AOG: What really happens when your airplane breaks

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Written by: Andrew Poure
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At one time or another, it will happen to almost every airline passenger. You’re waiting to board a flight and the gate agent picks makes an announcement over the PA telling you, usually euphemistically, that the airplane is broken, and no one is going anywhere anytime soon. Your fellow passengers groan and curse under their breath, and the flight crew and ground personnel outside probably do the same. But while everyone at the gate sits down and begins to wait, another group of people spring into action.

In airline operations, there is a misleadingly simple term for when an airplane cannot operate its scheduled flight due to a mechanical issue. It’s called “AOG,” or “Aircraft On Ground,” and it’s the airline’s AOG department who are now tasked with the ballet of parts, personnel, and procedures to get that airplane back in the sky.

The AOG department consists primarily of specialists who can locate, purchase, and move spare parts —and who can do all of that in a hurry. These AOG parts can come from the airline’s internal stock, parts vendors, direct from manufacturers, and frequently even from other airlines. AOG specialists coordinate with mechanics in the airline’s central Maintenance Control department to find the exact part or parts needed, and search for the most appropriate source. In order to get the proper part to the stricken airplane, the AOG department will take into account the locations of the part and the airplane, any logistical requirements such as if the part needs to be flown in or trucked, and, of course, the cost. At a hub airport, it is sometimes as simple as checking a warehouse on site and calling for the part to be brought to the airplane, but if the broken aircraft is AOG at a remote outstation (i.e., not an airline hub), it can quickly spiral into a frantic hunt.

While the AOG department is performing the key task of obtaining the needed parts for the broken airplane, another team at airline HQ must work fast to reshuffle flight operations to make passengers, mechanics, and flight crews happy. The airline’s dispatchers and flight operations support personnel need to quickly and accurately assess whether or not a replacement aircraft and/or a replacement crew are required, and must also evaluate the follow-on effects to other flights because of the AOG aircraft and its crew being out of their expected position on the network.

The operations staff requires careful coordination with Maintenance Control and the mechanics on site, with regular updates on how long the aircraft is estimated to be “red,” which is airline shorthand for out of service. With a good estimate of when the aircraft will be “green,” or ready for flight, operations can move forward with a service recovery plan, and if it will involve a replacement airplane or just delaying departure until the original can be fixed. Often, a replacement aircraft can be the best option, as it can be used to ferry the needed parts and extra crew, especially if the spare aircraft is coming from a hub.

Of course, there are cases when the aircraft is in such a state that the airline knows immediately to send a replacement and dig in for a logistical nightmare to get the broken aircraft back into service. One such situation is when a long-haul aircraft requires an engine change far from home. Perhaps a Boeing 777 descends into São Paulo after a 9-hour flight from the United States, only to ingest a couple of seagulls into an engine on final approach. In most cases, an airline will fly replacement parts in on its own aircraft, but a 777 engine is so massive that it can be carried only by the largest freighter aircraft, such as a 747 or the Antonov An-124, and a last-minute charter of that sort can take a day or more to arrange, and cost upwards of $250,000. It may only take a few hours for the airline to send a replacement 777 for the passengers, but it could be several days before the damaged plane is back in the air, even if some time is saved by using that replacement airplane to bring in the mechanics and necessary tools for the repair.

As is the case with any sort of flight delay, these scenarios, whether major or minor, will send ripple effects through an airline’s schedule. Managing the AOG situation at hand and its aftermath makes for a challenging day for everyone involved. The next time you’re sitting at the airport and your airplane goes AOG, keep in mind you’re not the only one frustrated, and even if you decide to take the opportunity to relax in the terminal bar, know there are plenty of people working feverishly behind the scenes to get you on your way as soon as possible.

Andrew Poure is a lifelong aviation geek with experience in multiple aspects of airline operations, both at the airport and behind the scenes. He’s currently employed at an international cargo airline and is always seeking out aviation adventures. Follow him on Twitter.

About the Author

Andrew Poure



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