Known bugs:
Thrust configuration is not realistic.
747-SOFIA sinks in the ground, press G two times to correct it.
Fuel configuration and ISP is not realistic.
Engines sounds are too loud and annoying.
TO-DO
Improve beacons.
Save/restore engines status from scenario file.
Fix ISP, fuel consumption and thrust configurations.
Make a mesh for the rear APU engine.
Etc.