Development Of The Precision Approach Path Indicator Light Unit

The Precision Approach Path Indicator (PAPI) is a simple visual aid that has been developed to assist pilots during their approach to landing. The development of the system by the RAE was reported in Ref 1 and the operational trials and technical evaluation by ICAO were reported in Ref 2. The PAPI system uses a set of four two-colour high intensity light projectors. Each beam consists of a white upper half and red lower half. The transition from one colour to the other occurs over a very small angle. This sharp transition is an essential feature of the PAPI system and it is therefore important that all units should exhibit this characteristic. Similarly, operational considerations dictate the minimum beam-spread and intensity requirements for the light projectors. It is essential that the correct isocandela specification is adhered to in all PAPI units. (Author).

The Precision Approach Path Indicator (PAPI) is a simple visual aid that has been developed to assist pilots during their approach to landing. It enables pilots to acquire the correct glideslope and subsequently to maintain their position on it, thus ensuring an accurate approach and landing. This paper discusses the operational requirements for current and future needs and shows why the PAPI system best meets these needs. (Author).