What is your Pi’s architecture? If it is arm64 or aarch64, you wont be able to upgrade from Flightaware repositories.
Please post output of these commands
uname -a
lsb_release -a
If output of first command shows 64-bit architecture, then use installation scripts from following post.
NOTE:
Installation by scripts is a lengthy process and takes some time. Please be patient and let the script run till it announces it has completed its job.
Install Piaware ver 8.1 on amd64 / x86_64, and arm64 / aarch64 Computers