Like aircraft engines, the Auxiliary Power Unit (APU), an engine located in the tail of an aircraft, emits [ultrafine particles](https://www.schiphol.nl/en/sustainability/living-environment/improving-air-quality/). The APU provides electrical and mechanical power whenever the main engines are off. It is used for air conditioning, starting the main engines and providing electricity for the equipment and lighting within the aircraft. We strive to create a healthier working environment for all those who work at the airport.
Although the topic of ultrafine particles is relatively new and lots of it is unexplored still - we do know they might be harmful to health. That’s why it is important for airports like Schiphol to reduce the number of ultrafine particles, so employees at the airport will work within a cleaner environment.
Various sector partners at Schiphol are committed to reduce aircraft APU usage at Schiphol. To do this, we at Schiphol are trying to accelerate the placement of more external equipment that replaces the APU’s functionality (e.g., electrical pre-conditioned air (PCA) units).
Furthermore, we try to measure the effects of alternative equipment, we test with solutions that remove ultrafine particles from the air (e.g., the water screen as well as collaborate with various airlines to minimize APU usage. The rules at Schiphol state that the APU is only allowed to be turned on just after arrival and before departing of a flight. In between, external equipment that replaces the APU’s functionality should be used when available (with some exceptions like extreme weather conditions). In order to facilitate conversations with airlines and partners about (authorized) APU usage, we need to accurately know when the APUs are being used.
In addition to better monitoring by authority officers, we are executing a Proof of Concept with acoustic sensors. Currently, 4 acoustic sensors of Sorama are placed at the gates to test if we can monitor APU usage of aircrafts (real-time). Using a specific frequency range and decibel levels, the sensors should send a signal whenever an APU is being used.
We are still validating the technology by cross-referencing the data with other data sources suggesting APU usage, but so far the technique looks promising. After validation, we will also combine the APU usage data with the ultrafine particles levels measured on airside, to get data-driven insights on how lowering APU usage at the stand will impact the quality of the working environment at airport. Results of the Proof of Concept are expected at the end of 2024.