Stand-Alone DMEs on Charts

As the FAA moves ahead it with its plans to decommission about one-third of the existing network of VORs in the continental U.S. (for more information, see Another Update on VOR Decommissioning and its related posts), a new type of navaid–a stand-alone DME facility–is appearing on aeronautical charts.

Here’s an example southwest of Las Vegas, NV. Note the identification and frequency box for the GOODSPRINGS DME (GOG). The site of the transmitter is shown by the small blue box indicated by the red arrow.


Here’s the same facility on a low-altitude IFR chart:


You can read more about these stand-alone DME facilities in DME Facilities – Charting and MAGVAR Issues (PDF), which describes the discussions of the Aeronautical Charting Forum, an FAA-industry group.

These stand-alone DMEs are primarily for use by aircraft with DME-DME area navigation equipment, and in many cases, they are left over when the VORs they were associated with are shut down. Where necessary, new DMEs will be added to support RNAV procedures based on DME-DME as an alternative to GPS. As you can see from the chart, these DMEs do not provide azimuth (course) information like a VOR-DME or VORTAC. They are simply DMEs.

If, like most IFR pilots flying typical GA aircraft, you use GPS as your primary navigation source, these charted stand-alone DMEs are of most interest as fixes that you can include in a route or flight plan. If you still have a DME receiver in your airplane, you can tune, identify, and reference these DMEs as you fly.

Garmin GTN Avionics and RF Legs

The release of updated operating software for Garmin GTN-series avionics brings new capabilities to many typical general aviation pilots who fly under IFR. One of the new features is the ability to fly curved radius-to-fix (RF) legs on some instrument approaches.


Until recently, RF legs were published only on so-called RNP procedures with authorization required (AR) restrictions (for more information, see AIM 5−4−18: RNP AR Instrument Approach Procedures). But FAA has started publishing some approaches with RF legs (like the example above) that are not designated as RNP AR procedures. And, with some limitations, pilots who fly aircraft equipped with GTN-series avionics should be able to fly the RF legs used as transitions/feeder routes on those approaches. (Note that so far, these approaches don’t require RF capability–conventional transitions/feeder routes and/or radar vectors are also available.)

For more information about RF legs, see RNP Procedures and Typical Part 91 Pilots and Garmin Radius to Fix Leg Project Report here at BruceAir. For additional background on GPS navigation and RNP procedures, see also Updated AC 90-105A.

The revised STC for the GTN series (document 190-01007-A5) notes that:

GPS/SBAS TSO-C146c Class 3 Operation
…The Garmin GNSS navigation system complies with the equipment requirements of AC 90-105 and meets the equipment performance and functional requirements to conduct RNP terminal departure and arrival procedures and RNP approach procedures including procedures with RF legs subject to the limitations herein [emphasis added].

Sections 2.12 RF Legs and 2.13.1 RNP 1.0 RF Leg Types of the STC add the following information:

2.12 RF Legs
This STC does not grant operational approval for RF leg navigation for those operators requiring operational approval. Additional FAA approval may be required for those aircraft intending to use the GTN as a means to provide RNP 1 navigation in accordance with FAA Advisory Circular AC 90-105. [Note that per AC 90-105A, domestic Part 91 operations do not require additional approval–only Part 91 subpart K operations and commercial operations need LOAs or the equivalent FAA approval.]

The following limitations apply to procedures with RF legs:

  • Aircraft is limited to 180 KIAS while on the RF leg
  • RF legs are limited to RNP 1 procedures. RNP AR and RNP <1 are not approved
  • Primary navigation guidance on RF legs must be shown on an EHSI indicator with auto-slew capability turned ON
  • GTN Moving Map, EHSI Map, or Distance to Next Waypoint information must be displayed to the pilot during the RF leg when flying without the aid of the autopilot or flight director.
  • The active waypoint must be displayed in the pilot’s primary field of view…

2.13.1 RNP 1.0 RF Leg Types
AC 90-105 states that procedures with RF legs must be flown using either a flight director or coupled to the autopilot.

This STC has demonstrated acceptable crew workload and Flight Technical Error for hand flown procedures with RF legs when the GTN installation complies with limitation set forth in Section 2.12 of this document. It is recommended to couple the autopilot for RF procedures, if available, but it is not required to do so. See section 4.5 of this manual to determine if this capability is supported in this installation.

At present, only a few non-AR approaches with RF legs meet the criteria in the STC and AC 90-105A. But RF legs could become more common on “standard” procedures to provide paths that offer better noise abatement, reduce airspace conflicts, and improve ATC efficiency, and pilots flying with GTN avionics (or similar navigators offered by other manufacturers) will be able to fly those procedures.

Updated AC 90-105A

FAA has published 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 (PDF available at the link).



This update to the previous edition (published in 2009) contains many important changes for pilots who use GPS to navigate under IFR.

FAA is gradually adopting the concept of performance based navigation (PBN), which includes the old systems of area navigation (RNAV) and refines details of required navigation performance (RNP). For more details about these standards, see AIM Section 2. Performance−Based Navigation (PBN) and Area Navigation (RNAV).

Update on VOR Decommissioning

The Aeronautical Charting Forum, a forum sponsored by FAA, met on April 29, 2014 outside Washington, DC. Among the items on the agenda was an update on FAA’s plans to reduce the number of VORs to a minimum operational network (MON). You can download and review a PDF version of the FAA’s PowerPoint presentation here. (Minutes from the full two-day meeting are available here.)

Key points:

  • FAA now plans to transition from a legacy network of 967 VORs to a MON of  approximately 500 VORs by FY2025. That’s a slip of five years from the previous goal of establishing the MON by 2020. For more background, see the FAA’s VOR Minimum Operational Network (MON) Information Paper (PDF).
  • The number of VORs comprising the MON may increase or decrease depending on the requirements for the Department of Defense and the Tactical Operations Committee.

You can find additional details about the FAA’s program to decommission VORs here at BruceAir’s blog:

IACO Flight Plan Equipment Codes for Aircraft with IFR GPS

In November 2012, FAA adopted new requirements and procedures for using ICAO-format flight plans.

FAA plans to require that all flight plans (VFR, IFR, domestic, and international) use the ICAO format beginning in early 2017. For more information, see a news item from AOPA here.

Pilots planning IFR flights within the borders of the U.S. are already required to file ICAO-format flight plans if:

  • The flight will enter international airspace (including Oceanic airspace controlled by FAA facilities). Even if your flight just crosses a border, such as flying through Canadian airspace on a trip that departs from and lands at a U.S. airport, you must file an ICAO flight plan.
  • You expect routing or separation based on Performance Based Navigation, for example, RNAV-based routes, departures, and arrivals. (More about PBN and RNAV levels in PBN and RNP Confusion, below.)
  • The flight will enter RVSM (Reduced Vertical Separation Minimum) airspace (i.e., above FL290).
  • You expect services based on ADS-B.

Detailed explanation of the ICAO flight plan form are available here.

In November 2013, FAA updated and simplified some of the requirements for filing ICAO flight plans for domestic use. You can read about those changes here (PDF). For most GA pilots operating under 14 CFR Part 91, the key changes are (1) The FAA requires PBN capability be filed in order to receive the desired PBN routing, e.g. RNAV routes; (2) Recent changes make the inclusion of the PBN/ field required and the NAV/ field optional when an R is filed in ICAO Item 10. (PBN/ has been required but it was not enforced by the automation until recently). A short summary of the simplified codes is also available here.

Other Reasons to File ICAO Flight Plans

Even if you aren’t required to file an ICAO flight plan, you may want to start using that format for IFR flight plans if you fly an airplane equipped with an IFR-approved GPS, especially if the box is WAAS-approved, or your aircraft is equipped with ADS-B in/out equipment, such as the Garmin GDL 88.

You can file an ICAO flight plan online through Lockheed-Martin Flight Services (the official FSS), tablet apps (e.g., ForeFlight) and several free third-party services, including DUATS and After you specify the ICAO codes for your aircraft, you can store them as part of your profile, and you’ll never have to provide them again.

Confusing Codes

Many pilots are confused by elements of the ICAO flight plan format, especially the multiple aircraft equipment codes that you must include to inform ATC of the gizmos and capability that are installed in your aircraft.

The following guide should help you sort out those ICAO codes if you fly a typical light GA aircraft equipped with at least one WAAS-capable, GPS navigator that is approved to fly RNAV (GPS) approaches. Examples of such avionics include:

Garmin has posted detailed information about the ICAO codes for its avionics, including a handy Microsoft Excel worksheet, here.


Here’s a look at the relevant parts of the ICAO flight plan form as shown on the Lockheed-Martin FSS website. I’ve filled in the information for my Beechcraft A36 Bonanza (ICAO identifier BE36), which is equipped with a GTN750, a Garmin GTX 327 transponder (not Mode S), and the GDL 88 ADS-B transmitter and receiver. This aircraft also has a Bendix/King DME receiver. The example is for an IFR trip from KBFI to KGEG in the Pacific Northwest. The route includes the ZOOMR1 STAR into KGEG.


Basic Information

The first few items are the same for all typical IFR general aviation flights:

  • Flight Rule: IFR
  • Flight Type: G (for general aviation)
  • Number of Aircraft: 1 (i.e., not a formation flight)
  • Wake Turbulence Category: L (for light)
  • Aircraft Type: The official ICAO designator for the make and model of aircraft you fly (e.g., BE36, C172, C210, M20P, PA28A, etc.)

Aircraft Equipment

On the familiar FAA domestic flight plan form, equipment suffixes for typical GA pilots are simple, and if you’re flying a GPS-equipped airplane with a Mode C transponder, the basic /G is all you need.

But the ICAO form captures many more details about the equipment installed in your aircraft, and the fun typically begins with this item.

For a WAAS-equipped aircraft such as we’re discussing, you should enter the following codes in the Aircraft Equipment box:



As you can see in the illustration from the Lockheed-Martin FSS web form, these letters represent the following equipment:

  • S: Standard communication and navigation receivers/transmitters (VOR, VHF communications radios, and ILS receiver). If you enter S in this box, you shouldn’t include the letters L (ILS), O (VOR), or V (VHF) here. S includes that equipment.
  • B: LPV approach capability. If you have a WAAS GPS, but your installation isn’t approved for LPV procedures (see the user’s guide and AFM supplement), omit this letter.
  • D: DME. If you don’t have DME, omit the D.
  • G: IFR-approved GPS (the preferred term is now GNSS, Global Navigation Satellite System)
  • R: PBN approved. This letter means that your aircraft meets basic RNP standards. You must include this letter, and associated information in the Other Information box, to ensure that the computer will accept a routing that includes RNAV routes, SIDs, STARs, or charted ODPs. See PBN and RNP Confusion, below.
  • Z: Indicates additional information to be added to the Other Information box, below.
  • If you still have an ADF, include F.

PBN and RNP Confusion

The aviation world uses RNP (required navigation performance) for two related, but different purposes.

In general, RNP is an RNAV specification (e.g., RNAV 5, RNAV 2, and RNAV 1) that indicates that an aircraft is capable of maintaining a course (track) within designated limits 95 percent of the time. For example, RNAV 5 means the aircraft as equipped can reliably maintain a track with 5 nm; RNAV 2 limits are 2 nm, and so forth. If your aircraft is equipped with an IFR-approved GPS authorized to fly RNAV (GPS) approaches, it matches this sense of RNP and PBN.

The basic RNP (RNAV) specifications used in the U.S. (RNP 0.3, RNP 1.0, RNP 2.0, and RNP 1.0) are shown in the following illustration from the Instrument Flying Handbook (FAA H-8083-15B). For more information about RNP and RNAV specifications, see “Required Navigation Performance” on page 9-44 of the IFH.


Current WAAS-approved GPS receivers for typical GA aircraft, such as those listed earlier, meet the U.S. RNP specifications, as described in AC 90-100A: U.S Terminal and En Route Area Navigation (RNAV) Operations and its associated AC90-100 Compliance Table (a Microsoft Excel worksheet). To confirm your GPS receiver’s capabilities, check the user guides and the AFM supplements for the equipment installed in your aircraft.

The term RNP is also applied as a descriptor for airspace, routes, and procedures (including departures, arrivals, and IAPs). RNP can apply to a unique approach procedure or to a large region of airspace. In this sense, RNP means something similar to Category II and Category III instrument approaches. For example, an approach with RNP in the title (e.g., RNAV (RNP) Z RWY 16R) requires special equipment and detailed crew training/qualification. Such RNAV (RNP) approaches include the note AUTHORIZATION REQUIRED on the chart.

For more information about RNP approaches, see RNP Procedures and Typical Part 91 Pilots and Garmin Radius to Fix Leg Project Report here at my blog.

Surveillance Equipment (Transponder and ADS-B)

This box on the ICAO form tells ATC what type of transponder and related equipment are installed in your aircraft.


  • For most GA pilots flying IFR, this box will include at least C, for a transponder with altitude-reporting capability.
  • If you have a Mode S transponder, you should select the appropriate letter, E, H, I, L, P, S, or X, based on the information in the user guide and AFM supplement for your transponder.
  • If you have ADS-B equipment installed (not a portable ADS-B receiver such as the Stratus or Dual XGPS170), include U1 or U2. The Garmin GDL 88 in my airplane both transmits and receives ADS-B signals, so I add U2 to this box.

Other Information

The final box for designating your RNAV capabilities is Other Information. You must use prefixes, followed by letters, to include different categories of information.

As described above here and here, it’s important to add a /PBN group in this box to ensure that the ATC system understands the RNP/RNAV capabilities of your aircraft.


If you have a GPS approved for at least IFR en route and terminal operations, add the following letters:

  • C2, which designates RNAV 2 capability based on GPS (GNSS)
  • D2, which designates RNAV 1 capability based on GPS (GNSS)

You could also add a /NAV group in this box to indicate your RNAV capability. The letters D1E2A1 after /Nav indicate that you have RNAV 1 capability for departure, RNAV 2 capability for the en route segment, and RNAV 1 capability for arrival.



These groups and letters mean that you can fly RNAV routes (e.g., T-routes), RNAV SIDs and STARs, and charted ODPs (charted ODPs are often RNAV procedures, usually based on GPS).

For more information about charted ODPs, see:

Don’t worry about the options in the RNP Specifications part of this box. Unless you are authorized to fly RNAV (RNP) procedures (see above), these items don’t apply to you.


Here’s a quick review of what to put in the equipment-related boxes of the ICAO flight plan form if, like me, you fly an aircraft with one of the common IFR-approved, WAAS-capable GPS receivers:

  • Aircraft Equipment: SBDGR.
  • Surveillance Equipment: C (for a Mode C transponder).
    (If you have ADS-B in/out capability, such as a Garmin GDL 88, add U2. If you have a Mode S transponder, include the appropriate letter for your model.)
  • Other Information: PBN/C2D2


August 22 Update to the Aeronautical Information Manual

The FAA has released Change 3 to the Aeronautical Information Manual, effective 22 August 2013. You can download the PDF of the update here. It will be incorporated into the complete AIM later this month.

Here’s a quick review of two of the significant changes that affect typical general-aviation pilots who fly IFR:

  • 1−1−18. Global Positioning System (GPS)
  • 5−4−6. Approach Clearance

1−1−18. Global Positioning System (GPS)

The change to paragraph (g) expands options for pilots with non-WAAS, IFR-approved GPS equipment. If you must file an alternate (based on the requirements of § 91.167—Fuel requirements for flight in IFR conditions), you can now choose an alternate airport served only by RNAV (GPS) approaches if your destination has procedures predicated on ground-based navaids (e.g., ILS, LOC, VOR, or NDB). If your destination has only RNAV (GPS) approaches, then your alternate must have a ground-based approach procedure.

In addition, you must plan for applicable alternate airport using the LNAV or circling MDA; you can’t expect to use the DA(s) specified by any RNAV (GPS) approaches with vertical guidance (i.e., LPV or LNAV/VNAV minimums). In other words, for planning purposes, you must assume that the approaches at the alternate airport offer only non-precision minimums. There is an exception to this restriction for aircraft with baro-aided approach systems, but those are rare in typical light GA aircraft.

5−4−6. Approach Clearance

Paragraph (e) of this section explains that ATC can now clear RNAV-equipped aircraft direct to an IF or to fix between the IF and the FAF. If you file an RNAV equipment suffix in your flight plan (e.g., /G), you can expect such clearances when flying both conventional (ground-based) and RNAV (GPS) procedures.

The details of the new procedure are in the updated section of the AIM. Basically, the controller must advise you at least five miles from the IF or other fix that you can expect a clearance direct to the fix instead of vectors to final. The controller also must clear you “straight-in” if you are cleared to a fix and the controller does not want you to fly a charted hold-in-lieu of a procedure turn or other course reversal.

Max Trescott has also addressed this issue at his blog, here.

This change also makes it clear that you shouldn’t use the vectors-to-final option when loading approaches (either RNAV or conventional approaches). For more information about the vectors-to-final trap, see Avoiding the Vectors-to-Final Scramble here at my blog.

Specially, the new notes to this section explain that:


1. In anticipation of a clearance by ATC to any fix published on an instrument approach procedure, pilots of RNAV aircraft are advised to select an appropriate IAF or feeder fix when loading an instrument approach procedure into the RNAV system.

2. Selection of “Vectors-to-Final” or “Vectors” option for an instrument approach may prevent approach fixes located outside of the FAF from being loaded into an RNAV system. Therefore, the selection of these options is discouraged due to increased workload for pilots to reprogram the navigation system.

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.