As of Jan 1st 2012, the aviation industry joined Europe’s emissions trading scheme. All carriers using European airspace are thus being charged for carbon emissions. This means that everybody has an interest in reducing the carbon emissions to a very minimum.
Replacing the onboard aircraft APU with a fixed 400 Hz and pre-conditioned air installation, once the aircraft has docked at the gate. leads to considerable savings both with regard to CO2 as regarding costs in general. The CO2 emissions can be reduced by 85% whereas industry figures reveal that typical savings of about 100.000 EUR per gate per year for a typical single aisle gate. For information, the onboard APU of a narrow-body aircraft consumes approx. 150 l/fuel/hour.
Other useful links
http://www.bbc.co.uk/news/10086349
http://www.bbc.co.uk/news/business-16421117