RNP to precision approach transition flight simulations

EUROCONTROL, in collaboration with the Technical University of Berlin and under the SESAR¹ work programme, has conducted an experiment investigating the behavior of 6 different aircraft types when performing a transition from a curved RNP procedure to a precision final approach (using an ILS, GLS or more generically an xLS landing system). Basic procedures were coded in ARINC 424 format whereby a Radius-To-Fix (RF) leg connected directly to the localizer/glideslope intercept point of a 3, 6 or 9 NM final segment. A set of alternative procedures were designed as well, which contained a short intercept leg with a defined intercept angle between the end of the RF and the final segment. To test the influence of navigation position errors on the xLS transition, lateral biases with various magnitudes up to 0.3 NM and in either northern or southern direction were introduced in the procedures (with the final approach course aligned to the east). The procedures were flown using RF capable certified full motion flight crew training simulators. Significant differences were observed in the capture capability of the localizer. In a category of aircraft it is not possible to transition from LNAV to LOC mode directly. Therefore a crew procedure is required, switching to heading mode near the end of the RF leg for some aircraft. All aircraft types were able to perform a simultaneous localizer and glideslope capture. In most of the scenarios, the aircraft was able to transition from a 2 degree barometric slope along the RNP procedure to a 3 degree glideslope at the capture point. In 95% of the cases the aircraft needed an additional 500 feet to stabilize after the localizer/glideslope capture altitude. This suggests a minimum capture altitude of 1500ft, corresponding to a required minimum final segment length of 5 NM. The alternative procedures containing an intercept leg did not provide advantages over the procedures without intercept leg. It was concluded that successf- l transitions to a 5 NM minimum final segment length would work if the Total System Error along the RNP procedure would be below 0.16 NM. In this case, a straight intermediate segment between localizer and glideslope capture would not be required according to the test results.