We have developed an automatic autopilot called OCTAVE (Optic flow based Control sysTem for Aerial VEhicles) that enables a rotorcraft to take off and land automatically at a constant ascent or descent angle without requiring any Terrestrial Aids. In previous studies, we described how a rotorcraft equipped with the OCTAVE visually based AFCS reacts suitably when encountering shallow terrain and wind disturbances. The OCTAVE autopilot involves a feedback loop designed to keep the downward optic flow (i.e., the ratio between groundspeed and ground height) constant by adjusting the rotor thrust. The downward optic flow is measured with an optronic angular velocity sensor that operates in the present version in the near IR but could work with millimetre waves as well. The electronic processing system required is so lightweight (it weighs only a few grams) that it can be mounted onboard Unmanned Air Vehicles and even on Micro-Air Vehicles. On the other hand, the OCTAVE autopilot could also provide guidance and / or warning signals to help pilots keep a constant ascent or descent slope in the absence of any off-board navigation aids.