Installation: 

1: Ensure you have the original "jet.yft" and "jet_hi.yft" files. If you do not, they are in the "backup" folder provided. 

2: Extract "jet.ytd" and "jet+hi.ytd" 

3: Add the .ytd files to "C:\Program Files (x86)\Steam\steamapps\common\Grand Theft Auto V\x64e.rpf\levels\gta5\vehicles.rpf\"