There is still plenty of activity on the HF Aeronautical bands. You can listen to civil and military aircraft every day with just some frugal hardware. Whether you are using a Software Defined Radio (SDR), an old school HF receiver, or utilizing a WebSDR, there is plenty to monitor when you know where to look.
Thew below video will give you the basics of where to find the Aviation Communications that take place from 3-30 MHz (HF / Shortwave). The video covers VOLMET broadcasts, the Major World Air Route Areas (MWARA), and Military Nets like the US Global Communications System (HFGCS). Remember, these signals travel thousands of miles. It can be quite exciting to receive them over such great distances. When editing this video I was listening to a VOLMET station in Auckland, New Zealand – a distance of over 7500 miles (12,200km) away!