Analysis of localizer and glide slope Flight Technical Error

A new wake turbulence procedure has been developed that permits two dependent arrival traffic streams during instrument meteorological conditions to runways with centerline separations less than 2500 ft. For the proposed procedure, aircraft approaching both runways of a closely-spaced pair under limited ceiling/visibility conditions utilize instrument landing system (ILS) localizer and glide slope guidance. A critical safety analysis building block was to quantify the risk posed by aircraft flight technical error (FTE), a measure of the deviations from the localizer/glide slope centerlines, under ceiling/visibility conditions when non-visual ILS approaches are normally performed. Flight track data from Lambert-St. Louis international airport (STL) under severe IMC conditions, when strict adherence to navigation aide guidance would most likely occur, were used to quantify the aircraft dispersion characteristics.