AIM Update June 17 2021

FAA has published the June 17, 2021 update of the Aeronautical Information Manual. You can download the PDF from the FAA website here.

Changes of interest to general aviation pilots in this update include:

4−1−11. DESIGNATED UNICOM/MULTICOM FREQUENCIES:

Over the Continental United States and Coastal Waters 123.4 MHz and 123.45 MHz are reserved by the Federal Communications Commission (FCC) for stations individually licensed to commercial aircraft and accessory manufacturers to use as flight test frequencies. Aircraft may only communicate with their associated company ground stations and these frequencies may not be used for air−to−air communications of any sort. In order to bring attention to the proper usage of 123.4 MHz and 123.45 MHz, this change adds these frequencies to TBL 4−1−3, Other Frequency Usage Designated by the FCC, along with the description of their use and the note that they are not for air−to−air communication.

Pilots have often informally used 123.4 (the so-called fingers) for formation flights and other air-to-air communications. This update makes it clear that the frequency isn’t to be used for that purpose.

7−1−5. PREFLIGHT BRIEFING
This change inserts language in the Aeronautical Information Manual that pilots do not need to call Flight Service in order to obtain a regulatory compliant briefing and encourages pilots to self−brief before calling a flight service station.

AIM Update: Approach Categories

FAA has released the January 30, 2020 update to the AIM. (Link to PDF and HTML editions here. You can read the explanation of changes here.)

The update includes several items of interest to IFR pilots, but one is of particular note here:

5−4−7. Instrument Approach Procedures
This change provides pilots with additional options when it is necessary to conduct an instrument approach at an airspeed higher than the maximum airspeed of its certificated aircraft approach category. It explains the flexibility provided in 14 CFR and emphasizes the primary safety issue of staying within protected areas.

Here’s the new text in that section:

a. Aircraft approach category means a grouping of aircraft based on a speed of Vref at the maximum certified landing weight, if specified, or if Vref is not specified, 1.3Vso at the maximum certified landing weight. Vref, Vso, and the maximum certified landing weight are those values as established for the aircraft by the certification authority of the country of registry. A pilot must maneuver the aircraft within the circling approach protected area (see FIG 5−4−29) to achieve the obstacle and terrain clearances provided by procedure design criteria.

b. In addition to pilot techniques for maneuvering, one acceptable method to reduce the risk of flying out of the circling approach protected area is to use either the minima corresponding to the category determined during certification or minima associated with a higher category. Helicopters may use Category A minima. If it is necessary to operate at a speed in excess of the upper limit of the speed range for an aircraft’s category, the minimums for the higher category should be used. This may occur with certain aircraft types operating in heavy/gusty wind, icing, or non−normal conditions. For example, an airplane which fits into Category B, but is circling to land at a speed of 145 knots, should use the approach Category D minimums. As an additional example, a Category A airplane (or helicopter) which is operating at 130 knots on a straight−in approach should use the approach Category C minimums.

c. A pilot who chooses an alternative method when it is necessary to maneuver at a speed that exceeds the category speed limit (for example, where higher category minimums are not published) should consider the following factors that can significantly affect the actual ground track flown:

1. Bank angle. For example, at 165 knots ground speed, the radius of turn increases from 4,194 feet using 30 degrees of bank to 6,654 feet when using 20 degrees of bank. When using a shallower bank angle, it may be necessary to modify the flight path or indicated airspeed to remain within the circling approach protected area. Pilots should be aware that excessive bank angle can lead to a loss of aircraft control.

2. Indicated airspeed. Procedure design criteria typically utilize the highest speed for a particular category. If a pilot chooses to operate at a higher speed, other factors should be modified to ensure that the aircraft remains within the circling approach protected area.

3. Wind speed and direction. For example, it is not uncommon to maneuver the aircraft to a downwind leg where the ground speed will be considerably higher than the indicated airspeed. Pilots must carefully plan the initiation of all turns to ensure that the aircraft remains within the circling approach protected area.

4. Pilot technique. Pilots frequently have many options with regard to flight path when conducting circling approaches. Sound planning and judgment are vital to proper execution. The lateral and vertical path to be flown should be carefully considered using current weather and terrain information to ensure that the aircraft remains within the circling approach protected area.

AIM Updates 28 February 2019

FAA has published changes to the AIM effective 28 February 2019. You can download the PDF that lists the changes and includes all of the updated text. The updates of most interest to general aviation pilots focus on the following sections.

1−2−1. General

1−2−2. Required Navigation Performance (RNP)

5−2−9. Instrument Departure Procedures (DP) − Obstacle Departure Procedures (ODP), Standard Instrument Departures (SID), and Diverse Vector Areas (DVA)

5−4−1. Standard Terminal Arrival (STAR) Procedures

5−4−5. Instrument Approach Procedure (IAP) Charts

There was not enough adequate information concerning Performance−Based Navigation (PBN) and Advanced Required Navigational Performance (A−RNP) available to flight crews and operators in the AIM. This expansion in the description and advantages of these navigation specifications (NavSpecs) will provide better guidance as to what A−RNP is, how it will be applied, and its applicability in the PBN NAS. Additional information is being added to better clarify NavSpecs, RNP, and PBN understanding in AIM Chapter 1. Associated paragraph changes are necessary to ensure harmonization between all the paragraphs in the AIM.

5−1−8. Flight Plan (FAA Form 7233−1) − Domestic IFR Flights

This change updates pilot guidance to incorporate air traffic control (ATC) procedures for GNSS−equipped aircraft operating on area navigation (RNAV) air traffic service (ATS) routes and on random point−to−point and random impromptu routes in airspace in which ATC procedures are applied, excluding oceanic airspace. This change also incorporates the use of the term GNSS in place of RNAV for space−based positioning and navigation systems.

Area Navigation, RNAV, RNP, and A-RNP

AIM 1−2−1 includes new explanations of RNAV and performance-based navigation (PBN). Before reviewing the new information in this section of the AIM, it’s important to remember that AIM 1−1−17. Global Positioning System (GPS) notes that:

(5) Aircraft navigating by IFR−approved GPS are considered to be performance−based navigation (PBN) aircraft and have special equipment suffixes.

The specific capabilities of the GNSS (GPS) in your panel are described in the AFM Supplement and operating handbooks for the equipment (as updated when new system software is installed). You can find more information about RNAV and RNP specs in AC 90-105 and at RNP Procedures and Typical Part 91 Pilots here at BruceAir.

With that in mind, it’s important to understand that if your airplane is equipped with, say, a Garmin GNS530W/GNS530W or GTN 750/650 (with an appropriate AFM supplement), you can fly RNAV SIDs and STARs based on RNP-1 criteria. And you can also fly en route segments that require RNP-2 accuracy. No special authorization is required at these RNP levels.

For more information about RNP levels, see “Required Navigation Performance” in the Instrument Procedures Handbook (2-34).

Figure 9-41 in the Instrument Flying Handbook is also helpful.

Update to AIM 1−2−1. General

Here’s the new language in AIM 1-2-1, the introduction to PBN. Note that RAIM, used to validate the accuracy and reliablity of non-WAAS GPS for use under IFR, qualifies as “onboard performance monitoring and alerting capability” for purposes of PBN and basic RNP. WAAS, which incorporates its own performance and accuracy checking system, also provides onboard performance monitoring and alerting capability.

a. Introduction to PBN. As air travel has evolved, methods of navigation have improved to give operators more flexibility. PBN exists under the umbrella of area navigation (RNAV). The term RNAV in this context, as in procedure titles, just means “area navigation,” regardless of the equipment capability of the aircraft…Many operators have upgraded their systems to obtain the benefits of PBN. Within PBN there are two main categories of navigation methods or specifications: area navigation (RNAV) and required navigation performance (RNP). In this context, the term RNAV x means a specific navigation specification with a specified lateral accuracy value. For an aircraft to meet the requirements of PBN, a specified RNAV or RNP accuracy must be met 95 percent of the flight time. RNP is a PBN system that includes onboard performance monitoring and alerting capability (for example, Receiver Autonomous Integrity Monitoring (RAIM)). PBN also introduces the concept of navigation specifications (NavSpecs) which are a set of aircraft and aircrew requirements needed to support a navigation application within a defined airspace concept. For both RNP and RNAV NavSpecs, the numerical designation refers to the lateral navigation accuracy in nautical miles which is expected to be achieved at least 95 percent of the flight time by the population of aircraft operating within the airspace, route, or procedure. This information is detailed in International Civil Aviation Organization’s (ICAO) Doc 9613, Performance−based Navigation (PBN) Manual and the latest FAA AC 90−105, Approval Guidance for RNP Operations and Barometric Vertical Navigation in the U.S. National Airspace System and in Remote and Oceanic Airspace.

Required Navigation Performance (RNP)

Here’s the new language in AIM 1−2−2.

a. General. While both RNAV navigation specifications (NavSpecs) and RNP NavSpecs contain specific performance requirements, RNP is RNAV with the added requirement for onboard performance monitoring and alerting (OBPMA). RNP is also a statement of navigation performance necessary for operation within a defined airspace. A critical component of RNP is the ability of the aircraft navigation system to monitor its achieved navigation performance, and to identify for the pilot whether the operational requirement is, or is not, being met during an operation. OBPMA capability therefore allows a lessened reliance on air traffic control intervention and/or procedural separation to achieve the overall safety of the operation. RNP capability of the aircraft is a major component in determining the separation criteria to ensure that the overall containment of the operation is met. The RNP capability of an aircraft will vary depending upon the aircraft equipment and the navigation infrastructure. For example, an aircraft may be eligible for RNP 1, but may not be capable of RNP 1 operations due to limited NAVAID coverage or avionics failure. The Aircraft Flight Manual (AFM) or avionics documents for your aircraft should specifically state the aircraft’s RNP eligibilities. Contact the manufacturer of the avionics or the aircraft if this information is missing or incomplete. NavSpecs should be considered different from one another, not “better” or “worse” based on the described lateral navigation accuracy. It is this concept that requires each NavSpec eligbility to be listed separately in the avionics documents or AFM. For example, RNP 1 is different from RNAV 1, and an RNP 1 eligibility does NOT mean automatic RNP 2 or RNAV 1 eligibility. As a safeguard, the FAA requires that aircraft navigation databases hold only those procedures that the aircraft maintains eligibility for. If you look for a specific instrument procedure in your aircraft’s navigation database and cannot find it, it’s likely that procedure contains PBN elements your aircraft is ineligible for or cannot compute and fly. Further, optional capabilities such as Radius−to−fix (RF) turns or scalability should be described in the AFM or avionics documents. Use the capabilities of your avionics suite to verify the appropriate waypoint and track data after loading the procedure from your database.

RNP Approach (RNP APCH) and RNP AR APCH

The new language in this section of the AIM intends to address confusion about RNP and approaches. Unfortunately, because FAA continues to use RNAV in procedure titles, many pilots remain puzzled about the differences between the terms RNAV, RNP APCH, and RNP AR APCH. As this part of the revised AIM 1−2−2 notes:

In the U.S., RNP APCH procedures are titled RNAV (GPS) and offer several lines of minima to accommodate varying levels of aircraft equipage: either lateral navigation (LNAV), LNAV/vertical navigation (LNAV/VNAV), Localizer Performance with Vertical Guidance (LPV), and Localizer Performance (LP).

A helpful guide from FAA, Required Navigation Performance (RNP) Approaches (APCH), succinctly explains the different lines of minimums and provides helpful links to ACs, the AIM, and other sources.

Here’s the detailed language in the updated AIM:

(1) RNP Approach (RNP APCH). In the U.S., RNP APCH procedures are titled RNAV (GPS) and offer several lines of minima to accommodate varying levels of aircraft equipage: either lateral navigation (LNAV), LNAV/vertical navigation (LNAV/VNAV), Localizer Performance with Vertical Guidance (LPV), and Localizer Performance (LP). GPS with or without Space−Based Augmentation System (SBAS) (for example, WAAS) can provide the lateral information to support LNAV minima. LNAV/VNAV incorporates LNAV lateral with vertical path guidance for systems and operators capable of either barometric or SBAS vertical. Pilots are required to use SBAS to fly to the LPV or LP minima. RF turn capability is optional in RNP APCH eligibility. This means that your aircraft may be eligible for RNP APCH operations, but you may not fly an RF turn unless RF turns are also specifically listed as a feature of your avionics suite. GBAS Landing System (GLS) procedures are also constructed using RNP APCH NavSpecs and provide precision approach capability. RNP APCH has a lateral accuracy value of 1 in the terminal and missed approach segments and essentially scales to RNP 0.3 (or 40 meters with SBAS) in the final approach. (See Paragraph 5−4−18, RNP AR Instrument Approach Procedures.)

(2) RNP Authorization Required Approach (RNP AR APCH). In the U.S., RNP AR APCH procedures are titled RNAV (RNP). These approaches have stringent equipage and pilot training standards and require special FAA authorization to fly. Scalability and RF turn capabilities are mandatory in RNP AR APCH eligibility. RNP AR APCH vertical navigation performance is based upon barometric VNAV or SBAS. RNP AR is intended to provide specific benefits at specific locations. It is not intended for every operator or aircraft. RNP AR capability requires specific aircraft performance, design, operational processes, training, and specific procedure design criteria to achieve the required target level of safety. RNP AR APCH has lateral accuracy values that can range below 1 in the terminal and missed approach segments and essentially scale to RNP 0.3 or lower in the final approach. Before conducting these procedures, operators should refer to the latest AC 90−101, Approval Guidance for RNP Procedures with AR. (See paragraph 5−4−18.)

Advanced RNP (A−RNP)

If you’re keeping up so far, the new language in AIM 1−2−2 provides more details about Advanced RNP (A-RNP), not to be confused with RNP (AR). Some features of A-RNP, such as the ability to fly some RF legs, are available if you have the current system software installed in a Garmin GTN navigator. For more information, see Garmin GTN Avionics and RF Legs here at BruceAir.

(4) Advanced RNP (A−RNP). Advanced RNP is a NavSpec with a minimum set of mandatory functions enabled in the aircraft’s avionics suite. In the U.S., these minimum functions include capability to calculate and perform RF turns, scalable RNP, and parallel offset flight path generation. Higher continuity (such as dual systems) may be required for certain oceanic and remote continental airspace. Other “advanced” options for use in the en route environment (such as fixed radius transitions and Time of Arrival Control) are optional in the U.S. Typically, an aircraft eligible for A−RNP will also be eligible for operations comprising: RNP APCH, RNP/RNAV 1, RNP/RNAV 2, RNP 4, and RNP/RNAV 10. A−RNP allows for scalable RNP lateral navigation values (either 1.0 or 0.3) in the terminal environment. Use of these reduced lateral accuracies will normally require use of the aircraft’s autopilot and/or flight director. See the latest AC 90−105 for more information on A−RNP, including NavSpec bundling options, eligibility determinations, and operations approvals.

NOTE−
A−RNP eligible aircraft are NOT automatically eligible for RNP AR APCH or RNP AR DP operations, as RNP AR eligibility requires a separate determination process and special FAA authorization.

(5) RNP 1. RNP 1 requires a lateral accuracy value of 1 for arrival and departure in the terminal area, and the initial and intermediate approach phase when used on conventional procedures with PBN segments (for example, an ILS with a PBN feeder, IAF, or missed approach). RF turn capability is optional in RNP 1 eligibility. This means that your aircraft may be eligible for RNP 1 operations, but you may not fly an RF turn unless RF turns are also specifically listed as a feature of your avionics suite.

(6) RNP 2. RNP 2 will apply to both domestic and oceanic/remote operations with a lateral accuracy value of 2.

PBN Requirement Boxes

AIM 1−2−2 now includes language about equipment requirement boxes on procedures that include PBN elements. For more information, see New Equipment Required Notes and An ILS that Requires GPS here at BruceAir.

(c) Depiction of PBN Requirements. In the U.S., PBN requirements like Lateral Accuracy Values or NavSpecs applicable to a procedure will be depicted on affected charts and procedures. In the U.S., a specific procedure’s Performance−Based Navigation (PBN) requirements will be prominently displayed in separate, standardized notes boxes. For procedures with PBN elements, the “PBN box” will contain the procedure’s NavSpec(s); and, if required: specific sensors or infrastructure needed for the navigation solution, any additional or advanced functional requirements, the minimum RNP value, and any amplifying remarks. Items listed in this PBN box are REQUIRED to fly the procedure’s PBN elements. For example, an ILS with an RNAV missed approach would require a specific capability to fly the missed approach portion of the procedure. That required capability will be listed in the PBN box. The separate Equipment Requirements box will list ground−based equipment and/or airport specific requirements. On procedures with both PBN elements and ground−based equipment requirements, the PBN requirements box will be listed first.

Flying and Flying Direct with GNSS (GPS)

AIM 5−1−8 now provides more details for pilots flying under IFR with GNSS about filing direct routes or requesting direct clearances from ATC. The new text focuses on direct routes that include legs that exceed navaid service volumes and provides more details about filing direct routes.

In particular, if you plan a direct flight you should:

• File and fly point-to-point using published waypoint names (airports, navaids, intersections, and RNAV waypoints) to define the route of flight.
• Include at least one named waypoint within each ARTCC through which the flight will pass.

4. Increasing use of self−contained airborne navigational systems which do not rely on the VOR/VORTAC/TACAN system has resulted in pilot requests for direct routes that exceed NAVAID service volume limits. With the exception of GNSS−equipped aircraft, these direct route requests will be approved only in a radar environment, with approval based on pilot responsibility for navigation on the authorized direct route. Radar flight following will be provided by ATC for ATC purposes. For GNSS−equipped aircraft, ATC may approve a direct route that exceeds ground based NAVAID service volume limits; however, in a non−radar environment, the routing must be “point−to−point,” defined as navigation from a published point to a published point, and navigational assistance will not be available. (See subparagraph 5−1−8d below.)

5. At times, ATC will initiate a direct route in a radar environment that exceeds NAVAID service volume limits. In such cases ATC will provide radar monitoring and navigational assistance as necessary. For GNSS−equipped aircraft, if the route is point−to−point, radar monitoring and navigational assistance is not required. (See subparagraph 5−1−8d below.)

d. Area Navigation (RNAV)/Global Navigation Satellite System (GNSS) 1. Except for GNSS−equipped aircraft, random impromptu routes can only be approved in a radar environment. A random impromptu route is a direct course initiated by ATC or requested by the pilot during flight. Aircraft are cleared from their present position to a NAVAID, waypoint, fix, or airport. Factors that will be considered by ATC in approving random impromptu routes include the capability to provide radar monitoring and compatibility with traffic volume and flow. ATC will radar monitor each flight; however, navigation on the random impromptu route is the responsibility of the pilot. GNSS−equipped aircraft are allowed to operate in a non−radar environment when the aircraft is cleared via, or is reported to be established on, a point−to−point route. The points must be published NAVAIDs, waypoints, fixes, or airports recallable from the aircraft’s database. The distance between the points cannot exceed 500 miles and navigational assistance will not be provided…

(f) File a minimum of one route description waypoint for each ARTCC through whose area the random route will be flown.

Use of IFR GPS on Conventional Approaches

FAA has published an update to the AIM, effective 26 May 2016, and it includes a big change if you have an IFR-approved GPS [i.e., a “suitable navigation system” as defined in AC 20-138 and AIM 1-2-3 (b).]

Now, if you fly a conventional approach based on a VOR or NDB (but not a localizer), you can fly the procedure entirely with the GPS, provided you can monitor (using a separate CDI or a bearing pointer) the VOR or NDB facility specified for the approach.

For more information about the use of GPS along the final approach course of a VOR or NDB approach, see Use of GPS on Conventional Approaches (Update)

If you prefer to switch the CDI to “green needles,” see Setting the CDI on a Conventional Approach (The “Kill Switch”) here at BruceAir.

The new language is in section 1−2−3. Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes.

The summary of changes to this AIM update notes that:

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.

The new text in the AIM is in paragraph 5 of AIM 1-2-3:

5. Use of a suitable RNAV system as a means to navigate on the final approach segment of an instrument approach procedure based on a VOR, TACAN or NDB signal, is allowable. The underlying NAVAID must be operational and the NAVAID monitored for final segment course alignment.

This change is the result of a discussion at the Aeronautical Charting Forum in 2014.

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.

“The AIM is not Regulatory”

“The AIM is not regulatory” is an often-heard refrain among pilots and flight instructors. And technically, of course, that’s correct.

From the introduction to the Aeronautical Information Manual:

This publication, while not regulatory, provides information which reflects examples of operating techniques and procedures which may be requirements in other federal publications or regulations. It is made available solely to assist pilots in executing their responsibilities required by other publications.

However, when aviators say, “The AIM is not regulatory,” they generally seem to argue that the procedures and guidance in the AIM (and related FAA publications, such as advisory circulars), are suggestions that pilots, at their discretion, may adopt or ignore.

For a detailed discussion of the AIM and other advisory documents published by the FAA, see AIM Is Non-Regulatory, an article by Mark Kolber, an aviation attorney, published at AVweb in 2020.

I’m certainly not an attorney. But I offer this background on the authority of the AIM from AOPA Flight Training. That Legal Briefing (written by an attorney) notes in part:

…In older NTSB cases, both the FAA and the airman have used sections of the AIM to assess whether an airman’s conduct was in violation of the FAR or not. For example, an airman attempted to justify a right turn during his approach to the airport as part of a “straight-in” approach as set forth in the AIM. But the case did not rely on the new statutory language of deference.

In a more recent NTSB case involving a pilot’s misunderstood readback of an ATC instruction that ATC failed to correct and which resulted in an altitude deviation, the NTSB found that because the pilot acted as best he could to understand and comply with the ATC instruction, he could not be held responsible for the deviation. But the FAA appealed the NTSB’s decision to the Court of Appeals, which held that the NTSB must defer to the FAA’s interpretation that the pilot is responsible for accurately understanding and complying with an ATC instruction absent an equipment malfunction or an emergency. The court sent the case back to the NTSB, which then had to find the pilot in violation.

These cases suggest that you may be held responsible for complying with FAA guidance. Or, you could find yourself defending against an interpretation of a regulation that the FAA announces, for the first time, in response to your conduct. In any event, while it may not be a regulatory requirement to comply with any FAA written guidance, you can certainly expect any such guidance to be used in a FAA enforcement case. And, you can expect that the NTSB will be bound to defer to the FAA’s interpretation of your conduct as a violation of the FAR, unless you are prepared to show the FAA’s interpretation to be arbitrary, capricious, or illegal.

So, while it’s true that guidance in the AIM is, technically, just that–guidance–the information in the AIM, ACs, etc. isn’t just the FAA’s suggestions or a matter of procedure. If you choose to invent techniques for complying with the letter of the regulations, you may find the “AIM isn’t regulatory” a weak defense.

Updates to AIM, Effective April 3, 2014

The FAA has published updates to the Aeronautical Information Manual, effective April 3, 2014. You can download the PDF version of the new AIM here. The Explanation of Changes section describes the updates to the AIM. The online version of the new edition will be available on the FAA website on the effective date, here.

Key changes for general aviation pilots include:

1−1−3. VHF Omni−directional Range (VOR)

The only positive method of identifying a VOR is by its Morse Code identification or by the recorded
automatic voice identification which is always indicated by use of the word “VOR” following the
range’s name…Some VOR receivers are capable of identifying the VOR and will display the identifier of the VOR if it has successfully done so. However, it is still the pilot’s responsibility to verify the identity of the VOR by conventional methods.

1−1−18. Global Positioning System (GPS)—j. 2. Computer Navigation Fix (CNF)

A Computer Navigation Fix (CNF) is also a point defined by a latitude/longitude coordinate and is required to support area navigation (RNAV) system operations. The GPS receiver uses CNFs in conjunction with waypoints to navigate from point to point. However, CNFs are not recognized by Air Traffic Control (ATC). ATC does not maintain CNFs in their database and they do not use CNFs for any air traffic control purpose. CNFs may or may not be charted on FAA aeronautical navigation products, are listed in the chart legends, and are for advisory purposes only. Pilots are not to use CNFs for point to point navigation (proceed direct), filing a flight plan, or in aircraft/ATC communications. CNFs that do appear on aeronautical charts allow pilots increased situational awareness by identifying points in the aircraft database route of flight with points on the aeronautical chart. CNFs are random five−letter identifiers, not pronounceable like waypoints, and placed in parenthesis. Eventually, all CNFs will begin with the letters “CF” followed by three consonants (for example, CFWBG). This five−letter identifier will be found next to an “x” on enroute charts and possibly on an approach chart. On instrument approach procedures(charts) in the terminal procedures publication, CNFs may represent unnamed DME fixes, beginning and ending points of DME arcs, and sensor (ground−based signal i.e., VOR, NDB ILS) final approach fixes on GPS overlay approaches. These CNFs provide the GPS with points on the procedure that allow the overlay approach to mirror the ground−based sensor approach. These points should only be used by the GPS system for navigation and should not be used by pilots for any other purpose on the approach. The CNF concept has not been adopted or recognized by the International Civil Aviation Organization (ICAO).

Here are examples of CNFs as shown on the plan view of the ILS Y RWY 27 at KYKM:

5−4−1. j. Waypoints

1. GPS receivers navigate from one defined point to another retrieved from the aircraft’s on board navigational database. These points are waypoints (5-letter pronounceable name), existing VHF intersections, DME fixes with 5-letter pronounceable names and 3-letter NAVAID IDs. Each waypoint is a geographical location defined by a latitude/longitude geographic coordinate. These 5-letter waypoints, VHF intersections, 5-letter pronounceable DME fixes, and 3-letter NAVAID IDs are published on various FAA aeronautical navigation products (IFR Enroute Charts, VFR Charts, Terminal Procedures Publications, etc.)…

3. GPS approaches use fly−over and fly−by waypoints to join route segments on an approach. Fly−by waypoints connect the two segments by allowing the aircraft to turn prior to the current waypoint in order to roll out on course to the next waypoint. This is known as turn anticipation and is compensated for in the airspace and terrain clearances. The MAWP and the missed approach
holding waypoint (MAHWP) are normally the only two waypoints on the approach that are not fly−by waypoints. Fly−over waypoints are used when the aircraft must overfly the waypoint prior to starting a turn to the new course. The symbol for a fly-over waypoint is a circled waypoint. Some waypoints may have dual use; for example, as a fly-by waypoint when used as an IF for a NoPT route and as a fly-over waypoint when the same waypoint is also used as an IAF/IF hold-in-lieu of PT. When this occurs, the less restrictive (fly-by) symbology will be charted. Overlay approach charts and some early stand-alone GPS approach charts may not reflect this convention.

4. Unnamed waypoints for each airport will be uniquely identified in the database. Although the identifier may be used at different airports (for example, RW36 will be the identifier at each airport with a runway 36), the actual point, at each airport, is defined by a specific latitude/longitude coordinate.

5. The runway threshold waypoint, normally the MAWP, may have a five−letter identifier (for example, SNEEZ) or be coded as RW## (for example, RW36, RW36L). MAWPs located at the runway threshold are being changed to the RW## identifier, while MAWPs not located at the threshold will have a five− letter identifier. This may cause the approach chart to differ from the aircraft database until all changes are complete. The runway threshold waypoint is also used as the center of the Minimum Safe Altitude (MSA) on most GPS approaches.

5−4−1. l. Impact of Magnetic Variation on RNAV Systems

1. Differences may exist between charted magnetic courses on ground-based navigational aid
(NAVAID) instrument flight procedures (IFP), area navigation (RNAV) procedures, and RNAV systems on enroute charts, approach charts, and Standard Instrument Departure/Standard Terminal Arrival (SID/STAR) charts. These differences are due to the magnetic variance used to calculate the magnetic course. Every leg of an instrument procedure is first computed along a desired ground track with reference to true north. A magnetic variation correction is then applied to the true course in order to calculate a magnetic course for publication. The type of procedure will determine what magnetic variation value is added to the true course. A ground-based NAVAID IFP applies the facility magnetic variation of record to the true course to get the charted magnetic course. Magnetic courses on RNAV procedures are calculated two different ways. SID/STAR procedures use the airport magnetic variation of record, while IFR enroute charts use magnetic reference bearing. RNAV systems make a correction to true north by adding a magnetic variation calculated with an algorithm based on aircraft position, or by adding the magnetic variation coded in their navigational database. This may result in the RNAV system and the procedure designer using a different magnetic variation, which causes the magnetic course displayed by the RNAV system and the magnetic course charted on the IFP plate to be different. It is important to understand, however, that RNAV systems (with the exception of VOR/DME RNAV equipment) navigate by reference to true north and display magnetic course only for pilot reference. As such, a properly functioning RNAV system, containing a current and accurate navigational database, should still fly the correct ground track for any loaded instrument procedure, despite any differences in magnetic course that may be attributed to magnetic variation application. Should significant differences between the approach chart and the RNAV system avionics’ application of the navigation database arise, the published approach chart, supplemented by NOTAMs, holds precedence.

2. The course into a waypoint may not always be 180 degrees different from the course leaving the previous waypoint, due to the RNAV system avionics’ computation of geodesic paths, distance between waypoints and differences in magnetic variation application. Variations in distances may also occur since RNAV system distance−to−waypoint values are along−track distances (ATD) computed to the next waypoint and the DME values published on underlying procedures are slant−range distances measured to the station. This difference increases with aircraft altitude and proximity to the NAVAID.

5−3−4. Airways and Route Systems

(b) Unpublished RNAV routes are direct routes, based on area navigation capability, between waypoints defined in terms of latitude/longitude coordinates, degree−distance fixes, or offsets from established routes/airways at a specified distance and direction. Radar monitoring by ATC is required on all unpublished RNAV routes, except for GNSS−equipped aircraft cleared via filed published waypoints recallable from the aircraft’s navigation database.

5−4−1. Standard Terminal Arrival(STAR), Area Navigation (RNAV) STAR, and Flight Management System Procedures (FMSP) for Arrivals

This change incorporates updated guidance on resumption of published altitude and speed restrictions, guidance on what is expected of aircrews when issued a “climb via” clearance, and clarifies the expectation that pilots will advise the receiving controller of the altitude being vacated and the altitude they are climbing to when changing frequencies.

For all the details, see this section in the update to the AIM.

i. 5−4−5. Instrument Approach Procedure Charts

This change updates guidance to reflect the fact that the initial approach fix (IAF) waypoint is not an IAF, but an intermediate fix (IF). This change also updates guidance on descent below the minimum descent altitude (MDA).

For all the details, see this section in the update to the AIM.

7−1−11. Flight Information Services (FIS)

This change updates information and guidance to modify outdated information, reflect policy and terminology changes, and address changing technologies.

For all the details, see this section in the update to the AIM.

7−1−14. ATC Inflight Weather Avoidance Assistance

This change was added to expand the meaning of the phrase “when able” when used in conjunction with a clearance to deviate around weather. The clearance to deviate is clarified to allow maneuvering within the lateral limits of the deviation clearance.

For all the details, see this section in the update to the AIM.

Changes in February 9 2012 Edition of the AIM

The FAA has released the basic version of the February 9 2012 edition of the Aeronautical Information Manual. (You can download the PDF version of the new edition here; the web version presumably will appear on the official publication date.)

According to the Explanation of Changes in the new edition, the key revisions include:

c. 4−1−20. Transponder Operation

This change explains that transponders should be turned on prior to moving on the airport surface – as opposed to “as soon as possible.”

d. 4−3−23. Use of Aircraft Lights

This change aligns the AIM guidance on the use of aircraft lights with AC 120-74A.

e. 4−4−3. Clearance Items

This change adds language to inform pilots of what to expect from controllers concerning clearance limits and associated phraseology.

h. 5−5−16. RNAV and RNP Operations

This change provides guidance for the definition of “established” for RNAV and RNP operations. [For a more detailed discussion of this update, see this post here at BruceAir.]

k. 7−1−21. PIREPS Relating to Airframe Icing

This change addresses the change to the icing intensity definitions, quantifiable icing rates, and an updated replacement for current terminology. It would also help satisfy NTSB Safety recommendations A-96-51 and -060.*

*(A-96-51)

Recommendation:
TO THE FEDERAL AVIATION ADMINISTRATION: Revise the existing aircraft icing intensity reporting criteria (as defined in the Aeronautical Info Manual (AIM) and other FAA literature) by including nomenclature that is related to specific types of aircraft, and that is in logical agreement with existing Federal Aviation Regulation (FARs).

Updated Definition of “Established” On Course

The basic definition of established, from the Pilot/Controller Glossary, is:

ESTABLISHED−To be stable or fixed on a route, route segment, altitude, heading, etc.

The ICAO definition, which appeared in an appendix of a former edition of the Instrument Procedures Handbook, included the following language:

…an aircraft is considered established when it is “within half full scale deflection for the ILS and VOR; or within ±5 degrees of the required bearing for the NDB.”

A more detailed definition of established in the AIM (see below) focuses on RNAV and RNP operations. (For most general aviation pilots, that means GPS/WAAS procedures.) It’s the result of a long discussion among members of the FAA Aeronautical Charting Forum–Instrument Procedures Group. The topic (item 96-01-166) began as a discussion of “on course” but eventually narrowed its focus to “Determining Descent Point of Flyby Waypoints,” which is another way of stating the primary issue: When is it OK to descend (consistent, of course, with your last clearance from ATC) as you join the next segment of an approach or transition?

AIM 5-5-16

11. Definition of “established” for RNAV and RNP operations. An aircraft is considered to be established on-course during RNAV and RNP operations anytime it is within 1 times the required accuracy for the segment being flown. For example, while operating on a Q-Route (RNAV 2), the aircraft is considered to be established on-course when it is within 2 nm of the course centerline.

NOTE: Pilots must be aware of how their navigation system operates, along with any AFM limitations, and confirm that the aircraft’s lateral deviation display (or map display if being used as an allowed alternate means) is suitable for the accuracy of the segment being flown. Automatic scaling and alerting changes are appropriate for some operations. For example, TSO-C129 systems change within 30 miles of destination and within 2 miles of FAF to support approach operations. For some navigation systems and operations, manual selection of scaling will be necessary.

(a) Pilots flying FMS equipped aircraft with barometric vertical navigation (Baro-VNAV) may descend when the aircraft is established on-course following FMS leg transition to the next segment. Leg transition normally occurs at the turn bisector for a fly-by waypoint (reference paragraph 1-2-1 for more on waypoints). When using full automation, pilots should monitor the aircraft to ensure the aircraft is turning at appropriate lead times and descending once established on-course.

(b) Pilots flying TSO-C129 navigation system equipped aircraft [i.e., non-WAAS GPS] without full automation should use normal lead points to begin the turn. Pilots may descend when established on-course on the next segment of the approach.

The key phrase is “within 1 times the required accuracy for the segment being flown.” To know that, you must understand how your GPS box works. For example, the  Pilot’s Guide and Reference for the Garmin GNS530W notes that:

…The [default] CDI scale is set to 2.0 NM during the “en route” phase of flight. Within 31 NM of your destination airport, the CDI scale gradually ramps down to 1.0 NM (terminal area). Likewise, when leaving your departure airport the CDI scale is set to 1.0 NM and gradually ramps up to 2 NM beyond 30 NM (from the departure airport). During approach operations the CDI scale gradually transitions down to an angular CDI scale. At 2.0 NM of the final approach fix (FAF), CDI scaling is tightened from 1.0 to the angular full scale deflection (typically the angular full-scale deflection is 2.0°, but will be as defined for the approach). (p. 182)

Those scales are consistent with TSO C146a standards for WAAS-based avionics, which, for example, tighten the default CDI scale for en route operations from 5 nm (1 nm/dot) to 2.0 nm. On units like the Garmin GNS530/430 series that show 5 dots either side of the center of the built-in CDI, that scale equates to 0.4 nm/dot. (For a good discussion of this topic, see “Changing CDI Course Sensitivity” and “Enroute CDI Sensitivity with WAAS” in Chapter 13 of Rod Machado’s Instrument Pilot’s Handbook.)

If you’re curious about the various RNAV levels associated with different phases of flight and types of procedures, and the capabilities of various avionics (subject to any limitations in your AFM), see:

• AIM 1-2-3. Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes
• AC 90-100A, U.S. Terminal and En Route Area Navigation (RNAV) Operations
• AC 90-100A Compliance Table (PDF)

*To keep up with substantive changes to the AIM in each new edition, see the Explanation of Changes sections published at the AIM home page. You can find PDF versions of the AIM and updates here.

Clarifications in the 25 August 2011 Update to the AIM

FAA has published the 25 August 2011 update to the Aeronautical Information Manual (AIM). This set of changes includes a couple of clarifications worth calling out for IFR pilots:

• 1-2-3. Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes
• 5-4-6. Approach Clearance

The change in section 1-2-3 reflects the content of a new advisory circular, AC 90-108 Use of Suitable Area Navigation (RNAV) Systems on Conventional Routes and Procedures (PDF), published on 3 March 2011. This AC describes in detail how you can use an IFR-approved GPS (subject to any limitations in the supplements to your AFM) as a substitute for courses and fixes defined by VOR, DME, LOM, and NDB navaids. It also describes limitations on using both basic and WAAS GPS equipment, in particular when flying the final approach course on an instrument approach.

The update to 5-4-6 clarifies ATC approach clearances, in particular:

e. The following applies to aircraft on radar vectors and/or cleared “direct to” in conjunction with an approach clearance:
1. Maintain the last altitude assigned by ATC until the aircraft is established on a published segment of a transition route, or approach procedure segment, or other published route, for which a lower altitude is published on the chart. If already on an established route, or approach or arrival segment, you may descend to whatever minimum altitude is listed for that route or segment.
2. Continue on the vector heading until intercepting the next published ground track applicable to the approach clearance.
3. Once reaching the final approach fix via the published segments, the pilot may continue on approach to a landing.
4. If proceeding to an IAF with a published course reversal (procedure turn or hold-in-lieu of PT pattern), except when cleared for a straight in approach by ATC, the pilot must execute the procedure turn/hold-in-lieu of PT, and complete the approach.
5. If cleared to an IAF/IF via a NoPT route, or no procedure turn/hold-in-lieu of PT is published, continue with the published approach.
6. In addition to the above, RNAV aircraft may be issued a clearance direct to an Intermediate Fix followed by a straight-in approach clearance.