Like so many operations in the world of aviation, airfield runway maintenance is increasingly becoming a problem related to traffic volume. Airports are getting busier and busier with every passing year. That means more wear and tear and it also means fewer windows of opportunity to carry out routine daily maintenance. When it comes to the major refurbishments of runways, the airports have to figure out a way of preventing a steep fall in the number of flights
The International Civil Aviation Organization (ICAO) makes it clear that airports have the responsibility to look after pavement surfaces. “The surface of a paved runway shall be maintained in a condition so as to provide good friction characteristics and low rolling resistance,” says ICAO Annex 14. “Snow, slush, ice, standing water, mud, dust, sand, oil, rubber deposits and other contaminants shall be removed as rapidly and completely as possible to minimize accumulation.”
It is no wonder that ICAO is so insistent that airports look after pavement. The consequences of a poorly maintained runway can be dramatic; runway excursions are dangerous at worst, and highly inconvenient for passengers, airline and airport involved at best. Clément Charpentier, marketing manager of Blastrac, a manufacturer of pavement maintenance systems, notes: “As the number of flights multiplies every year, it’s ever more imperative for everyone’s security that airports upgrade and maintain their surfaces.”
ICAO also stresses the dangers of aircraft striking foreign object debris (FOD) on the runway. FOD is usually either broken pieces of pavement at the edge of the gate area, or loose pieces of construction material blown from the gate to the manoeuvring areas.
At the world’s busiest airports, such as Dubai International (DXB), the challenges of addressing all the potential pitfalls outlined by ICAO are highly complex. “At Dubai International, the main consideration is that with our 24/7 operation, we must take an innovative approach to maintenance,” observes Saud Al Humoudi, head of airfield infrastructure, Dubai Airports. “Add to that the pressure of ever-increasing air traffic and it makes for a real challenge. At the end of last year we had an average of 980 flight movements every day. When we close the runways for maintenance we have to be efficient with our time and resources in order to maximise reliability without compromising safety.”
Dubai International invested US$1 billion in the 80-day complete refurbishment of both its runways last summer. The 4,500-metre long southern runway was closed from 1 May to 31 May, while the 4,000-metre long northern runway was out of operation from 31 May to 20 July. To maintain service levels, the airport reduced scheduled passenger flights and diverted all freighter, charter and general aviation flights to Al Maktoum International at Dubai World Central (DWC).
In all, there was a 26% reduction in aircraft movements at Dubai International during the maintenance period. The airport’s home carriers – Emirates Airline and flydubai – suffered 52.8% of the reductions, while the restriction of freighters and charter operators and other scheduled passenger airlines accounted for the other 47.2%. “The northern runway was nearing the end of its design life and required resurfacing and other modifications,” Al Humoudi explains. “At the same time, we needed to upgrade runway lighting and construct new rapid exit taxiways on the southern runway to boost capacity.”
The scale of the runway refurbishments is revealed in a few figures. The rehabilitation consumed 800,000 tonnes of aggregate, 11,000 airfield lighting luminaires, 1,050km of cabling, 1,750 new manholes and 8.3km of drainage piping. More than 2,500 employees were involved.
A considerable amount of advanced planning minimised inconvenience, Al Humoudi says. “We had to ensure co-ordination between all stakeholders and do a lot of pre-planning, including doing some construction work ahead of the refurbishment. Pre-works included the construction of a new taxiway around the northern runway that allows aircraft using the southern runway to taxi to the north side of the airfield, avoiding crossing over the northern runway. It improves traffic flow on both runways during and after refurbishment,” he remarks.
In addition to undertaking major upgrades every 10 to 15 years, Dubai International has an ongoing maintenance programme. When runways are closed for maintenance, crews carry out several key tasks in just a few hours. One of the most important jobs is to remove about 10kg of excess rubber every week so as to maintain the required level of runway friction. The airport also checks every light fitting and repaints runway markings, and there is a daily check for FOD.
Two departments at Dubai look after airfield maintenance. The Airfield Lighting team checks all visual-aided navigational systems, while the Airfield Civil Works teams maintain pavements, including aprons, taxiways and runways. A detailed monthly test ensures the correct friction levels of the pavement area and weekly photometric testing maintains the category level of the runways. Meanwhile, flight check calibration is conducted every six months.
To preserve apron surfaces, Dubai International uses three types of machines. The hydro blast machine removes unwanted markings, deposited rubber and spilled oil in parking bays. It releases water under extreme pressure at between 22,000psi and 40,000psi onto the surface and sucks up the removed material. The airport also uses a sweeper machine to wash parking bays and suck up waste materials. Finally, a magnetic FOD collector gathers up unwanted metal items from the apron.
There are two main drivers for future innovation at Dubai International. One is to reduce the time required for maintenance. The second is to develop more robust systems that reduce the need for maintenance. To achieve these aims, Dubai has been quick to introduce new technology. “As part of last year’s runway refurbishment programme, a new LED lighting system was installed on both runways and the taxiways. It will reduce maintenance costs and power consumption while providing pilots with a better visual aid,” Al Humoudi says.
“We have also introduced an advanced MALMS cleaning machine which cleans light units more efficiently with fewer people. And we’re installing RFID (radio frequency identification) for lighting units on our runways and MALMS system. This is linked to a GPS guidance system, which makes identifying specific lighting units extremely easy during maintenance.”
MAINTENANCE IN VIENNA
Austria’s Vienna International Airport may not be quite as large as Dubai International Airport, but it’s still in the list of the top 20 busiest European airports. “We have to preserve 2.7 million square metres of paved areas, including runways, taxiways, stands and streets,” says Clemens Schleinzer, from Vienna Airports’ communications team. “Besides technical matters, the main challenge is co-ordinating all the jobs with operational needs so that we minimise the impact on passengers at a 24/7 airport.”
Vienna carries out a full-scale inspection at the end of each winter to determine the annual maintenance programme required for all paved areas. The inspection at the end of 2012 revealed that for safety reasons runway 16/34 required complete renewal. This meant replacing the surface and base courses, as well as the shoulders over the entire 220,000m2 runway area. “If we had failed to schedule this work in 2013 we would have created a serious safety risk for aircraft take-offs and landings due to asphalt breakage,” Schleinzer notes. “Runway 16/34 was built in 1976 and only underwent one general renovation in 1993. The wear and tear on a runway is huge. A single aircraft landing exerts several hundred tonnes of pressure on the surface, and nearly 270 landings take place each day on that particular runway.”
Major resurfacing is not possible in winter, but it must be finished in time to handle the heavier traffic in summer. This leaves only a small window in spring. So, the renewal programme began in early April and was completed seven weeks later. The refurbishment work was further restricted to certain times of day. Renovation took place from 9pm to 7am on 25 nights and from Friday at 9pm to Sunday at 4pm across five weekends. Runway 16/34 was shut down completely during these times and traffic was diverted to Vienna’s second runway, 11/29. This second runway will take its turn at being resurfaced in the next few years.
In addition to the major projects at Vienna, the airside operations department examines pavements during both day and night operations. Their visual checks are supported by technology such as the Skiddometer. “The inspections check for FOD and bird strikes. They also ensure clean surfaces, legible markings, functional lights, the correct levels of runway friction and bird strikes,” Schleinzer informs. “If there’s immediate danger, our maintenance personnel carry out the smaller maintenance works immediately. They clean surfaces, or markings, or repair broken lights and electrical components. Most maintenance work is done at night from 10pm to 6am when traffic is at its lowest.”
The increase in traffic has created problems for Vienna, just as it has done for Dubai International. Schleinzer says that growing traffic volumes mean there is less flexibility for maintenance crews. “We are confronted with increasing co-ordination work and costs and the three departments of Operations Infrastructure, Airport Operation and the Maintenance Department have to work closely together to ensure continuous operations. We also use modern management techniques and tools to help us to react flexibly.”
NOCTURNAL ACTIVITY
Hong Kong International Airport carries out five daily inspections on both its runways to ensure compliance with ICAO standards and HK Civil Aviation Department (CAD) Licensing Requirements. Ad hoc inspections are carried out by CAD’s Air Traffic Control. In addition, each runway is closed from 1.30am to 7.59am at least two nights a week for more in-depth checks. These include measuring friction, rubber removal by high-pressure jets, the re-painting of pavement markings, cutting of grass to the optimal height of 100-200mm and the repair of pavements.
After the nocturnal inspections, Hong Kong carries out a thorough inspection before opening each runway to make sure workers have left the area, all equipment has been cleared away and runway facilities are ready for operations. “We have to gear up our resources to complete all the airfield maintenance works within the limited time window. That timeframe is the greatest challenge as we are already running very close to the limits of our capacity,” considers Timothy Wu of the Hong Kong International Airport communications department.
Thankfully, modern technology is coming to the aid of time-strapped airports. Blastrac’s Charpentier says his company’s machines have got larger over the years to deal with greater surface areas. The largest can now clean 3,000 m2 in an hour, he says. “We’re also developing a new multi-tasking machine that saves even more time for airport operators. It will have both a shot-blasting head and a scarifying head. It will also be possible to drive on the highways in it like a normal vehicle, then add the different tools at the airport.”
Modern technology also plays a significant role in policing the runways for FOD. Machines tracking FOD include stationary radar, which detects metallic cylindrical objects at ranges of up to a kilometre. Meanwhile, the Stationary Electro-optical Detection System spies small objects at ranges of up to 300m using only ambient lighting.
Airports can also call on Stationary Hybrid Technology that uses both an electro-optical and radar sensor in a unit collocated with the runway edge lights. These systems can detect a small object on a runway. Finally, the Mobile Radar Detection system is mounted on top of a vehicle that scans the surface in front of the vehicle when moving. It provides a useful supplement to visual inspections.
