Definition
AOG describes urgency, not severity. The same failed component can be an AOG on one aircraft and a routine item on another; what makes it an AOG is that the aircraft cannot fly and that fixing it has been escalated above the normal queue.
The term carries real operational meaning through the supply chain. An AOG order to a parts distributor triggers different handling from a stock order — dedicated desks, out-of-hours contact, courier or hand-carry shipping, and pricing to match. A school that orders an AOG part without meaning the aircraft is grounded is spending a substantial premium for nothing, and a school that fails to flag a genuine AOG waits in the ordinary queue while the aircraft sits.
The escalation exists because the cost profile inverts. Under normal maintenance planning, work is sequenced to minimise total cost — batching tasks, waiting for economical shipping, scheduling labour efficiently. Under AOG, the dominant cost is the aircraft not flying, so it becomes rational to pay several times the ordinary price for a part to arrive tomorrow instead of next week. The decision turns on what an aircraft-day is worth, which is a number the operator knows and the supplier does not.
In airline operations AOG has formal machinery behind it: dedicated AOG desks, parts pooling agreements, and loan or exchange arrangements between operators. In general aviation and flight training the concept is the same while the machinery is mostly absent — a school typically has no spares pool, no exchange agreement and no out-of-hours engineering cover, which means its practical AOG response is limited to how fast a part can be sourced and how quickly a licensed engineer can attend.
The distinction worth holding is between AOG and deferral. Where a defect is deferrable — permitted under a Minimum Equipment List with conditions and a rectification interval — the aircraft can continue operating and the fault is not an AOG at all. AOG applies where no such relief exists, or where the operator chooses not to use it. For most training aircraft operated under general aviation rules without an approved MEL, the deferral route is narrower than it is for an airline, so a wider range of faults ground the aircraft outright.
A school's most effective AOG mitigation is therefore not a faster response but a shelf: holding the parts that historically ground its own fleet.
Why It Matters for Flight Schools
For a school, the useful discipline is deciding in advance what an aircraft-day is worth, so the AOG premium becomes a calculation rather than a panic. A tail generating meaningful daily contribution justifies expensive expediting; one that flies twice a week does not, and paying AOG shipping on it is a reflex rather than a decision.
The more common mistake is treating AOG as a category of event rather than a choice. Declaring AOG on every unserviceability trains suppliers to discount the signal and spends premium freight on aircraft that had spare capacity in the schedule anyway.
The inverse error is worse: leaving a genuinely grounded aircraft in the routine queue because nobody escalated, then discovering a week later that the part could have arrived in two days. Both errors come from the same gap — nobody having decided what a grounded day actually costs.
How Aviatize Handles This
Aviatize tracks open squawks and maintenance status per aircraft and limits that aircraft's availability to the schedule while the status requires it, so a grounded tail stops being bookable rather than being discovered as unserviceable at the ramp. Work is organised as work orders and work packs with assigned tasks, and technicians record time, parts and tools used as they work.
Because parts usage is recorded against the work, a school builds its own history of which components actually ground its fleet — which is the input to deciding what to hold on the shelf. Aviatize reports utilisation per aircraft from bookings and flights recorded, so the daily contribution a grounded tail is forgoing can be set against the cost of expediting rather than guessed at.
Frequently Asked Questions
- What does AOG mean in aviation?
- Aircraft on Ground — an aircraft grounded by a fault that must be rectified before it can fly again, escalated above the normal maintenance queue. It describes urgency rather than severity: the same component failure may be an AOG on one aircraft and a routine item on another, depending on whether the aircraft can continue operating.
- What happens when you place an AOG parts order?
- It is handled differently from a stock order — dedicated desks, out-of-hours contact, and courier or hand-carried shipping, at a substantial price premium. That premium is justified only when the aircraft is genuinely grounded, so declaring AOG routinely both wastes money and teaches suppliers to discount the signal.
- Is a deferred defect an AOG?
- No. If a defect can be deferred under an approved Minimum Equipment List, with its conditions met and within its rectification interval, the aircraft may continue operating and the fault is not an AOG. AOG applies where no relief exists or the operator chooses not to use it. Training aircraft operated without an approved MEL have a narrower deferral route, so more faults ground them outright.
- How can a flight school reduce AOG time?
- Mostly by holding stock rather than by responding faster. A school usually has no spares pool, exchange agreement or out-of-hours engineering cover, so its response time is bounded by sourcing and engineer availability. Recording which parts have historically grounded its own fleet tells it which few items are worth keeping on the shelf.