluid level in a hydraulic reservoir is below the specified minimum for safe system operation.
View termIn-flight Engine Start
The procedure of starting an engine during flight, often due to engine flameout or following maintenance.
View termInspection due soon
Notification that a scheduled inspection interval will be reached within a short time frame, requiring planning.
View termInterim Procedural Revision
A temporary update to operational or maintenance procedures, issued before the next official revision, to address urgent safety, regulatory, or operational requirements. Used in documentation and flight operations until formal revision is published.
View termInterphone inoperative
Internal crew communication system not functioning, affecting cockpit-cabin coordination and triggering MEL action.
View termLife vest missing
Required passenger flotation device absent from its assigned seat location, rendering that position unserviceable until replaced in accordance with the MEL.
View termlogbook entry
A formal record in the aircraft technical log documenting the status, action, or deferral of an MEL/CDL item for legal and maintenance tracking.
View termMaintenance check flight
Post-maintenance air test conducted to verify aircraft performance and systems before return to commercial service.
View termMaintenance control center
Centralized department overseeing aircraft technical status, defect clearance, and authorizing maintenance actions and MEL deferrals.
View termmaintenance procedure
A required action by maintenance personnel to address an MEL/CDL item, often prerequisite for dispatch or rectification.
View termminimum equipment
The essential items that must be serviceable for an aircraft to be dispatched under the MEL; if not available, flight is not permitted.
View termMinimum Equipment List
An approved document listing the minimum equipment required for safe operation of an aircraft, permitting specified inoperative items under controlled conditions.
View termno-go item
An inoperative or missing item which, according to MEL or regulatory requirements, prevents the aircraft from being legally dispatched.
View termNon-routine Work Entry
A maintenance log entry documenting unscheduled or unexpected technical issues or discrepancies detected during aircraft operations, requiring attention beyond regular or planned maintenance.
View termnonessential equipment and furnishings
Equipment or furnishings that are not essential for the airworthiness or safety of the flight and may be deferred.
View termNonessential Equipment and Furnishings
Equipment and furnishings that are not required for safe operation or regulatory compliance and may be inoperative without affecting dispatch eligibility.
View termOperational impact note
Written record in technical log noting operational effects or limitations resulting from an aircraft defect, MEL, or deferred item.
View termoperational procedure
A mandatory action or set of actions required by flight crew to safely operate an aircraft system, especially with an MEL/CDL item.
View termOperator Minimum Equipment List
The MEL approved by the state of the operator, tailored to specific airline operations, listing minimum equipment required for dispatch.
View termOut-of-phase check
Maintenance inspection not aligned with normal cycle, scheduled according to special interval or condition.
View termParts awaiting supply
Maintenance action deferred because required replacement part is not yet available in inventory or supply chain.
View termPerformance Penalty
A reduction in aircraft performance, such as climb, takeoff, or landing, resulting from inoperative systems or configuration deviations.
View termPitot cover installed
Protective pitot-tube cover still fitted, blocking dynamic-pressure input and rendering airspeed indications unreliable.
View termplacard
An official sign or label installed in the cockpit or cabin to indicate equipment limitations, status, or required procedures per MEL or CDL.
View termProtective breathing equipment missing
Required PBE smoke-hood absent from crew station or galley, violating safety regulations until replaced.
View termRectification interval extension
Formal approval to extend the allowable period for repair of a deferred defect beyond original MEL interval.
View termrepair interval
The maximum period permitted by the MEL for rectifying an inoperative item before mandatory maintenance is required.
View termrepeat item
A recurring defect or observation required to be checked, recorded, or repeated at intervals specified in the MEL or logbook.
View termScheduled component change
Pre-planned replacement of a part or system component at a specified interval or due time according to maintenance schedule.
View termScheduled component change
Pre-planned replacement of an aircraft component at specific intervals in accordance with the maintenance schedule.
View termService bulletin pending
Manufacturer’s recommended modification or inspection not yet incorporated; outstanding action listed in maintenance records.
View termService difficulty report
Official report filed to aviation authority documenting significant aircraft/system in-service malfunction, defect, or repeated failure.
View termSpoiler Deactivated
A system status where one or more spoiler panels are intentionally or automatically rendered inoperative for the flight.
View termStandby ADIRU
Independent backup ADIRU providing attitude, heading, and air-data when primary systems are degraded or failed.
View termStatic wick missing
Static electricity discharge wick absent from wing or control surface, potentially increasing radio interference until replaced.
View termTask card completed
Documented evidence that all steps of an assigned maintenance task card have been performed and signed off.
View termTechnical Dispatch Sheet
A formal document or electronic record certifying an aircraft’s airworthiness and readiness for flight after maintenance actions or inspections, required to be completed and signed by authorized personnel before each departure.
View termThrust Reverser Inoperative
The thrust reverser mechanism cannot be deployed, requiring alternative braking methods and possibly affecting landing performance.
View termTransponder Failure
The aircraft’s transponder is not transmitting, impacting radar identification and requiring ATC notification and alternate procedures.
View termTroubleshooting required
Further diagnostic action needed to isolate cause of technical fault or failure not resolved by initial inspection.
View termVery High-Frequency Radio 1 Inoperative
Primary VHF radio channel 1 is not functional, requiring use of alternate radio or backup for ATC communications.
View termWeight Penalty
An increase in operational weight or a reduction in allowable weight imposed due to specific inoperative equipment or configuration deviations.
View termWork card reference
Unique identifier of a maintenance work card specifying approved procedures for inspection, repair, or modification.
View term