At the DC-based Air & Space Museum they have a fascinating display of what the sky looked like for a 24 hour period some years ago. Each dot is an airliner. As you watch the video, the change of color means a specific airline’s flights are tracked. Note also the flow into the USA from the EU at the top right during the day and the reverse at night. Watching this activity and knowing there are no crashes demonstrates what a marvelous job is being done by everyone to keep the system running as safely as it does.