New ATC Phraseology for RNAV Aircraft

The FAA has updated its Air Traffic Control handbook (JO 7110.65) with changes to approach clearances issued by controllers. The new procedures and phraseology, which primarily affect RNAV-equipped aircraft, were published in this notice (PDF), are effective June 3, 2013.

Here’s a summary of the key changes:

• This change provides guidance when a controller does not require an aircraft to fly the hold-in-lieu-of procedure turn but requires the aircraft to fly the straight-in approach.
• Vectoring to a fix along the final approach course prior to the final approach fix (FAF) is permitted. Appropriately -equipped area navigation (RNAV) aircraft may be cleared to the intermediate fix (IF) on conventional and RNAV instrument approach procedures when the IF is identified with an “IF” on the instrument approach procedure. Procedures and graphics are provided for an aircraft on unpublished routes cleared direct to a fix between the IF and FAF.
• Guidance is provided for when an aircraft will fly a radius to fix (RF) leg, published on an RNAV approach.

The first item should eliminate confusion among many pilots when a approach chart shows a holding pattern in lieu of a procedure turn. Controllers will now explicitly clear aircraft “straight-in” when they don’t want the pilot to fly the holding pattern.

The second item will reduce radio chatter and make it easier for RNAV-equipped aircraft to fly efficient approaches. Pilots may want to review how they load approaches into GPS navigators to avoid what I call the

vectors-to-final scramble

.

The last item in the summary refers to RF legs, which at present are part of authorization-required

RNP approaches

that aren’t available to typical GA pilots.

New FAA Policy on IFR Alternates with GPS

The FAA has updated its policies for filing alternate airports for pilots who use an IFR-approved GPS.

According to the new policy, which will added to future versions of the AIM, advisory circulars, and other documents, pilots with non-WAAS GPS navigators can now file an alternate airport that is served only by GPS-based instrument approaches, provided the original destination airport has ground-based procedures, or vice-versa.

Pilots flying WAAS-equipped aircraft with baro-VNAV capability (typically only business jets and airliners) can now use the LNAV/VNAV decision altitude for applicable alternate airport weather minimums.

Pilots without baro-aided LNAV/VNAV capability must still meet the requirements of 14 CFR § 91.169, which specifies alternate airport weather minima for non-precision approach procedures. In other words, at the estimated time of arrival at the alternate airport, the forecast weather at the alternate must call for a ceiling of at least 800 feet and visibility of at least 2 statute miles.

The new NOTAM, issued April 4, explains that:

The FAA [has] also studied the availability of GPS and Wide Area Augmentation System (WAAS) for GPS­ and WAAS-based instrument approaches at destination and alternate airports. As a result, the FAA has updated the policy and provided clarification to enable additional flexibility for users while maintaining safety in the National Airspace System (NAS).

Non-WAAS Users

For pilots who fly with IFR-approved GPS navigators without WAAS capabilities, the NOTAM explains that:

The current alternate airport planning policy allows users equipped with non-WAAS navigators…to plan for GPS-based instrument approach procedures (IAP) at their destination but not at their alternate airport.

The FAA has updated this policy to allow an option to flight plan for use of a GPS-based IAP at either the destination or the alternate airport, but not at both locations. At the alternate airport, pilots may plan for applicable alternate airport weather minimums using:

1. Lateral navigation (LNAV) or circling minimum descent altitude (MDA);

2. LNAV/vertical navigation (LNAV/VNAV) decision altitude (DA) if equipped with and using approved barometric vertical navigation (baro-VNAV);

3. RNP 0.3 DA on an RNAV (RNP) IAP if specifically authorized with approved baro-VNAV equipment.

…The FAA based this policy clarification on the facts that GPS-based lateral guidance is the same for LNAV, LNAV/VNAV and RNP 0.3 DA and approved barometric vertical navigation equipment does not rely on GPS information. Therefore, a loss of GPS vertical would not affect these WAAS users navigating vertically with baro-VNAV.

WAAS Users

The change in policy for WAAS users does not affect most pilots who fly light GA aircraft with IFR-approved WAAS navigators. According to the NOTAM:

The current alternate airport planning policy explicitly prohibits TSO-C145() and TSO-C146() equipped users (WAAS users) from planning to use WAAS vertical guidance at their alternate airport.

There are some WAAS integrations that use baro-VNAV for vertical guidance. WAAS users should consult their flight manuals for this information. This policy clarification allows properly trained and approved, as required, WAAS users equipped with and using approved baro-VNAV equipment to plan for applicable alternate airport weather minimums using:

1. LNAV/VNAV DA at an alternate airport.

2. RNP 0.3 DA on an RNAV (RNP) IAP at the alternate airport if specifically authorized.

The FAA based this policy clarification on the facts that GPS-based lateral guidance is the same for LNAV, LNAV/VNAV and RNP 0.3 DA and approved barometric vertical navigation equipment does not rely on GPS information. Therefore, a loss of GPS vertical would not affect these WAAS users navigating vertically with baro-VNAV.

LP Approaches are now Available

The 7 February 2013 NavData update from Jeppesen includes RNAV approaches with LP (localizer performance) minimums. You can read more about LP at my blog here and in AIM 1-1-20 (b)(3):

A new nonprecision WAAS approach, called Localizer Performance (LP) is being added in locations where the terrain or obstructions do not allow publication of vertically guided LPV procedures. This new approach takes advantage of the angular lateral guidance and smaller position errors provided by WAAS to provide a lateral only procedure similar to an ILS Localizer. LP procedures may provide lower minima than a LNAV procedure due to the narrower obstacle clearance surface.

NOTE–WAAS receivers certified prior to TSO C-145b and TSO C-146b, even if they have LPV capability, do not contain LP capability unless the receiver has been upgraded. Receivers capable of flying LP procedures must contain a statement in the Flight Manual Supplement or Approved Supplemental Flight Manual stating that the receiver has LP capability, as well as the capability for the other WAAS and GPS approach procedure types.

As noted above, you must have a WAAS-capable, IFR-approved GPS navigator to fly LP procedures. In addition, your unit must have the correct operating system software installed, and the supplement to your AFM must permit you to fly to LP minimums based on the equipment installed in your aircraft.

At present, there are 413 Localizer Performance (LP) approach procedures in the U.S. The map below is a bit out of date, but it gives you a general idea of where these procedures are located. You can find lists of approaches with LP minimums at this FAA website. The information is in Microsoft Excel worksheets that you can filter and sort.

March 7, 2013 AIM Update

FAA has published the 7 March 2013 update (PDF) to the AIM. The full version of the updated AIM will be available here. Changes include:

1−1−14. User Reports on NAVAID Performance
This change updates guidance to specifically address the Global Navigation Satellite System (GNSS).

1−1−19. Global Positioning System (GPS)
This change describes the requirements for two independent navigation systems. It also clarifies the application of different Technical Standard Orders and updates the guidance for standalone GPS approaches. In addition, this change clarifies the term UNRELIABLE as used in conjunction with GPS notices to airmen. Document references have also been updated throughout the paragraph where applicable.

5−2−7. Departure Control
This change incorporates verification of the assigned area navigation (RNAV) standard instrument departure (SID) to pilots prior to departure into the Aeronautical Information Manual and other Air Traffic publications.

5−3−4. Airways and Route Systems
This change adds guidance for using “T−Routes” and “Q−Routes.” Document references have also been updated throughout the paragraph where applicable.

5−4−5. Instrument Approach Procedure Charts
This change updates guidance regarding the Ground Based Augmentation System (GBAS) and updates document references where applicable.

Substituting GPS for Ground-Based Navigation Aids

Questions continue about when and how a pilot may substitute GPS for indications and information from ground-based navigation aids, such as VORs, DME, and NDB, including intersections and fixes defined by ground-based navaids. I provided background on this topic in October 2011. But the new edition of the Instrument Flying Handbook (described here) consolidates and expands on the guidance offered in the AIM and AC 90-108, and it bears mention here.

(The simple explanation is straightforward. If you have an IFR-approved GPS, and absent restrictions in the AFM supplement for that GPS, you can use it instead of a VOR, DME, or NDB indicator, even when a charted navaid is out of service or noted as “required” on an approach chart. GPS can also substitute for fixes (e.g., step-down-fixes) that are part of a conventional approach, such as an ILS. The ground-based navaids and defined fixes must be in the GPS database. You cannot, however, use GPS for lateral guidance along the final approach course of an IAP that is based on a localizer, VOR, or NDB.)

Chapter 9 of the new edition of the IFH (see p. 9-27) includes the following information.

GPS Substitution
IFR En Route and Terminal Operations
GPS systems, certified for IFR en route and terminal operations, may be used as a substitute for ADF and DME receivers when conducting the following operations within the United States NAS.
1. Determining the aircraft position over a DME fix. This includes en route operations at and above 24,000 feet mean sea level (MSL) (FL 240) when using GPS for navigation.

2. Flying a DME arc.
Navigating TO/FROM an NDB/compass locator.

3. Determining the aircraft position over an NDB/compass locator.

4. Determining the aircraft position over a fix defined by an NDB/compass locator bearing crossing a VOR/LOC course.

5. Holding over an NDB/compass locator.

GPS Substitution for ADF or DME
Using GPS as a substitute for ADF or DME is subject to the following restrictions:

1. This equipment must be installed in accordance with appropriate airworthiness installation requirements and operated within the provisions of the applicable POH/AFM or supplement.

2. The required integrity for these operations must be provided by at least en route RAIM or equivalent.

3. WPs, fixes, intersections, and facility locations to be used for these operations must be retrieved from the GPS airborne database. The database must be current. If the required positions cannot be retrieved from the airborne database, the substitution of GPS for ADF and/or DME is not authorized.

4. Procedures must be established for use when RAIM outages are predicted or occur. This may require the flight to rely on other approved equipment or require the aircraft to be equipped with operational NDB and/or DME receivers. Otherwise, the flight must be rerouted, delayed, canceled, or conducted under VFR.

5. The CDI must be set to terminal sensitivity (1 NM) when tracking GPS course guidance in the
terminal area.

6. A non-GPS approach procedure must exist at the alternate airport when one is required. If the non-GPS approaches on which the pilot must rely require DME or ADF, the aircraft must be equipped with DME or ADF avionics as appropriate.

7. Charted requirements for ADF and/or DME can be met using the GPS system, except for use as the principal instrument approach navigation source.

NOTE: The following provides guidance that is not specific to any particular aircraft GPS system. For specific system guidance, refer to the POH/AFM, or supplement, or contact the system manufacturer.

To Determine Aircraft Position Over a DME Fix:

1. Verify aircraft GPS system integrity monitoring is functioning properly and indicates satisfactory integrity.

2. If the fix is identified by a five-letter name that is contained in the GPS airborne database, select either the named fix as the active GPS WP or the facility establishing the DME fix as the active GPS WP. When using a facility as the active WP, the only acceptable facility is the DME facility that is charted as the one used to establish the DME fix. If this facility is not in the airborne database, it is not authorized for use.

3. If the fix is identified by a five-letter name that is not contained in the GPS airborne database, or if the fix is not named, select the facility establishing the DME fix or another named DME fix as the active GPS WP.

4. When selecting the named fix as the active GPS WP, a pilot is over the fix when the GPS system indicates the active WP.

5. If selecting the DME providing facility as the active GPS WP, a pilot is over the fix when the GPS distance from the active WP equals the charted DME value, and the aircraft is established on the appropriate bearing or course.

To Fly a DME Arc:
1. Verify aircraft GPS system integrity monitoring is functioning properly and indicates satisfactory integrity.

2. Select from the airborne database the facility providing the DME arc as the active GPS WP. The only acceptable facility is the DME facility on which the arc is based. If this facility is not in your airborne database, you are not authorized to perform this operation.

3. Maintain position on the arc by reference to the GPS distance instead of a DME readout.

To Navigate TO or FROM an NDB/Compass Locator:
1. Verify aircraft GPS system integrity monitoring is functioning properly and indicates satisfactory integrity.

2. Select the NDB/compass locator facility from the airborne database as the active WP. If the chart depicts the compass locator collocated with a fix of the same name, use of that fix as the active WP in place of the compass locator facility is authorized.

3. Select and navigate on the appropriate course to or from the active WP.

To Determine Aircraft Position Over an NDB/Compass Locator:
1. Verify aircraft GPS system integrity monitoring is functioning properly and indicates satisfactory integrity.

2. Select the NDB/compass locator facility from the airborne database. When using an NDB/compass locator, the facility must be charted and be in the airborne database. If the facility is not in the airborne database, pilots are not authorized to use a facility WP for this operation.

3. A pilot is over the NDB/compass locator when the GPS system indicates arrival at the active WP.

To Determine Aircraft Position Over a Fix Made up of an NDB/Compass Locator Bearing Crossing a VOR/LOC Course:
1. Verify aircraft GPS system integrity monitoring is functioning properly and indicates satisfactory integrity.

2. A fix made up by a crossing NDB/compass locator bearing is identified by a five-letter fix name. Pilots may select either the named fix or the NDB/compass locator facility providing the crossing bearing to establish the fix as the active GPS WP. When using an NDB/compass locator, that facility must be charted and be in the airborne database. If the facility is not in the airborne database, pilots are not authorized to use a facility WP for this operation.

3. When selecting the named fix as the active GPS WP, pilot is over the fix when the GPS system indicates the pilot is at the WP.

4. When selecting the NDB/compass locator facility as the active GPS WP, pilots are over the fix when the GPS bearing to the active WP is the same as the charted NDB/compass locator bearing for the fix flying the prescribed track from the non-GPS navigation source.

To Hold Over an NDB/Compass Locator:
1. Verify aircraft GPS system integrity monitoring is functioning properly and indicates satisfactory integrity.

2. Select the NDB/compass locator facility from the airborne database as the active WP. When using a facility as the active WP, the only acceptable facility is the NDB/compass locator facility which is charted. If this facility is not in the airborne database, its use is not authorized.

3. Select non-sequencing (e.g., “HOLD” or “OBS”) mode and the appropriate course in accordance with the POH/AFM or supplement.

4. Hold using the GPS system in accordance with the POH/AFM or supplement.

Garmin Radius to Fix Leg Project Report

The accuracy provided by GPS (especially with WAAS augmentation) has vastly expanded the number and quality of instrument approaches available to properly equipped aircraft, including procedures that provide guidance comparable to the ILS. For example, as of January 10, 2013, in the U.S., there were 3,052 approaches with LPV (localizer performance with vertical guidance) minimums, more than double the number of category 1 ILS approaches (the current inventory of instrument flight procedures in the U.S. is available here).

At present, however, approaches that take full advantage of the capabilities of satellite-based navigation remain in a special “authorization required” category. Flying these RNAV (RNP) procedures requires additional crew training and approved avionics, such as flight management computers, autopilots, and cockpit displays, as described in AC 90-101A and AIM 5-4-18. At present, RNAV (RNP) (required navigation performance) procedures, like Category II ILS approaches, are available to authorized airline crews and pilots flying business jets equipped with the appropriate avionics, but not to typical instrument-rated pilots, even those flying aircraft with WAAS-capable IFR GPS navigators such as the Garmin GNS430W/530W and newer GTN750/650 series boxes.

Garmin, working with the FAA and Hughes Aerospace Corporation, has recently completed the first part of a study that may persuade the FAA to change the requirements and make some RNP procedures available to most pilots flying aircraft equipped with WAAS-capable avionics. You can download the complete Garmin Radius to Fix Leg Project Report (PDF) published January 15, 2013, here.

A key feature of RNP procedures is the radius-to-fix (RF) leg, a curved flight path that resembles the familiar DME arc. The Instrument Procedures Handbook describes RF legs this way:

Constant radius turns around a fix are called “radius-to-fix legs,” or RF legs. These turns, which are encoded into the navigation database, allow the aircraft to avoid critical areas of terrain or conflicting airspace while preserving positional accuracy by maintaining precise, positive course guidance along the curved track. The introduction of RF legs into the design of terminal RNAV procedures results in improved use of airspace and allows procedures to be developed to and from runways that are otherwise limited to traditional linear flight paths or, in some cases, not served by an IFR procedure at all. (5-23)

Figure A-13 from Appendix A of the IPH shows a hypothetical RF leg.

Unlike DME arcs, RF legs are defined by points in space, not distances from a ground-based transmitter. They can be strung together into sinuous paths, that, as noted above, provide lower minimums while avoiding obstacles, airspace conflicts, and noise-sensitive areas. The plan view from the RNAV (RNP) Z RWY 13R approach at Boeing Field in Seattle (KBFI) shows such RF legs.

You can find examples of RF legs in non-RNP approaches at Carlsbad, CA (KCRQ) and Ketchikan, AK (PAKT) [thanks to John D. Collins for those references]. Because of the restrictions placed on flying RF legs, however, those procedures are not currently available to typical IFR pilots. RF legs are also features of some RNAV instrument departure and arrival procedures (SIDs and STARs).

FAA includes RF legs in procedures assuming that an aircraft can follow the curved path with great precision, hence the detailed requirements spelled out in AC 90-101A and AIM 5-4-18. Chief among those requirements are a flight director and/or a roll-steering autopilot, stipulations that rule out many, if not most, light general aviation aircraft.

The new Garmin study demonstrates, however, that:

Instrument-rated general aviation pilots are able to hand fly RF legs and meet the 0.5 nm 95% FTE [standard flight technical error]  target and RF leg altitude restrictions without the aid of a flight director or autopilot in Part 23 Category A and B aircraft that are either minimally equipped or technically advanced…All pilots demonstrated acceptable proficiency on both straight legs and RF legs. The increase in RF leg FTE over straight leg FTE can be expected to be about the same magnitude from a minimally equipped aircraft to a technically advanced aircraft.

In other words, pilots were able to remain well within the boundaries specified for an RF leg, whether flying a Cherokee equipped with just a Garmin 430W and basic instrumentation or a speedier Cessna 400 outfitted with Garmin’s latest G2000 integrated glass cockpit and autopilot. The pilots achieved this performance while hand-flying challenging procedures that incorporated multiple RF legs specifically designed to stress-test both the avionics and their flying skills. You can see diagrams of these special procedures in the Garmin report.

Based on the findings (described in great detail in the Garmin document), Garmin concludes that:

Garmin recommends FAA revise its installation and operational guidance for RF legs to make clear that applicants may obtain airworthiness approval for installations without flight director/autopilot. To preclude the need to demonstrate adequate FTE margin for aircraft flying RF legs at greater than 200 knots without flight director/autopilot, Garmin recommends FAA revise its installation and operational guidance for RF legs to allow applicants to utilize an Aircraft Flight Manual limitation that restricts flying RF legs to 200 knots or less.

Furthermore, the study showed that a moving map, while a great benefit to situational awareness, isn’t necessary to fly RF legs accurately:

As this project has shown, FTE is decreased when a moving map is available and is thus consistent with the MLS curved path study conclusion that led to the FAA installation and operational guidance that “an aircraft must have an electronic map display depicting … RF legs.” However, this project has also clearly shown that a moving map is not required to maintain acceptable RF leg FTE, even during complex procedures and missed approaches.

The executive summary of the Garmin report outlines additional conclusions and recommendations that address specific issues related to flying RF legs in typical light GA aircraft.

The FAA isn’t saying when or if it will adopt the recommendations in Garmin’s report. So far, the agency has said only:

This demonstration project has shown early success and will continue with more flight testing and data collection.

But the well-designed study and detailed analysis suggest that many more pilots may in future be able to take advantage of some advanced RNP procedures, if the FAA agrees with the recommendations and avionics manufacturers and database providers include RF legs in future updates to the WAAS units now common in light GA aircraft.

Database Currency for IFR Operations

Most instrument-rated pilots now fly with GPS-based navigation equipment. (according to AOPA, 78 percent of its members rely on GPS as their primary navigation tool). To use an IFR-approved GPS when operating IFR, the unit’s database must be current or you must verify the accuracy of the data (for more details, see note 4 in AIM 1-2-3: Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes). Keeping a typical GPS unit up-to-date usually involves downloading fresh data to a card every 28 days.

Of course, the dates of those updates don’t always fall conveniently between trips, and FAA has outlined procedures to help pilots ensure that the data in GPS avionics matches the key information on current charts, especially instrument approach plates.

Regarding instrument approaches, the key information for matching the database to the chart is the procedure amendment reference date, not necessarily the date printed at the top of the chart. On charts published by the FAA, the procedure amendment reference date appears in the lower-left corner, next to the amendment number.

The best description of the procedure amendment reference date and how to use it is in Jeppesen Briefing Bulletin JEP 09-C (PDF)–even if you use charts published by FAA AeroNav Products. The Jeppesen briefing bulletin includes a simple flow chart that helps you use the procedure reference date.

FAA published a safety alert (PDF) in 2009 that explains the difference between chart dates and procedure amendment dates.

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.

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.

Localizer Performance (LP) Procedures

Instrument rated pilots have started noticing a new type of RNAV (GPS) procedure appearing in their chart updates. These localizer performance (LP) procedures are described, among other places, in AIM 1-1-20 (b)(3):

A new nonprecision WAAS approach, called Localizer Performance (LP) is being added in locations where the terrain or obstructions do not allow publication of vertically guided LPV procedures. This new approach takes advantage of the angular lateral guidance and smaller position errors provided by WAAS to provide a lateral only procedure similar to an ILS Localizer. LP procedures may provide lower minima than a LNAV procedure due to the narrower obstacle clearance surface.

NOTE–WAAS receivers certified prior to TSO C-145b and TSO C-146b, even if they have LPV capability, do not contain LP capability unless the receiver has been upgraded. Receivers capable of flying LP procedures must contain a statement in the Flight Manual Supplement or Approved Supplemental Flight Manual stating that the receiver has LP capability, as well as the capability for the other WAAS and GPS approach procedure types.

In other words, LP procedures are non-precision approaches (they don’t offer vertical guidance) that use WAAS signals and data to emulate a localizer-only procedure. Don’t confuse LP approaches with LPV procedures; LPV approaches offer vertical guidance like an ILS.

According to the FAA’s summary of IAPs, there were 344 published LP procedures at the end of July 2012.

But as of September 2012, you still can’t fly these procedures, because the data needed to fly them haven’t been added to the Jeppesen NavData updates that most IFR-approved GPS units use. A notice from Jeppesen (PDF) reported that the company anticipated adding LP data in “mid-2012,” but the data still aren’t available, and Jeppesen hasn’t updated its plans to include LP procedures.

When the LP procedures are available in the database (and assuming the box you’re flying is approved for LP procedures and that you have the approved supplements to your AFM), you’ll be able to select an LP approach from the list of procedures for an airport and you’ll see an LP annuniciation when an LP approach is available. In this respect, preparing to fly an LP approach will be like loading other RNAV (GPS) procedures, and you’ll fly the procedure to the LP line of minimums printed on the approach chart.

You can find additional information about LP approaches elsewhere in the AIM (e.g., 5-4-5):

LP will be published in locations where vertically guided minima cannot be provided due to terrain and obstacles and therefore, no LPV or LNAV/VNAV minima will be published…

(d) LP. “LP” is the acronym for localizer performance. Approaches to LP lines of minima take advantage of the improved accuracy of WAAS to provide approaches, with lateral guidance and angular guidance. Angular guidance does not refer to a glideslope angle but rather to the increased lateral sensitivity as the aircraft gets closer to the runway, similar to localizer approaches. However, the LP line of minima is a Minimum Descent Altitude (MDA) rather than a DA (H). Procedures with LP lines of minima will not be published with another approach that contains approved vertical guidance (LNAV/VNAV or LPV). It is possible to have LP and LNAV published on the same approach chart but LP will only be published if it provides lower minima than an LNAV line of minima. LP is not a fail−down mode for LPV. LP will only be published if terrain, obstructions, or some other reason prevent publishing a vertically guided procedure. WAAS avionics may provide GNSS−based advisory vertical guidance during an approach to an LP line of minima (reference section 9.b for further information on advisory vertical guidance). Barometric altimeter information remains the primary altitude reference for complying with any altitude restrictions. WAAS equipment may not support LP, even if it supports LPV, if it was approved before TSO C−145B and TSO C−146B. Receivers approved under previous TSOs may require an upgrade by the manufacturer in order to be used to fly to LP minima. Receivers approved for LP must have a statement in the approved Flight Manual or Supplemental Flight Manual including LP as one of the approved approach types.

RNP Procedures and Typical Part 91 Pilots

Some pilots remain confused about GPS-based RNAV approaches, especially procedures with “RNP” (Required Navigation Performance) in the title and “AUTHORIZATION REQUIRED” notes on the chart. For many reasons, those approaches are currently off-limits to a typical IFR pilot flying an airplane equipped with a WAAS-capable, IFR-approved GPS.

The situation is becoming more complicated with the forthcoming publication of RNAV approaches such as the RNAV (GPS) Y RWY 24 at KCRQ (see below). Although that procedure is not labeled RNP, one transition (from VISTA) includes an RF (radius-to-fix) leg, a curved path that resembles a DME arc, but which requires specific equipment and training to fly–see below. Most of us flying with GPS units like the Garmin GNS400/500W and new GTN-series navigators may not see this procedure in the database, but it may appear among the updated charts you receive from Jeppesen or FAA AeroNav Products.

For a basic explanation of why you need specific authorization to fly RNP procedures, see the Instrument Procedures Handbook:

In the United States, all RNP procedures are in the category of Special Aircraft and Aircrew Authorization Required (SAAAR). Operators who seek to take advantage of RNP approach procedures must meet the special RNP requirements outlined in FAA AC 90-101, Approval Guidance for RNP Procedures with SAAAR. Currently, most new transport category airplanes receive an airworthiness approval for RNP operations. However, differences can exist in the level of precision that each system is qualified to meet. Each individual operator is responsible for obtaining the necessary approval and authorization to use these instrument flight procedures with navigation databases. (5-22)

Note that authorities have dropped the use of “Special Aircraft and Aircrew Authorization Required (SAAAR)” in favor of AUTHORIZATION REQUIRED notes on charts, in ACs, and the like. And the current advisory circular is AC 90-101A.

That AC explains in part:

a. AR. RNP AR approaches include unique capabilities that require special aircraft and aircrew authorization similar to Category (CAT) II/III instrument landing system (ILS) operations. All RNP AR approaches have reduced lateral obstacle evaluation areas and vertical obstacle clearance surfaces predicated on the aircraft and aircrew performance requirements of this AC. In addition, selected procedures may require the capability to fly an RF leg and/or a missed approach, which requires RNP less than 1.0. Appendix 2 of this AC identifies specific aircraft requirements that apply to these capabilities.

b. Navigation Performance Monitoring. A critical component of RNP is the ability of the aircraft navigation system to monitor its achieved performance and to identify for the pilot whether the performance meets set standards during an operation.

A more detailed description of an RNP procedure (from AC 90-101A), helps you understand why a typical WAAS-capable piston flown by a single pilot doesn’t qualify:

2. Characteristics of RNP AR Approaches.
a. RNP Value. Each published line of minima has an associated RNP value. For example, Figure 2 shows both RNP 0.3 and RNP 0.15 lines of minima. Each operator’s RNP AR authorization documents a minimum RNP value, and this value may vary depending on aircraft configuration or operational procedures (e.g., use of flight director (FD) with or without autopilot). RNP AR approaches will have an RNP value of RNP 0.3 or less.

b. Procedures with Radius to a Fix (RF) Legs. Some RNP AR approaches include RF legs. The instrument approach charts will indicate requirements for RF legs in the notes section or at the applicable initial approach fix (IAF). Figures 1 and 2 provide examples of procedures with an RF leg segment (e.g., between SKYCO and CATMI).

c. Missed Approaches Requiring Less Than RNP 1.0. At certain locations, the airspace or obstacle environment may require RNP capability of less than 1.0 during a missed approach. Operation on these approaches typically requires redundant equipment. This requirement ensures that no single point of failure can cause loss of RNP capability. Figure 2 provides an example of a missed approach requiring RNP less than 1.0. The notes section of the chart indicates this requirement.

d. Non-Standard Speeds or Climb Gradients. Normally, RNP AR approach procedure design relies on standard approach speeds and climb gradients including on the Missed Approach Segment (MAS). The approach procedure will indicate any exceptions to these standards, and the operator must ensure it can comply with any published restrictions before conducting these approach operations. Figure 2 provides an example of a non-standard climb gradient and speed restrictions.

AC 90-101A also describes the training necessary for crews authorized to fly RNP procedures and the equipment requirements (beyond a WAAS-capable GPS receiver) necessary to fly those approaches.

With all that in mind, it’s important to understand that if your airplane is equipped with, say, a GNS530W or one of the new GTN boxes (with an appropriate AFM supplement), you can fly RNAV SIDs and STARs based on RNP-1 criteria. And you can, of course, fly en route segments that require RNP-2 accuracy. No special authorization is required at these RNP levels. For an explanation of RNP levels, see “Required Navigation Performance” in the Instrument Procedures Handbook (1-13).

For more information about operations approved for different IFR-approved GPS units, see AC 90-100A, “U.S. Terminal and En Route Area Navigation (RNAV) Operations,” and the associated Excel compliance worksheet. A good summary of AC 90-100A is available here.