Getting more passengers on a bigger modern planes on certain routes will lower the emitted carbon dioxide per passenger as well as optimize the use of flight crews.

Make the app as lightweight as possible. Remove images, animations and leave only the bare necessities. This saves data transfer and storage - which in turn saves energy.

Collaborate with public transport companies at popular destinations to reduce car usage.

Implement the potential to offset carbon footprint by CDR technologies like enhanced rock weathering;

When the crew collects trash before landing, why not make separate rounds for collecting, cans, plastic cups, paper, etc instead of collecting all trash in the same bin.

At check-in and at kiosk ask if they really need paper boarding card or can use SAS app instead.