Because the aircraft and helicopters are capable of high speed and have to stop on a small area, you may need to place speed signs to slow the helicopters down for landing.
The speed signs are visible in Surveyor and invisible in Driver. They place in the centre of the track, the speeds available (kph) on the DLS are:
This makes them very useful for all vehicles using invisible track, or where the use of a visible speed sign at the side of the track is not prototypical, as in the use of Trams or Tramcar operations. Note that stopping location is not consistent in Trainz, it depends on speed of approach and the mass of the vehicle or train.
The kuids are too extensive to list. Look for the assets on the Download Station as, for example:
Speed Sign 100kph Invisible kuid2:60238:230019:1
There are two other very useful assets, not mine. The red and green switch levers can be replaced by an invisible version, and the invisible signal will control the aircraft:
Invisible lever snd kuid:211025:41007
Invisible Signal kuid2:45324:24010:2
In recent versions of Trainz, the default setting for derailment mode is Arcade. The aircraft travel at high speed and unless you re-set this to None, they will derail even on gentle curves. This should be changed in Surveyor then it will be locked in for any Session.