What Is AOG (Aircraft on Ground)? The Recovery Clock and Who Moves the Part
Short answer
AOG stands for aircraft on ground: an aircraft that cannot fly until a specific part is fitted. It is a maintenance status, not a shipping service. What makes it expensive is that the aircraft earns nothing while it sits, and the delay spreads down the schedule to every flight behind it. The freight job is narrow — move one part, often a small one, to one airfield before the aircraft runs out of time. How much time you actually have is set by the maintenance category of the fault, not by how urgent the phone call sounds.
What Does AOG Actually Mean?
AOG is the code a maintenance organisation uses when an aircraft is unserviceable and stays that way until a part arrives. It says nothing about how the part travels. A carrier does not “provide AOG” — it provides a vehicle for a shipment that happens to have an AOG behind it.
That distinction matters when you are buying. The urgency in an AOG is real, but it is not evenly spread across the recovery. Most of it sits in places freight cannot touch, and a carrier that offers to solve your AOG is selling something it does not control.
How Long Do You Actually Have?
Not every fault grounds an aircraft. Under an approved Minimum Equipment List, an operator may dispatch with certain equipment inoperative for a defined period. The conditions are set out in 14 CFR §91.213, and each MEL item carries a repair category that fixes how long the aircraft may keep flying before that item has to be dealt with:
- Category A — the interval is written into the item’s own remarks. There is no standard number.
- Category B — three consecutive calendar days.
- Category C — ten consecutive calendar days.
- Category D — 120 consecutive calendar days.
The count generally begins the day after the fault is recorded, not the moment it is found. So a great many “urgent” parts are moving against a three or ten day clock rather than an hourly one.
A true AOG is the case with no category left to hide in: the item is not on the MEL at all, or the interval has already run out. That is the difference between a part that should arrive soon and a part that has to arrive by a named hour. It is worth asking which one you have before anyone quotes a team run, because the two justify very different money.
The AOG Recovery Clock
An AOG is not one delay. It is four consecutive intervals, and they are owned by four different people. Counting them in order is the fastest way to find out where the time is really going.
- Diagnosis — from the fault appearing to a confirmed part number. Owned by maintenance. Freight cannot start until it ends, and it frequently takes longer than the drive.
- Sourcing — from part number to a part that somebody will physically release. Owned by procurement and the parts distributor. This is where the hours quietly disappear: locating the part is rarely the hard bit, getting it released and paperworked is.
- Transit — from the released part to the airfield. This is the only interval a carrier owns.
- Fit and return to service — installation, inspection and sign-off. Owned by maintenance again, and it needs a technician who is still on shift when the part lands.
Interval three is typically the shortest of the four and the only one anyone shops for. The practical goal of an AOG freight decision is not simply to make interval three fast — it is to land the part inside a window where interval four can still happen the same day.
Why Is Transit the Interval You Can Compress?
Because it is the only one where more money buys less time in a predictable way. Diagnosis takes what it takes. Sourcing depends on somebody else’s stock and somebody else’s release process. Fit depends on a licensed technician and a hangar slot.
Transit is different: you can put the part in a dedicated vehicle that leaves now and does not stop, and the arrival time becomes arithmetic instead of hope. That is the whole proposition behind expedited freight — one shipment, one vehicle, no terminals, no consolidation, no handoffs where the part can sit overnight in the wrong building.
It is also why an arrival time is worth more to a maintenance planner than a fast average. A part that arrives at 2 a.m. to a hangar staffed from 7 a.m. has not saved five hours. It has saved nothing.
When Does Ground Beat Air on an AOG Part?
More often than people expect, because the flight is only one leg of the journey. Next flight out means drive to the airport, tender, wait for the cutoff, fly, clear, then drive again from the destination airport to the airfield or the MRO. A dedicated vehicle that leaves in ninety minutes is one leg, door to door, with no cutoff to miss.
The ground side is governed by hours, not effort. Federal hours-of-service rules allow a property-carrying driver up to 11 hours of driving after 10 consecutive hours off duty, inside a 14-hour on-duty window, and driving is not permitted past 8 hours of driving time without a consecutive 30-minute interruption of driving status (49 CFR §395.3). In practice one driver covers roughly 600 road miles in a day. Past that, the truck stops for ten hours regardless of what the part is worth.
So there are three honest answers on any AOG lane, and a carrier worth using gives you one of them rather than a hopeful time:
- A single driver makes it, because the distance fits inside the hours available.
- It needs a team — two drivers alternating so the vehicle never stops, which roughly doubles the ground covered in a day and prices accordingly.
- Ground cannot make it, and the conversation has to move to air, or to what the deadline really is.
That third answer is the valuable one, because you can still act on it. The full comparison, including the distances where each mode stops winning, is laid out in when ground beats air.
What Slows an AOG Move Down?
Almost never the vehicle. The delays cluster in the same five places, and every one of them can be settled while the truck is still being assigned:
- Release authority. A part nobody is cleared to hand over is not a collection. If a distributor or another operator is holding it, someone has to agree to let it go, and that conversation routinely outlasts the drive.
- Dimensions and packaging. Aircraft parts are not uniform. A control unit fits in a van; a cowling, a slide raft or a wheel and brake assembly picks the vehicle for you, and a wrong guess means a second dispatch you do not have time for.
- Regulated contents. Some aircraft parts are classified as dangerous goods — lithium batteries, chemical oxygen generators, components holding fuel or hydraulic residue. That classification belongs to the shipper, and it changes what can fly and how it must be packed. Establish it before the mode is chosen, not after the part reaches the airport.
- Airfield access at the far end. Airside delivery, gate passes and escort requirements are not universal, and a driver without one waits at the perimeter. Landside handover to the MRO is often faster.
- Receiving hours and who signs. Name the person, not the company. Overnight arrivals only help if someone is there to take the part.
None of that is exotic. It is the same failure pattern behind most emergency freight recovery — the freight is ready long before the answers are.
Who Actually Moves the Part?
Usually four parties, and knowing which one you are talking to prevents a lot of wasted calls:
- The operator’s AOG desk declares the situation and owns the deadline.
- The parts distributor or MRO stores holds the part and controls when it is released.
- A forwarder books the mode and the paperwork, and may or may not control any vehicles.
- The carrier physically moves it. On dedicated ground, that is a driver assigned to one shipment.
The number of handoffs between those four is a better predictor of arrival time than the headline transit estimate, which is the argument for the shortest chain you can arrange. Where a flight genuinely is the right answer, the trade-offs across expedited air freight options come down to cutoffs and ground legs rather than flight time. Where it is not, a dedicated vehicle out of the nearest stocking location usually wins on the door-to-door number.
Vic’s Freight runs the transit interval — dedicated vehicles, one shipment at a time, across aerospace and AOG freight lanes in the US and Canada. The broader picture of how these parts move is covered in moving aircraft parts.
Key Takeaways
- AOG is a maintenance status, not a freight product. No carrier resolves an AOG; it resolves one of four intervals.
- The deadline is set by the MEL repair category — A, B (3 days), C (10 days) or D (120 days) — or by the absence of one. Establish which before buying speed.
- Diagnosis and sourcing usually consume more of the clock than transit does.
- Land the part inside a window where installation can still happen the same day. An arrival before the hangar opens saves nothing.
- Federal hours-of-service limits put a single driver at roughly 600 road miles a day; a team roughly doubles it. Distance decides mode, not urgency.
- Most AOG delays come from release authority, part dimensions, dangerous-goods classification, airfield access and receiving hours — not from vehicle availability.
AOG Logistics: Common Questions
What does AOG stand for?
AOG stands for aircraft on ground. It is the status a maintenance organisation assigns when an aircraft cannot be returned to service until a specific part is fitted. It describes the aircraft’s condition, not a shipping method.
How fast does an AOG part need to be delivered?
It depends on the repair category of the item, not on the label. Under an approved Minimum Equipment List an aircraft may keep flying with certain items inoperative for three, ten or 120 calendar days depending on category. A genuine AOG is the case where no interval applies or the interval has expired, and there the deadline is measured in hours and set by the operator’s schedule. The practical target is arrival while a technician is still on shift to fit it.
Is AOG shipping always by air?
No. Air wins on long distances, but next flight out is a chain of legs: drive to the airport, tender, wait for a cutoff, fly, then drive from the destination airport to the airfield. Across a wide band of domestic distances a dedicated vehicle that leaves immediately arrives sooner door to door, because it never queues and never misses a cutoff.
Who declares an AOG?
The aircraft operator or its maintenance organisation. Nobody in the supply chain can declare it on their behalf, and nobody downstream can lift it. The declaration is what unlocks the budget for a dedicated vehicle, which is why the first useful question on any AOG call is who made the call and what deadline they are working to.
Have a Part That Cannot Wait?
Vic’s Freight runs dedicated vehicles for time-critical aerospace freight across the US and Canada — one shipment, one truck, a real arrival time.