Airport Runways - Lengths and Strengths
25 Jan 2019
Runways are at the core of an airport’s infrastructure. Along with the terminal building, the runway, taxiways (how aircraft get from the runway to the apron area) and the apron areas (where aircraft park to embark/disembark passengers and cargo) are the most essential pieces of the airport’s DNA.
This long piece of specially-designed pavement is also one of the most expensive parts of an airport to construct and maintain. In our second blog on Wanaka Airport, we look at why runways are important including their length and strength. As part of the Wanaka Airport Master Plan we will be looking at the airspace possibilities, weather and wind patterns, and then possible runway positions and lengths.
Runway lengths vary, depending on the aircraft size and runway elevation.
Why are runways so important?
The International Civil Aviation Organization (ICAO) and Civil Aviation Authority (CAA) consider runway safety to be one of the highest priorities when operating an aerodrome. Following correct landing and take-off procedures, conducting regular Foreign Object Debris (FOD) checks and wildlife management are just some of the things undertaken to ensure aircraft can take-off and land safely. Each airport is different depending on the location and climate, for example at Queenstown Airport, the Operations and Rescue Fire team are full steam ahead on a snow day to clear the runway and get the airport operational ASAP. Or strong winds, like the ones experienced this week in Central Otago, can cause branches and other debris to cross the runway.
To determine the length of a runway, several factors are considered, including airport elevation, temperature, wind velocity, aircraft operating weights, take-off and landing flap settings and runway surface condition (dry or wet). Length isn't the only consideration. The runway surface itself is normally thicker than usual highway surfaces to handle the extra weight and impact forces of modern aircraft.
Fast Facts: The Boeing 747-8F has a maximum design maximum take-off weight (MTOW) of 442,253 kg.
In New Zealand, a runway of at least 1,900 metres is needed for aircraft such as the Airbus A320, plus 240-metre-long runway end safety areas (RESAs) at each end. The 70-passenger ATR-72 aircraft need at least 1,500m and the 50-passenger Dash 8-Q300 around 1,200m. Larger aircraft, such as wide-bodied jets like A380s, Boeing 777 etc will usually require at least 2,500 m (plus RESAs) at sea level and somewhat more at higher altitude airports. Runway length requirements are generally greater at higher altitudes as the increased altitude reduces the density of air. This reduction in air density means the aircraft engines produce less thrust/power, thus requiring more runway length or a lower operating weight. Wanaka Airport is 348m above sea level.
Wanaka Airport’s runways today: The sealed runway at Wanaka Airport is 1,200 metres long by 30m wide. It is supplemented by a parallel grass runway of 900m by 40m wide. Strengthening work would be needed in order to carry ATR-72s or larger aircraft.
Above: Wanaka Airport
Wide bodied jets
International wide-body flights (Boeing 777, Airbus A380 etc), which carry substantial amounts of fuel and thus are heavier, have landing and take-off length requirements in excess of 3,000m at maximum take-off weight. It is not uncommon for the larger widebody aircraft to have a maximum take-off weight that is greater than the maximum landing weight. This is why these aircraft will often need to dump or burn off fuel before returning to the airport if needs be.
Fast Fact: The world's longest paved runway is at Qamdo Bamda Airport in Tibet (China) and has a total length of 5,500 m (18,045 ft). It is also the world’s second highest airport at an elevation of 4,334 m (14,219 ft) above sea level. The length of this runway is underpinned by the high elevation and thus lower air density.
Above: Qamdo Bamda Airport in Tibet
The choice of material used to construct a runway depends on the use and local ground conditions. For some airports, where the ground conditions permit, the most common pavement for long-term minimum maintenance is concrete. If it’s anticipated that settlements of the runway will occur over the years because of unstable ground conditions, some runways may be constructed using asphalt as it’s easier to repair on an ongoing basis. Soil and land tests are undertaken at various points around the airport land to ensure a good understanding of the underground make-up, especially important living in the Southern Lakes of New Zealand around earthquake fault lines.
Once constructed, the Runway surface is regularly maintained to ensure continued safety and to maximize friction for wheel braking. There is a balance to be struck with respect to runway friction, as it needs to be sufficient enough to allow good braking, but not too great that it causes significant rolling resistance for an aircraft when it takes-off. To minimize hydroplaning following heavy rain (or in the case of Queenstown Airport snow and ice that melts), the pavement surface is usually grooved so that the surface water flows into the grooves and then away from the runway.
Fun fact: The Queenstown Airport runway was grooved in April 2017 at a cost of $750,000. You can read all about the Queenstown Airport runway grooving project here.
So next time you land at ZQN or any airport, you might think a little more about the pavement beneath you, wondering what it’s made from and what the operations team does to maintain it.
Blog #3 – coming up….runway names and positions.
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