Use a Gantt chart to manage aircraft MRO events from A-check to D-check heavy maintenance, covering induction, findings, airworthiness compliance, and on-time delivery.
An aircraft sitting in a maintenance bay is an airline's most expensive non-revenue asset. Every day the aircraft is not flying, the airline loses the revenue it would have generated — typically $50,000–$500,000 per day for a widebody — while still paying the debt service, lease payments, and maintenance costs associated with it. Aircraft on ground (AOG) time is the primary financial driver behind MRO scheduling, and a Gantt chart is the primary tool MRO facilities use to compress that time while maintaining every required airworthiness standard.
Before building a Gantt chart, teams must understand which check type is being scheduled, because the scope, duration, and complexity differ by orders of magnitude.
A-Check: Performed every 400–600 flight hours or approximately monthly, depending on airline and aircraft type. An A-check takes 8–24 hours and is performed overnight at the airline's line maintenance facility. A Gantt for an A-check fits on a single page: aircraft arrives → pre-input inspection → work package execution (typically 20–50 tasks) → functional tests → release to service. Total elapsed time: one night shift.
B-Check: Historically performed every 1,000–2,000 flight hours. Many modern airlines have eliminated B-checks through engineering escalation, rolling the tasks into A and C checks. Where retained, a B-check takes 2–5 days.
C-Check: The first true "heavy" check. C-checks are performed every 4,000–6,000 flight hours or every 18–24 months. Duration: 1–3 weeks. The aircraft is inducted into a hangar bay, major structural inspections are performed, systems are overhauled, and Airworthiness Directives (ADs) and Service Bulletins (SBs) due during the interval are incorporated. The C-check Gantt is a multi-track document managing simultaneous work packages across airframe, avionics, cabin, engines, and landing gear.
D-Check (Heavy Maintenance Visit, HMV): The most comprehensive maintenance event in an aircraft's life. D-checks occur every 25,000–30,000 flight hours (approximately 10–12 years). Duration: 4–6 weeks for narrowbodies, 6–10 weeks for widebodies. The aircraft is essentially stripped: interior completely removed, cabin panels pulled, insulation blankets removed, paint stripped (for full corrosion inspection), all systems inspected and overhauled. D-check Gantt charts are highly detailed, multi-track documents managed by dedicated schedule engineers.
Before the aircraft arrives, the MRO facility plans the input: hangar bay assignment, tooling requirements, manpower loading, pre-ordered parts based on the planned maintenance program, and pre-purchased components for known findings. Planning begins 60–90 days before the check input date for C-checks, 90–180 days for D-checks. A well-planned input reduces the time spent waiting for parts and tooling once the aircraft is in the bay.
The aircraft arrives, is parked in the hangar bay, access stands and dock structures are positioned, initial paperwork is completed, and the first inspection walk-around is performed. Fuel is drained or defueled to a safe working level. All aircraft doors are opened, panels are removed, and the initial access configuration is established. Induction typically takes 1–2 days.
With the aircraft accessible, the inspection team conducts the initial survey: looking for obvious corrosion, damage, wear, and deferred defects from the airline's maintenance records. Corrosion findings are mapped — physically marked and documented — across the airframe. Structural findings discovered at this stage determine whether the check scope will expand beyond the planned work package.
This is the core of the Gantt chart — a multi-track parallel work execution phase. Typical work package tracks running simultaneously:
NDT (Non-Destructive Testing) Track: Eddy current, ultrasonic, and radiographic inspections of specified structural locations. NDT findings trigger repair tasks that add to the workscope.
Structural Repair Track: Corrosion treatment, skin panel repairs, frame repairs, doubler installation. Each repair requires an engineering disposition and an FAA or EASA Form 8130-3 (or EASA Form 1) for the repair documentation.
Systems Overhaul Track: Flight control system rigging check and adjustment, hydraulic system flushing, avionics operational test, bleed air system inspection, oxygen system service.
Airworthiness Directive Compliance Track: This is mandatory and non-negotiable. Every AD that is due during the check interval must be accomplished and documented before the aircraft can be released to service. ADs are regulatory requirements with hard compliance dates; "we'll get to it next check" is not an option. The Gantt must show each AD as a separate task with its due date, assigned technician, and documentation requirement.
Engine Track (for checks that include engine shop visits): Engine removal → shop visit at engine MRO → module inspection and overhaul → reassembly → test cell run → reinstallation. Engine shop visits often run on a longer timeline than the airframe check and must be pre-scheduled at the engine MRO facility months in advance.
Landing Gear Track: Landing gear overhaul involves removal of the gear, disassembly to component level, inspection of all structural members, replacement of seals and bearings, NDT of critical components, reassembly, and functional test. Landing gear overhaul often goes off-wing to a specialized landing gear shop.
Cabin Track: For airlines using the check to perform cabin modifications (new seating, in-flight entertainment upgrades, passenger service unit changes), the cabin track runs parallel to structural and systems work. Cabin modification often involves significant seat removal, seatrail inspection, and sidewall removal — creating useful access for structural inspectors.
Unplanned findings are the primary source of schedule risk in aircraft MRO. When an inspector finds corrosion that wasn't anticipated, a cracked frame member, or a failed component, the work scope expands. The MRO facility must:
Each step takes time. A significant structural finding can add 3–7 days to a C-check. Gantt charts for MRO events must include contingency buffers — typically 15–20% of planned duration — specifically for findings management. Airlines that schedule zero buffer are planning for trouble.
After all work packages are complete, the close-out phase begins: panels are reinstalled, all access stands are removed, final system operational tests are performed, and the maintenance records are audited. Every task card must be signed off by the technician who performed the work and the inspector who verified it. Missing sign-offs hold up release to service just as surely as incomplete maintenance does.
With the aircraft reassembled, functional tests verify that systems work as required: control surface travel check, avionics power-on and self-test, hydraulic system functional, landing gear retraction test (usually done with the aircraft on jacks in the hangar), and engine run (for checks involving engine work).
Many heavy maintenance events require a test flight before return to airline service. The test flight follows a specific test card that verifies aircraft performance, pressurization, autopilot function, and other parameters that cannot be fully verified on the ground. Test pilots (often airline check captains or designated test pilots from the MRO) perform the flight. If the test flight reveals discrepancies, the aircraft returns to the bay for correction.
Aircraft release requires the completion of all task cards, signature of the Authorized Release Certificate (FAA Form 8130-3 in the US, EASA Form 1 in Europe), and sign-off by a certificated Inspection Authorization (IA) holder or equivalent. The aircraft then returns to the airline for line maintenance configuration check, passenger loading, and return to revenue service.
For ETOPS-certified aircraft (Extended-range Twin Operations — allowing twin-engine flights over oceanic routes), specific maintenance requirements apply at each check interval. ETOPS maintenance tasks are tracked separately on the Gantt and must be completed by ETOPS-authorized technicians with ETOPS-specific documentation.
An effective aircraft MRO Gantt uses:
The Gantt is the instrument that keeps an MRO check on time, on budget, and fully airworthy. In an industry where the regulatory stakes are absolute and the commercial stakes are substantial, it is non-optional.