Airport growth will only be permitted through sustainable operations.
The Auxiliary Power Unit (APU) is an on-board turbojet engine, generally located at the rear end of the fuselage of an aircraft and powered by kerosene from its tanks. The APU provides the aircraft with power for the cockpit, lighting, the galley, air conditioning and engine starting when on the ground. Some degree of APUs use is therefore essential for aircraft operations on the ground.
APUs HOWEVER HAVE SIGNIFICANT DRAWBACKS
The environmental and economic impacts of APUs cannot be ignored. Indeed, in the long term, their use can have a significant impact on local air quality, such as emissions of air pollutants and greenhouse gases, affecting both ground staff and the local environment.
In addition, APUs use a lot of expensive fuel; over 2000 litres per hour for a wide bodied aircraft. They also create noise just above the heads of apron workers. This noise can also affect local communities – depending on proximity.
In France, the Airport Noise Pollution Control Authority (ACNUSA) has also drafted a report  in which they strongly recommended airports and the French Aviation Civil Authority (DGAC) to limit the use of APUs. In this study, ACNUSA states that by promoting alternatives to APUs an Airport Operator can reduce atmospheric emissions and noise from aircraft ground operations, whist helping to reduce the fuel cost of flights – to benefit airlines and passengers.
 To know more : http://www.acnusa.fr/web/uploads/media/default/0001/02/1081_rapportacnusa2016.pdf
OPTIONS FOR REDUCING APU USE
Whilst APUs are still needed for some stages of ground operation, it is possible to provide alternative to allow their use to be reduced. These alternatives can replace the APU from shortly after the aircraft docks until it is ready to push-back. These alternatives include:
* External electricity via a heavy duty cable to the aircraft supplied from: – The airport electrical supply – fixed electrical ground power (FEGP); or,- Small mobile diesel ground power units (GPU) on the apron.* Externally supplied air conditioning via a large hose supplied by:– A dedicated Pre-Conditioned Air (PCA) unit on the stand; or ,- A mobile diesel air conditioning unit on the apron* A mobile diesel compressor (Air-start) to start the engines.
Where these alternatives are supplied from airport systems this removes local emissions and noise completely and allows the use of renewable energy. Where the alternative is diesel powered, some noise and emissions will remain on the apron.
It should be remembered that some degree of APU use will still be required even with these alternatives being provided.
According to the Union of French Airports (UAF)  an APU emits between 15 and 30 times more CO2 than a GPU, which itself emits 7 times more than fixed installations of 400 Hz.
For example, Air France has succeeded in reducing its fuel consumption related to APUs by 11% in 2015 as compared to 2014 as a result of the implementation of fixed electrical ground power (FEGP) .
Therefore, it appears that the long-term use of FEGPs would both reduce emissions of air pollutants (including greenhouse gas emissions) and financial costs. It would also remove a potential health risk to apron workers.
 To know more: “Enquête sur le Développement Durable dans les Aéroports français”, 2011 To know more: http://csrreport2015.airfranceklm.com/web/app.php/fr/article/15/fr/pdf
A SOLUTION THAT NEVERTHELESS INCLUDES A CERTAIN COST
According to the “Handbook for Evaluating Emissions and Costs of APUs and Alternative Systems”, the following parameters must be taken into account by airports:
* The investment costs for basic equipment purchase, installation and various upgrades of FEGPs,* The operational costs corresponding to the use of alternative systems to supply electrical energy and air conditioning to the aircraft. The purchase of electricity from the local supplier for this purposes is the main expense,* The maintenance costs involving the repair or upgrade of the system components. In addition, the implementation of various alternative solutions, whether they are fixed or mobile, requires an interdepartmental mobilization between maintenance teams, ground operations departments, air operations divisions and so on.
Envisa recognises the particular importance of the operational aspect of the use of alternatives means and APUs.
Although it is possible to identify certain general practices that can be applied at several airports which would generate significant environmental and economic gains, it should be noted that there is no universal solution. Case-by-case studies are necessary to have tailor-made solutions for each airport. For example, if we just take the “climate change” factor into account, it would imply several benefits or challenges that are different for each airport!
In other words, strategies to reduce the use or substitute APUs may not only vary according to the size, type and geographical location of airports, but also depend on the regulations imposed at national and European levels and also the benefits that will arise for a particular airport. There is no ‘one-size-fits-all’ solution.
This is why Envisa considers that in order to analyse and calculate the real costs of implementing fixed or mobile alternatives, a multi-criteria evaluation (economic, environmental, technical and operational) must be conducted.
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Established in 2004, Envisa is an environmental consulting company specialised in sustainable aviation.Our focus areas are mainly local air quality, greenhouse gas (GHG) emissions, noise & energy management. Download our brochure!