An Analytical Comparison of Three Visual Approach Slope Indicators: VASIS, T-VASIS and PAPI,

This report compares the three Visual Approach Slope Indicators VASIs, Red-White VASIS, T-VASIS and PAPI Precision Approach Path Indicator approved by the International Civil Aviation Organisation ICAO for use by turbojet aeroplanes. The discussion is based upon published performance data including approach path measurements and pilot opinion, ergonomics and the ability to fulfil operational requirements. It is concluded from flight trial data and operational experience that T-VASIS is a more precise and sensitive aid than Red-White VASIS which has several deficiencies known for many years. The current policy of not using Red-White VASIS for routine operations in Australia is supported by the conclusions of this report. It is predicted that PAPI also will be less satisfactory than T-VASIS. This prediction is based mainly on ergonomic principles. Performance data about PAPI is limited and consists mainly of relatively uninformative pilot acceptance surveys. Because insufficient objective parameters describing trajectories of aircraft from the intended user-population have been published, most of the claims for PAPI superiority remain unsubstantiated. Accordingly, it is recommended that PAPI be evaluated using objective measures in a controlled experimental environment with transport aircraft. Further, because of its ergonomic deficiencies, PAPI should not be installed in Australia for routine operational use by turbojet aeroplanes at this stage. Keywords Visual aids Approach indicators Landing aids Aircraft landing Visual approach Slope indicators. Australia