Study guide
14.3 Master Minimum Equipment List (MMEL), MEL & CDL Procedures
FAA Aircraft Dispatcher Certificate ADX
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1 Chapter 1: Regulations, Certification & Operational Control
1.1 Part 65 Subpart C: Certification, Eligibility & Currency 1.2 Operational Control & Dispatcher-PIC Joint Responsibility 1.3 Domestic, Flag & Supplemental Operations Framework 1.4 Dispatch Release Elements, Signatures & Recordkeeping 1.5 Regulations, Manuals, Crew Qualifications, and Source Control
2 Chapter 2: Atmospheric Physics, Pressure Systems & Fronts
2.1 Atmospheric Structure, Standard Atmosphere & Altimetry 2.2 Air Masses, Frontal Systems & Frontogenesis 2.3 Atmospheric Stability, Lapse Rates & Cloud Formation 2.4 Earth Motion, Regional Weather, Local Winds, and Water Phase Changes
3 Chapter 3: Aviation Weather Hazards & Severe Weather Avoidance
3.1 Structural and Induction Icing: Types, Accretion & Operations 3.2 Thunderstorms, Squall Lines, Microbursts & Low-Level Windshear 3.3 Clear Air Turbulence (CAT), Mountain Waves & Jet Streams 3.4 Low Ceilings, Fog Types & Visibility Restrictions 3.5 Hurricanes, Typhoons, Tornadoes, and Tropical Dispatch Hazards
4 Chapter 4: Weather Observations, Forecasts & Advisories Decoding
4.1 METAR and SPECI Surface Observations: Decoding & Operations 4.2 Terminal Aerodrome Forecasts (TAF): Groups & Timing 4.3 Pilot Weather Reports (PIREP): Coding, Severity & Urgent Alerts 4.4 In-Flight Advisories: AIRMETs, SIGMETs & Convective SIGMETs 4.5 Weather Collection, NWS Facilities, GFA, and EWINS
5 Chapter 5: Aviation Weather Charts & Upper-Air Analysis
5.1 Surface Analysis & Radar Summary Charts 5.2 Constant Pressure Analysis & Winds Aloft (FB) 5.3 Significant Weather Prognostic Charts (SIGWX) 5.4 Satellite Imagery, Moisture-Stability Analysis, and Forecast Integration
6 Chapter 6: Air Navigation, Airspace Architecture & Route Structure
6.1 National Airspace System: Classes, Rules & Special Use 6.2 Ground-Based Navigation Aids & Standard Service Volumes 6.3 Area Navigation (RNAV), GNSS/GPS, PBN & RNP Fundamentals 6.4 En Route Airways, SIDs, STARs & Chart Interpretation 6.5 Earth Coordinates, UTC, Chart Projections, and Flight Instruments 6.6 North Atlantic, Pacific, RVSM, and Global Navigation Differences
7 Chapter 7: Instrument Approaches, Minimums & Airport Operations
7.1 Precision Approach Systems: ILS Categories & Tolerances 7.2 Non-Precision Approaches, RNAV & Decision Minimums (MDA/DA) 7.3 Takeoff Minimums, Lower-Than-Standard & Takeoff Alternates 7.4 Holding Procedures: Patterns, Speed Limits & Timing
8 Chapter 8: Subsonic Aerodynamics & Jet Aircraft Performance
8.1 Subsonic Jet Aerodynamics: Lift, Drag & Flight Regimes 8.2 High-Altitude Flight: Mach Number, Buffet & Coffin Corner 8.3 Transport Turbine Engines: Thrust, Specific Fuel & Bleed Air
9 Chapter 9: Transport Category Takeoff & Landing Runway Analysis
9.1 Takeoff Performance Speeds & Balanced Field Concept 9.2 Takeoff Climb Segments & Obstacle Clearance Gradients 9.3 Landing Performance: Field Lengths, 60% Rule & Contamination
10 Chapter 10: En Route Performance, Driftdown Profiles & ETOPS Operations
10.1 One/Two-Engine-Inoperative En Route Net Profiles & Driftdown 10.2 Extended-Range Operations (ETOPS): Philosophy & Regulations 10.3 ETOPS En Route Alternates: Adequate vs. Suitable & Critical Fuel
11 Chapter 11: Aircraft Weight & Balance, Center of Gravity, and Loading
11.1 Transport Aircraft Structural Weight Limits: Definitions & Rules 11.2 Center of Gravity Computations: Datum, Arm, Moment & Index 11.3 Mean Aerodynamic Chord (%MAC) Computations & Stability 11.4 Payload-Range Analysis, Zero Fuel Weight Tradeoffs & Loading
12 Chapter 12: Destination Alternate Airport Selection & Weather Rules
12.1 Destination Alternate Selection: 91.169 & Part 121 1-2-3 Rule 12.2 Flag & Supplemental Operations Destination Alternate Rules 12.3 Derived Alternate Minimums: 1-Nav and 2-Nav Facility Rules
13 Chapter 13: Part 121 Fuel Planning, Reserves & En Route Re-Release
13.1 Part 121 Domestic Fuel Requirements: Reserves & Calculations 13.2 Part 121 Flag Fuel Requirements: 10% Reserve & Island Rules 13.3 Supplemental Fuel Requirements & Holding Fuel Management 13.4 Redispatch and En Route Re-release Procedures
14 Chapter 14: Transport Systems, Pressurization & MEL/CDL Procedures
14.1 Transport Jet Auxiliary Power, Electrical, Hydraulic & Pneumatic Systems 14.2 Cabin Pressurization, Rapid Decompression & Oxygen Requirements 14.3 Master Minimum Equipment List (MMEL), MEL & CDL Procedures 14.4 Flight Controls, Autoflight, Fuel, Oil, Brakes, and Fire Protection
15 Chapter 15: Hazardous Materials, Duty Regulations & Emergency Procedures
15.1 Dangerous Goods Carriage by Air (49 CFR Part 175) & NOTOC 15.2 Dispatcher Duty Limitations, Rest Requirements & Fatigue 15.3 Emergency Authority, Declaration & Diversion Decision-Making 15.4 NTSB Part 830 Accident Reporting & Wreckage Preservation 15.5 Security, Overdue Aircraft, and FAA Emergency Services
16 Chapter 16: Communications, ATC, and Flight Plan Procedures
16.1 Voice, Data Link, Position Reports, and Lost Communications 16.2 ATC Facilities, Separation, ICAO Flight Plans, and Traffic Management
17 Chapter 17: Human Factors and Practical Dispatch Applications
17.1 Dispatch Resource Management, Human Error, and Risk Decisions 17.2 Manual Flight Planning, PIC Briefing, Flight Watch, and Postflight Closeout
14.3 Master Minimum Equipment List (MMEL), MEL & CDL Procedures
Key Takeaways Explain This Topic AI
An MMEL entry alone does not authorize dispatch; use the operator’s approved MEL and § 121.628 authority.
MEL and CDL limitations can affect route, altitude, fuel, runway performance, and approach capability.
B, C, and D ordinarily use three, ten, and 120 calendar days excluding discovery day; Category A uses its stated terms.
A Category B calendar-day deadline is not exactly 72 elapsed hours after the discovery timestamp.
Any repair-interval extension requires actual authorized procedures and eligible-category conditions; it is not automatic.
Last updated: October 2026
MEL, CDL, and the Dispatch Decision
An aircraft discrepancy does not automatically ground a flight, but neither a maintenance log entry nor a pilot's acceptance supplies independent permission to operate with required equipment inoperative. Under § 121.628 , dispatch with inoperative instruments or equipment depends on the approved Minimum Equipment List (MEL) and its authorization, applicable conditions, and required procedures. Dispatchers verify the operational implications; qualified maintenance personnel perform the maintenance actions required by the approved system.
Document hierarchy
The Master Minimum Equipment List (MMEL) supplies the type-level basis for relief. The operator's approved MEL applies to its aircraft and operation and may be more restrictive. The AFM, airworthiness requirements, issued OpSpecs, maintenance program, and operating procedures can impose additional restrictions. The existence of an MMEL item alone does not authorize a particular carrier to defer it.
A Configuration Deviation List (CDL) addresses specified missing external parts and associated limitations or penalties. It is not permission to dispatch with any damaged or missing structure. Its approved conditions can affect drag, weight, altitude, speed, performance, or fuel. Some missing equipment can be covered by an MEL provision; the difference should not be reduced to “every internal item is MEL and every external item is CDL.” Identify the actual approved item.
Read the whole entry
A typical MEL entry specifies equipment quantity installed, quantity required, remarks or exceptions, and repair category. Check the aircraft applicability and operational purpose. A generator permitted inoperative for one kind of operation might not be acceptable for ETOPS or for a low-visibility approach. A release to a destination needing that capability can be unacceptable even though the airplane is eligible for some other flight.
The (M) symbol identifies required maintenance procedures; (O) identifies operating procedures. Authorized personnel and documentation requirements come from the approved procedures. Do not invent a rule that every (M) step universally requires one particular license irrespective of approved task permissions, or that only a dispatcher can perform every (O) step. Confirm the required actions have been completed by the proper personnel and that flight-specific restrictions are conveyed.
Repair intervals and the day of discovery
- Category Ordinary framework, subject to the actual entry
- A Repair within the time specified in the item's remarks/conditions
- B Three consecutive calendar days, excluding the day of discovery
- C Ten consecutive calendar days, excluding the day of discovery
- D 120 consecutive calendar days, excluding the day of discovery
Calendar days are not simply elapsed hours from the discrepancy timestamp. If a Category B item is discovered Monday at 1400, with an approved local-calendar-day system and no different applicable provision, Tuesday, Wednesday, and Thursday are its three counted days. It expires at the end of Thursday, rather than exactly 72 hours after Monday at 1400. An operator's defined time reference can be UTC or another approved basis; establish it before making the calculation.
Category A requires special attention because the entry can use calendar days, flight hours, cycles, or another stated interval. Do not apply the B/C day-of-discovery convention automatically to every A item. For example, an entry requiring repair within two flight cycles is counted using that entry's terms, not a two-day window.
Extension authority
An extension is not created by writing “parts unavailable” in the log. The operator must have the applicable continuing single-extension authority and comply with its approved procedures, oversight, and limits, as addressed in the issued MEL authorization such as D095. Do not attribute this universally to an invented M005 MEL-extension provision or claim Category D can never be extended under any authority.
Identify the eligible category, authorized extension duration, reason, approval, records, and any notification requirement from the actual issued authority. Category A's specific interval cannot simply be converted into a B/C/D extension by the dispatch desk. A practical test can provide a particular authorization; use its exact conditions. Without evidence of an allowed extension, treat the ordinary deadline as controlling and arrange repair or a different aircraft/plan.
Cumulative restrictions
An MEL fuel allowance and a CDL drag allowance can both affect the same flight. Apply the approved combination method, not a guessed additive or multiplicative rule. If a supplied exercise explicitly says independent multipliers of 1.03 and 1.02 apply, a 10,000-pound baseline becomes 10,000 × 1.03 × 1.02 = 10,506 pounds . If the approved procedure prescribes addition or a special combined table, that method controls instead.
Likewise, one acceptable item can interact with another. An inoperative APU plus a generator issue can compromise a redundancy assumption; a pack restriction can limit altitude and alter route fuel; an anti-skid defect can change runway performance; and a navigation defect can make a chosen approach or oceanic approval unavailable. Read interaction restrictions rather than assuming two individually deferable items are always acceptable together.
Worked dispatch review
A hypothetical airplane has an inoperative pressurization component. The MEL permits operation only at or below a supplied altitude and requires an operating procedure. Dispatch first confirms the maintenance action and repair interval. Next, the route is replanned at the permitted altitude using approved performance, terrain, oxygen, weather, and fuel data. Destination and alternate capability are checked at the expected landing weights. If the lower altitude puts the route into unsafe icing or terrain that the aircraft cannot clear, the flight cannot use that original plan.
A signed maintenance deferral establishes the item disposition; it does not prove all those route-specific checks were made. Conversely, a dispatcher cannot authorize a mechanic to ignore an expired interval simply because the route is short. The flight requires both a valid maintenance basis and a valid operational plan.
Flight-specific documentation
Preserve the discrepancy, deferral basis, interval, required procedures, operational restrictions, performance/fuel corrections, and crew briefing under the operator's approved workflow. During flight, a new failure calls for the AFM/QRH and operational reassessment; an MEL is principally a dispatch document, not a replacement for airborne emergency procedures. At arrival, ensure new discrepancies and follow-up actions reach maintenance control and the next dispatch team.
Official References
Source check: 2026-10-12 . Transport systems certification ; Part 121 oxygen and equipment ; FAA aircraft systems handbook . For operational use, apply current issued authorizations and the assigned aircraft’s approved data.