I recently took advantage of solid IMC in the Seattle area to fly several instrument approaches. Flying in actual instrument meteorological conditions is different from practicing with a view limiting device (e.g., a “hood”), especially when the visibility beneath the clouds is limited.
An important new Advisory Circular 90-119 Performance-Based Navigation Operations was released for comment in May 2021 and is now in the review and coordination phase at FAA. You can find the draft PDF in my Aviation Documents folder here. FAA has not announced when the final AC will be published, but if past review cycles are a guide, it may appear by the end of 2022 or early 2023.
You can read my detailed initial comments to FAA here (PDF).
This advisory circular (AC) replaces and consolidates several ACs…and provides guidance for operators using Performance-based Navigation (PBN) in the United States, in oceanic and remote continental airspace, and in foreign countries that adopt International Civil Aviation Organization (ICAO) PBN standards.
The draft AC includes updates to FAA policy in some key areas, and it will replace several existing guidance documents, including:
AC 90-100A CHG 2, U.S. Terminal and En Route Area Navigation (RNAV) Operations, dated April 14, 2015;
AC 90-105A, Approval Guidance for RNP Operations and Barometric Vertical Navigation in the U.S. National Airspace System and in Oceanic and Remote Continental Airspace, dated March 7, 2016;
AC 90-107, Guidance for Localizer Performance with Vertical Guidance and Localizer Performance without Vertical Guidance Approach Operations in the U.S. National Airspace System, dated February 11, 2011; and
AC 90-108 CHG 1, Use of Suitable Area Navigation (RNAV) Systems on Conventional Routes and Procedures, dated April 21, 2015.
The language in this AC also affects sections of the AIM; FAA handbooks such as the Instrument Flying Handbook and Instrument Procedures Handbook; and Airmen Certification Standards that include instrument tasks.
Here are some of the key updates to FAA guidance and policy in the new AC. Detailed discussion of each item follows.
Use of suitable RNAV systems on conventional routes and procedures, which clarifies how you can use an IFR-approved GPS on all types of IFR procedures, including those that use localizer courses, until you reach the final approach segment.
Expanded definition and clarification of the term RNP APCH, which many pilots confuse with RNP AR APCH. FAA adds RNP APCH notes to approaches with RNAV (GPS) in the title and does not plan to adopt current ICAO conventions for naming PBN procedures (for background, see this post here at BruceAir). More details on this topic appear below.
Updated definition of precision approach, which now explicitly includes all RNAV (GPS) approaches with LPV minimums. The AC also aligns FAA terminology with the ICAO definitions for procedures that include 2D (lateral navigation) and 3D (lateral and vertical navigation).
Use of Suitable RNAV Systems on Conventional Routes and Procedures
For general aviation pilots who use IFR-approved GPS and WAAS avionics, the draft AC clarifies a key issue, the use of RNAV (i.e., GPS and WAAS) while flying routes and procedures based on navaids. In particular, Chapter 11 describes specific situations in which pilots can use RNAV as an alternate means of navigation or as a substitute for navaids, and the document clarifies when you can use GPS to navigate along localizer courses outside the final approach segment.
(I recently gave a webinar for the American Bonanza Society on this topic. You can watch that presentation here and read more about the topic here.)
The draft AC provides the following updated definitions:
188.8.131.52 Alternate Means of Navigation. The pilot’s use of a suitable RNAV system to navigate on a conventional route or procedure without monitoring the operational NAVAID(s) defining the route or procedure. “Alternate means” applies to a situation where the pilot has options or a choice, and uses the suitable RNAV system primarily for convenience.
184.108.40.206 Substitute Means of Navigation. The pilot’s use of a suitable RNAV system to navigate on a conventional route or procedure in an aircraft with inoperative or not-installed conventional navigation equipment and/or when conventional NAVAIDs are out of service. “Substitution” applies to a situation where the NAVAID or the aircraft equipment are inoperative or unavailable (i.e., the pilot cannot use or monitor the conventional NAVAID).
220.127.116.11 Suitable RNAV System. Per § 1.1, an RNAV system is suitable when it (1) is installed for IFR operations, and (2) meets the navigation performance criteria required by ATC for the route or procedure to be flown. Put simply, suitable RNAV systems are those that meet the criteria identified in this AC for RNAV operations.
Section 11.4.2 Authorized Uses of Suitable RNAV Systems describes specific situations in which you can use GPS to complement or substitute for ground-based navaids.
The most significant update is item 6 (reinforced by paragraph 18.104.22.168), which clarifies that you can use GPS to navigate all legs of any conventional approach procedure, including procedures based on a localizer, until you reach final approach segment:
1. Determine aircraft position relative to, or distance from, a conventional NAVAID, DME fix, or named fix based on a conventional NAVAID.
2. Navigate to or from any conventional NAVAID or fix, via direct or a defined course.
3. Hold over any conventional NAVAID or DME fix.
4. Fly a published arc based upon DME.
5. Fly a route, comprised of charted airways, fixes, and/or NAVAIDs.
6. Navigate to the FAS of a conventional IAP.
7. Navigate the lateral course of the FAS on an IAP based on a VOR, Tactical Air Navigation System (TACAN), or Non-Directional Beacon (NDB) signal. The aircraft equipment and underlying NAVAID must be operational and monitored for FAS course alignment. The underlying NAVAID remains the primary source of navigation for the FAS course and should be used for course alignment if the RNAV system track differs from the underlying NAVAID course.
Items 1-2 also mean that you can use RNAV to fly departures and arrivals based on conventional navaids.
Item 6 is backed up by additional paragraphs:
22.214.171.124 On Unusable or Not Authorized (NA) Procedures. Pilots may not fly any portion of a conventional route or procedure identified (by chart annotation or NOTAM) as unusable or not authorized (“NA”).
Note: Pilots should take particular care when loading routes by name or title, especially routes defined solely by conventional NAVAIDs. Conventional routes designated as “unusable” by chart notation or NOTAM are unusable by any user. Pilots should not file for, and ATC should not use, the unusable route title or name in the IFR clearance. This does not preclude the use of direct clearances to usable waypoints along or across a charted route designated as “unusable.” [For more background on this issue, see Unusable Airways, Routes, and Segments here at BruceAir.]
126.96.36.199 As Sole Means of Navigation on Conventional FAS. Pilots may not use RNAV as the sole means of navigation to fly the final approach course on a conventional instrument approach.
188.8.131.52 To Navigate a Localizer (LOC) Final Approach Course. Pilots may not use RNAV to fly a FAS defined by an LOC signal.
Together, these sections mean that you can use an IFR-approved GPS to fly departures; airways; arrivals; feeder routes; track a VOR radial or localizer course to a course reversal or HILPT; fly DME arcs; fly holds, including holds based on DME fixes; and to fly the legs of missed approach procedures based on navaids, including localizers.
Paragraph 184.108.40.206As Sole Means of Navigation on Conventional FAS emphasizes that you cannot use GPS for lateral guidance along the final approach segment of a VOR or NDB approach unless the navaid is operational and you can monitor the course on a bearing pointer or CDI. This paragraph aligns with previous guidance in the AIM and AFM supplements, as I’ve noted in several posts here at BruceAir.
Paragraph 12.3 RNP APCH Overview provides background on the use of the note RNP APCH, which now appears on many charts.
This note is one way that FAA attempts to align its naming conventions for PBN approaches with updated ICAO standards (for background, see FAA InFO16020). As the AC explains:
In the United States, RNP APCH applies to all approach applications based on Global Positioning System (GPS), normally titled “RNAV (GPS)” or with “or GPS” in the title. These procedures provide operators one or more lines of minima (i.e., LNAV, LNAV/VNAV, LPV, or LP)…The RNP APCH NavSpec is intended to encompass all segments of the terminal approach operation: initial, intermediate, final, and missed approach…Charts for RNP APCH procedures will prominently display a standardized PBN Notes Box containing the procedure’s requirements including NavSpec(s) and, if needed, any required sensors or additional functionality (e.g., RF capability), as well as any minimum RNP value required for the procedure, and applicable remarks.
In other words, in the U.S., GPS-based approaches are titled RNAV (GPS) RWY xx. These approaches also include a RNP APCH note to confirm that they require the equipment needed to fly to the RNP terminal and final approach standards (i.e., RNP 1 and RNP 0.3 for LNAV minimums to an MDA or LPV, LNAV/VNAV to a DA, or LP standards for lateral guidance to an MDA).
RNP APCH is not the same as the authorization required to comply with the RNP AR APCH standard. In the U.S. approaches that require the RNP AR APCH standard are titled RNAV (RNP) RWY xx.
As the draft AC notes:
This AC does not apply to Required Navigation Performance Authorization Required Approach (RNP AR APCH) approaches, titled “RNAV (RNP)” (ICAO: RNP RWY xx (AR)). Guidance for RNP AR operations is in AC 90-101( ), Approval Guidance for RNP Procedures with AR.
Definition of Precision Approach
The draft AC updates the definition of precision approach, which now explicitly includes all RNAV (GPS) approaches with LPV minimums. The AC also aligns FAA terminology with the ICAO definitions for procedures that include 2D (lateral navigation) and 3D (lateral and vertical navigation).
In the past, precision approach applied only to procedures based on ground facilities that provide a glideslope or other approved vertical guidance to a DA–viz., an ILS or PAR. That obsolete definition required the creation of a new term, APV (approaches with vertical guidance), for RNAV procedures that offer approved vertical guidance to LPV or LNAV/VNAV decision altitude minimums.
Today, ICAO has updated its definition of precision approach by describing procedures that include approved vertical guidance to a DA, so-called 3D navigation. ICAO also describes so-called 2D approaches to MDAs.
With that change in mind, the new AC explains precision approaches (PA) and nonprecision approaches (NPA) that use GPS:
220.127.116.11 NPA Operations. These two-dimensional (2D) operations use GPS-derived lateral guidance from the RNP system. The procedure provides obstruction clearance as long as the pilots strictly adhere to the published minimum altitudes along the approach course, primarily by reference to the barometric altimeter. These 2D procedures typically have LNAV lines of minima to a minimum descent altitude (MDA).
18.104.22.168 PA Operations. These 3D operations use either ground-based, GPS-derived, and/or integrated electronic vertical guidance from the RNP system to enable lateral and vertical navigation to decision altitude (DA)/decision heights (DH) at or below 250 feet above ground level (AGL) (depending on the presence of obstacles). Typically, these are shown as LPV or LNAV/VNAV (and ILS/GLS) DA/DHs.
This section of the AC also notes that:
Note 2: Some approach procedures that contain both precision and nonprecision features are internationally designated as “Approaches with Vertical Guidance (APV).” These 3D approach procedures use GPS or SBAS to generate integrated electronic vertical and lateral guidance from the RNP system. These procedures typically have LNAV/VNAV lines of minima to DA/DH as low as 251 feet AGL. In the United States, all procedures to a LPV DA (regardless of height above touchdown (HAT)) are considered 3D precision operations. [Emphasis added]
This change should help reduce confusion about when IFR students and applicants for instrument ratings can use RNAV (GPS) approaches with LPV minimums to accomplish requirements for practicing and demonstrating precision approaches on practical tests.
The AC includes updated guidance in several other areas, beyond technical requirements for approval and use of RNAV systems.
For example, paragraph 22.214.171.124 Extract Procedures by Name notes that:
Pilots should extract PBN procedures by name from the onboard navigation database and ensure the extracted procedures match the charted procedures.
Note 1: Pilots operating aircraft with some early-model legacy RNAV navigators may not be able to extract certain PBN departure and arrival procedures by name from the navigation database. In these aircraft, pilots may load the departure or arrival procedures by extracting the individual fixes defining the procedures from the navigation database and loading them into the flight plan for their aircraft’s RNAV system. When this is necessary, pilots should confirm the resulting flight plan content matches the charted PBN procedure.
Note 2: Pilots are also cautioned that some procedures, even if extracted by name from the database, may not contain every segment, turn point, or conditional waypoint, or may contain “computer navigation fixes (CNF)” not shown on the procedure. It is always the pilot’s responsibility to ensure the aircraft’s flightpath conforms to the ATC clearance.
Paragraph 126.96.36.199 Extract PBN Routes in Their Entirety cautions that:
Pilots should extract the PBN routes from the navigation database whenever possible rather than loading the route by stringing individual fixes defining the route in sequence.
Note 1: This does not preclude a pilot’s use of a legacy RNAV navigator that cannot auto-load a PBN route into the navigator’s flight plan. A pilot may load a PBN route by extracting the individual fixes defining the route from the onboard navigation database and loading into the flight plan, fix by fix. When this is necessary, pilots should confirm the resulting flight plan route entries match the charted routes.
Note 2: Caution is warranted when loading routes into the RNAV system for convenience, especially conventional routes defined by ground NAVAIDs. Routes designated as “unusable” by chart notation or NOTAM are unusable by any user. Pilots should not file for, and ATC should not use, the unusable route title or name in the IFR clearance. This does not preclude the use of “direct to” clearances to usable waypoints along a charted route designated as “unusable.”
Paragraph 188.8.131.52 Creating or Altering Waypoints also warns that:
For any published (i.e., charted) PBN routes or procedures, pilots may only use waypoints downloaded from the aircraft navigation database. Pilots may not create waypoints (e.g., by using latitude/longitude coordinates, place/bearing, or any other means) for use on published PBN routes or procedures. Pilots also may not change any parameters of waypoints downloaded from the navigation database (e.g., changing a flyover waypoint to a flyby waypoint).
Paragraph 184.108.40.206 Cross-Check Flight Plan Against ATC Clearance recommends that:
Pilots should cross-check the navigation system’s flight plan against their ATC clearance and the charted routes and procedures. Both the flight plan’s textual display and the aircraft’s electronic moving map display (when available) can aid in this cross-check. When required by NOTAM or by the aircraft’s operating manual and SOP, pilots should confirm exclusion of specific ground-based navigation aids. If at any time during these cross-checks, a pilot doubts the validity of the route or procedure they extracted from the navigation database, they should not attempt to execute the route or procedure.
Note: Pilots may notice a slight difference between the navigation information portrayed on the chart and their primary navigation display. Differences of up to 5 degrees may result from avionics’ application of magnetic variation. These differences are acceptable.
Paragraph 3.6.10 and others in that section explain equipment required notes on PBN procedures. I won’t repeat all those details here. You can find background at Equipment Required Notes on IFR Procedure Charts here at BruceAir. I’ll update that post when I can distill the current FAA guidance as described in the new AC.
Finally, section 3.7 Training offers detailed guidance on the steps pilots should take to ensure that they understand how to use RNAV systems. A list appears in paragraph 3.7.3. Many of these items are also covered in existing industry guidance, such as the free Garmin GTN 750 Sample Training Syllabus (PDF).
Flying this procedure requires preparation. It’s not a basic ILS or straight-in RNAV approach where the only significant deviations from “standard” are the altitudes and tracks along the final approach course. In fact, flying this approach in IMC or at night also requires study of the Chart Supplement, not just the procedure chart. Comparing the approach chart with the sectional and low-altitude IFR charts for the area also helps you understand some of the challenges associated with this procedure.
Planning for and flying an approach like this highlights an advantage of using EFB app like ForeFlight, Garmin Pilot, or FlyQ. Those tools make it easy to switch between IFR and VFR charts, review the Chart Supplement, and look up other important information, but only if you study those resources before takeoff.
This RNAV approach has a bit everything to challenge an IFR pilot, including:
A series of (sometimes short) segments from the IAF to the missed approach point, each with a change of track.
LP andLNAV minimums to MDAs (and LP+Vadvisory vertical guidance if you have a WAAS navigator with the appropriate system software).
A steeper-than-normal (3.45 degrees) descent angle from the FAF to the MAP, if you follow advisory vertical guidance. That descent path is shown on Jeppesen charts, but not on the FAA chart.
Two crossing restrictions inside the FAF that you must observe even if you do follow advisory guidance.
Obstacles in the visual segment.
A 29.15-degree offset from the final approach to the threshold (barely inside the 30-degree limit for straight-in minimums).
A short runway at 3100 ft., but with a displaced threshold that leaves only 2775 ft. available for landing.
An arrival holding pattern anchored at ILGEZ , not to be confused with the missed-approach hold shown at JOEYL (see AIM 5-4-9, cited in part below) or with a holding pattern used as a course reversal (i.e., a HILPT).
Other subtleties such as an off-airport altimeter source (no AWOS) and one frequency for the CTAF, another for activating the runway lights and PAPIs.
Important information related to this approach that is available in the Chart Supplement entry for N20, but which isn’t published on the chart.
Kingston-Ulster-Airport lies along the Hudson River in upstate New York, with rising terrain west of the runway. The sectional chart shows why bends are required to get you to the runway from the north and why the final approach segment isn’t lined up with the pavement.
The low-altitude IFR en route chart for the area also offers puzzles to ponder, such as an airway segment that is unusable, but only if you’re flying V292 using VORs, not T295, the overlapping T-route that runs east-west, north of the airport. In fact, the area around 20N is crisscrossed by T-routes, which in many cases have replaced or supplanted VOR-based airways, especially where VORs have been decommissioned.
A Detailed Review
Let’s take a closer at this interesting approach, preferably during preflight planning, not while descending from cruise.
The procedure title indicates that this approach offers straight-in minimums (the title includes the runway number; it isn’t RNAV (GPS) – A or – B). But as we’ve seen, this approach barely meets the alignment criterion for straight-in minimums.
The notes at the top of the chart, which often include information that isn’t relevant to pilots of light, piston-powered airplanes, warrant special attention here. For example, the runway length available for landing–2775 ft.–doesn’t match the the 3100 ft. shown on the inset airport diagram, a detail that’s easy to miss if you don’t notice the displaced threshold symbols.
You need to consider how that short runway might affect the speed you’ll fly on final. For example, I fly most approaches in my A36 Bonanza at 110 KIAS, but when approaching a runway less than 4000-5000 feet long, I plan to fly final at 90 KIAS, which is just 10 knots above the 80 knot minimum speed for engaging the GFC 600 autopilot in my panel, should I choose to use it.
The notes also reveal that the airport has non-standard takeoff minimums, often a hint about nearby terrain, and that 20N can’t be filed as an alternate, probably because it doesn’t have on-site weather reporting.
Another important note specifies that the primary source for setting the altimeter is Hudson (KPOU), 22 nm south. That detail requires additional attention when you set up and then brief the approach.
The frequency blocks include an oddity: 122.8 for the CTAF, but a different frequency, 123.3, to activate the pilot controlled lighting at this nontowered airport.
The plan view shows an arrival hold at ILGEZ, depicted with thin lines. Arrival holds aren’t common. When reviewing holds on charts, it’s important to distinguish between arrival holds and their cousins: holds in lieu of a procedure turn (HILPT), missed approach holds, and holds shown at alternate missed approach holding points.
Note: Some approach charts have an arrival holding pattern depicted at the IAF using a “thin line” holding symbol. It is charted where holding is frequently required prior to starting the approach procedure so that detailed holding instructions are not required. The arrival holding pattern is not authorized unless assigned by Air Traffic Control. Holding at the same fix may also be depicted on the en route chart…. (AIM 5−4−9. Procedure Turn and Hold−in−lieu of Procedure Turn)
As the AIM notes, flying an arrival hold requires ATC clearance. Unlike a HILPT, the hold at ILGEZ isn’t shown when you load the procedure in a GPS navigator such as a GTN 750. If ATC clears you fly the hold, perhaps to lose altitude before you begin the approach, you must build the hold in the box or use OBS mode.
The plan view shows four segments from the IAF at ILGEZ to the MAP at NEWMN, which is 0.7 nm from the threshold. The last segment, from FRLDI to NEWMN, is just 1.8 nm long. Flying these “final” segments involves 3 course changes. Landing requires another turn of almost 30 degrees at NEWMN to align with the runway centerline.
The profile view hints at more challenges, including a steep descent angle from IMIBE to FRLDI, which you must cross at or above 1080 ft. The FAA chart for this approach doesn’t show a visual descent angle (VDA), because, as a note points out, the visual segment isn’t clear of obstacles.
If there are obstacles in the visual segment that could cause an aircraft to destabilize the approach between MDA and touchdown, the profile will not show a VDA and will instead show a note that states “Visual Segment-Obstacles”. (Aeronautical Chart Users Guide)
Notice also that the heavy black line levels off before NEWMN, and that this approach does not include a visual descent point (VDP). These details are more clues that obstacles loom close to the runway. Fortunately, a check of the inset airport diagram reveals a PAPI available on the left side of the runway, definitely something to look for when (if) you break out.
For more information about VDP, see “Arrival Procedures” in the AIM:
The Visual Descent Point (VDP), identified by the symbol (V), is a defined point on the final approach course of a nonprecision straight−in approach procedure from which a stabilized visual descent from the MDA to the runway touchdown point may be commenced. The pilot should not descend below the MDA prior to reaching the VDP. The VDP will be identified by DME or RNAV along−track distance to the MAP. The VDP distance is based on the lowest MDA published on the IAP and harmonized with the angle of the visual glide slope indicator (VGSI) (if installed) or the procedure VDA (if no VGSI is installed). A VDP may not be published under certain circumstances which may result in a destabilized descent between the MDA and the runway touchdown point. Such circumstances include an obstacle penetrating the visual surface between the MDA and runway threshold, lack of distance measuring capability, or the procedure design prevents a VDP to be identified. (AIM
The leg from WOBVU to IMIBE is 7.5 nm long, allowing a comfortable descent from 3200 ft. to 1600 ft. But if you continue from IMIBE and level off at 1080 ft. to observe the restriction at FRLDI (which applies even if you’re following advisory vertical guidance), you have another 360 ft. to descend to the LP MDA of 720 ft. (280 ft. if you use the LNAV MDA of 800 ft.). And you have just 1.8 nm to make that last step-down descent.
As we’ve seen, the MAP is at NEWMN, located 0.7 nm from the threshold. That offset may be a surprise if you’re accustomed to RNAV approaches where the MAP coincides with the threshold. Moreover, the minimum visibility required for this approach is 1 sm. The runway doesn’t have approach lights, just the PAPI noted earlier, so you need to pick up the required visual references (see 14 CFR 91.175) before you reach NEWMN.
The PAPI is set at a 4.5 degree descent angle to cross the threshold at 50 ft. That important detail, by the way, is in the Chart Supplement entry for 20N, not on the approach chart.
The Chart Supplement also reveals that the PCL on 123.3 activates the PAPIs at both runway ends, and the runway lights, which are available from dusk to dawn. In addition, the PAPI serving runway 15 is unusable more than 5 degrees left and 8 degrees right of the final approach course. In other words, you won’t see–or shouldn’t follow–the PAPI visual guidance until you turn toward the runway at NEWMN. And another note–on the procedure chart–prohibits night landings on runway 15. Again, those close-in obstacles, probably unlit, loom.
All of the preceding details should make you consider carefully how you’ll configure the airplane and use an autopilot and flight director when you fly this approach. When will you extend the landing gear and flaps? What power settings will you use as the approach progresses through the various segments?
An autopilot could be a great help as you track all the course changes, but managing the descent, even if the autopilot offers VNAV and can follow glidepaths, requires a plan and close monitoring.
An approach like this also highlights the advantages of an electronic PFD and moving map. The following images, captured with the free Garmin PC Trainer Suite, show some of the key details discussed above.
When you load the approach in a WAAS navigator, LP+V minimums may be available. Note that LP+V indicates LP minimums to an MDA with advisory vertical guidance. LP+V is not the same as LPV, which provides approved vertical guidance to a DA. For more information, see Handy WAAS and RNAV (GPS) Approach Fact Sheets.
Note that the GTN 750 map doesn’t show the arrival hold at ILGEZ. If ATC clears you to fly that hold, you must set it up in your navigator. If you’re prepared, that’s easy to do in a GTN navigator. If you have an older GPS, you may have to use OBS mode to fly the arrival hold.
If you fly the arrival hold, you must manually resume sequencing (unsuspend/cancel OBS mode) to continue flying the approach.
At this point, your PFD should show LP+V if advisory vertical guidance is available.
As you continue inbound, you (or the autopilot) can follow the advisory vertical guidance to the MDA. But make sure you observe the crossing restrictions as you continue toward the missed approach point.
A PFD with a map also helps you anticipate the last turn to align with the runway.
I hope this approach helps you appreciate the need for thorough preflight planning, even if you use an EFB and have a panel that features advanced avionics. Those tools are terrific aids, especially when flying single-pilot IFR. But using them effectively requires preparation.
A recent flight to Aurora, OR (KUAO) south of Portland ended with the RNAV (GPS) RWY 17 approach almost to the published LPV (localizer peformance with vertical guidance) minimums, which provide an ILS-like descent. (But keep in mind: The Runway Environment in the RNAV Era.)
A gusty, wet front blew across the Pacific Northwest that day, creating unusual IFR conditions for early August. This video, with ATC communications, shows the approach, starting with the descent from cruise altitude (7000), through touchdown.
For more information about flying approaches, see these posts here at BruceAir:
During training for the instrument rating, we fly most approaches to published minimums. But in real-world IFR flying, the weather is usually well above the visibility (which actually controls) and ceiling required to complete an approach and land.
I recently flew a couple of approaches in VMC (visual meteorological conditions), albeit with light rain reducing visibility. I couldn’t log the approaches for currency, but they were still good opportunities to practice IFR procedures, use the avionics in the A36, and keep my head in the IFR game.
The following videos also show what the runway environment looks like as you approach the decision altitude (DA), first on an RNAV (GPS) approach with LPV minimums, then an ILS.
This is an exercise I do with my instrument students as they begin flying approaches. It’s useful to observe several approaches, preferably with the autopilot engaged, to help new IFR pilots correlate what they see out the window with the navigation displays, aircraft attitude, power settings, and configurations used during an IFR approach. Watching the autopilot fly the approach helps students clearly see the subtle corrections needed to track courses and glidepaths. And observing the proximity to terrain and obstacles reinforces the need to fly the published courses and altitudes precisely.
You can still fly IFR in the U.S. without an IFR-approved GNSS (i.e., GPS), but being “slant G” (/G in the soon-to-be obsolete FAA domestic flight plan format) increasingly offers advantages, even if you fly only conventional procedures based on ground navaids. And sometimes an IFR-approved GNSS is required to fly even an ILS.
But the equipment required notes for this ILS approach include “RNAV-1 GPS required.”
A review of the plan view and missed approach track show why GPS is necessary to fly this procedure.
First, you need GPS to fly transitions from most of initial fixes, which are RNAV waypoints marked by a star symbol.
Only LIBGE, directly north of the runway, is a non-RNAV IAF.
For example, HOBOA, KLOCK, BELBE, and WINRZ are all RNAV waypoints that serve as IAFs or IFs. Now, NORCAL Approach might provide vectors to the final approach course, but if you want to fly this procedure you should be prepared for a clearance direct to one of those fixes (see Avoiding the Vectors-to-Final Scramble).
Note also that entire missed approach track requires use of GNSS.
Two of the transitions are of special note. The “arcs” that begin at ZONBI and SLABS are radius-to-fix (RF) legs that are part of the transitions that begin at HOBOA and KLOCK. Each of those fixes is distinguished by the notes “RNP-1 GPS REQD” and “RF REQD.”
The first note means that your GPS must meet the RNP 1 standard, which is used for terminal procedures such as SIDs and STARs, the initial phases of approaches, and missed-approach segments. (For more information about RNP, see RNP Procedures and Typical Part 91 Pilots.)
Until recently, RF legs were included only in Authorization Required (AR) procedures. But as I explained in Garmin GTN Avionics and RF Legs, certain RF legs are now available if you have an appropriate GNSS navigator, updated system software, an electronic HSI, and other equipment. Some limitations on flying such RFs also apply, as described in that earlier post.
Suppose that you choose the less intimidating ILS X or LOC X RWY 16R to the same runway. A review of the notes and the plan view shows that even this conventional-looking ILS also requires RNAV 1 GPS, both to fly the transition from WINRZ and the missed approach track.
The FAA continues to publish more GPS-based instrument procedures. The latest inventory shows that as of February 6, 2014, there are 13,134 RNAV (GPS) approaches available for general use in the U.S. National Airspace System. (That number doesn’t include the RNP authorization-required procedures available only to pilots and aircraft that meet the requirements of AC 90-101A. More about RNP and AR procedures here.)
By comparison, there are 5,794 ILS, LOC, NDB, and VOR approaches (again, not counting CAT II, CAT III, and other procedures that require special training, equipment, and authorizations).
RNAV (GPS) Procedures
GPS (Stand – Alone)
Here’s a pie chart that shows the relative shares of different types of instrument approach procedures in the U.S.
Perhaps more important to general-aviation pilots is the fact that so many of the RNAV (GPS) procedures—especially those with LPV minimums—are at smaller airports that don’t have an ILS:
3,364 LPVs serving 1,661 airports
2,262 LPVs to non-ILS runways
1,535 LPVs to non-ILS airports
1,102 LPVs to ILS runways
2,020 LPVs to non-Part 139 airports (airports not approved for airline operations)