Clearances to GNSS Equipped Aircraft Below the MEA

FAA recently updated Air Traffic Control (JO 7110.65W) to allow IFR clearances to GNSS (i.e., GPS) equipped aircraft on airways below the published minimum en route altitude.

N JO 7110.741, published on September 25, 2017 (now incorporated in Air Traffic Control paragraph 4-5-6), explained that:

This notice…allow[s] IFR certified Global Navigation Satellite System (GNSS) equipped aircraft to be cleared below published Minimum En Route Altitudes (MEA)…

The notice explained that:

MEAs are based in part on ground-based navigational aid reception. The advent of satellite technology provides the opportunity for lower minimum altitudes along certain airways, allowing more altitudes to be usable for more aircraft. This change will facilitate IFR certified GNSS equipped aircraft to fly below published MEAs, but no lower than Minimum Obstruction Clearance Altitudes, Minimum IFR Altitudes, or Minimum Vectoring Altitudes, regardless of radar coverage. This would apply to all applicable airways, rather than being limited to those published with GNSS MEA minimums.

Note that the rule (in 14 CFR §91.177 Minimum altitudes for IFR operations) about flying at the MOCA  when you are using VORs still applies:

For aircraft using VOR, VORTAC or TACAN for navigation, this [i.e., flying at the MOCA] applies only within 22 miles of that NAVAID.

The low-altitude en route chart below points out examples of MEAs and MOCAs. (Click here to see the chart at SkyVector.com.)

MEA-MOCA

For example, along a segment of V187 between MOG and MSO, the MEA is 13000. The MOCA is 9900. There is no published GPS MEA (which would appear in blue with a G appended to the altitude). But if you are flying with an IFR-approved GPS, ATC could clear you to 9900, if, for example, you encountered ice.

Similarly, along V120 east of MLP, the MEA is 13000 and the MOCA is 9600, potentially giving you more than 3000 feet to work with if necessary.

Note, however, that not all airway segments have published MOCAs. For example, the only published IFR altitude between PUW and MLP is the MEA of 9100. You still might be cleared below that MEA if ATC has a lower minimum IFR altitudes or minimum vectoring altitudes available in that area, but those altitudes are not typically published on charts that pilots use.* You would just ask for a lower altitude, and the controller could clear you to the appropriate MVA or MIA.

The updated FAA handbook specifically notes that controllers may clear you to an MVA or MIA, but they must also issue lost communications instructions:

(a) In the absence of a published MOCA, assign altitudes at or above the MVA or MIA along the route of flight, and

(b) Lost communications instructions are issued.


*You can download MVA and MIA charts as PDFs from the FAA website, here. But at present, these charts are not available in a format that allows for easy integration with apps that pilots typically use or straightforward comparison with other aviation charts.

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A Quick Way to Search for GPS NOTAMs

The FAA NOTAM search site (https://notams.aim.faa.gov/notamSearch) provides the quickest way to find GPS NOTAMs that alert you to disruptions in the satellite-based navigation system. If you’ve ever tried to find and sort through the text descriptions of these alerts, you’ll appreciate the lists and map views that show how GPS tests and other issues may affect your ability to navigate using GPS.

To learn more about using the FAA NOTAM search site, you can download the User Guide from the FAA website or from my Aviation Documents folder at OneDrive.

NOTAMs-UserGuide

To find GPS-related NOTAMs at the FAA website follow these steps:

After acknowledging the disclaimer, on the main page, select the Predefined Queries option and choose GPS.

FAANotams-PredefinedQuery
FAANOTAMS-selectGPS

Click the Search button, and you’ll see a list of GPS NOTAMs.

FAAGPSNOTAMs-List.jpg

You can also show the NOTAMs in a table.

FAAGPSNOTAMs-Table.jpg
Or in a table with an adjacent map.

FAAGPSNOTAMS-Map+List.jpg
You can filter the list to show only the NOTAMs effective in one or more air route traffic control centers.

FAAGPSNOTAMs-ARTCCListFilter

And you can zoom in on the map and click a NOTAM flag to see more information about that notice.

GAAGPSNOTAMs-MapWide

FAAGPSNOTAMS-MapZoomed.jpg

Use the +/- buttons in the upper-left corner of the map to zoom in and out. To print a NOTAM, click the print icon next to the text.

Changes in AIM Effective 26 May 2016

FAA has published an update to the AIM, effective 26 May 2016, and it includes several important changes of interest to typical general-aviation pilots:

1−2−3. Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures
and Routes

This change allows for the use of a suitable RNAV system as a means to navigate on the final approach segment of an instrument approach procedure (IAP) based on a VOR, TACAN, or NDB signal. The underlying NAVAID must be operational and monitored for the final segment course alignment. [For more information about this item, see the detailed discussion here.]

3−2−3. Class B Airspace
This change adds an RNAV Receiver as an option for instrument flight rule (IFR) navigation requirement IAW 91.131 (c)(1).

3−2−6. Class E Airspace

This change updates the definition, vertical limits, and types of Class E airspace. The change more accurately reflects Class E airspace regulatory information in 14 CFR Part 71 and more clearly states that Class E arrival extensions have the same effective times as the airport surface area airspace….

4−3−22. Option Approach
This changes adds verbiage advising pilots to inform air traffic control (ATC) as soon as possible of any delay clearing the runway during their stop−and−go or full stop landing.

5−2−8. Instrument Departure Procedures (DP) − Obstacle Departure Procedures (ODP) and Standard Instrument Departures (SID)
This change adds language advising pilots what to expect when vectored or cleared to deviate off of an SID.

5−4−1. Standard Terminal Arrival (STAR) Procedures
This change adds language advising pilots what to expect when vectored or cleared to deviate off of a STAR. Pilots should consider the STAR cancelled. If the clearance included crossing restrictions, controllers will issue an altitude to maintain. It also adds language advising pilots when to be prepared to resume the procedure. Since all clearances on STARS will not include Descend Via clearances, the word “will” was replaced with “may.”

5−4−7. Instrument Approach Procedures
This change adds a note to provide guidance to pilots regarding what to expect when clearances are issued by ATC to altitudes below those published on IAPs.

Avoiding Confusion when Flying GPS Legs

Garmin has published a useful document on the topic of the types of legs that appear in various instrument procedures.

For example, many departure procedures include fix-to-altitude legs.

Fix-to-Altitude-Leg

GNS 400(W)/500(W) Series and GTN 6XX/7XX Series Instrument Procedure Leg Awareness (PDF) is a good summary of key types of legs that are used in DPs, STARs, and approaches, and it describes the features and limitations of the GNS and GTN units.

You can also find information on IAP legs in Chapter 6 of the Instrument Procedures Handbook.

Update on RNAV (GPS) Approaches

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)

140

RNAV (LNAV)

5,832

RNAV (VNAV)

3,254

RNAV (LPV)

3,375

RNAV (LP)

533

Total

13,134

Conventional Approaches  

ILS

1,285

LOC

1,439

LOC (B/C)

72

NDB

780

VOR

1,273

VOR/DME

945

Total

5,794

Here’s a pie chart that shows the relative shares of different types of instrument approach procedures in the U.S.

RNAVApproaches

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)
  • 880 LPVs with DA < 250 HAT
  • 854 LPVs with DA = 200 HAT

When a VOR is Decommissioned

The recent shutdown of the Lake Henry VOR (LHY), which lies northeast of Wilkes-Barre PA (VFR chart at SkyVector here), is an example of how the FAA is handling the gradual decommissioning of VORs. (See also More Details about VOR Shutdowns)

As the latest IFR low-altitude en route charts show, the VOR (at present still depicted on the charts to help pilots become familiar with the new routes) has been replaced by a five-letter waypoint, LAAYK.

LAAYK-02

Note that the frequency for the VOR (110.8) is now shaded to indicate that the facility has been shut down, as described on p. 54 of the Aeronautical Chart User’s Guide.

VOR-ShutdownFreq

A wider view of the area shows that several victor airways or segments of airways have been replaced with T-routes, depicted in blue on charts published by the FAA.

LAAYK-01

T-routes and their associated G (GPS-based) MEAs are described in AIM 5−3−4. Airways and Route Systems and in “Area Naviation (RNAV) ‘T’ Route System” on page 56 of the Aeronautical Chart User’s Guide (12th edition).

You can expect similar changes as more VORs are shut down over the next several years, leaving what the FAA calls the Minimum Operational Network. That plan at present calls for all VORs in the mountainous regions (essentially the western U.S.) to remain online, while many VORs elsewhere in the country are decommissioned.

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 latest 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.)

FAA updated its guidance on this issue with the May 26, 2016 update to the AIM. For more information, see this item here at BruceAir.

Chapter 9 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. (For an update on filing alternates with an IFR-approved GPS, see New FAA Policy on IFR Alternates with GPS.)

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.