RNP to xLS

The term xLS relates to any precision approach landing system.

This page considers the use of PBN to connect with a Precision Approach system.

RNP to ILS approach with automatic NAV source switching (Frankfurt, Germany)

The ILS X approach to RWY 07R in Frankfurt (EDDF) flown in an Airbus A319 has an initial approach with a Radius-to-Fix (RF) leg which puts the aircraft on a short intercept leg to the final approach. Until the aircraft is established on the localiser, the approach is flown in ''NAV" mode. This means that the FMS is the navigation source, providing steering inputs to the Flight Director and Autopilot. It will steer the aircraft along the curved Radius-to-Fix (RF) leg by adapting bank angle in function of turn radius and aircraft groundspeed. Once on the localiser, the steering inputs are generated by the Multi-Mode Receiver (MMR) which processes the ILS signals. This means that the navigation source needs to switch from NAV (FMS based navigation) to ILS (MMR based navigation). In this aircraft, this switch occurs automatically once the flight crew has armed the approach (APP) mode and the aircraft is in a position which enables localiser capture. ILS modes are indicated by LOC (lateral) and G/S (vertical).

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RNAV to ILS approach without automatic NAV source switching (Frankfurt, Germany)

In some aircraft, the flight crew needs to change the navigation source manually when transitioning from the initial approach (flown using FMS based navigation) to the ILS final approach segment. This approach, ILS 25L to Frankfurt (EDDF), was flown in the Bombardier CRJ200. Note that the initial approach (from CHA to DF621) is a conventional procedure but in a modern aircraft it is flown just like an RNAV procedure, using the aircraft's Flight Management System (FMS). Initially, the navigation source is FMS1. At the end of the initial approach, the flight crew needs to switch the navigation source manually to LOC. During this switch, the lateral flight guidance typically reverts to a basic “ROLL HOLD” mode. When the approach mode is armed, the flight guidance reverts to “heading (HDG)” mode which will roll out the aircraft on the heading selected by the flight crew. The aircraft will maintain the selected heading until the aircraft is in a position under which the LOC capture criteria are met. LOC and G/S indications will appear on the Primary Flight Display (PFD) after capturing the localiser and glideslope.

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