Automatic Install instructions:

Drag the "Custom Aircraft Engine Sounds v1.4 Installer.oiv" file into OpenIV, or open it with the Package Installer.
Install it to the mods folder.
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Manual Install instructions:

Open the .oiv file as a zip archive
Navigate to content/mod
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>

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To use on any vehicle, edit the vehicles.meta, find where the car is defined, and replace this line:
<audioNameHash></audioNameHash>
with a valid audio name; Check 'glossary.txt' for audio names as well as the type of aircraft they should be used on.

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