AOG means aircraft on ground: an aircraft cannot be dispatched until a defect, damage or airworthiness issue is repaired or legally deferred.
Aircraft on ground (AOG) means an aircraft cannot be released for its intended flight because a technical defect, damage or unmet airworthiness requirement needs urgent action. In aviation, AOG is a maintenance and logistics status—not a literal label for every parked aircraft—and it triggers priority engineering, parts and operational support.
In our Aviation & Real-World Flying coverage, the key distinction is dispatchability. A serviceable aircraft may be sitting on the ground, while an AOG aircraft is unavailable for its intended operation until the problem is rectified or approved dispatch relief applies.
When is an aircraft classed as AOG?
An aircraft is classed as AOG when its operator cannot safely and lawfully dispatch it in its present condition.
Common causes and the usual routes back to service include:
- No-go system faults: Engine, flight-control, brake, avionics or hydraulic defects require approved fault isolation, corrective work and testing. Problems affecting landing-gear systems and their failure points can also prevent dispatch.
- Aircraft damage: Bird strikes, lightning strikes, hard landings, foreign-object damage and ground-vehicle contact normally require a defined inspection. Damage outside published limits needs an approved repair or engineering disposition.
- Overdue maintenance: A mandatory inspection, life-limited component change or other required task must be completed before release unless an approved provision says otherwise.
- Missing resources: The diagnosis may be known, but the aircraft remains unavailable while the operator obtains an approved part, specialist tool or appropriately authorised maintenance personnel.
- Incomplete records: Work may be physically finished yet the aircraft cannot return to service until the required technical records, inspections and certification are complete.
A cockpit warning does not establish the final AOG status by itself. Maintenance must consider fault persistence, redundancy, fault-memory data, approved troubleshooting and any applicable dispatch conditions. Simply resetting a warning is not proof that the underlying defect has been corrected.
Is every aircraft on the ground considered AOG?
No; aircraft on ground has a narrower industry meaning than an aircraft merely being parked, delayed or unavailable.
| Situation | Normally AOG? | Why |
|---|---|---|
| Serviceable aircraft parked between flights | No | It remains available for dispatch. |
| Flight delayed by weather, crew availability or airport closure | Usually no | The disruption is operational rather than an aircraft defect. |
| Defect deferred under an approved MEL | Not necessarily | The aircraft may be dispatchable when every stated condition is met. |
| Unplanned no-go defect | Yes | The aircraft cannot be released until maintenance takes approved action. |
| Planned heavy maintenance | Usually no | The aircraft is unavailable, but its downtime is scheduled rather than an urgent AOG event. |
| Regulatory or administrative grounding | It depends | It may create an AOG case, but not every legal or administrative restriction is described that way. |
An aircraft can become AOG at its home base or at a remote airport. It does not have to be stranded away from its usual maintenance facilities.
What does “AOG flight” mean?
An AOG flight usually means a flight delayed, cancelled or otherwise affected because its assigned aircraft has AOG status; it is not a standard class of passenger flight.
The airline may repair the aircraft, substitute another one or cancel the service. A public flight-status display will normally show the resulting operational status—such as delayed or cancelled—rather than treat AOG as a universal passenger-facing status code.
What does “AOG basis” mean on a parts or support request?
Supplying a part or service on an AOG basis means treating it as an urgent request needed to return an unavailable aircraft to service.
When Airbus or another aircraft manufacturer uses AOG in support material, the core meaning is the same: an aircraft-unavailability case requiring priority technical or logistics attention. AOG priority does not guarantee a particular delivery time, and it does not bypass stock availability, export controls, customs, dangerous-goods rules or maintenance approval.
A useful AOG request normally identifies:
- the aircraft registration, type and serial number where required;
- its airport location and an available local contact;
- the exact defect or technical-log wording;
- the required part number, quantity, tooling or engineering support;
- the next planned flight or required-by time; and
- relevant transport, customs or dangerous-goods constraints.
Calling every routine order AOG is a mistake. The priority should be reserved for a genuinely undispatchable aircraft so that engineering and logistics teams can distinguish urgent cases from normal replenishment.
Can an AOG aircraft fly with an inoperative component?
An aircraft may fly with certain equipment inoperative only when an approved dispatch basis permits it and all associated conditions have been met.
The operator’s approved Minimum Equipment List (MEL) may allow a defect to be deferred subject to maintenance actions, crew procedures, placarding, operating restrictions and a repair interval. A Configuration Deviation List can provide defined relief for certain missing external parts. Neither document is blanket permission to ignore a defect, and a manufacturer’s Master Minimum Equipment List is not normally a substitute for the operator’s approved MEL.
An inoperative APU, for example, does not automatically make every aircraft AOG. Dispatch may be allowed when the MEL permits it and suitable starting, electrical and airport arrangements are available. Our explanations of why the APU matters during ground operations and engine starting and how a ground power unit supplies an aircraft provide the relevant system context.
If normal dispatch is prohibited, a specially authorised non-revenue positioning flight may sometimes be possible under a special flight permit, permit to fly or equivalent approval. That depends on the defect, jurisdiction and imposed limitations. AOG status alone never authorises such a flight.
Who decides that an aircraft has AOG status?
The operator’s maintenance control function normally classifies and coordinates an AOG event, while authorised maintenance personnel determine and certify the technical action required for return to service.
Pilots report the defect and provide the circumstances in which it occurred. The captain retains authority to reject an aircraft but does not replace the required maintenance certification. Dispatch or operations control may re-plan the service, arrange another aircraft and assess operational restrictions; our guide to how aircraft dispatchers coordinate operational decisions explains that side of the response.
The exact responsibilities vary by operator and regulatory system. If an aviation authority has formally grounded the aircraft, satisfying the operator’s internal maintenance process alone may not remove that restriction.
What happens after an AOG report?
An AOG response progresses from an accurate defect report to a documented maintenance release or approved deferral.
- Record the defect. Maintenance needs the aircraft identity, location, exact indications or logbook wording, operating circumstances and any actions already taken.
- Establish dispatch status. Maintenance control checks approved technical data, the MEL and any other permitted relief rather than relying on assumptions about system redundancy.
- Diagnose the fault. Engineers follow approved troubleshooting instructions and review relevant fault messages, test results and maintenance history.
- Mobilise support. The operator arranges personnel, parts, tooling, technical data and transport, using AOG priority where justified.
- Rectify or defer correctly. Maintenance completes the repair or every action required by an approved deferral, including placards and operating procedures.
- Test and release. Required inspections and functional checks are completed before authorised personnel certify the work and the crew accepts the aircraft.
Repeatedly cycling power or clearing a message without following approved procedures can erase useful evidence and delay diagnosis. A successful reset may be part of troubleshooting, but it does not close the technical-log entry or establish airworthiness by itself.
How long does an AOG event last?
An AOG event lasts until the aircraft is repaired or approved relief makes it dispatchable; there is no fixed minimum or maximum duration.
A simple replaceable component may be diagnosed, changed and tested quickly. Structural damage, an intermittent fault, an uncommon part or a remote location can extend the event for days. AOG priority accelerates support but does not waive inspections, repair procedures, transport restrictions or release-to-service requirements.
Does AOG mean the aircraft is unsafe or written off?
AOG means the aircraft must not be dispatched in its present state; it does not mean the aircraft is permanently unsafe, beyond repair or destined for retirement.
The cause could be major damage, but it may also be a failed sensor, a required inspection, incomplete documentation or an ordinary component awaiting replacement. The status is deliberately conservative: the aircraft remains out of service until the applicable airworthiness and dispatch requirements are satisfied.