This sets down in extremely simple terms the principles by which navigation aids may be coupled to autopilots and autohelmsmen. These principles apply to human pilots and human helmsmen for a craft cannot be navigated by positional aids alone.

Control by an aid that provides position only is shown to be unstable and, therefore, heading is introduced. This quickened system will be stable unless the control is unduly fierce. Such a system may not allow a craft to follow a required track exactly and, accordingly, ‘over-burdening’ may be required or, alternatively, course substituted for heading.

The type of navigation aid introduces special problems. Approach to a point source aid such as a radio beam leads to an increasingly acute sensing of deviation which tends to reduce stability. The craft will, therefore, need to be settled on to the beam at a reasonable distance from the transmitter and this need will introduce special problems in ‘capturing’ the beam.

Coupling to navigational aids is a basic technique in air navigation which will affect the choice of future air navigation systems. Coupling has not, however, been introduced into marine navigation. In space navigation coupling is confined to precise terminal navigation which at present is limited to launch and docking.