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(b) Expected speed changes.
(c) Appropriate engine failure and shutdown (feathering if applicable) provisions, if the approach was assumed to be initiated with all engines operative.
(d) Any lateral differences of the missed approach flight path from the corresponding takeoff flight path, and
(e) Suitable balked landing obstacle clearance, until reaching instrument approach missed approach or enroute procedurally protected airspace.
(f) Any performance or gradient loss during turning flight, if necessary to follow a flight path that is not over the runway or is not aligned with the runway after the balked landing transition.
(g) Any relevant related situations such as if the aircraft cannot dump fuel and may need to make an emergency return landing above maximum landing weight immediately after takeoff.
(h) Methods used for takeoff analysis, such as “Overspeed V2”, “engine-out maximum angle climb,” or other such techniques may be used if determined to be appropriate by the operator or aircraft manufacturer.
(i) Applicable flight guidance system operational procedures used. Information about any techniques required to achieve the specified performance should be available to the flightcrew (e.g., appropriate mode selection).
(j) Operators may make obstacle clearance assumptions similar to those applied to corresponding takeoff flight paths (e.g., Section 121.189) in the determination of net vertical flight path clearance or lateral track definition or lateral track obstacle clearance within an airport boundary or beyond an airport boundary, until the point at which cruise or other obstacle clearance requirements apply.
c. Go-Around Assessment Conditions.
(1) Assessments may assume the following initial conditions:
(a) A “balked landing” starts at the end of the Touchdown Zone (TDZ).
(b) An engine failure occurs at the initiation of the balked landing, from an all-engine configuration.
(c) Balked landing initiation speed > VREF or VGA (as applicable).
(d) Balked Landing initiation height is equal to the specified elevation of the TDZ.
(e) Balked landing initiation configuration is normal landing flaps, gear down.
(f) At the initiation of the maneuver, all engines are at least in a spooled configuration.
(2) A TDZ typically is considered to be the first 3000 ft. of a designated landing runway. When appropriate for the purposes of this provision, Operators may propose to use a different designation for a touchdown zone. For example, alternate consideration of a TDZ may be appropriate for runways that:
(a) Are less than 6000 ft. in length and which do not have standard TDZ markings;
(b) Short runways requiring special aircraft performance information or procedures for landing;
(c) Runways for STOL aircraft; or
(d) Runway where markings or lighting dictate that a different TDZ designation would be more appropriate.
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d. “One Way” Airports, “Commit Point,” or Other Special Situations.
(1) Where obstacle clearance is determined by the operator to be critical such as for:
(a) “One-way in,” “opposite way out” airports in mountainous terrain, or
(b) Runways at which a landing is to be planned or attempted, but at a weight which is significantly greater than that which would otherwise be allowed for a takeoff, or
(c) Where rejected landing obstacle clearance may not be readily ensured, a review should be completed by the operator to determine whether a contingency go-around path can be appropriately defined or whether a “commit point” or equivalent condition is necessary (e.g., limit weight, speed, or configuration).
(2) A “commit point” or equivalent condition however, should only be used where it is not otherwise possible to identify a safe go-around path. For a “commit point,” the operator should either provide a representative weight, configuration or condition at which obstacle clearance can be ensured after initiation of a balked landing at the TDZ, or identify a path related waypoint, location, altitude, height, or fix, beyond which a go-around should not be attempted. For such determinations, the operator should consider at least the runway elevation, temperature, and appropriate aircraft configurations or configuration changes. If a “commit point” is used, the operator should provide any necessary advisory information to flightcrews to address any events which, while unlikely, could nonetheless occur beyond the designated “commit” point or condition (e.g., unforeseen significant wind shear, unacceptable winds, turbulence, or runway clutter, loss of visual reference, flare extending beyond the touchdown zone, or an obstruction on the runway).
e. TERPS/ICAO PANS-Ops Criteria Not Applicable to “Non-Normal” Operations. TERPS or ICAO PANS-Ops- based criteria do not typically address “special” instrument approach procedures, and they do not and are not intended to address non-normal operations (engine inoperative) or operations below published segments of instrument procedures (e.g., operations below DA(H) or MDA(H)). TERPS or ICAO PANS-Ops based criteria are intended only to address “standard procedures”, normal operations (e.g., all-engine), and published segments of the resulting procedures. Thus, operator assessments of missed approach safety related to operations below published segments of instrument procedures, or operations with non-normal configurations or situations, need not apply provisions of TERPS or ICAO PANS-Ops. Compliance with TERPS or ICAO PANS-Ops based instrument procedure requirements alone may not necessarily ensure missed approach or rejected landing go-around safety. For example, it is recognized that certain types of aircraft (e.g., two-engine aircraft) may operate at weights that achieve gradients with an engine inoperative that may be less than TERPS or PANS-Ops gradients. Go-around from below DA(H) or MDA(H) (e.g., following loss of visual reference, or runway not suitable or available) does not necessarily provide for and does not need to apply TERPS or PANS-Ops criteria or provide for TERPS or PANS-Ops specified levels of obstacle clearance vertically or laterally. Methods related to TERPS or PANS-Ops criteria such as “Collision risk model (CRM)” also are not applicable to assessments other than for TERPS and PANS-Ops related procedure elements.
f. Flight Guidance System (FGS) Use. If not already assessed for the aircraft type during basic type certification, or STC, flight guidance systems (FGS) suitability for the intended procedure(s) should be considered.
The operator may need to assess FGS mode use to ensure compatibility with intended flight path, mode transitions, and gradient determinations. This may be achieved by demonstrating (in simulation or flight) a safe go-around from 100 ft. above the TDZ (HAT) operationally for the specific procedure or, if applicable, for the most critical runway for that operator. For aircraft that have airworthiness demonstrations conducted IAW Appendix 2 or 3 or with AC 120-28D this provision is considered to be addressed.
g. Performance and Obstacle Data Availability and Use.
(1) Information or methods used by the operator for this assessment may be the best available information or methods from applicable aircraft manuals, terrain or obstruction charts, or supplementary information from aircraft or engine manufacturers. In the event that performance, obstacle, or flight path data are not otherwise available to support the necessary analysis from the above sources, the operator may develop, compute, demonstrate,
Par 4 Page 13 or determine such information to the extent necessary to provide for safe obstacle clearance during an engine-out missed approach or an engine-failure following a rejected landing. Data or methods used need not necessarily be from the applicable AFM or from the original aircraft manufacturer. Data or methods may be developed by the operator based on equivalence to other data or methods (e.g., takeoff data) or may be derived by using standard practices applicable to aircraft performance assessment or procedure construction, or may be derived by appropriate aircraft performance or engineering analysis, techniques, or methods.
(2) Information on terrain or obstructions for these assessments may be based on the best available information to the operator or to the agency or entity supporting the operator at the time the information is supplied
(e.g., data available to a performance information contractor, or chart supplier). Best available information may be used, notwithstanding that certain information or data may not necessarily be “approved” by an authority, or may be data that is not necessarily recent (e.g., certain types of charting or obstruction information is not frequently updated). FAA Order 8260.19, paragraph 271 describes how the accuracy of the source data should be considered when constructing the procedure.
h. Related Information. Other paragraphs of this AC contain information related to this paragraph. Paragraph
5.14 describes typical factors to be considered when assessing go-around capability for a particular aircraft and flight guidance system. Paragraph 6 addresses procedures including those used for go-around or rejected landing, and Paragraph 7 addresses Training and Crew Qualification including relevant aspects of missed approach, go-around, or rejected landing.
4.3.2. ILS, GLS, or MLS (xLS) Instrument Approach Operations. ILS, GLS, or MLS (i.e., xLS) operations may be authorized to the lowest applicable DA(H) for the procedure used, and to the lowest visibility minima specified in the OpSpecs for the NAVAID, facilities, and lighting systems used (see Appendix 7, Standard OpSpecs Part C Paragraph C053 for Category I, and Standard OpSpecs Part C paragraph C059 for Category II).
a. ILS, GLS, or MLS (e.g., xLS) operations are typically authorized based on use of two or more navigation receivers or multi-mode receivers (MMRs) of a pertinent type (see 14 CFR, part 121, section 121.349, and part 125 section 125.203), each providing independent information to the appropriate flight guidance system elements and pilot displays.
b. Provisions of sections 121.349, and 125.203 applicable to ILS may also be considered as applicable to GLS or MLS.
c. Provisions of section 121.349 for use of a single navigation (e.g., ILS) receiver are typically limited to operations using minima at or above RVR4000, or for Minimum Equipment List (MEL) authorization for dispatch with a NAVAID receiver inoperative.
d. Precision Approach Radar (PAR) procedures are not considered xLS procedures( see paragraph 4.3.3).
4.3.3. Instrument Approaches other than ILS, GLS, or MLS (xLS). Instrument approach procedures other than ILS, GLS, or MLS (xLS) that may be authorized for air carriers include the procedure types shown in the following paragraphs.
a. Standard Instrument Procedures Other Than xLS. The following NAVAID specific instrument procedures are considered to be standard procedures for the purpose of air carrier operation specification approval.
Typically these procedures do not inherently specify use of vertical guidance (i.e., most were traditionally considered as non-precision approaches).
(1) Some of these approach types may provide vertical guidance (e.g., a glideslope), however, the procedure may be offset from the runway, may not otherwise permit a straight in landing in the touchdown zone when flying the specified path, or may not have flight deck display of path information. Hence the approach is not considered to be an xLS approach.
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(2) Approvable standard approach types other than xLS are considered to include:
• Localizer (LOC)
• Localizer Back Course (BC)
• SDF
• LDA
• VOR
• VOR/DME
• NDB
• Dual NDB
• NDB/DME
• TACAN, and
• RNAV (2D)* based on a procedurally specified NAVAID (e.g., typically when a particular VOR/DME is specified as a “Procedure tuned” facility to serve as a basis for a particular RNAV procedure - These RNAV procedures usually are those which meet U.S. TERPS Chapter 15 criteria for RNAV).
b. Standard Procedures Flown Using Vertical Navigation Path Guidance (VNAV). The procedures specified in paragraph a. above may also be flown in conjunction with use of FMS derived vertical guidance (e.g., FMS VNAV capability). In this instance, VNAV capability is considered to be based on a pre-specified and defined vertical path.
c. Standard Procedures Flown Using “Constant Vertical Descent Rate” Techniques. NAVAID specific procedures other than xLS may be flown using “Constant Vertical Descent Rate” Techniques as a “pilot procedural technique” to maintain a pre-determined vertical speed to achieve a corresponding assumed descent path (e.g., “open-loop” vertical speed descent profile). Operators may use these techniques, particularly when xLS or VNAV path guidance is not available or cannot otherwise be used. However, such “Constant Vertical Descent Rate” techniques are not considered to be “VNAV vertical guidance”. This is true regardless of whether such a procedure or technique is based on an altitude/distance cross check or not. While use of such techniques may be desirable for aircraft that are not using xLS or VNAV, they are not considered to be eligible for DA(H) use or credit.
d. “RNAV” Procedures (3D or 2D)* Based On RNP. Operators may use RNAV procedures based on RNP criteria that are found to be acceptable to FAA. Those RNAV procedures may use minima based on RNP criteria, or may use RNP for definition of some or all procedure segments (e.g., initial, intermediate, final, or missed approach segments).
e. Other “RNAV” Procedures (3D or 2D)*.
(1) When determined acceptable to FAA, Operators may also use RNAV Procedures (3D or 2D)* other than those based on criteria specified in U.S. TERPS Chapter 15 for RNAV (e.g., RNAV procedures as listed in paragraph a. above), or other than procedures based on RNP (RNAV procedures as listed in paragraph d. above), as follows:
• RNAV procedures identified as “GPS” instrument approach procedures, if those procedures are determined to be suitable for the aircraft and navigation system to be used (e.g., use of FMS with GNSS sensor inputs).
• International RNAV procedures, when appropriate for use at non-U.S. airports.
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• RNAV procedures based on multi-sensor FMS using inertial systems and NAVAIDs other than specific “procedure-tuned” VOR or DME facilities. For example, RNAV Procedures (3D or 2D)* may be based on multi-sensor FMS systems which use DME-DME updating, or scanning DME updating, or VOR/DME updating, or VOR/VOR updating, from suitable and available NAVAIDs.
• RNAV procedures based on multi-sensor FMS using inertial systems and GNSS, or GNSS with Ground Based Augmentation System (GBAS), or Space Based Augmentation System (SBAS)).
(2) RNAV procedures may also be based on combinations of sensors if equivalent performance, availability, and integrity are established compared with any of the above methods.
*NOTE: For the purpose of this AC a “3D” approach procedure (3D) is considered to be one having both lateral and vertical path guidance (e.g., three dimensions - with x, y, and z path coordinates). These procedures may be identified as LNAV/VNAV. A “2D” procedure (2D) is considered to be one having only lateral path guidance (two dimensions - x and y path coordinates). These procedures may be identified as LNAV.
f. Airport Surveillance Radar (ASR) Procedures. ASR or international equivalent procedures may be used.
g. Precision Approach Radar (PAR) Procedures. PAR or international equivalent procedures may be used.
h. Other Limited Use Special Procedures. Other special instrument approach procedures (e.g., LORAN, Transponder Landing System (TLS), airborne radar approach, Eastern European KRM). Special procedures include use of LORAN C, airborne radar, or any other landing system or non-ICAO NAVAID. Special procedures typically require unique approval of an operator’s operational procedures, flightcrew qualification, and maintenance programs as well as proof of concept demonstration prior to operational authorization. Special Category I operations, by definition, require the use of airborne and/or ground based or satellite-based equipment over and above the minimum equipment necessary to operate in the U.S. national airspace. Special Category I operations usually also require special knowledge, skills, proficiency, and procedures. As a result, changes and amendments to the operator’s overall Category I operations program are usually necessary to ensure safe conduct of these operations. There is additional criteria which must be incorporated into an operator’s program for special Category I operations.
4.3.4. Applicability of a DA(H), MDA(H), or RA. Instrument approach and landing operations have limitations related to the minimum altitude (height) to which descent can be made without establishing visual reference (e.g., 14 CFR part 91, section 91.175). Minimum altitude or height to which descent can be made is typically related to assurance of clearance over terrain or obstacles, airborne instrumentation and equipment, NAVAIDs, and visual aids.
Such a minimum altitude or height is usually specified as a DA(H), or MDA(H). A DA(H) may be intended for use as either a Decision Altitude (DA), or as a Decision Height (DH). A DH may be used directly, or it may be specified as a corresponding radio altitude (RA) value above underlying approach terrain. The type of instrument approach procedure determines whether a DA or DH is used, and whether a DH is specified directly, or is defined in terms of a corresponding radio altitude (RA) value above terrain. For a Category I procedure, a DA is typically used. For a Category II procedure, a DH with a corresponding radio altimeter (RA) height above approach terrain is usually used. When a RA value above approach terrain is specified, it typically corresponds to a particular desired DH value for the intended height above the TDZ (HAT).
Uses of DA(H), MDA(H), and RA are further described in paragraphs 4.3.4.1 through
a. DA, DH, RA, OCA, OCH, OCL. For xLS approaches (e.g., precision approaches), and certain RNAV approaches with VNAV, the minimum altitude or height for flight without having established the necessary visual reference during an approach is specified as a DA(H). For Category I within the U.S., the DA element of a DA(H) usually defines the applicable minima. For Category II, applicable minima are usually based on a DH, expressed in the published procedure as an RA value. In other countries, for Category I, either a DA or a DH may be used. For Category II outside the U.S., minima may be based either on a direct specification of DH, or on a corresponding RA value, as is done within the U.S. Other expressions of minima equivalent to a decision altitude (DA) or decision
Page 16 Par 4 height (DH) may also be encountered outside of the U.S., such as when an obstacle clearance altitude (OCA), obstacle clearance height (OCH), or obstacle clearance limit (OCL) is specified, and is to be treated as a corresponding DA or DH.
(1) In the United States and other countries that use U.S. TERPS criteria, the minimum instrument flight altitude for xLS approaches is considered to be the DA element of the DA(H) if minima are based on a barometric altimeter, or the (H) value of the DA(H) expressed as an RA minima, if minima are based on use of a radio altimeter.
When a DH applies, it is usually specified as an RA value above the pertinent underlying approach terrain, considering a nominal approach vertical path. When a barometric altimeter specified DA is used to establish minima, the associated height value (H) is typically considered to be advisory. When a DH specified in terms of a radio altitude (RA) value is used, the corresponding published RA value is considered to be controlling, and any associated barometric altitude value shown in a procedure is typically considered to be advisory.
(2) For procedures with minima based on a DA, the DA is specified as a decision altitude referenced to mean sea level (MSL) using QNH altimeter settings. While the (H) element of the DA(H) is typically advisory for such procedures, in certain circumstances the (H) value may be the basis for minima, such as when a QFE referenced barometric altimeter setting is used.
(3) Obstacle Clearance Height (OCH) and Obstacle Clearance Limit (OCL) are used in some countries IAW various versions or revision levels of ICAO PANS-OPS. OCA, where used, is referenced to a barometric altitude (MSL). OCH and OCL are referenced to height above either the elevation of the airport, the elevation of the touchdown zone, or the elevation of the landing threshold.
b. Minimum Descent Altitude (MDA), Minimum Descent Height (MDH), HAT, Height Above Airport (HAA), Obstacle Clearance Altitude (OCA), OCH, OCL.
(1) For approaches other than xLS, the minimum height or altitude may be specified as a decision altitude DA or a DA(H) if suitable vertical guidance is authorized and provided (e.g., VNAV path), or specified as a minimum descent altitude MDA of an MDA(H) if vertical guidance is not provided. Minima may also be specified height above touchdown (HAT), height above airport (HAA), minimum descent height (MDH), obstacle clearance altitude (OCA), obstacle clearance height (OCH), or obstacle clearance limit (OCL). MDA, HAT, and HAA are typically used by certain countries that use various earlier versions of U.S. TERPS criteria. OCA, OCH, and OCL are used in countries having procedures established IAW ICAO PANS-OPS. Although ICAO PANS-OPS now does not use OCL, some procedures still use OCL criteria from previous versions of PANS-OPS. Some countries, in addition to OCA and OCH, provide MDA and MDH. MDA and OCA are barometric flight altitudes referenced to mean sea level (MSL). HAT, HAA, MDH, OCH, and OCL are radio or radar altitudes referenced to either the elevation of the airport, the elevation of the touchdown zone, or the elevation of the landing threshold.
(2) Accordingly, for international operations, the following equivalent minima formulations should be used by U.S. Operators:
(a) Use the altitude value of the MDA(H) where OCA may be specified for procedures other than xLS.
(b) Use the equivalent altitude value of the MDA(H) where HAT, OCH, or OCL are specified for “straight-in” approach procedures.
(c) Use the equivalent altitude value of the MDA(H) where HAA, OCH, or OCL may be specified circling approach maneuvers.
c. Lowest Permissible DA(H) or MDA(H). The lowest permissible DA(H) or MDA(H) for instrument flight (IMC) for any approach should not be lower than the most restrictive of the following, as applicable:
• Minimum height or altitude published or otherwise established for the instrument approach
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• Minimum height or altitude authorized in OpSpecs for the approach
• Minimum height or altitude authorized for the flightcrew
• Minimum height or altitude authorized for the operator, aircraft, and airborne equipment
• Minimum height or altitude permitted by operative airborne equipment and NAVAIDs
• Minimum height or altitude for which required NAVAIDs can be relied upon*
• Minimum height or altitude which provides adequate obstacle clearance*, and
• Minimum altitude which provides compensation for extremely cold temperatures, if applicable** * Note: Item normally addressed by the published instrument approach procedure.
** Note: Applicable only when an operator has a procedure to correct altimeter errors for extremely cold temperatures (Typically T less than -22F/-30C).
4.3.4.1. Application of a DA(H) for Category I. Procedures established based on use of NAVAID electronic vertical guidance (e.g., ILS, MLS, or GLS) use the barometrically based DA (of the specified DA(H)) for minima determination. Radio altitude above the approach terrain or touchdown zone, if provided, is advisory.
Procedures established based on use of other acceptable electronic vertical guidance (e.g., Baro VNAV meeting provisions of this AC, GNSS based geometric path VNAV) may use a barometrically based DA (of the specified DA(H)) for minima determination if an appropriate obstacle assessment has been completed for the region between the earliest point along the approach path at which the DA may be reached, to the runway threshold. Radio altitude, if provided, is advisory.
For Category I a decision height (DH) is not used.
DA(H) is applied to Category I instrument approach procedures as follows:
a. Category I ILS, MLS, or GLS (xLS) Approaches.
(1) For Category I approaches based on ILS, MLS, or GLS (e.g., xLS, or precision approaches), a DA(H) is typically specified. The DA(H) represents the minimum altitude in an approach to which descent may continue, or by which a missed approach must be initiated, if the required visual reference to continue the approach has not been established. The DA(H) “altitude” value is typically measured by a barometric altimeter, and is the determining factor for descent minima for an xLS approach procedure. The “height” value specified in parenthesis is typically a radio or radar altitude equivalent height above the TDZ (HAT) used only for advisory reference, and does not necessarily reflect actual height above underlying terrain. Where a Middle Marker (MM) beacon is installed, it may be used as advisory information, confirming a barometrically determined DA(H) that is coincident with the glide slope altitude at that point.
(2) For approaches which normally provide vertical guidance (e.g., xLS), but when vertical guidance capability cannot be used, such as due to an airborne system failure, see paragraph 4.3.4.2 below.
b. Category I Approaches with VNAV. For Category I approaches other than ILS, MLS, or GLS which use a published VNAV descent path to the runway threshold, a DA(H) may be specified instead of an MDA(H). See (a) above for DA(H) applicability.
c. Precision Approach Radar (PAR) procedures. For Category I minima, a DA(H) may be specified for PAR. See paragraph a. above for DA(H) applicability. Category II is not typically applicable to civil aircraft use of PAR (see 4.3.8.g).
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4.3.4.2. Application of an MDA(H) for Category I. Procedures that are not based on use of vertical guidance
(e.g., VOR, NDB, Back Course ILS) use the barometrically based MDA (of the specified MDA(H)) for minima determination. Radio altitude, if provided, is advisory.
a. Category I Approaches other than ILS, MLS, or GLS. For Category I approach other than ILS, MLS, or GLS (e.g., non-precision approaches), an MDA(H) is typically specified. The MDA(H) represents the minimum altitude in an approach to which descent may continue, until either the required visual reference is established and the aircraft is in a position to continue the descent to land using normal maneuvering, or until reaching the specified missed approach point. The MDA(H) “Altitude” value is typically measured by a barometric altimeter, and is the determining factor for descent minima for approaches other than ILS, MLS, or GLS (other than xLS) Category I instrument approach procedures. The “Height” value specified in parenthesis is typically a radio or radar altitude equivalent height above the touchdown zone (HAT), and is used only for advisory reference. This height value does not necessarily reflect actual height above underlying terrain. Where a VHF marker beacon (e.g., FM) is used, it may indicate a longitudinal position for a step-down fix, if identified in the procedure.
b. Circling Approaches. Many instrument procedures provide for circling approach minima. U.S. criteria require SIAP publication of circling maneuver minima if the inbound course does not meet straight-in alignment criteria, or when a specified descent gradient for a straight-in approach is steeper than a maximum value allowed by instrument procedure design criteria. Sufficient visual references for manually maneuvering the aircraft to a landing must be maintained throughout a circling maneuver. The pilot must keep the aircraft’s position within the established maneuvering area while performing the circling maneuver. The circling MDA(H) or equivalent must be maintained until an aircraft is in a position from which a normal descent can be made to touchdown within the touchdown zone, using normal maneuvers and a safe descent path.
4.3.4.3. Application of a DA(H), or equivalent (i.e., Inner Marker), for Category II. Procedures using Category II minima typically use a radio altimeter and the associated DH (of the specified DA(H)) for minima determination. Barometric altitude is advisory.
a. Procedures that have “Radio Altitude Not Authorized (RA NA)” (for example, due to irregular underlying terrain) typically use the first indication of arrival at the “inner marker” as a means to establish DA(H). However, an operator may elect to use first indication of arrival at either the “inner marker” or the barometric altitude DA, which ever comes first, as the means for minima determination. In the first instance, both radio altitude and barometric altitude are advisory. In the second instance barometric altitude may be an acceptable means to establish DA(H), but only if it occurs before arriving at the “inner marker.” When a procedure specifies “RA NA,” a DA(H) greater than 100 ft. HAT is typically not used, since a marker beacon is not located in a position along the approach path corresponding to that minima.
b. While for Category II the use of barometric decision altitude (DA) is advisory, this does not preclude an operator or flightcrew from initiating a missed approach if the altitude equivalent to the barometric altitude minima (DA) is reached prior to arrival at the specified DH. A barometrically specified “DA” is not currently used for air carrier Category II minima. This applies regardless of whether radio altimeter or inner marker determines the DH.
c. For Category II a Decision Height of a published DA(H) (or an equivalent Inner Marker (IM) for irregular pre-threshold terrain) is used as the applicable descent minima. Any “altitude” value specified is considered to be advisory. The altitude value is available for cross-reference and backup. Use of the barometrically referenced DA element of a published DA(H) is not currently authorized for parts 121, 129, or 135 operations at U.S. facilities. If an operator elects to base discontinuance of an approach on the DA, if the DA is reached prior to the applicable DH, the DA element of a DA(H) may be considered applicable to Category II in other than an advisory capacity.
4.3.4.4. “Specified Visual Reference” Requirements for Category I or Category II.
a. Section 91.175 and Standard OpSpecs specify that for operation below the DA(H) or MDA(H) on an instrument approach, the required visual reference to continue the approach must be established. Unless otherwise
Par 4 Page 19 authorized by the CMO (e.g., POI or APM for a particular type) the required visual reference may be considered to be those provisions as listed in section 91.175 items (c) and (d).
b. Circumstances in which the operator may request and the CMO may authorize use of alternative visual reference provisions might be situations such as certain Category I and II minima are based on use of autoland or HUD (see paragraph 10.5.3). In this instance provisions such as those shown in section 91.175 (c) (3) (i) for “red terminating bars” or “red side row bars” may not be necessary or appropriate. This is because these particular approach lighting visual references or configurations may not always be needed when operations are predicated on HUD or autoland use. They may not even be installed or applicable as a part of the approach lighting system for the runway or runways to be specially authorized. Conversely, for operations such as the ones noted above for autoland or HUD, it may be determined by the operator and CMO that continued descent below the DA(H) based solely on visual contact with a VGSI (which may in instances be otherwise permitted by 14 CFR), but without having sight of either the runway, runway lights, touchdown zone lights, centerline lights, or runway markings would not be appropriate. In this instance, the CMO may authorize the operator to define and use alternate visual references or visual reference combinations for Category I and II operations, rather than relying solely on the sighting of a VGSI as a basis for continued descent below a DA(H).
c. Refer to FAA Order 8400.13 for lower Category I operations. Changing the required visual reference requires the use of a Special Procedure and additional authorization.
4.3.5. Visibility and RVR Minima. Visibility minima are as specified in Standard or Special Instrument Approach Procedures approved for use by the operator, or as otherwise listed in standard OpSpecs applicable to that operator for Category I or II landing. Operating minimums may be expressed as meteorological visibility (VIS), runway visual range (RVR), or runway visibility values (RVV).
a. Meteorological Visibility (VIS). Meteorological visibility may be used as reported by the NWS, a source approved by the NWS, by FAA, or a source approved by the FAA.
(1) Outside of the U.S., the FAA may accept meteorological reporting sources for use by a particular operator. Outside the U.S. meteorological visibility determination may vary, and the operator should ensure that the meaning, definition, and significance of any meteorological visibility reported for use in determining minima is understood by that operator’s pilots.
(2) For approval of use of weather sources other than the NWS (e.g., international), Operators should consult their respective CMO, CMU, or POI. FAA FSDOs, CMOs, or CMUs that need assistance in responding to operator inquiries regarding approval of weather sources that are not otherwise already addressed by current directives (e.g., FAA Order 8400.10) should consult AFS-400.
b. Runway Visual Range (RVR). RVR is considered to be an instrumentally derived value measured by transmissometers. RVR is calibrated by reference to runway lights and/or the contrast of objects.
(1) Controlling RVR means the reported values of one or more RVR reporting locations (TDZ, Mid, Rollout, or equivalent international locations) used to determine whether operating minima are or are not met, for the purpose of approach initiation, or in some cases, approach continuation.
(2) All U.S. Category I operating minimums below 1/2 statute mile (RVR2400) and all Category II and III operating minimums are based on RVR.
(3) Where RVR is used, the controlling RVR for Category I minima is touchdown RVR. All other readings are advisory.
(4) For Category II minima, controlling RVR is as specified by OpSpecs.
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(5) RVR use has practical limitations that should be familiar to both the operator and pilot. For example, RVR is a value which typically only has meaning for the portions of the runway associated with the RVR report (TDZ, MID, or Rollout). RVR is a value that may vary with runway light step settings (1 through 5). Operators should ensure that pilots are familiar with runway light setting effects on reported RVR. RVR may not be representative of actual visibility along portions of the runway due to the location of the transmissometer baseline and limited length of the baseline, or due to variable conditions of fog, blowing snow, or other obscurations along the runway, or due to obscurations varying rapidly in time (e.g., patchy fog). Additionally, newer RVR systems may have localized performance sensitivity since they do not use a baseline along the runway (e.g., a scatter array may be used for visibility assessment). Thus, pilots and Operators should note that RVR is an instrumentally derived value that has operationally significant limitations and can be greater than or less than the actual visibility available to a pilot at typical flight deck eye height (ground level) at the runway. This is particularly true at night, if runway lights are not at settings standard for the prevailing conditions, or if unusual daylight conditions are experienced such as when a runway is aligned with a sunrise or sunset condition, in shallow or patchy fog.
(6) Outside of the U.S. some RVR reports may not necessarily be instrumentally derived by transmissometers or scatter meters, and may alternately be made by pilots or other weather observers. Accordingly, Operators should ensure that the meaning, definition, significance, and variability of any non-instrumentally derived value of RVR reported to the pilot for use in determining minima is understood by that operator, and that operator’s pilots.
c. Runway Visibility Values (RVV). RVV minima are now used infrequently, are being phased out, and should be used only where minima cannot otherwise be specified as a meteorological visibility (VIS) or runway visual range (RVR).
4.3.6. Visibility Assessment and RVR Equivalence for Landing.
a. For instrument procedures where minima are expressed in terms of meteorological visibility, but reported visibility available to the flightcrew is specified as an RVR, the tables referenced in standard OpSpecs may be used to establish equivalent meteorological visibility minima. (see Appendix 7, OpSpecs paragraph C051).
b. Conversely, for instrument procedures outside of the United States where minima available to the flightcrew on instrument procedures are expressed only in terms of RVR, but reported visibility available to the flightcrew by ATS or other approved source is specified only as a meteorological visibility and RVR is not reported, the “Visibility-RVR Equivalence” table referenced in standard OpSpecs may be used to establish an equivalent RVR value (see Appendix 7, OpSpec paragraph C051). Use of this provision, however, specifically requires FAA authorization in addition to issuance of paragraph C051, and should be limited by the POI or CMO to only those Operators and locations outside of the U.S. that have a need to use the “visibility-RVR” equivalence table for this type of determination.
4.3.7. General Requirements for Category I Operations and Minima.
4.3.7.1. Category I Definition, Background, Classification, and General Criteria.
a. Category I Definition. Within the United States, a Category I instrument approach is considered to be any instrument approach or approach and landing with a decision altitude (height) not lower than 60m (200 ft) and with either a visibility not less than 1/2 statute mile (800m), or a runway visual range not less than 550m (1800 ft).
b. Background. Originally the term Category I applied only to the difference between basic turbojet ILS minima and use of a 200 foot DH with a commensurate low RVR. Subsequently, the definition and common use of the Category I classification evolved several additional times, and variations in its use developed internationally. For U.S. air carriers, the current Category I definition has been in use since FAA’s standard OpSpecs were revised in the 1980s. Air carriers since that time have been issued these revised OpSpecs, in both domestic and international operations.
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(1) This latest adjusted U.S. Category I definition was necessary because previous criteria for instrument approaches relating to “precision” and “non-precision” approach classification was inadequate to address modern air carrier operations. Provisions were not made for numerous levels of navigation system performance capability that are possible and needed by operators. Systems or methods such as FMS, RNAV, VNAV, electronic map displays, multi-sensor filtering, GPS, inertial systems, RNP, and various GPS augmentation schemes such as GBAS or SBAS now make possible significant improvements in instrument approach capability and cannot be suitably addressed by former criteria or classifications. Combinations of the above approach capability also cannot be adequately classified, represented, or used. Former classifications and criteria failed to appropriately consider the linear nature of modern RNAV systems, certain rare-normal and non-normal conditions, and often did not properly relate to necessary supporting airport systems (e.g., lighting, markings) or meteorological reporting capabilities (e.g., RVR).
Previous criteria did not recognize that some procedures or systems formerly considered as “non-precision” (RNAV) may actually have superior performance to systems considered as “precision” systems (e.g., FMS can have better performance than ILS at and beyond distances several miles from the runway). With former criteria and classifications, it was not easy to appropriately classify these systems or derive appropriate benefits.
(2) An important consequence of the U.S. definition for Category I is that, for an air carrier, any instrument approach with minima not less than a DA(H) or MDA(H) of 200 HAT, and visibility not less than RVR 1800, is considered to be Category I. This means that VOR, NDB, RNAV, LOC, Back Course LOC and other such approaches, other than ILS or MLS, are also treated as Category I. This is true even though those approach types may have been considered “non-precision.”
(3) This use of Category I is important to consistently apply to certification and authorization criteria for modern systems and procedures. It is also necessary to ensure that Operators or authorities can implement safety and efficiency advances in a timely and effective way, provide effective and uniform training, and provide necessary facilities, meteorological services, and air traffic services.
c. Instrument Approach Classification.
(1) Accordingly, this AC is based on and uses the definition of Category I as provided in 4.3.7.1. a. The AC treats classification of instrument approach procedures as being grouped into any one of three broad classes:
(a) “xLS,”
(b) “RNAV,” and
(c) “Instrument procedures other that xLS, or RNAV” (e.g., traditional or classic procedures such as VOR, NDB, LOC, and ASR).
(2) Procedures identified as “xLS” may apply to ILS, MLS or GLS.
(3) Procedures identified as RNAV include procedures based on use of
• FMS
• RNAV systems using traditional VOR/DME sensors systems, or
• GNSS (GPS) or augmented GNSS systems (e.g., includes SBAS/WAAS)
(4) RNAV procedures are addressed as either three-dimensional (3-D) if suitable LNAV and VNAV is used, or two-dimensional (2-D) if only lateral navigation is used. It is recognized that various levels of performance are possible either laterally or vertically. Hence, provision is made to address Required Navigation Performance (RNP). RNAV procedures are also considered to include those which may use RNAV methods, techniques or systems to fly traditional sensor specific VOR, NDB, or Localizer based approaches (e.g., use of FMS to fly a VOR, NDB or Back Course Localizer approach in LNAV and VNAV, based on an electronic map display rather than using a “raw data” readout of course deviation). The remaining instrument procedure group titled “Instrument approaches other than xLS, or RNAV” address traditional or classic procedures such as VOR, VOR/DME, NDB, LOC, BC
Page 22 Par 4 LOC, and ASR. This group is considered to include any other remaining types of instrument approach procedures that are not already covered by or addressed by the groups xLS or RNAV.
(5) The AC and associated classification schema do not use former terminology of “precision” or “non-precision” as applies to xLS or RNAV instrument approaches. However, it does not preclude continued use of the term by Operators as apply to classic procedures, particularly when training materials or manuals may take a very long time to eventually be amended in the normal course of longer term revision. Since the terms “precision” and “non-precision” are not necessary to implement or conduct operations and can be confusing and ambiguous, their use is discouraged in favor of use of the common generic term “instrument approach” or use of “xLS”, “RNAV”, or “approaches other than xLS or RNAV” for many important applications (e.g., Inappropriately classifying as “non-precision” operations of aircraft using RNAV systems to fly multi-sensor based and highly accurate levels of RNP and accurate VNAV paths, to a low DA(H)).
d. General Criteria For Category I. The following general requirements apply to the operational authorization of Category I instrument approach procedures:
(1) The airborne system(s) should meet the requirements of the applicable paragraphs of 5.2 for the type of Category I procedures to be flown;
(2) Appropriate NAVAIDs and airport/lighting facilities for the procedures to be flown should be available, consistent with paragraph 8;
(3) Flightcrew qualification consistent with provisions of paragraph 7 for Category I has been completed;
(4) An acceptable airworthiness (maintenance) program for the airborne system is provided IAW paragraph 9;
and
(5) An operational authorization has been completed IAW paragraph 10 for a U.S. operator or paragraph 11 for a Non-U.S. operator.
e. Minimum authorized DA(H). For simplicity of description, where a minimum authorized DA(H) is cited in this paragraph as applicable to Category I minima, it is stated in terms of a height above touchdown zone elevation
(e.g., HAT value), even though operational minima for Category I are specified as a DA, based on MSL altitudes.
4.3.7.2. “xLS” Procedures - Minima not less than 200 feet DA(H). Instrument approach operations that may be authorized Category I minima not less than 200 ft. DA(H) include at least the following:
a. ILS.
b. GLS (GBAS/LAAS).
c. MLS.
d. Special Procedures - Special procedures having individual FAA approval for each operator or location that are capable of supporting a DA(H) down to at least 200 ft. HAT may be authorized (e.g., PAR, GLS SCAT I). Such special procedures typically require associated conditions or limitations for special flightcrew training, for navigation facility use coordination, site-specific suitability review, or operator or other agency monitoring (e.g., as for DOD provision of PAR capability).
4.3.7.3. “3D” RNAV Procedures - Minima not less than 200 feet DA(H). Instrument approach operations that may be authorized Category I minima not less than 200 ft. DA(H) include:
a. 3D RNAV procedures based on suitable levels of RNP and VNAV capability (e.g., RNP.15/125 ft. or lower)