School of Social and Political Science

Description

1 April 2010 - 30 September 2013

Although not the largest contributor to greenhouse gases even from transportation, air travel is growing, conspicuous, and hard to regulate. One way to reduce or moderate aviation’s climate change impact is through innovation in aircraft technology. More fuel-efficient technologies include the use of lighter structural materials such as carbon fibre, more efficient turboprop engines, and more aerodynamic airframes such as flying wings. However, these have either been introduced very slowly (carbon fibre), only used for certain short-haul routes (turboprop engines), or have not been used at all (flying wings).

The key research question is why such technologies have not been used more substantively to produce greener aircraft. Since the introduction of the Boeing 707 in 1958 most subsequent airliners have followed a paradigmatic dominant design – a fuselage with swept-wings powered by ‘jet’ engines and largely constructed of aluminium. Even though improving fuel efficiency would be a ‘win-win’ solution – reducing costs and environmental impacts – this has tended to come about only through incremental rather than radical technological innovation.

This project seeks to explain why certain technologies get 'locked-in' to incremental improvement whilst alternative approaches are neglected. This analysis unpicks the processes that favour incremental technological change over radical innovation, and provide insight into what policy options might overcome this resistance and thus speed up the transition to less polluting airliner technologies.

Researchers: Dr Graham Spinardi; Prof Donald MacKenzie

Challenges

Aviation is not at present a major contributor to climate change; the authoritative 1999 Intergovernmental Panel on Climate Change study concluded that globally aviation accounted for about 13% of CO2 emissions produced by transport, and 2% from all sources. Nevertheless, without action, aviation’s impact is expected to grow. For example, the Federal Aviation Administration predicted US air travel to more than double between 2011 and 2031, and rapidly growing economies such as China and India will likely see more rapid growth.

A wide range of factors contribute to the environmental impacts of air travel, including operational practices on the ground (e.g. using the aircraft engines longer than necessary), the location of airports relative to population centres, the ‘embedded energy’ of materials used, and the density of seating (with spacious luxury accommodation making particularly inefficient use of aircraft). However, the main contribution comes from what happens during flight.

Fuel-efficiency is critical because the use of aviation fuel is the main way in which air travel contributes to greenhouse gas (GHG) emissions. However, total ‘radiative forcing’ – simply put, atmospheric warming - due to aviation is thought to be about three times that due to aircraft carbon dioxide emissions alone because of the way that the ‘contrails’ (condensation trails) from high altitude flights stimulate the creation of cirrus clouds that reflect more energy back to the earth than they reflect away from the earth.

The challenge is to find ways to reduce aviation’s contribution to greenhouse gas production, and to reduce the impact of contrails on global warming. An obvious solution would be to fly less. Taxation and/or alternatives such as high-speed trains could reduce air travel, though the evidence from taxation so far (for example, the UK’s Air Passenger Duty that was introduced in 1994) is that taxation would have to be very punitive to have a significant curbing effect. Leisure travel accounts for the majority of air travel from the UK, and it would be inequitable for flying to be priced so high as to be a luxury available only to the affluent.

Technological Solutions

If air travel is to continue at current levels, or even increase as predicted, then climate change effects can only be significantly ameliorated by substituting biofuels for aviation fuel, better air traffic management, or the use of more fuel-efficient aircraft. Biofuels (not considered in detail in this project) involve well-known problems. Although feasible in theory, the challenge is to produce sufficient quantities, and to do so without causing other environmental problems, or damage to local economies. 

Improved air traffic management could reduce environmental impacts, but history shows that such improvements are difficult to achieve. This is discussed further here. Airliner fuel efficiency can be improved in three ways: by making aircraft lighter, by adopting more aerodynamic designs, and by making engines more efficient. In general, however, most such improvements to date have only involved incremental improvements, yielding steady but modest gains in fuel efficiency (and the transition to jet airliners in the 1950s resulted in markedly poorer fuel efficiency compared to the propeller driven aircraft they replaced).

Although high-strength carbon fibre was first developed in the 1960s, and used in military aircraft soon thereafter, its adoption in civil airliners was very gradual. Only with the Boeing 787 ‘Dreamliner’, introduced in 2011, has carbon fibre become a major structural airliner material. Radical aerodynamic improvements have seen even less success. Techniques such as flying wings and Laminar Flow Control (LFC) date back to the first half of the 20th century, but have not yet found use in airliners. Finally, more efficient turboprop type engines have only limited use in some short-haul airliners, despite many years of research devoted to making such engines more generally suitable.

Air Traffic Management

The potential environmental benefits of improved ATM lie in two areas. First, better ATM could reduce fuel use. The ideal flight path for an aircraft would be for it to be able to operate as if there were no other aircraft around, and so no potential conflicts that would force it to take a sub-optimal flight path. An ideal flight path, in terms of fuel efficiency, would not only take the shortest route, and involve no ‘stacking’ while waiting for a landing slot, but it would also fly at the optimum (high) altitude for most of the journey, with smooth ascents and descents. Enabling aircraft to utilise ‘idle thrust’ descents, with low engine power, is a key challenge for ATM because of the complexity and time pressure of many different types of aircraft converging on a limited landing space at an airport.

Second, more sophisticated ATM automation could enable aircraft to avoid areas most likely to produce contrails, thus minimising the radiative forcing resulting from cloud formation, although there would be trade-offs involved in not flying the most direct routes

Although improvements in ATM do not offer huge reductions in carbon emissions or other climate change effects, they have the advantage that they could be implemented without the need to replace the current inventory of aircraft. Improvements in ATM efficiency would provide environmental benefits with both current and future aircraft. However, significantly better ATM would require higher levels of automation, and this raises concerns about safety, particularly as regards the reliance on complex software that is hard to test fully before it is used. Moreover, ATM systems are highly complex with many different components often involving a mixture of private and public ownership, and thus investment in improvements typically happens slowly.

Barriers to Greener Airliners

Why have more efficient airliner technologies only been adopted slowly (carbon fibre), partially (turboprop engines), or not all (flying wings and Laminar Flow Control)? Or to put it another way, why does airliner innovation appear to happen gradually, with incremental improvements of existing technology, rather than through radical changes?

The most significant factors stem from the risk-averse nature of the aviation industry. Not only is there an obvious priority on avoiding high-profile disasters that kill hundreds of people, but also designing a new aircraft is a lengthy and expensive process. The commercial risks are thus also very high, and the experience of the British De Havilland Comet – the world’s first jet airliner – provided a salutary lesson on how new designs can also introduce unknown dangers. Three fatal crashes in the mid-1950s as a result of metal fatigue showed that radical innovation often brings new risks.

Any new airliner design must be approved by the regulatory authority (the Federal Aviation Administration in the US), and this process again favours incremental rather than radical innovation. Regulation of such complex technologies necessarily involves a great deal of trust as the regulators must rely to a large extent on the industry to carry out most data collection, and much of its analysis. Given the limited ability of tests to mimic operational practice, the FAA’s judgements about performance rely heavily on the belief that the proven record of earlier generations of airliners can be extrapolated to each new generation, so long as the technologies used are considered sufficiently similar.

This risk-averse innovation system exacerbates the well-known phenomenon of ‘path dependence’, whereby once a particular technology is adopted it can become ‘locked in’ as it gains further investment at the expense of alternative approaches, and thus gets improved, and as it becomes embedded into society (for example in necessary infrastructure). In addition, social attitudes to aviation can present an obstacle to greener aircraft, when, for example, the public’s expectations regarding noise, comfort, and speed are in conflict with technical alternatives that could reduce GHG emissions.

Overcoming Lock-in

Traditional polices aimed at encouraging greener technologies typically follow two approaches: seeking to produce innovative environmental solutions by supporting R&D; and/or providing financial incentives, usually through taxation or regulatory fines that aim to internalise environmental costs. Typically, the latter types of policy are effective in reducing environmental damage, but only through incremental improvements of existing approaches. Incremental innovation usually can be relied upon to provide performance improvements, given sufficient investment, whereas seeking radically new solutions can be more risky. However, incremental innovation can lock-in outdated practices, and limit the potential for making a ‘step-change’ in environmental performance.

Stimulating radical innovation is difficult, and supporting R&D, whilst necessary, is clearly not sufficient. For example, decades of work on Laminar Flow Control established that it can offer significant reductions in aircraft fuel use, but the business case has been hard to make for its incorporation in commercial aircraft given that the extent to which it would complicate day-to-day operations is hard to gauge without operational experience. Radical new airliner technologies thus suffer from a ‘Catch-22’ effect. In-principle benefits, demonstrated in tests, provide insufficient evidence to convince risk-averse managers to sanction adoption of a technology by operational aircraft, but the only evidence that would convince them requires that such technologies are used operationally.

To overcome this type of lock-in thus requires R&D in innovative greener aircraft technologies to be supplemented by support for more realistic testing, and ideally sponsorship of operational use. ‘Technology-push’ must thus be coupled with ‘demand-pull’ to provide practical evidence that radical greener aviation technologies are both safe and sufficiently reliable for day-to-day use.