Ramping up runways
|
Posted Date: 01/03/2008
Issue: Airside International March 2008
Publication: Airside International
Never before has the demand for airside engineering expertise been so high; equally never before have environmental, materials management and planning concerns been so prominently on the agenda. Runway design and construction is a complicated science that relies upon layers of expertise and minds open to innovation. Richard Smallegange is a Director of Unihorn – a consultancy which forms part of the Ooms Avernhorn group of companies and specialises in pavement engineering. He explains that prior to commencement of any airfield construction project there are a number of studies that must take place.
“These studies depend upon whether the project in mind is a
From the bottom up
As with all things in the built environment, what goes on below the surface project is key. Smallegange explains that special settlement techniques, with deep drainage systems, allow an engineering team to settle the existing soil much faster than in a natural way. “Using a cement treated base as a foundation in combination with a polymer-modified bitumen for the asphalt, and with asphalt reinforcements against cracks, you can achieve a better pavement with a longer lifetime and less maintenance,” says Smallegange. “Even if there is some settlement or some cracks from the bottom of the foundations, these modern materials will hinder them.”
In terms of the harshness of these materials in relation to the environment, Smallegange points out: “If you look at polymer-modified bitumen compared with normal bitumen for the asphalt, there is no additional impact on the environment. In the past, tar was used as a component of the bitumen for the asphalt to give it a longer life and better properties but this is no longer allowed in most parts of the world because it is carcinogenic.”
Lime is now also being used as an alternative to cement for the base. Lime is not only very hard, but also has considerable environmentally beneficial properties given that it is a natural material.
On the surface
Foundations may be key but what is on top can make or break a successful aircraft landing. Richard Jenman, Director of Pavestech PST Ltd, a pavement surface technology consultancy, explains that heavy traffic and short landing distances contribute towards the deterioration in skid resistance on runways, thereby reducing surface friction properties.
“The runway surface condition is critical to the safety of the airport’s operation,” says Jenman. “There are many elements that can affect this, including structure, the materials used, the surface type, snow, ice, water and contamination from various sources, but especially from rubber deposits.” He explains that pavement grooving was the first major step in achieving safer pavement surfaces and then research proved that an open graded, thin hot-mix asphalt surface course called “porous friction course” could also achieve satisfactory results.
Whatever process or technique is employed to improve runway surfaces, Jenman points out that runway friction characteristics will change over time, depending upon the type and frequency of aircraft activity, the weather and environmental issues, amongst other factors. “Contaminants such as rubber deposits, dust particles, jet fuel, oil spillage, water, snow, ice and slush all cause friction loss on runway pavement surfaces,” he comments. “All major airports now continually monitor the skid resistance levels and surface condition of the runways and have routine rubber removal and maintenance programmes in place.”
A thorough technical understanding of runway surfaces is intrinsic to the development of new runway surface products. Jenman explains that there are three types of texture that are important factors in the performance of a runway surface:
? megatexture – a component of the surface profile which tells us how flat the surface is – and if the megatexture is poor, this causes vibration to the aircraft structure, patchy drainage and water ponding;
? macrotexture – the average depth of the gaps or voids between the course aggregate particles in a surface – which is an important characteristic of runway surfaces and affects stopping distances at high speed; and
? microtexture – this is provided by the roughness or texture of the surface of the individual aggregate particles.
Jenman comments: “An adequate combination of both macrotexture and microtexture is required to provide sufficient frictional properties for aircraft to manoeuvre safely throughout their landing and take off speed range.”
Dreaded deposits
Blastrac is a manufacturer and supplier of surface preparation equipment to airport operators and other organisations. Over the years, Blastrac has worked with airport authorities to develop and improve technologies for the effective removal of rubber contamination and the regeneration of texture and skid resistance to runway surfaces. Jenman comments: “
Within the runway construction
No runway is a solid slab. Within the cross-section of the runway there is a myriad of cables and drainage channels. In particular, runway lighting is powered via cables buried under the airfield surface. “In the past, these cables were placed in the asphalt or the foundation; nowadays they are put into ducts so that they are easier to move without breaking up the asphalt pavement,” says Smallegange. “Runways are usually located in open fields and so there are not usually many drainage systems in the vicinity of the runways themselves. Drainage is usually located close to the aprons or where the taxiways are connected to the aprons, or where the taxiways are connected to the runways,” he comments. Airports are notorious for one kind of spillage or another. Be it, glycol, fuel or oil, there is considerable run-off that is often contaminated in one way or another. But this effluent has to be filtered prior to removal, thereby adding a further cost and engineering dimension to any project.
Materials management
Given the large numbers of runways currently being moved or reconfigured – especially in the US – the salvage of runway materials and their reemployment in new runways is vital for environmental and cost reasons. “Asphalt can generally be reused in new asphalt, depending on the level of contamination,” says Smallegange.
Of course the alternative to an asphalt runway is one built of concrete; but concrete is a very inflexible material which may require extensive and expensive maintenance. Smallegange comments that modern technology allows the enhancement of concrete for runway construction but should the airport operator choose to change the layout of the airfield, the reconfiguration of an airfield comprising concrete runways is a very expensive project. “This is why an increasing number of operators choose asphalt,” he adds.
According to Smallegange, a successful runway project depends upon the expertise of the design team. “If you design your runway properly, you do not cause problems for yourself in the future,” he concludes. “You have to expect normal pavement ageing through use, temperature, ultra-violet light and mechanical damage; but the success of the runway is all in the initial design.”
Special friction course for operational safety at
Hans Hager is a member of the Technical Support team at Possehl Spezialbau. Its Antiskid surfacing has been put in place at more than 70 civil airports and military airfields for over 40 years to increase operational safety on the runway during take-off and landing. Hager comments: “Air travel is safe but incidents are unavoidable, and, when they happen, they occur during landing and take-off in nearly 50% of all cases. Very often, runway surface conditions, especially in inclement weather, when surfaces are wet and slippery, are the cause of the mishap.” He continues: “The International Civil Aviation Organisation (ICAO) recognises this and requires certain pavement friction values for runways. These values, at a speed of 65km/hr, vary from a friction coefficient of 0.74 for new pavements to a minimum friction level of 0.43 for existing pavements.”
At the
At
Antiskid is a single surface treatment composed of a mix of a special epoxy binder and basalt chips, carefully graded between 1.5 and 3.5mm. It is placed with high precision, using customised equipment.
Runway analysis service offered for business jet users
Runway conditions are not only of the highest concern to airlines; business jet operators are equally dependent on the best runway qualities to ensure the safe and timely operation of their aircraft. Universal Weather and Aviation can now provide business jet clients with runway analysis services as an integrated feature of its flight planning offerings through an agreement with Aircraft Performance Group (APG). Runway Analysis is the calculation of safe take off parameters based on aircraft weight and type, actual runway conditions (including obstructions and terrain), and real-time weather. APG Runway Analysis is available via any standard Internet connection.
Runway Analysis allows operators to increase their maximum takeoff and landing weights based on specific runways and actual conditions. In some cases, the allowance may increase by thousands of pounds, a tremendous benefit when a flight crew might otherwise have to limit passengers or cargo. Using actual data, Runway Analysis often allows aircraft to take on enough fuel to eliminate an unwanted technical stop.
This service covers over 100 types of business aircraft. It determines the maximum allowable takeoff and landing gross weights based upon specific aircraft/engine combinations, aircraft configurations, airport/runway characteristics and operating rules.
Related Headlines
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
Issue Advertisers
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
| > |
