Airlines are taking different approaches to how they schedule their maintenance requirements, as they weigh up the gains of shorter, more regular work against the traditional bigger block checks.

As airlines had to hand over their aircraft to maintenance repair and overhaul providers for rigid, lengthy letter checks in the past, they were regularly left to get on with their business without the aircraft for up to several weeks. With the transition from letter checks with set inspection intervals to condition-based maintenance, however, MRO schedules have become much more flexible and could be closely customised around airlines’ flight operations.

This has increased aircraft availability and reduced maintenance costs for operators. But it has also raised competition for different MRO approaches that aim to optimally suit airlines’ individual flight operations with the most efficient use of technical resources.

EasyJet has been evaluating a potential change from its current equalised maintenance model to a more conventional regime of fewer, but larger block-checks. The pan-European low-cost carrier is employing a philosophy whereby all regular A- and C-check tasks are allocated into work packages that can be accomplished during overnight stops. After six years, aircraft undergo a heavy maintenance event, dubbed the intermediate layover (IL) check, which typically lasts two weeks. But until that point, the aircraft are not undergoing traditional C-checks.

Swiss MRO specialist SR Technics – which developed the equalised maintenance system for EasyJet together with Airbus – says that the smaller, more frequent check regime more than halves the number of ground days versus traditional block-maintenance. The schedule is repeated after the IL-check until an overhaul is required when the aircraft reaches 12 years of age.

At that point, however, aircraft are transferred to block-maintenance because the equalised check regime becomes impractical as the risk of unexpected findings increases with aircraft age, which likely requires more repair time than is available during overnight stops. Flightglobal’s Ascend Fleets database shows that EasyJet’s current fleet includes five Airbus A319s, which will reach an age of 12 years in 2015.

Swaran Sidhu, head of fleet technical management, says the carrier’s engineering team has developed a block maintenance regime for the aircraft in question, and that it would be no problem to accommodate that schedule for a few aircraft, while the rest of the fleet continues to be serviced as before. For the foreseeable future, EasyJet is continuing to pursue equalised maintenance, says Sidhu. But he adds that the review is ongoing and that management could opt for an MRO philosophy change in future.

Air Berlin adopted an equalised maintenance approach in 2012, although the programme is covering a narrower scope than that of EasyJet. A-checks and out-of-phase maintenance tasks – which are not tied to individual checks – have been allocated under Air Berlin’s equalised schedule. But the carrier is still conducting C-checks where base maintenance tasks are combined with other work, such as cabin refurbishments, that requires the aircraft to be on the ground for several days.

Air Berlin Technik

Pic: Air Berlin Technik

Air Berlin is employing the equalised maintenance approach across its fleet, comprising Airbus A320 family aircraft, A330s, Boeing 737s and Bombardier Dash 8 Q400 turboprops. However, the model is not ideal for widebodies, says Werner Rothenbacher, managing director of the carrier’s MRO arm Air Berlin Technik. While narrowbodies are naturally on the ground overnight – especially in Europe where night flights are curtailed at most airports – long-haul aircraft fly around the clock.

Air Berlin included the A330s in the equalised maintenance regime, because the 14-strong fleet is configured with two different cabin layouts. “If we had a homogenous fleet, we would have chosen a different maintenance concept,” says Rothenbacher. “If all aircraft had the same cabin interior and there wasn’t a challenge of replacing aircraft, then you would probably opt for block-maintenance events where the aircraft is on the ground for 24 hours, and all [relevant] maintenance activities can be channelled into that phase.”

From an MRO provider’s point-of-view, it is more practical and efficient to work on aircraft in fewer, but larger checks, comprising a range of support tasks. “Maintenance cost will rise when the work is performed in more frequent checks. The use of more checks is less efficient,” says Han van Norde of KLM Engineering and Maintenance’s engineering department.

Air France-KLM UK engineering

Pic: Air France-KLM UK engineering

Especially when components, which are difficult to access, have varying inspection intervals, it makes sense to group items together to avoid multiple opening of aircraft areas. It is also possible to extend stipulated inspection intervals for certain equipment, if those periods fall in-between wider maintenance cycles. If a component is scheduled by its manufacturer for inspection after 18 months – while other equipment is checked after two years – it may be possible to escalate the former part’s interval to match the latter timetable. But this will depend on appropriate in-service data and sufficient engineering expertise by the airline or its MRO provider.

Van Norde also says that “an increase in maintenance-induced errors is more likely in a maintenance schedule with more [frequent] smaller checks compared to a schedule with fewer, larger checks”. But unless maintenance savings are greater than the loss of airline revenues as a result of longer aircraft downtime, operators will favour maximisation of aircraft operating time over greater process efficiency for MRO providers. Narrowbody operators in particular are thus aiming to use night stops to accomplish as many maintenance tasks as possible outside the operating hours to keep aircraft running during the daytime.

The split of maintenance tasks into smaller and more frequent checks also requires a more complicated process control than would be necessary for traditional letter checks. Whenever technicians are working on the aircraft, their activity needs to be planned and recorded, and spare part supplies need to be put in place. “You need more complex controls, that’s the disadvantage,” says Rothenbacher. “You need to control and follow processes in great detail.”

The flexibility of arranging tasks in the manufacturer’s maintenance planning document (MPD) allows customisation of work packages to the airline’s flight schedule. But this can be complex for carriers with limited engineering capability, especially if their operation involves different aircraft types and stakeholders, such as lessors and maintenance providers, says Van Norde: “Every airline has to develop its own packages. This can be difficult for an airline dependant on available experience and knowledge.”

Perhaps the greatest downside of a maintenance schedule with frequent checks is an increased risk of finding unexpected issues that could impact on the operator’s flight schedule. Any finding during a maintenance event leads to evaluations whether the aircraft can continue flying or must be immediately repaired. The latter option leads to further queries, such as availability of spare parts, MRO capacity, engineering resources, need for correspondence with manufacturers, and how much time will be needed to return the aircraft to service. “The more often you start working on an aircraft, the more often you will need to answer that question. And the more often, there is a theoretic risk of finding something that requires more time than planned,” says Rothenbacher.

Iberia has evaluated potential benefits of including light C-check tasks into the more frequent A-checks to avoid ground time for base maintenance. But the Oneworld carrier concluded that it was more beneficial to continue its existing C-check approach, says technical director Juan Antonio Diaz Palacios, because the base maintenance events provide greater flexibility to accommodate more labour-intensive MRO activities. “From time to time,” he says, “you need to have certain appreciable ground time to clear up certain maintenance activities, such as structural repairs or perhaps corrosion tasks or scheduled modifications that cannot be incorporated during A-checks.”

Iberia has customised A-checks for its narrowbody fleet into packages that can be accomplished in single shifts during overnight stops. For its A330 and A340 fleet, maintenance tasks have been allocated into packages that require one to three shifts to fit varying breaks in the widebodies’ flight schedule.

Lufthansa is transferring its Airbus A380 fleet from a phased to a block-maintenance schedule. Apart from the double-deck type, the Star Alliance carrier is employing a block-maintenance philosophy for its entire fleet. But when it introduced the A380 in 2010, maintenance tasks were phased into four medium-sized base checks to reduce the number of C-checks. That decision was driven by the small fleet and limited number of A380 routes, which resulted in longer ground periods.

The reduction to fewer, but more extensive checks was also useful because it provided flexibility to accommodate modifications, which tend to occur frequently during the early service period of new types. Meanwhile, however, the flight schedule has become tighter with the increasing fleet size and route network.

Lufthansa is pursuing an approach where large tasks are grouped into block-checks that typically take place during the quieter winter months, while light and out-of-phase maintenance tasks are allocated into work packages to fit natural gaps in the operational schedule without creating additional ground time. “We are evaluating at least once, if not twice a year whether our concept still teases out the optimum [maintenance efficiency] between the airline and MRO,” says Jürgen Wiegmann, key account manager aircraft engineering/maintenance programmes at Lufthansa Technik. “That construct can change with any timetable adjustment, additional route profiles, and fleet expansion,” he says.

Maximising aircraft availability is the main objective of Lufthansa’s maintenance concept as aircraft represent the largest capital investment. But this does not automatically mean a minimisation of ground time for MRO – it is rather a delicate and changeable balance between maintenance effort and achieving targeted reliability levels.

Achim Zoller, key account manager aircraft engineering/maintenance programmes, reports that Lufthansa Technik has had third-party customers for whom the highest priority was not aircraft availability, but stability. Maintenance activities, which could not be completed within the allocated timeframe and resources, were deferred to ensure that aircraft were available for flights as planned. But a build-up of unfinished maintenance tasks eventually led to operational instabilities as the tasks could no longer be deferred.

“We are aiming for constant [task] packages that can be planned [ahead], so that not every maintenance event leads to some sort of surprise,” says Zoller. While the maintenance plan should provide certain scope to accommodate unexpected issues, its purpose is to establish consistency and routine which should, in turn, result in aircraft reliability and shop floor efficiency.

But especially with increasing aircraft age, “the great art is to plan for the unexpected,” says Wiegmann. Based on reliability data, MRO specialists calculate probabilities of finding unexpected issues during certain inspections, and how such findings will likely impact on the aircraft’s downtime. Operators can thus decide how much risk should be associated with the maintenance event and, by extension, how much back-up capacity needs to be in place in case aircraft require more work than planned. Inspections with higher risks may thus be allocated to larger checks that provide more time for unscheduled repairs.

The ideal situation of exactly matched maintenance demand and supply between airline and MRO provider is “rather theoretical”, says Zoller. Occasionally Lufthansa Technik needs to provide additional resources to ensure high aircraft availability, while “the benefit is mostly at the airline… because they may be able to serve additional destinations or frequencies with the same number of aircraft”, he says. As “aircraft cost easily $200 million, it does not matter whether we allocate another 100 or 200 man hours”, he says.

But airlines tend to undertake base maintenance on their fleets at the same time during the quieter winter months, MRO capacity may be an issue. Iberia’s Diaz Palacios admits that hangar slot availability can be a challenge during that period. That race for space intensifies especially when aircraft require more work than expected.

Questions around MRO capacity arise not only for airlines with block-maintenance schedules during the peak C-check season. Hangar slot availability is also an issue for followers of equalised maintenance, because the focus on shorter, frequent checks translates to greater need for MRO capacity. EasyJet’s Sidhu admits that hangar slot constraints could be a driver in the airline’s decision to change its maintenance policy: “As our fleet is increasing, we are starting to see some constraints, some choke points that we just cannot get hold of sufficient maintenance slots within our MRO network… But that does not mean that you have to block the entire fleet”.

He says that the existing maintenance philosophy is “sufficiently flexible and quickly adaptable” to support the airline’s fleet through equalised checks. But he adds that it would be an option to apply a block-schedule to aircraft that are older than six years, while younger equipment continues to be serviced under the current regime.

Source: Cirium Dashboard