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blogJanuary 24th 2023 • 3 m read

Sustainability in ground operations - APU, GPU & PCA

Almost every airport, airline and industry institution has committed to net zero carbon emission targets and the research and investment needed to achieve this. Most of the industry’s emissions happen during flight, hence, research and development into sustainable aviation fuels (SAFs), electric and hydrogen propulsion is to be expected. However, ground operations are also an important aspect of emissions reduction, contributing 30% of total airport emissions and twice an airport's direct emissions.

The primary source of ground emissions is taxi and holding times. Second, is the use of aircraft auxiliary power units (APUs) during ground operations. The APU is an engine inside the tail of the aircraft which is not used to propel the aircraft but rather to generate electricity to power the onboard systems, including the air conditioning.

Airport emissions-mckinsey2020 .png Source: McKinsey 2020

Typically, the pilot will turn this engine on after landing, during taxi-in, to ensure power to the aircraft after the main engines are shut down. In the past, this engine would run for the entire duration of the active turnaround and would be switched off after the main engines had been started during the taxi-out. Unfortunately, the APU is a very noisy and inefficient engine, using up to six times as much energy as a ground power unit for the same load. Most airports recognized the need to minimize APU usage many years ago. Many made investments into ground power solutions which supply electricity to the aircraft either via a generator or a fixed power supply connected to the terminal building. Pre-Conditioned Air (PCA) facilities were created to minimize the power requirement of aircraft during the turnaround.

Most medium to large airports offer PCA facilities and ground power resulting in an almost 50% decrease in APU emissions. If available, the reduction of APU usage still depends on several factors;

  • The speed at which the aircraft is connected to ground power and PCA after arrival
  • The amount of time before departure that the aircraft gets disconnected from them
  • Whether or not the pilot turns off the APU once connected

    Based on visual observations and anecdotal evidence, airports have realized that the usage of ground power and PCA is often not optimised. A recent study has estimated that there is room for another 50% improvement in APU usage times.

CO2 APU emissions.png Source: Sustainable Aviation

In order to improve the use of ground power and PCA facilities, therefore, reducing APU usage, many airports have imposed APU regulations which stipulate when the APU must be turned off (e.g. 10 minutes after arrival) and when it is allowed to be turned on (e.g. 15 minutes before departure). For these kinds of regulations to be effective, some sort of monitoring and/or enforcement is required. Till now, there was no way other than ineffective and time-consuming visual observations by airside agents to monitor adherence to these rules.

Assaia has introduced APU Emissions Detector, a sensor solution that can ‘hear’ whether APUs are in use. Airports can configure their own APU usage threshold in the system and receive alerts in case of violations. Furthermore, historic data on APU usage is available at the gate, airline, ground handler and aircraft type level for emissions management and reporting. APU Emissions Detector is a powerful tool that helps airports and airlines achieve their net zero emissions targets because you can’t manage what you can’t measure!

Learn more about Assaia's APU Emissions Detector