NOTE.
Some GPS receiver installations inhibit GPS navigation whenever ANY ILS frequency is tuned. Pilots flying aircraft with receivers installed in this manner must wait until they are on the intermediate segment of the procedure prior to the PFAF (PFAF is the active waypoint) to tune the ILS frequency and must tune the ILS back to a VOR frequency in order to fly the GPS based missed approach.
12.11.3.2 Charting. There are charting differences between ILS, RNAV (GPS), and GLS approaches.
a) The LAAS procedure is titled “GLS RWY XX” on the approach chart.
b) The VDB provides information to the airborne receiver where the guidance is synthesized.
c) The LAAS procedure is identified by a four alpha.numeric character field referred to as the RPI or approach ID and is similar to the IDENT feature of the ILS.
d) The RPI is charted.
e) Most RNAV(GPS) approach charts have had the GLS (NA) minima line replaced by an LPV line of minima.
f) Since the concepts for LAAS and WAAS procedure publication have evolved, GLS will now be used only for LAAS minima, which will be on a separate approach chart.
12.11.4 Required Navigation Performance (RNP)
12.11.4.1 Pilots are advised to refer to the “TERMS/LANDING MINIMUMS DATA” (Sec-tion A) of the U.S. Government Terminal Procedures books for aircraft approach eligibility requirements by specific RNP level requirements.
12.11.4.2 Some aircraft have RNP approval in their AFM without a GPS sensor. The lowest level of sensors that the FAA will support for RNP service is DME/DME. However, necessary DME signal may not be available at the airport of intended operations. For those locations having an RNAV chart published with LNAV/VNAV minimums, a procedure note may be provided such as “DME/DME RNP.0.3 NA.” This means that RNP aircraft dependent on DME/DME to achieve RNP.0.3 are not authorized to conduct this approach. Where DME facility availability is a factor, the note may read “DME/DME RNP.0.3 Authorized; ABC and XYZ Required.” This means that ABC and XYZ facilities have been determined by flight inspection to be required in the navigation solution to assure RNP.0.3. VOR/DME updating must not be used for approach procedures.
12.11.5 CHART TERMINOLOGY
12.11.5.1 Decision Altitude (DA) replaces the familiar term Decision Height (DH). DA conforms to the international convention where altitudes relate to MSL and heights relate to AGL. DA will eventually be published for other types of instrument approach procedures with vertical guidance, as well. DA indicates to the pilot that the published descent profile is flown to the DA (MSL), where a missed approach will be initiated if visual references for landing are not established. Obstacle clearance is provided to allow a momentary descent below DA while transitioning from the final approach to the missed approach. The aircraft is expected to follow the missed instructions while continuing along the published final approach course to at least the published runway threshold waypoint or MAP (if not at the threshold) before executing any turns.
12.11.5.2 Minimum Descent Altitude (MDA) has been in use for many years, and will continue to be used for the LNAV only and circling procedures.
12.11.5.3 Threshold Crossing Height (TCH) has been traditionally used in “precision” approaches as the height of the glide slope above threshold. With publication of LNAV/VNAV minimums and RNAV descent angles, including graphically depicted descent profiles, TCH also applies to the height of the “descent angle,” or glidepath, at the threshold. Unless otherwise required for larger type aircraft which may be using the IAP, the typical TCH is 30 to 50 feet.
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