With more and more aircraft using them, it is more important than ever that airports keep their runways in good condition. But at the same time, the ever-growing number of flights means that finding a window in which to do this vital work is increasingly difficult. Chris Lewis reports
Runways surely represent the most important and critical feature of any airport; whereas taxiways and other aspects of infrastructure are usually to some extent duplicated, “if you don’t have a runway, you don’t have an airport,” points out Chris Chalk at Mott MacDonald.
Chalk, the global practice leader for aviation at the global engineering, management and development consultancy firm based in Croydon in the UK, explains that shutting even one runway at multiple-runway airports can be tricky at very busy locations, so it’s often only something that can be done at night, usually within quite tight time windows.
As with most maintenance, doing work in good time often pays greater dividends than letting things deteriorate to the point that a major rebuild from the foundations up is required. The problem, in most parts of the world, is persuading airport paymasters that this is an effective use of public or shareholders’ funds. Runway maintenance just isn’t exciting compared with building new terminals or so many of the other demands on the public purse.
Some airports are better at planning maintenance than others. The same applies to documenting their assets, although an increasing proportion of such information is now available in electronic rather than paper format. The better things are documented, the easier the maintenance task, says Chalk. “Otherwise, you need to start drilling holes to find exactly what you’ve got.”
The length of time a runway can last before needing significant work undertaken on it depends on many factors, including the number and weight of aircraft using it, the prevailing climatic conditions and the materials it is built from, but as a very rough rule of thumb a bitumen runway might last 20 years, while the top layer will need replacing every 10 years.
Another factor that can affect the interval between maintenance operations relates to the ground conditions underneath the runway. Generally speaking, the stronger the underlying terrain (granite as opposed to light soil or crushed coral, for example) the longer lasting the runway, although weak ground conditions can to some extent be compensated by a thicker bitumen layer on top.
An important part of the equation, as noted above, is the number and type of aircraft that use a runway. Just as heavy lorries tend to cause more damage to roads than private cars, so larger, heavier widebody aircraft cause proportionately more wear than narrowbody types. Another, related factor relates to the number of wheels on those aircraft. Older narrowbodies with fewer wheels like the B727 or Tristar used to cause a relatively large amount of damage, whereas some of the newer widebodies such as the B787 are relatively gentle by comparison.
The materials used for runway maintenance, and indeed the actual techniques involved, haven’t changed much over the years, Chalk informs. Polymers are often added to the asphalt mix to allow it to be laid during a wider range of climatic conditions.
The laying equipment is essentially similar to that used for roads, although runway operations have to take place under far greater time constraints – and clearly, quality control has to be even higher. GPS and IT systems have replaced string lines, improving accuracy as well as speeding operations. But the milling or material and the asphalting process have remained largely unchanged.
Modern, powerful systems used to light the work site have eased the contractors’ task, given that levels of air traffic intensity mean that most maintenance at major airports will take place in darkness. In the more developed parts of the world, there are specialist contractors who will carry out runway maintenance operations. US contractors, for example, tend to do business primarily in their home country, whereas in Europe, for example, there is an element of cross-border operation. French-owned Colas, for instance, works in a number of different European countries.
Expertise will probably have to be imported in less developed countries, possibly with a foreign firm acting as lead contractor.
While there are similarities to road repair and maintenance, it’s unlikely that the local contractors will have the skills – or the necessary airside and security clearance – to carry out runway operations themselves. Mott MacDonald itself works all over the world.
Runway maintenance periods are also a good chance to renew or replace fixtures such as apron lighting infrastructure. Light fittings will often have to be removed durin
g runway maintenance operations anyway, and many airports might take the opportunity to replace existing lights with superior (perhaps LED) ones. Runway markings will also be removed; these get replaced more often than the surface itself.
The opportunity may also be taken to groove the runway surface to improve skid performance.
It is rare for major work to take place on taxiways at the same time as runways. There is less pressure on taxiways and it is usually reasonable to take some out of use during the daytime rather than at night.
The weather – principally rain and low temperatures – is the biggest hindrance to smooth-running maintenance work. Long-term forecasts are of very little use in trying to decide whether it will rain or be unusually cold on a particular day several months hence, though obviously maintenance planners do avoid periods such as monsoon seasons or times when winter freezes can be expected. In some respects, the weather can cause most problems in temperate climates (such as Britain’s), when rain can happen at any time, including midsummer.
Usually, planners will build a ‘weather margin’ into their schedules, which is usually – but not always – sufficient to allow the operation to take place within the planned time-scale.
DIY – or contract out?
The extent to which airport authorities perform their own maintenance varies hugely around the world. Dan Meincke, director of traffic and airside operations at Copenhagen Kastrup Airport, says that the airport authority, Københavns Lufthavne, carries out daily technical maintenance itself but that asphalt coating is subcontracted via a framework agreement to a contractor. As with all significant pieces of work at the airport, the task is subject to EU tenders.
Like any major airport, there is a lot of pressure to keep Copenhagen’s runways open, says Meincke, so “maintenance is assessed from time to time. We are carrying out night work on the runways, where possib
le in terms of quality and cost. We have also chosen to close one day and night at times. The outlook for wind direction and wind speed affects our decisions.”
A maintenance programme is also crucial “so that we can make replacements or maintenance at the right time”, both to ensure continuity in operation, and to keep a handle on costs. But, above all, safety and maintaining the operation are the most important factors, Meincke declares.
Multiple-runway airports can have more flexibility in how and when they carry out maintenance operations. Stockholm’s Arlanda Airport, for example, has three runways and, says its head of airside and landside operations, Anders Östlings, “the strategy is to close one of the three runways every third year for heavy maintenance”. So, RWY08/26 will be closed during 2017 and the next time it will be closed will be 2020. RWY01L/19R will be closed in 2018 and in 2021, RWY01R/19L will be closed 2019, 2022 and so on.
Each time, the runway is closed for between four and seven weeks for resurfacing, instrument landing system (ILS) upgrades, runway lights upgrades and other work. Different teams are responsible for the various aspects of the work, but a single project manager is responsible for the overall plan.
Östlings adds that Arlanda has not so far been forced to do runway maintenance at night, “but as the traffic has increased for a number of years we are looking into the possibility to do that in the future in order to reduce the number of weeks of closure.” (Arlanda has no night curfew and is open 24/7).
The airport authority uses contractors for runway maintenance such as asphalt sealing and resurfacing, with only minor jobs performed by its own staff. The availability of labour can be a barrier to maintenance operations around the clock – as can cost, although clearly “the cost can never affect the quality of work because safety is always a priority”, Östlings promises.
At Germany’s Munich Airport, runway inspections and short-term maintenance are carried out by the airport operator, but larger-scale scheduled maintenance is undertaken by reliable long-term partners and contractors – for example, rubber removal, which can be scheduled and takes place about three times a year.
Economy, functionality, quality and durability all come into the equation when deciding what maintenance equipment to buy, explains the Bavarian gateway’s vice-president of airport operations, Alexander Hoffmann. Moreover, compliance with legal, industry and internal standards, and laws on occupational safety and health must also be taken into account.
Electronics and IT are also now key drivers in increasing maintenance process efficiency, reducing costs and improving quality while meeting demanding safety standards, Hoffmann adds.
Munich says it operates one of the world’s most efficient dual-runway systems, serving around 1,100 aircraft movements every day, although national regulations stipulate that it is subject to night curfews from midnight to 5:00am, with one runway available for emergency and other special-permission traffic. Schedulable
maintenance usually takes place on the second, inactive runway during night curfews.
As at other airports in developed Western countries, availability and cost of labour is an issue, “but as with any other stakeholder in airport operations, Munich Airport always puts safety first, when it comes to airport operations as well as maintenance”, says Hoffmann. “Therefore, economics is a secondary – yet not-to-be-neglected – criterion.”
For the world’s busiest international hubs, planning and scheduling major work is as big a task as the physical work itself. Chris Garton, executive vice-president for operations at Dubai Airports, notes that Dubai International doesn’t have the luxury of time. “Dubai International is a bit different from other airports. Many close at night, but we are open 24 hours and in fact our busiest time is between midnight and 3am.”
Moreover, Dubai International handles large, heavy aircraft including A380s and B777s that will be fully loaded and also fully fuelled for the long sectors operated out of Dubai, so its runways take quite a pounding.
When Dubai Airports carried out an 80-day comprehensive upgrade project at Dubai International in May 2014 – resurfacing the entire 4,000-metre long northern runway – some services were diverted to the emirate’s new Dubai World Central (DWC) Al-Maktoum Airport, while flights at Dubai International were thinned out; in some cases, two flights normally operated by smaller aircraft were combined into a single A380-operated service. Planning for the event had to start two years in advance, Garton explains, which made it possible for airlines to reduce flights well in advance rather than cancel them and disappoint pre-booked passengers.
Long-term closure of what is now the world’s busiest international passenger air hub just isn’t an option. Quite apart from the estimated 28% of Dubai’s GDP that is dependent on aviation, it would have far-reaching consequences for the global economy too.
Other airports in colder climates have to deal with the problem of snow removal; but for Dubai the issue is rubber removal from the deposits left by close on 1,200 movements a day, a problem exacerbated by the hot temperatures. As night work isn’t an option, the task has to be undertaken during the heat of the day and Dubai Airports has developed specialised vehicle-mounted removal equipment – essentially a combined water scrubber and vacuum – to avoid sending crews out in 52 degree temperatures. The system has been enlarged to the point where it can sweep a 2-metre width of runway.
Dubai Airports uses a mix of in-house engineering expertise and sub-contractors – in the latter case, often the original equipment manufacturers (OEMs) that supplied the equipment in the first place – to carry out its regular maintenance. Sourcing labour is not an issue in this part of the world, although the airport tries to do as much vehicle-based work as possible rather than send crews out in the midday sun.
The rather colder weather conditions on the east coast of Canada also influence maintenance operations at Halifax Stanfield International Airport, explains its manager of air-side services, Chris Altass. Asphalt repairs generally only take place in the warmer months between mid-May and 1 December; conditions are too cold in the depths of winter (Halifax recorded a total snowfall of 165cm last winter).
Halifax Airport Authority’s own infrastructure department carries out line painting and smaller asphalt repairs; larger work is subcontracted through a “robust” project management procedure.
There are four runways at Halifax, which makes for a high degree of flexibility, although the intersecting runway pattern means that closing one runway may restrict the available length for the one that remains operational. Whenever possible, the airport tries to ‘batch’ maintenance activities, programming the work for pairs of runways at a time. That way, it can be carried out on whichever runway has the less favourable conditions for aircraft operations at that time, while the other remains active.
Line painting is a big part of Halifax’s maintenance operation, as the chemicals used for de-icing tend to affect the paint. On the other hand, rubber removal is less of an issue than at airports in hotter climates.
Halifax also has sophisticated systems both to detect current temperature and weather conditions and to predict incoming weather. These are very useful for avoiding unnecessary application of de-icing chemicals and they also play a role in deciding whether and when operations can be carried out.
Two runways don’t necessarily give a great deal of spare capacity at the world’s biggest hubs. For instance, Hong Kong International Airport (HKIA) – the world’s busiest international air cargo gateway and one of the busiest passenger airports – is now handling over 412,000 movements a year, or an average of over 1,100 flights per day.
In fact, informs an airport spokesperson, the pressure to complete runway maintenance in a shorter and shorter time due to that increasing air traffic demand is one of the reasons why there is a pressing need for HKIA to expand to a three-runway system. The third runway project is scheduled to be completed in 2024 and is expected to allow the airport to handle 607,000 flight movements a year by 2030.
The Airport Authority of Hong Kong’s own team works with contractors to maintain HKIA’s runways, including routine maintenance such as rubber removal and the painting of runway markings. It also closely monitors the condition of the runway pavement, including evaluating and analysing its structure, roughness and ride quality.
As well as this, there is preventive maintenance, such as runway asphalt resurfacing works to improve or keep the runway condition at a high standard. The airport also carries out corrective maintenance to rectify defects that negatively impact runway performance, such as pavement crack sealing and pothole repair.
Under the current two-runway system, HKIA can close one of the runways for maintenance every night from 1:30am until before 8am, while the other remains open to allow 24-hour operation of the airport. But with increasing traffic, it is exploring different ways, including enhanced equipment, to boost efficiency of the work to release more time slots for aircraft movement.
Measures introduced since 2014 include automated distress survey equipment to increase the reliability of the results and quality of the data in the pavement condition survey. Recently, the airport operator also conducted a trial run to test the feasibility of using high-speed imaging technology for airfield ground lighting to enhance speed and precision of lighting checks to spot faulty lights more quickly.