In the Fuel & Flight Efficiency subject, we often talk about “low hanging fruits”, those actions that can be done relatively easily by the airline to reduce fuel burn, lower CO2 emissions and more globally reduce operating costs.
The Auxiliary Power Unit (APU) is seldom treated as a low hanging fruit, however, those airlines that have investigated the subject and ultimately implemented rules for its use have made very significant cost savings in a relatively short time period.
Most modern aircraft are equipped with an APU which is a small jet engine (like the larger main engines found under the wing) and like these main engines, the APU also burns fuel.
The APU supplies the aircraft with pneumatic & electrical power when the main engines are not running or when external ground sources are not connected.
Most of the time the APU will be running when the aircraft is on the ground, for example during the turnaround when the aircraft is being serviced and prepared between flights (it can also be used during flight as a back-up source).
Many airlines have little visibility on when and how the APU is used and are often surprised to learn how much fuel is consumed by these machines.
Airlines that have reduced APU use have done so by the combined efforts of all those involved in the subject including pilots, ground handlers, maintenance staff and flight operations engineers. These reductions have been achieved by changes driven by procedures and policy without investment in additional ground sources.
Improving communication and providing relevant data can also be a good way to raise awareness and increase understanding of subjects such as the APU, topics which I would like to discuss in future articles.
Fuel & Flight Efficiency Expert at NAVBLUE