Actually the rotor brake system. I'm not really clear what would happen if the rotor brake is off when you move the power levers from the Idle to Fly position. Procedures say DONT, return the switch back to on until the engines are at flight speed (approx 100%). Once the engines are happily settled at flight speed flip the brake off and the rotors begin to turn. Watch the rotor RPM gauge on the MFD until it's in the yellow close to 100% then you're good to go.
Conversely, I'm not too clear what damage might occur when then rotors are at 100% and the rotor brake switch is is turned on. A lot of heat and grinding metal noise? A nasty letter from the Boeing company? Currently I just have it decay the RPM to zero under a constant until I get a better answer.
I added more realism options to the config.xml for control over individual items like startup, targetting, flight model.
OOOH, I just remembered why I was really happy today. AD fixed the road physics problem by using displacement mapping in 3DS MAX. So no hacky hacks may be required for road driving afterall. Well done sir. I knew I was feeling buoyant for a reason. If you want to know what the hacky hack means, the road surface was aligned to the terrain with a vertex shader which moves each point on the model level with the ground (relatively) but physics engines don't know what vertex shaders do to geometry, as far as they are concerned the model is unchanged. So there's a disconnect between what the physics engine updates and what the 3D card renders on screen. Using displacement mapping with our heightmap as source, the road meshes are baked at the right elevations to fit, the physics model and visual model are now united and traffic may now use the roads without any problems.
So, way to go AD. Another cracking solution.