Runways suffer a great deal of wear and tear, simply as a result of normal operations. Maintaining those surfaces with minimal disruption to flights is part of any airport’s responsibility to its users
Environmental and climate-related factors such as changes in temperature or harsh winter weather can affect airport pavements, as can the natural deterioration of the materials used in their construction – and the regular passage of aircraft filled with passengers, baggage and cargo.
The main impact of aircraft on runways is caused by their weight and braking, which causes reflective cracking over time, explains Paul Bastock, head of aerodrome management at Broughton (Airbus’s facility in North Wales). “Managing reflective cracks is part and parcel of the general maintenance programme for our runway (and all other runways),” he says.
Besides cracking, other types of damage that can occur include joint seal damage, distortion, disintegration and loss of skid resistance, a US Federal Aviation Administration (FAA) presentation outlines.
“We also experience damage to some lighting fixtures caused by nose gear strikes,” Bastock adds. The principal difference between Broughton’s runway and that of its closest regional airport (Liverpool) is the type and volume of aircraft. In 2017 Broughton averaged 18,500 movements – probably about half of Liverpool’s movements, he believes.
The largest aircraft to use Broughton’s runway is the 150-tonne Beluga. The airfield also caters for smaller general aviation traffic, which he describes as low impact and lightweight; high-value business jets, which are low impact; and fast jets, which are low weight and low impact.
“We will get a better understanding of the impact of bigger aircraft in a few years’ time after the Beluga XL (a new aircraft to be launched in 2019) has been in operation for a period of time,” Bastock says.
Visiting military aircraft, on the other hand, have had no impact on Broughton’s operations or maintenance; they are often better equipped than other types of aircraft to land on a range of surfaces.
The busier an airport, the more challenging it can be to maintain a hectic flight schedule while also keeping up with the ongoing maintenance of its runways and other surfaces.
David Whalley, engineering and facilities manager at London’s Heathrow International Airport, points out: “As we are the UK’s busiest airport operating at 99% capacity, we need to carefully plan a number of regular runway inspections to ensure the safety of our passengers.”
Heathrow has an airfield ground lighting (AGL) system, which turns the runway lights on, highlights routes around the runway and taxiways and controls the brilliance of the lights. This system requires photometric testing, integrity checks and approach lighting checks, as well as regular precision approach path indicators (PAPI) checks to ensure accuracy, as pilots use the system to work out the angle of their approach.
The runway also requires pavement condition inspections (PCI), condition and friction checks and repainting of the runway markings – all of which are carried out in addition to the daily checks performed by Heathrow’s airside safety team.
According to Whalley, a flight takes off or lands at Heathrow every 45 seconds; that adds up to an average of 210,000 passengers each day. This level of activity limits the time that the airside safety team is able to work on the runway.
“Our maintenance work and inspections require a high level of planning. Most of our checks need to be carried out during a six-hour window at night, a window that can get even smaller if weather disruptions or low visibility issues impact the airport’s schedule.”
Furthermore, in order to allow local communities respite from noise, Heathrow has a runway alternation programme to switch the runways used for landing and take-off. This means that only one runway can be kept open on a two-week alternation pattern; therefore only one runway is available for maintenance every month, Whalley observes.
Heathrow’s two runways are both surfaced with Marshall Asphalt for airfields. This is a hardwearing, aerodrome-specific material, which serves the 473,231 flights landing and taking off at Heathrow each year. The surfaces of both runways are grooved to create the friction needed for take-off and landing, and to help rainwater drain away.
However, Whalley points out that “as the material is much harder than the standard asphalt on the road, it’s inflexible, more brittle and can be susceptible to fracturing, a characteristic whic our maintenance team takes into account.”
The team uses Track Jet for runway rubber removal, necessary to prevent a build-up that in turn could affect stopping distances of landing aircraft. This high-pressure water jetting method uses small amounts of water to remove rubber skid marks and old markings without damaging the runway. It also uses photometric testing equipment to accurately measure the performance of high-intensity lighting on Heathrow’s runway and taxiways.
“Going forwards, our team will also be looking to introduce electronic torque wrenches, which will help us to collect data when an AGL fitting has been checked,” Whalley confirms.
He goes on to note: “While the weight of aircraft landing gear has decreased in recent years, reducing the amount of wear incurred on the runway surface and sub level, the weight of the aircraft has actually increased. This can be challenging as it results in higher point loads being imparted onto the runway’s surface.
“We don’t use any localised surface treatments for this, as we find a homogenous surface more durable; this prolongs the life of the runway and minimises joints and material interfaces.”
Still, it is necessary to resurface runways from time to time. In May last year at another of Europe’s busiest gateways, Frankfurt airport’s Runway 18 West had its 14cm-thick asphalt surface and binder course renewed.
Ahead of the work, a statement from airport operator Fraport said: “Over the course of five days, a surface of around 44,000 square meters – roughly corresponding to the size of five soccer pitches – will be renewed. Around 30,000 metric tons of asphalt will be moved over the course of the operation. The maintenance work will involve some 100 workers in multiple shifts.
“The maintenance work will also include replacement of the entire lighting system of Runway 18 West – comprising roughly 600 surface and underfloor lights – with energy-saving, long-lasting LED lights.”
The resurfacing had to be carried out at a time when traffic was relatively low, with close co-ordination between airlines, government agencies and German Air Navigation Services ensuring that the flight schedule and other operations were well planned. The new surface is expected to last between seven and 10 years.
Back in 2011, Frankfurt Airport’s fourth runway came into service, allowing the gateway to accommodate more flights. Heathrow is currently assessing a range of options relating to its expansion – approval for the construction of a third runway having been granted in 2016. Maintenance and material considerations will come later in the process, a spokesperson said.
Starting from scratch
Among the new gateways under construction today is Istanbul New Airport. Once all phases of its construction are completed it will offer no less than six runways, all of which will require ongoing maintenance.
Yusuf Akçayoğlu, CEO of İGA Airports Construction, outlines: “The first phase (phase 1A) will be completed this year, on 29 October 2018. Then the airport will be ready to operate with two independent runways, which comprise in total 6 million square metres of pavement. The maintenance plan will be in line with ICAO [International Civil Aviation Organization] recommendations and is seen as a best practice worldwide.
“In the other phases it will be very important for us to contemplate some automated surveys and there are several systems which are currently under selection. To highlight its scale, those systems are the first ones tested progressively worldwide,” he reveals.
Akçayoğlu goes on: “Referring to the emergency criteria, we follow a unique emergency plan. From a design point of view, I would like to emphasise that we have a high level of resilience of the platform. Every single critical area of segments has an alternative. These processes only work due to our automated smart routeing system: the Advanced Surface Movement Guidance & Control System.”
Supplied by Saab, the A-SGMCS includes aircraft routing and guidance, airfield ground lighting control and monitoring, electronic flight strips, a large array of multilateration sensors, and five SR-3 Surface Movement Radars. This system will provide full coverage for the first phase of the airport construction, and will be expanded as later phases are completed.
Runway maintenance was of great importance in the design and construction of Istanbul New Airport and IGA selected “special runway systems with enough separation to allow independent operations”. Every main runway will have an emergency or auxiliary runway to allow IGA’s teams to carry out maintenance operations safely.
Akçayoğlu is also confident that the increasing size and weight of aircraft will not pose a problem at the new airport, because IGA took this into account. Its runways are designed to cope with widebody aircraft.
“We decided to use an SMA (stone mastic) design for the surface layers of the runways because this is the most beneficial for us and it fulfils the international standards,” he says.
Istanbul has “a very advantageous climate” when it comes to building an airport. Subject neither to heavy sand storms like those that affect the Middle East Gulf region, nor to heavy snowfalls like those that can occur in Northern Europe, the gateway’s design will also protect it from flooding, with a simple gravity-based drainage system that benefits from the general slope of the site.
In terms of lighting, IGA intends to use LED and inset lights, because these two types are the easiest to maintain, helping to minimise disruptions to flights during maintenance as well as being an important safety consideration. Painted markings will include special glass reflecting elements that satisfy the requirements of IGA’s safety plan.
“Our project is totally on time and we are very proud about this fact,” Akçayoğlu declares. “The official opening date is set for 29 October 2018. We are working very hard and at full speed to achieve our goal. Currently, 78% of the construction is completed.”