helicopter approach path indicator

helicopter approach path indicator (HAPI)

A device similar to a VASI (visual approach slope indicator) used for fixed-wing aircraft. The helicopter gets a steady green indication when it is on the desired glide-slope. The indication is flashing green when it is above the glide-slope, and a steady red when it is below it. This changes into flashing red if the helicopter is well below the desired glide-slope.