After flying a low approach at Port Angeles (KCLM) on the north side of the Olympic Peninsula, I picked up my clearance back to Boeing Field (KBFI), which was in a south flow, using runway 14R and 14L.
ATC typically vectors IFR traffic from the north or northwest—from points such as the San Juan Islands and airports on the Olympic Peninsula—to join the localizer for 14R (in fact, ATC really wants you track the final approach course; the LOC is just the time-honored way of accomplishing that goal). Often the clearance comes when you’re 30 to 40 miles from the airport, well outside the 18 nm standard range for a localizer.
When I receive such a clearance, I use a technique, demonstrated in this video, that’s available in most GPS navigators (for more information, see Setting a Course v. Vectors to Final).
A November 2022 update to the AIM includes a note in paragraph 1-1-9 Instrument Landing System, explaining that:
Unreliable signals may be received outside of these areas. ATC may clear aircraft on procedures beyond the service volume when the controller initiates the action or when the pilot requests, and radar monitoring is provided…All charted procedures with localizer coverage beyond the 18 NM SSV have been through the approval process for Expanded Service Volume (ESV) and have been validated by flight inspection.
A figure showing a chart for an ILS at Chicago O’Hare complements the note. It confirms that fixes along a localizer have been verified during the flight check process.
On the chart for the ILS to runway 14R at Boeing Field, however, the fix farthest out on the localizer is ISOGE, recently moved out to 12 nm from the runway, but still within the standard LOC service volume.
As the AIM notes, if ATC is monitoring you, controllers can direct you to join the LOC far from the airport, but such a clearance still leaves you with the problem of intercepting and tracking a course that may be wobbly—if it appears at all.
As the first part of the video shows, after loading the approach and transition, I select the appropriate course to an initial fix along the localizer, and I leave the CDI set to GPS. That setup, similar to using vectors-to-final, but preserving options if ATC changes the plan, draws a magenta reference line along the LOC that I can join and track inbound until I am close enough to receive a stable LOC signal, and then I switch the CDI to green needles.
When you are sure that you’re within the LOC service volume, change the CDI to LOC, and continue the approach with the approved lateral and vertical guidance for an ILS.
Because the weather was VMC when I flew the ILS for this video, I tested the technique and cross-checked what the LOC showed when I was far from the airport. The green needle was, to use a technical term, wonky, until I got close to ISOGE. My track would have been smoother and more accurate had I followed the magenta line until the LOC settled down near the initial fix.
If you fly an airplane with a suitable RNAV system (for most of us, that’s an IFR-approved GPS navigator in the panel), you’re accustomed to flying RNAV (GPS) approaches and other procedures, such as RNAV departures and arrivals. And since most RNAV navigators currently in use also support flying ILS and VOR procedures, you also probably still fly the occasional ILS or VOR approach, even if you prefer all-GPS procedures.
But as the shift to Performance-Based Navigation (PBN) continues, the FAA is publishing more approaches that include–and sometimes require–using both GPS-based RNAV systems and ground-based navaids.
Consider the ILS or LOC RWY 12 at Huron (KHON), a small town in South Dakota.
In many respects, this is a typical ILS. It offers a DA at 200 AGL and requires 1/2 sm visibility (the RNAV (GPS) approach to RWY 12 offers the same LPV minimums). It also has an old-school locator outer marker (LOM) at BEADY that serves as the final approach fix for the LOC-only version of the approach and as the anchor for the missed-approach holding pattern.
But read the note in the required equipment box.
In most light aircraft these days, you must also have an IFR-approved GPS to fly the feeder routes and to identify BEADY, because your panel probably doesn’t include DME or an ADF.
ATC could provide vectors to steer you from the enroute environment to the final approach course. But as I’ve noted elsewhere, if you filed IFR as an RNAV/PBN-capable aircraft, a controller can clear you direct to any initial approach or intermediate fix, even if you’re flying a conventional procedure like an ILS.
The enroute chart for the area around Huron shows why you might expect such a clearance. The closest VOR at Watertown (ATY) is nearly 40 nm away, and the airways that converge at KHON are all GPS-based T-routes. The VOR at HON has been decommissioned; only the DME component remains (for more information, see Stand-Alone DMEs on Charts).
A controller can avoid issuing a series of vectors and altitudes as you fly toward the airport and offer one simple instruction, “Cross HUMSO [or WEDEM] at or above 3000, cleared for the ILS RWY 12 approach.”
Your task is to brief the plan for changing from GPS guidance to fly the feeder route from either HUMSO or WEDEM to “green needles” to intercept and track the localizer as you turn inbound toward the airport. And decide, if necessary, how you’ll fly the missed approach.
So today, even if you’re flying to a GA airport far from the big city, you should be prepared to load and fly such hybrid procedures if, for training or practice, you want to fly an ILS, LOC, or VOR approach.
Most of us understand how paired LOC and GS signals provide a course and a glideslope to follow when flying an ILS to a decision altitude (DA). (If you’d like a detailed review, see, for example, How ILS Works on the FlightInsight YouTube channel).
But the glidepath you see when flying an RNAV (GPS) approach to LPV minimums (usually shown as a magenta diamond on the vertical deviation scale) is more mysterious.
To make an LPV mimic an ILS’s behavior, LPV relies on programmed coordinates and instructions contained in a Final Approach Segment (FAS) data block. The FAS data block contains instructions for the approach, including coordinates for the runway, threshold crossing height, elevation, glidepath angle, and horizontal and vertical alert limits. The GPS receiver computes both linear and angular deviation but, as previously mentioned, only angular is displayed. They can be thought of as instructions to provide a pseudo localizer and glideslope.
In other words, the IFR-approved navigation receiver in your panel receives GPS-WAAS signals from space, and then creates a glidepath. The GP that you see and your AP/FD follows doesn’t emanate from a transmitter on the ground. That’s one reason we have so many RNAV (GPS) approaches with LPV minimums, even at small, quiet airports. Except for runway lights and (optional) approach lights, an approach with LPV minimums that mimics an ILS does not require expensive transmitters on the ground.
You GPS-WAAS receiver uses the same principles to create the advisory glidepaths (e.g., LNAV+V and LP+V) that you can use to help you descend to the MDA when flying a 2D (non-precision) approach, or to fly the vertical guidance on the visual approaches available with the latest GPS navigators.
After flying a low approach almost to minimums at Bremerton (KPWT), I made the quick return to Boeing Field (KBFI) via radar vectors to the ILS RWY 14R, where the weather was better, with a ceiling of about 1000 ft. and good visibility below the clouds. As you’ll see, it’s a moderately busy flight given the short distance and the usual challenge of fitting into the flow at KBFI.
On this late-November afternoon, however, I enjoyed the rare treat of cloud surfing above a solid undercast, with blue skies above, at least for a few minutes. Keen observers will even spot Mt. Baker in the distance as I turn northeast.
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.
I am not a fan of the vectors to final (VTF) option when loading instrument approaches in GPS navigators like the Garmin GNS and GTN series avionics.
Even with recent improvements to how the Garmin GTN series boxes handle VTF, it’s usually best to choose an initial fix (IF) or initial approach fix (IAF) based on the direction from which you’re arriving in the terminal environment, and then, depending on your clearance from ATC, activate a leg of the procedure or proceed direct to an IF or IAF. See the example at KMWH below.
Occasionally, however, you may encounter an approach such as the ILS or LOC RWY 14R at Boeing Field (KBFI) (chart below).
Knowing how to use a handy technique that straddles the line between the VTF and setting a specific course (a variation on OBS mode) can help you smoothly join the final approach course. Bear with me for a somewhat convoluted explanation.
For more information about setting a specific course to a fix and the OBS feature, search for Direct To and OBS in the pilot guide for the avionics you use.
The plan view for this approach shows two key fixes along the localizer: ISOGE and TOGAE.
TOGAE is step-down fix with a crossing restriction and a GS intercept altitude at 1600 (the beginning of the final approach segment when you fly the full ILS with glideslope). TOGAE also serves as the FAF when you fly the LOC-only version of the procedure.
APPROACH GATE− An imaginary point used within ATC as a basis for vectoring aircraft to the final approach course. The gate will be established along the final approach course 1 mile from the final approach fix on the side away from the airport and will be no closer than 5 miles from the landing threshold.
Definition of approach gate in the P/C Glossary
The approach also chart shows ISOGE, a fix 9 nm from the ruwnay, as an IF/IAF. (You will never fly the depicted hold/course reversal anchored at ISOGE.)
And ISOGE appears in the list of transitions when you load this approach in a GPS navigator such as a Garmin GTN 750.
If you choose either Vectors or ISOGE, the fix appears in the flight plan.
If you activate VTF for this approach, the GTN draws an extended centerline from TOGAE (the FAF) out along in the localizer course. But you loose ISOGE as a reference.
If you activate the approach with ISOGE as the transition, the navigator draws a magenta line from your present position to ISOGE, and if you hand-fly that course or put the autopilot in NAV mode, you will head directly to that fix.
But Seattle Approach always issues a series of vectors to sequence you into the flow of traffic for KBFI and to avoid conflicts (wake turbulence and otherwise) with airliners aiming for nearby KSEA. Regardless of the direction from which you’re arriving, ATC places you on the localizer at least a few miles outside of ISOGE.
In other words, you don’t want to go direct to ISOGE, and it’s helpful to have a reference to the localizer course as ATC vectors you into the flow.
This typical routing from the northeast involves a long vector on a southwest heading to intercept the localizer. Even if you have the navaid tuned, you may not be able to identify it and confirm its appearance on the CDI until you are almost on top of the course. If ATC is busy or if you’re flying a fast airplane, it’s easy to blow through the localizer or be tempted to make an aggressive turn to capture it when you get the final vector from ATC.
(For another demonstration of this technique, see the video below.)
Here’s the “trick” to help you fly a smooth intercept. It involves setting a specific course direct to a fix–in other words, it’s similar to using OBS mode:
If you’re using the autopilot, make sure you’re in HDG mode to follow vectors from ATC.
Because you’re flying vectors to join the localizer, confirm that you’re showing “green needles” on the HSI or CDI used to fly the ILS. You don’t need GPS guidance from this point on.
Load the approach with ISOGE as the transition (i.e., as the first fix in the procedure).
Confirm the list of fixes in the flight plan.
Select ISOGE and choose direct-to.
In the direct-to window, enter the course inbound to ISOGE along the localizer–135 degrees.
On the map, you’ll see a magenta line extending to ISOGE along the course 135 degrees–in effect, an extension of the localizer.
Here’s how that sequence looks using a GTN 750:
To draw an extension of the localizer from ISOGE, select ISOGE again, choose Direct-To, and enter the course 135.
Now you can monitor your progress toward the final approach course and prepare for the turn onto the localizer, even if you’re not currently receiving the signal or showing a flyable localizer CDI.
As you join the localizer and then pass ISOGE, the GTN sequences to the next fix in the approach, TOGAE. If you used OBS mode to set a course to ISOGE, the GTN would suspend waypoint sequencing past ISOGE, but setting a direct-to course preserves that feature.
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.
Clear skies recently offered an opportunity to log a little night flying time and to practice an ILS at Boeing Field (KBFI). I can’t log the approach for IFR currency (I wasn’t under the hood and didn’t have a safety pilot), but it’s still good practice to fly approaches in VMC when possible to reinforce IFR procedures.
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.