The Runway Environment in the RNAV Era

As of January 30, 2020, the FAA had published 4,048 RNAV (GPS) approaches with LPV (localizer performance with vertical guidance) minimums at 1,954 airports; 1,186 of those airports are not served by an ILS. The number of LPV-capable procedures is almost three times the 1,550 approaches with Category I ILS minimums, and 2,838 of the procedures with LPV minimums serve runways without an ILS,

For the latest totals, visit the Instrument Flight Procedures (IFP) Inventory Summary and Satellite Navigation — GPS/WAAS Approaches pages at the the FAA website.

This capability to fly ILS-like procedures to thousands of runways at small-town and rural airports is a boon to IFR pilots. But you must carefully prepare to fly approaches to runways that don’t have the ground infrastructure associated with an ILS–most importantly an approach lighting system and accessories such centerline and touchdown zone lighting. And keep in mind that a non-ILS runway may not be as a long as you’re accustomed to–the minimum length for a runway served by an approach with LPV minimums is just 3200 ft. (more details here).

For more information about GPS-based approaches, see Required Navigation Performance (RNP) Approaches (APCH) .

For example, here’s video of the final approach segment of the RNAV (GPS) RWY 16 procedure at Chehalis, WA (KCLS) during a night approach.

As the video shows, the runway can be hard to spot. It has REILs and a PAPI, but it’s in a dark area near a river. And you must remember to activate the lights by clicking the transmit button on the CTAF as you approach the airport. (The camera makes the scene look a little darker than it really was to human eyes–but you get the idea.)

Chehalis (KCLS) airport

That approach has an LPV decision altitude of 476 ft MSL (300 ft. AGL). The visibility requirement is 1 sm. That’s not much greater than the 200 ft DA and 1/2 sm visibility for a typical Category 1 ILS. But the environment is vastly different than that presented by an ILS runway with its bright lights and other big-city features.

Here’s an overview of the approach lighting systems associated with ILS procedures.

Instrument Procedures Handbook:
Figure 9-36. Precision and nonprecision ALS configuration.

Contrast the view at KCLS with the scene at Boeing Field (KBFI) in Seattle during the final stages of an ILS approach.

ILS RWY 14R at Boeing Field (KBFI)

Here’s an approach to runway 20 at Bremerton, WA (KPWT). KPWT is a non-towered airport, but runway 20 is served by an ILS approach, which includes an ALS.

RNAV RWY 20 approach at KPWT

So, regardless of the type of approach you’re flying, make sure you review and prepare for the runway environment that you’ll encounter when you break out of the clouds and go visual. It’s especially important to know which of the visual cues described by 14 CFR §91.175 Takeoff and landing under IFR will be available.

RNAV Approach at KCLS

I flew an RNAV (GPS) approach at Chehalis, WA (KCLS) to show how low LPV minimums can take you, even to a runway at a typical small-town, non-towered airport that doesn’t have approach lights and other components associated with precision approaches. I flew this procedure in VMC to help you see the runway environment.

Now, an RNAV (GPS) approach to LPV minimums isn’t technically a precision approach, at least according to the current ICAO definition of the term. But as a practical matter, flying to a localizer performance with vertical guidance DA is just like flying an ILS. The lateral guidance funnels you toward the runway, just like a localizer, and the glidepath generated by the GNSS box in the panel acts just like an ILS glideslope. In fact, I prefer flying an LPV approach even when an ILS is available. You don’t have to switch navigation sources, there are no false glideslopes, and there is no ILS critical area.

If the runway served by the RNAV (GPS) approach doesn’t also have an ILS, you probably won’t see approach and runway lights except for edge lighting. And the minimums (DA and visibility) will be a little higher than they would be for a typical category 1 ILS (i.e., 200-1/2). At KCLS, the LPV minimums are 300 AGL (DA 476) and 1 mile.

But those minimums are a substantial improvement over the LNAV MDA (900 MSL; 724 AGL), the lowest you can go without the approved vertical guidance available with WAAS.

An RNAV Approach in VMC

In this video, I depart Jefferson County International Airport (0S9) on the Olympic Peninsula and fly the RNAV RWY 20 approach at Bremerton (KPWT) in visual conditions.

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.

Update on WAAS Approaches from FAA

By the end of 2016, every runway in the U.S. that qualifies for an approach with LPV minimums will have one. According to the fall 2012 edition (PDF) of SatNavNews, published by FAA:

The agency intends to publish another 2,500 procedures by 2016, which will allow every runway in the nation that qualifies for an LPV to have one.

The latest data available from FAA, as of September 20, 2012, show the total number of approaches with LPV minimums has reached 2,989. By comparison, there were 1,281 category 1 ILS approaches in the inventory as of that date. More than 50 percent of the so-called LPV approaches serve airports that have no approaches that rely on ground-based navigation aids (i.e., ILS, localizer, VOR, or NDB). LPV procedures truly are expanding the options for instrument-rated pilots who fly aircraft equipped with IFR-approved, WAAS-capable GPS navigators.

LPV approaches can serve runways that may not meet the requirements for an ILS–indeed, many of those runways are suitable only for small general aviation aircraft. To learn about some of the criteria, see Table A16-1B Airport Infrastructure (from AC 150/5300) below. For example, the minimum runway length for an LPV approach is 3200 feet; the comparable number for an ILS is 4200 feet.

Now, the minimums for an LPV approach to a 3200-ft runway are at least 1 statute mile visibility and a DA of 350-400 feet. If an LPV procedure is to match the best minimums for a typical ILS (1/2 statute mile visibility and a DA of 200 feet), the LPV procedure must be to a runway that meets criteria for a conventional precision approach, including runway length, lighting, parallel taxiways, and markings.

Approach Procedure with Vertical Guidance (APV). Runways classified as APV are designed to handle instrument approach operations where the navigation system provides vertical guidance down to 250 feet HATh and visibilities to as low as 3/4 statute mile. May apply to the following approach types: Instrument Landing System (ILS), LNAV/ Vertical Navigation (VNAV), Localizer Performance with Vertical Guidance (LPV), or Area Navigation (RNAV)/Required Navigation Performance (RNP). These runways must be at least 3,200 feet (975 m) in length with a width at least 60 feet (18.5 m) (with 75 or 100 feet [23 or 30 m].

Precision Approach (PA). Runways classified as precision are designed to handle instrument approach operations supporting instrument approach with HATh lower than 250 feet and visibility lower than 3/4 statute mile, down to and including Category (CAT) III. Precision Instrument Runways (PIR) support IFR operations with visibilities down to and including CAT-III with the appropriate infrastructure. The navigational systems capable of supporting precision operations are ILS, LPV, and Global Navigation Satellite System (GNSS) Landing System (GLS). These runways must be at least 4200 feet (1280 m) long, and are at least 75 feet (23 m) wide with the typical width being at least 100 feet (30 m). These runways are typically lighted by High Intensity Runway Lights (HIRL) and must have precision runway markings as defined in AC 150/5340-1. (AC AC 150/5300-13A)

Of course, an LPV procedure is essentially just data in a GPS navigator. To establish an LPV procedures, the owners of an airport don’t have to invest in or maintain ILS transmitters. Once the FAA has the required obstacle surveys and gathered related information, publishing LPV procedures to both ends of an eligible runway (indeed, to the ends of all eligible runways at an airport) requires little incremental investment (for example, to cover the costs of designing and flight-testing each additional procedure). That’s the main reason that the FAA can publish so many new LPV procedures and plan to meet the goal, in four years, of making LPV approaches available to all eligible runways.

Another reason for WAAS: New approach at Petaluma, CA (O69)

The latest batch of Jepp revisions just arrived. They include a new RNAV (GPS) RWY 29 approach at Petaluma, CA (O69).* (According to NACO, the RNAV approach was published on 25 August, but for some reason, it didn’t show up in my Jepps until now.)

The new RNAV approach has LPV minimums [DA 347 (270) and 7/8 sm] and an LNAV MDA of 820 (743) with visibility minimums of 1 (A) and 1-1/4 (B) miles.**

Previously, O69 had a VOR RWY 29 approach off SGD with an MDA of 1260 (1174) and 1-1/4 sm required visibility. The old GPS approach to the same runway offered an MDA of 900 (813) and 1 sm visiblity. And that GPS approach (now NA) had a 22-degree dogleg at the FAF.

The new approach is a significant improvement that shows the value of WAAS-based procedures, even to a 3600-ft runway, and it allows you to file O69 as an alternate if you have WAAS.

Here are links to the NACO versions of the new charts:

N.B. that the VOR RWY 29 procedure, updated for a new airport elevation, etc., still has a note that requires using the Santa Rosa altimeter setting, otherwise, the approach is NA. But the RNAV RWY 29 approach takes advantage of the on-field AWOS, and local weather is required for filing O69 as an alternate. I’m betting someone at FAA neglected to remove the Santa Rosa altimeter requirement for the VOR approach.

*The airport has an AWOS-3PT (AWOS-3PT contains all the AWOS-3 sensors, plus a precipitation identification sensor and thunderstorm detector). Phone: 707-773-1529.

**The new RNAV approach includes LNAV/VNAV mins–484 (707) and 1-3/8 sm–but if you’re using WAAS and the satellite configuration is good enough for vertical guidance, you’ll almost certainly see LPV annunciated, not LNAV/VNAV.