TL;DR: Install it like any add-on mod. Drag into your dlcpacks folder, list in dlclist.xml
--------------------------------------------------------------------------------------------------------------------
Manual Install instructions:

Drag the aircraftsounds folder into GTAV/mods/update/x64/dlcpacks
Edit the dlclist.xml in GTAV/mods/update/update.rpf/common/data
Add the following line - <Item>dlcpacks:/aircraftsounds/</Item>
--------------------------------------------------------------------------------------------------------------------
Automatic Install instructions:

Drag the "Custom Aircraft Engine Sounds v1.3 Installer.oiv" file into OpenIV, or open it with the Package Installer.
Install it to a mods folder, I will not be responsible for damages.
--------------------------------------------------------------------------------------------------------------------
To use on any vehicle, edit the vehicles.meta, find where the car is defined, and replace this line:
<audioNameHash></audioNameHash>
with any of the following strings below. If you are confused which planes you should use what sound for, check 'glossary.txt'.

Questions, comments? Contact me on Discord: https://discord.gg/pBtVf5m

Consider supporting my content!
Patreon: https://www.patreon.com/Aquaphobic
PayPal: hansgutana@gmail.com