AOG ANALYSIS
AOGs – ‘The single most disruptive event in aviation’
Aircraft on ground (AOG) events continue to plague business aviation. If they can’t be eliminated, can they be minimised? Words: Mike Stones
AOG ANALYSIS
AOGs – ‘The single most disruptive event in aviation’
Aircraft on ground (AOG) events continue to plague business aviation. If they can’t be eliminated, can they be minimised? Words: Mike Stones
AOG: THE three least popular letters in business aviation. Measured by their impact on clients and operators, there’s nothing quite like an AOG striking at a crucial moment with a time-pressed and particularly demanding client.
A good starting point to fathom the nightmares AOGs can unleash is to accept they are not solely technical problems. Paul Kinch, MD, MRO at Gama Aviation puts it like this: “An AOG event in business aviation is never simply a maintenance issue. It is an operational, commercial and reputational issue. These aircraft are often being used by owners, senior executives, charter clients, or time-critical organisations where the schedule is built around precision and availability.”
It’s different from airlines, where multiple aircraft can operate the same route. Business aviation operators may have never flown to the airport where an AOG happens. When a grounding occurs, clients – who understandably expect (and pay for) top levels of service – can quickly find themselves with very limited alternatives.
“It can affect passenger confidence, crew planning, onward connections, commercial commitments and, in some cases, the client’s wider business operations,” says Kinch.
If the aircraft becomes grounded late in the day, the disruption can escalate rapidly. Additional costs for crew accommodation, passenger hotels, repositioning and replacement travel arrangements quickly mount. If the problem cannot be resolved within a reasonable timeframe, the operator may need to source another aircraft entirely or risk losing the flight altogether.
“From an MRO perspective, the priority is always safety and compliance first, but the second priority is speed of recovery,” says Kinch. “That means accurate diagnosis, the right approvals, the right parts route and the right engineering response from the outset.”
For AMAC Aerospace Switzerland, supporting operators through AOGs is a daily responsibility, where rapid response and recovery are critical to minimising disruption. “For a business jet owner or operator, the expectation is simple: the aircraft is ready 100% of the time, outside of scheduled maintenance,” the company’s Russell Lowman, manager, Parts & Services tells CJI. “An AOG breaks that expectation the moment it happens, and it can happen anywhere in the world with no warning. That makes it the single most disruptive event in aviation and the ultimate test of a supply chain team.”
Plus, trying to understand the scale and costs of AOGs is like trying to wrestle an octopus – just when you think you have it pinned down, another bit pops up. But Air Charter Service (ACS) has a view based on the 35,000-plus charter flights it organises each year.
Joe Gallimore, assistant group private jets director, ACS says: “There isn’t any global dataset, but industry estimates would be a few AOG events per aircraft, per year, dependant on age and utilisation.” But he estimated the rough cost for a minor AOG event as about $10,000-50,000 with a medium level AOG event costing $50,000-250,000. The cost of a major event – such as a structural failure or significant engine problem could cost $500,000 or more.
“The biggest cost of an AOG event is indirect opportunity cost in the form of missed meetings, missed deals and the potential for reputation damage, which really can’t be quantified,” says Jeremy Rangel, vice president of Duncan Aviation Aircraft Services. “Then you have to add in charter and supplemental lift charges. It can be very expensive.”
Whatever the precise numbers, it can be an eye-wateringly expensive problem that a growing number of owners and operators are encountering. Part of the problem lies in business aviation’s ageing fleet, according to Andy Nixon, co-founder, Alpha Wingman, a platform that connects operators with maintenance providers. “It's becoming more common and the reason is new planes are so expensive people want to continue operating the older, higher-time aircraft because they are cheaper than putting up the money for a brand new one,” he tells us.
Scott Stoki, vice president of Engine Operations, Duncan Aviation says the percentage of AOG events for each aircraft has remained consistent over the past decade or so. But the total number of events has risen. “With the increase in business aircraft flight hours and the fact that the number of business aircraft as well as their years in service has grown, the number of AOGs in the industry have increased,” he says. “Our AOG teams are busy all the time. We keep growing them and we still can’t support every AOG that comes our way.”
So, what are the most common causes of AOGs and how best to remedy them? Rangel divides them into two categories: “Those caused by system failures, be they mechanical, electrical, or avionics-related, and acts of nature. The systems in today’s aircraft are so integrated that a fault in one may cause a fault in another, making it impossible to dispatch the aircraft. Of those two types, the most common is a component failure.”
Tellingly, in recent years, Wi-Fi failures are often considered AOG events by owners and operators. This is because productivity and connection during flights is considered so critical to business. (For those events, Duncan Aviation has a network of satellite operations and technicians who can help troubleshoot the problem and reimplement connectivity).
Nixon says most business jet operators use a minimum equipment list (MEL) and without one aircraft can easily be grounded when non-essential equipment fails. Notable examples he recalls include: a broken coffee maker and a failed latch on a toilet door. One supplier warns operators to update their minimum equipment list regularly and keep it as short as possible.
For ACS, mechanical and technical failures, supply chain issues, wear and ageing of aircraft conspire with operational factors to ground aircraft. Deciding whether AOGs have stabilised, become worse or improved is complicated. “New aircraft designs are allowing for quicker/better diagnostics along with more reliable avionics,” says Gallimore. “However, supply chain fragility, particularly post Covid, is still having an effect.”
“It delivers predictable maintenance expenses and safeguards against financial risk ...”
Gama Aviation identifies the usual suspects behind AOG events as being familiar line maintenance problems such as: electrical faults, avionics messages, batteries, wheels, brakes, tyres, hydraulic leaks, oxygen servicing issues, door or cabin defects and lighting faults. Occasionally faults with engines or APUs (ancillary power units) cause problems, says Jon Horsfall, the company’s line maintenance manager, Fixed Wing MRO. “Some are straightforward once diagnosed, but others require methodical troubleshooting because modern business aircraft are complex and integrated.”
Also, a fault message may be generated by one system but caused by another. “The key is not to make assumptions. Good line maintenance is disciplined, structured and evidence led,” says Horsfall.
Nixon, at Alpha Wingman, says AOGs are not just an issue for older aircraft. “An aircraft could be brand new, with five hours on it, and still have technical issues causing an AOG,” he says. “But the age of the aircraft doesn't really matter. Sometimes we see AOGs following a heavy aircraft inspection because there are still some loose ends that need tying up.”
Gama Aviation says AOG culprits include electrical faults and engine problems.
“Good line maintenance is disciplined, structured and evidence led.”
Gama Aviation identifies the usual suspects behind AOG events as being familiar line maintenance problems such as: electrical faults, avionics messages, batteries, wheels, brakes, tyres, hydraulic leaks, oxygen servicing issues, door or cabin defects and lighting faults. Occasionally faults with engines or APUs (ancillary power units) cause problems, says Jon Horsfall, the company’s line maintenance manager, Fixed Wing MRO. “Some are straightforward once diagnosed, but others require methodical troubleshooting because modern business aircraft are complex and integrated.”
Also, a fault message may be generated by one system but caused by another. “The key is not to make assumptions. Good line maintenance is disciplined, structured and evidence led,” says Horsfall.
Nixon, at Alpha Wingman, says AOGs are not just an issue for older aircraft. “An aircraft could be brand new, with five hours on it, and still have technical issues causing an AOG,” he says. “But the age of the aircraft doesn't really matter. Sometimes we see AOGs following a heavy aircraft inspection because there are still some loose ends that need tying up.”
Right: Gama Aviation says AOG culprits include electrical faults and engine problems.
“Good line maintenance is disciplined, structured and evidence led.”
Gama Aviation identifies the usual suspects behind AOG events as being familiar line maintenance problems such as: electrical faults, avionics messages, batteries, wheels, brakes, tyres, hydraulic leaks, oxygen servicing issues, door or cabin defects and lighting faults. Occasionally faults with engines or APUs (ancillary power units) cause problems, says Jon Horsfall, the company’s line maintenance manager, Fixed Wing MRO. “Some are straightforward once diagnosed, but others require methodical troubleshooting because modern business aircraft are complex and integrated.”
Also, a fault message may be generated by one system but caused by another. “The key is not to make assumptions. Good line maintenance is disciplined, structured and evidence led,” says Horsfall.
Nixon, at Alpha Wingman, says AOGs are not just an issue for older aircraft. “An aircraft could be brand new, with five hours on it, and still have technical issues causing an AOG,” he says. “But the age of the aircraft doesn't really matter. Sometimes we see AOGs following a heavy aircraft inspection because there are still some loose ends that need tying up.”
“The biggest cost of an AOG event is indirect opportunity cost in the form of missed meetings, missed deals and the potential for reputation damage, which really can’t be quantified,” says Jeremy Rangel, vice president of Duncan Aviation Aircraft Services. “Then you have to add in charter and supplemental lift charges. It can be very expensive.”
Older aircraft can become more exposed where ageing systems, parts availability or component obsolescence become factors. Certain issues, such as small fuel leaks, can also become increasingly difficult to diagnose and rectify efficiently as aircraft mature.
At the same time, newer aircraft are not immune. Modern technology and increasingly integrated systems can introduce their own reliability challenges. While those technologies are extensively tested, some systems are still relatively unproven compared with more mature platforms that have accumulated years of operational experience. In some cases, advanced technology can create new troubleshooting complexity rather than removing it entirely
Duncan Aviation’s Rangel says the environment can help to prompt AOG incidents. “These incidents rise when aircraft are based or stored in harsh environments and left unhangared,” he says.
Gallimore identifies areas that are particularly prone to problems: “Higher impact regions are Africa, South America and parts of Asia due to a limited MRO infrastructure and fewer parts depots. Lower impacted regions are North America and Western Europe.”
Large cabin aircraft have a lower frequency of AOGs but a higher impact when they occur, he adds. “Mid-size, older aircraft have a higher frequency of events but turboprops – such as King Airs – are generally robust with simpler systems but still susceptible to part delays.”
Then, there are the random acts of mischance that can strike any aircraft, anytime and anywhere. One such nightmare is recalled by Ian Houseman, founder and president, ZenithJet. This involved an aircraft refuelling at Halifax, Nova Scotia, after transiting the Atlantic, bound for the Kentucky Derby in Louisville. Unfortunately, the fuel bowser struck the jet’s wing – disabling the aircraft.
“AOGs always happen at the worst time,” says Houseman. “This was a Sunday in the holiday season. The client and his family were on a tight timeline [to reach the racetrack] and we had to find him interim lift at very short notice to ensure he arrived before the race started.” Another aircraft owner was less lucky. After a similar encounter in Vilnius, his aircraft was grounded for an extended period in Lithuania, as the Covid pandemic disrupted the supply chain and the availability of specialist on site support. Also, the legal and political issues surrounding the event did not speed the recovery.
To recover AOG aircraft as quickly as possible, Duncan Aviation employs 35 engine technicians located throughout the US in areas near large commercial airport hubs. There are also 17 airframe and engine technicians based at its main MRO facilities but dedicated for travel to assist operators in need of short notice assistance. In 2020, Duncan formed its first team of engine Rapid Response AOG support technicians in the Dallas area. Today, similar teams support nearly 1,500 AOG and in-field events each year.
Duncan Aviation’s technical knowledge database enables its technicians to see where common failures occur with certain airframe models, it says. The company believes AI has a lot of potential and has begun exploring ways it can help customers. “We are focusing on using our decades of technical data, knowledge, and experience to develop troubleshooting guides that our technicians can use to help resolve AOGs more quickly and obtain more reliability from the aircraft we work on,” says Stoki.
Gama Aviation also operates Mobile Support Teams based in strategic locations across the London area and the United Arab Emirates – supported by its Bournemouth maintenance base on the UK’s south coast. The best remedy for AOGs is a combination of prevention and response, according to Gama Aviation. Prevention means good scheduled maintenance, proper defect management, accurate technical records, component trend monitoring and early intervention when something starts to deteriorate, says Kinch.
Response means having line maintenance and Mobile Support Team capability that can mobilise quickly when an issue does occur. Predictive maintenance will continue to improve, but it must be supported by people, parts, tooling and approvals. Technology helps identify risk. Engineering capability still resolves it.
“Many events are manageable if the operator has access to responsive engineering support, current technical records, parts supply and a maintenance organisation that knows the aircraft,” says Kinch. “Problems become more difficult when documentation is incomplete, parts are unavailable, or the aircraft is operating away from its normal support network.”
The first few hours of an AOG are critical, agrees his colleague Horsfall. The difference between a short delay and a prolonged grounding is often the quality of the first response. “You need an engineer who understands the aircraft type, can troubleshoot properly, knows what can be rectified on site and knows when the aircraft needs a deeper maintenance input,” he says.
Ensure all aircraft technical records are current, use experienced engineers for troubleshooting and position mobile teams close to areas of aircraft concentration, he advises. It also pays to maintain access to commonly needed parts and tooling.
Houseman at ZenithJet says aircrew can always play a key role in minimising AOGs. “The crew are central in the sort of preventive measures that they can take, the way they fly the aircraft, the way they manage the aircraft on the ground and the way they work with maintenance teams and suppliers to help manage communication,” he says. Plus, resolving AOGs requires “a massive team effort” involving crew, the operator, OEMs, shippers and a myriad of other players in the whole supply chain and wider recovery team.
AOG support should not be treated as “a distressed purchase,” but part of an operator’s wider maintenance strategy, says Gama Aviation. The company’s Horsfall ends on an optimistic note: “The best AOG outcomes come from preparation. When the operator, CAMO, flight crew and maintenance provider work together, the recovery is usually faster and cleaner.”
AOGs: ‘Clients expect immediate solutions’
Disappointment is an emotion seldom handled well by aircraft owners and charterers. After investing millions in acquiring their aircraft or thousands to charter it, they rarely exhibit Zen-like calm on learning that their jet has gone AOG.
Reactions to such bad news, if anything, are hardening, according to AOG specialists surveyed by CJI. Plus, clients increasingly expect regular updates – often in digital format. “There is typically a lower tolerance overall with most clients expecting immediate solutions,” says Joe Gallimore, assistant group private jets director, Air Charter Service.
Clients are less tolerant of uncertainty, agrees Paul Kinch, MD, MRO, Gama Aviation. “That is not only a generational issue,” he tells us. “It reflects how people now experience service in every other part of their lives. They expect visibility, speed and clear communication.” It’s not hard to understand why. “In business aviation, the aircraft is often chosen because it gives control over time. When an AOG removes that control, the response needs to restore confidence as quickly as possible,” says Kinch.
“Patience is not as high as it used to be.”
Duncan Aviation thinks changing attitudes to AOGs partly reflects the industry’s evolving view of risk. “As an industry, we are more cautious about risk,” says Scott Stoki, vice president of Duncan Aviation Engine Operations. “With more organisations implementing safety management systems and safety-related policies, more pilots and operators recognise that if something isn’t right, the best thing to mitigate risk is to down the aircraft rather than assume everything will be okay.”
Andy Nixon, co-founder of AOG maintenance coordination platform Alpha Wingman attributes changing attitudes to the age of instant gratification. “People increasingly receive instant gratification on almost everything – whether that’s ordering something from Amazon on the app or a home-delivered meal. Patience is not as high as it used to be.”
All the specialists consulted by CJI agreed on the priority clients increasingly give to full and effective communication. Gallimore, at ACS, puts it like this: “If client expectations are managed professionally and accordingly, AOG is part of flying on aircraft and when handled professionally does not pose issues. The quality of response matters more than the failure itself.”
Gama Aviation’s Jon Horsfall says: “The technical answer matters, but so does the communication. Operators want regular updates, not silence while the engineering work is happening. They want to understand whether the aircraft is likely to depart, whether a part is required, whether a replacement aircraft should be considered, and what the next decision point is. A good AOG response gives the operator options.” Horsfall is the company’s line maintenance manager, Fixed Wing MRO.
The form of communication is also changing, according to Jeremy Rangel, vice president of Duncan Aviation Aircraft Services. “Another change we have noticed is that newer pilots and operators are more comfortable with digital communications. They would prefer to communicate with MROs through text, website chat, or emails than with phone calls,” says Rangel.
Joe Gallimore, Air Charter Service
Getting to grips with AOGs remain a constant challenge.
Getting to grips with AOGs remain a constant challenge.
‘AOGs are a bruise’
“AOGS ARE like a bruise. They can bruise an operator’s reputation and hurt clients who cannot use their aircraft.” This is the considered view of Mark Thibault, founder and CEO of Crew Chiefs – the aviation firm specialising representing clients for private jet pre-buy inspections, completions and maintenance.
Grounded aircraft are familiar challenges for Thibault. His first AOG, at the tender age of 17, was a US Marine Corps F-4 Phantom supersonic jet fighter. Since then, he has worked on hundreds of aircraft while the companies he has set up – including Metrojet – have handled thousands more.
"We must have covered more than 800 AOGs worldwide."
So, Thibault is well placed to offer an authoritative view of the AOG landscape. “In our first year at Metrojet in 2008, we must have covered more than 800 AOGS worldwide,” he tells us. Nearly 20 years later, the problem of AOGs show no sign of diminishing. His company T3 Aviation Group, based in Bangkok, Thailand is recovering about 400 aircraft a year.
Thibault believes AOGs are growing in number. There’s no single reason but a range of factors involving the expanding business jet fleet, the complexity of newer models and the longer service life of older models of aircraft.
To solve the problem, he believes more manufacturers ought to follow Embraer’s lead in outsourcing more AOG support teams. Also, operators should forge an AOG plan before their aircraft leave the ground, he says.
Thibault believes advancements in predictive maintenance will over time help to reduce the incidence of AOGs. “The airplane is talking to a ground station all the time,” he says. “Engineers can look at the synoptic pages, they can see exceedances, they can see any problems or potential problems through the flight quality management system live almost anywhere in the world.”
That enables ground-based control hubs to dispatch people and parts as quickly as possible. “The guys on the ground – knowing the parts, the people, the tooling and equipment to be on site – can dispatch whatever is needed to mee the airplane when it lands.”
But even predictive maintenance cannot prevent (or protect against) random acts of mischance – whether lightning strike, hangar rash or the like, Thibault acknowledges. If AOGs are bruises, the industry is going to need the mechanical equivalent of cold poultices for the foreseeable future.
Below: Mark Thibault, Crew Chiefs
‘AOGs are a bruise’
“AOGS ARE like a bruise. They can bruise an operator’s reputation and hurt clients who cannot use their aircraft.” This is the considered view of Mark Thibault, founder and CEO of Crew Chiefs – the aviation firm specialising representing clients for private jet pre-buy inspections, completions and maintenance.
Grounded aircraft are familiar challenges for Thibault. His first AOG, at the tender age of 17, was a US Marine Corps F-4 Phantom supersonic jet fighter. Since then, he has worked on hundreds of aircraft while the companies he has set up – including Metrojet – have handled thousands more.
We must have covered more than 800 AOGs worldwide.
So, Thibault is well placed to offer an authoritative view of the AOG landscape. “In our first year at Metrojet in 2008, we must have covered more than 800 AOGS worldwide,” he tells us. Nearly 20 years later, the problem of AOGs show no sign of diminishing. His company T3 Aviation Group, based in Bangkok, Thailand is recovering about 400 aircraft a year.
Thibault believes AOGs are growing in number. There’s no single reason but a range of factors involving the expanding business jet fleet, the complexity of newer models and the longer service life of older models of aircraft.
To solve the problem, he believes more manufacturers ought to follow Embraer’s lead in outsourcing more AOG support teams. Also, operators should forge an AOG plan before their aircraft leave the ground, he says.
Thibault believes advancements in predictive maintenance will over time help to reduce the incidence of AOGs. “The airplane is talking to a ground station all the time,” he says. “Engineers can look at the synoptic pages, they can see exceedances, they can see any problems or potential problems through the flight quality management system live almost anywhere in the world.”
That enables ground-based control hubs to dispatch people and parts as quickly as possible. “The guys on the ground – knowing the parts, the people, the tooling and equipment to be on site – can dispatch whatever is needed to mee the airplane when it lands.”
But even predictive maintenance cannot prevent (or protect against) random acts of mischance – whether lightning strike, hangar rash or the like, Thibault acknowledges. If AOGs are bruises, the industry is going to need the mechanical equivalent of cold poultices for the foreseeable future.
Below: Mark Thibault, Crew Chiefs
‘The future is faster, better informed AOG recovery’
LOOKING forward to an AOG-free future is a misplaced hope, according to the maintenance managers consulted by CJI.
“AOGs will not disappear by 2030,” says Paul Kinch, MD, MRO at Gama Aviation. “Aircraft are machines operating in demanding environments and technical defects will continue to occur. What should improve is the industry’s ability to predict, prevent and shorten AOG events”
But it’s not all bleak news. Some unplanned groundings will be avoided by better data, better connectivity, improved parts forecasting and more sophisticated maintenance planning, he adds. “But there will always be a need for skilled engineers who can respond quickly and make safe, compliant decisions.”
His colleague Jon Horsfall, line maintenance manager, Fixed-Wing MRO agrees that by 2030, AOG responses will be more connected and more informed, but not fully automated. “You may have better fault data before the engineer reaches the aircraft,” he says. “You may know what part is most likely to be required. But somebody still has to inspect the aircraft, confirm the defect, carry out the work and certify it correctly. The future is not AOG-free. It is faster, better informed AOG recovery.”
Similar evolution over the next four years is predicted by Joe Gallimore, assistant group private jets director, Air Charter Service. “While AOGs will not disappear, we believe they will evolve,” he tells us. “Improvements will come from earlier detection, faster recovery through better logistics and smarter supply chain visibility. So, in short, we expect to see fewer surprise AOGs in the future. The competitive edge lies in how fast and effectively you recover them, not whether they happen.”
Scott Stoki, vice president of Duncan Aviation Engine Operations sees no end to grounded aircraft. “As reliable as aircraft have gotten, they are such intricate and complicated assets that there will always be challenges,” he says. Regular, high-quality maintenance and nourishing a good relationship with your maintenance service provider are the keys to the consistent operation of your aircraft while ensuring the least amount of AOG issues, says Stoki.
Andy Nixon, co-founder of AOG maintenance coordination platform Alpha Wingman worries AOGs could rise as MRO resources are pressurised by the twin pressures of global conflict and demographic changes. War in the Middle East has resulted in the loss of 15% of global MRO capacity, he argues. “There’s a massive hole now in the global availability for base maintenance. Everybody in India used to go to the Middle East for maintenance [before the conflict]. People don’t want to take their aircraft to China and Singapore is overloaded. And the next nearest facilities are in Australia.”
MRO availability aside, Nixon believes AOGs will remain an unpleasant, but inevitable, fact of life. Until the perfection of “humanoid robots”, we can expect AOGs to continue because it’s (fallible) people who build, fly and maintain aircraft.
