Par 4 Page 47
f. The approach segment connects with the rollout segments. An approach flight path is considered to terminate at the beginning of the rollout segment.
4.6.1. Landing and Rollout Flight Path. The following criteria specifies certain reference points and other criteria necessary to effectively implement landing and rollout operations using a landing system where the required flight path (e.g., FAS and RWS) is not inherent in the signal structure of the navigation aid (e.g., for satellite based sensor systems).
4.6.2. Runway Datum Point (RDP). The RDP is used in conjunction with the FPAP and the vector normal to the WGS-84 ellipsoid at the RDP to define the geodesic plane of a final instrument approach flight path to touchdown and rollout (e.g., FAS). It is a point typically at the designated center of the landing runway. An RDP is defined by a specified latitude, longitude, ellipsoidal height, and orthometric height. The RDP is a reference point used to connect the approach flight path with the runway. The RDP may or may not be coincident with, and need not necessarily be coincident with the designated runway threshold.
4.6.3. Flight Path Alignment Point (FPAP). The FPAP is a point, usually at or near the stop end of a runway, used in conjunction with the RDP and a vector normal to the WGS-84 ellipsoid at the RDP, to define the geodesic plane of a final approach and landing flight path (e.g., FAS and RWS). The FPAP typically may be the RDP for the reciprocal runway.
4.6.4. Flight Path Control Point (FPCP). The Flight Path Control Point (FPCP) is a calculated point located above the RDP in a direction normal to the WGS-84 ellipsoid. The FPCP is used to establish the vertical descent path and descent angle of the final approach flight path (e.g., FAS) to the landing runway.
4.6.5. Datum Crossing Height (DCH). The height of the Flight Path Control Point (FPCP) above the Runway Datum Point (RDP). Note that the FPCP may be specified in units of feet or meters, but is typically specified in units of feet.
NOTE: A standard datum crossing height should typically be 50 ft. For sloped runway touchdown zones, a DCH in the range of 50 to 55 ft above the designated datum point is acceptable. Other values are accepted on a case by case basis considering the airport need for a different value, and the type of aircraft and operations to be used (e.g., STOL). Typically a DCH is coincident with the runway threshold (TCH). (Also see Sections 5.12.3 and 5.12.4).
4.6.6. Glide Path Angle (GPA). The glide path angle is an angle, defined at the FPCP, that establishes the descent gradient for the final approach flight path (e.g., FAS) of an instrument approach procedure. It is measured in the geodesic plane of the approach (defined by the RDP, FPAP, and a vector normal to the WGS-84 ellipsoid at the RDP). The vertical and horizontal references for the GPA are a vector normal to the WGS-84 ellipsoid at the RDP and a plane perpendicular to that vector at the FPCP, respectively.
4.6.7. Glide Path Intercept Reference Point (GIRP).
a. The GIRP is the point at which the extension of the final approach path (e.g., FAS) intercepts the runway.
Page 48 Par 4 Points, Heights, Angles Or Other Considerations For Definition of An Approach And Landing Flight Path Figure 4.6-1 Datum Crossing Height (DCH) Runway Datum Point (RDP) Glidepath Intercept Reference Point (GIRP) Flight Path Control Point (FPCP) Flight Path Alignment Point (FPAP)η η = Glide Path Angle
b. The locations established for, and the values assigned to, the RDP, FPCP, DCH and GPA will be selected based upon the operation need to establish the required GIRP. Operational considerations include:
(1) Path of wheels over threshold(s),
(2) Need for coincidence with other aids and systems - visual and non-visual,
(3) Runway characteristics (upslope and downslope, crown, etc.),
(4) Actual threshold, displaced threshold or multiple threshold characteristics,
(5) Actual clearway or stopway characteristics.
4.6.8. Approach and Missed Approach Segments. Figure 4.6-2 below shows the applicable reference points, path points, waypoints and leg types typically used to construct instrument approach procedures applicable to air carrier operations.
Par 4 Page 49 Waypoint and Segment Placement Figure 4.6-2 IMAWP GPIWP APIWP FPCP EFAS FAS IMAS RWS FPAP GIRP
4.6.9. Procedure Design Related Waypoint Definitions and Use. The following procedure design-related waypoint definitions and uses are provided:
a. Glide Path Intercept Waypoint (GPIWP) - The point at which the established glide slope intercept altitude (MSL) meets the Final Approach Segment (FAS), on a standard day, using a standard altimeter setting (1013.2 HPa or 29.92 in).
b. Approach Intercept Waypoint (APIWP) - A variable waypoint used when necessary to link a barometric LNAV/VNAV flight path with a Final Approach Segment (FAS) that is fixed in space (e.g., a xLS final segment).
The APIWP permits LNAV and barometric VNAV segments, which may vary vertically in location on an approach as a function of barometric pressure setting or temperature variation from standard, to join or be connected to a FAS which is otherwise fixed in vertical location with respect to a runway.
c. Initial Missed Approach Waypoint (IMAWP) - (Used only for MAP) A Waypoint generally aligned with the runway centerline, beyond the touchdown zone, used to establish a suitable initial climb segment beyond the touchdown zone. The IMAWP intends to provide a safe path and altitude, if applicable, in the vicinity of the runway, to be used to establish a safe initial go-around path following a low altitude go-around or rejected landing.
d. Procedure Design Related Segment Definitions. The following procedure design related segment definitions are provided:
Final Approach Segment (FAS) The segment of an approach extending from the Glidepath Intercept Waypoint (GPIWP) or Approach Intercept Waypoint (APIWP), whichever occurs later, to the Glidepath Intercept Reference Point (GIRP). For the purpose of procedure construction, The Final Approach segment is defined as beginning at the FAF and ending at the Flight Path Control Point (FPCP) or point at which the missed approach segment starts (e.g., point of lowest nominal DA(H)).
Extended Final Approach That segment of an approach, co-linear with the Final Approach Segment, but
Page 50 Par 4 Segment (EFAS) which extends beyond the Glidepath Intercept Waypoint (GPIWP) or Approach Intercept Waypoint (APIWP).
Runway Segment (RWS) That segment of an approach from the glidepath intercept reference point (GIRP) to Flight Path Alignment Point (FPAP).
Initial Missed Approach Segment (IMAS) That segment of an approach from the Glide Path Intercept Waypoint (GIRP) to the Initial Missed Approach Waypoint (IMAWP).
Missed Approach Segment (MAS) That segment of an instrument approach procedure from a point on the FAS corresponding to the position where the lowest DA(H) occurs under nominal conditions, to the designated IMAWP, or missed approach holding WP, as specified for the procedure.
Par 5 Page 51
5. AIRBORNE SYSTEM REQUIREMENTS.
5.1. General. The following accuracy, integrity and availability criteria are specified for aircraft systems intended for Category I or II. Aircraft related systems are addressed by 5.1.1. Non-aircraft systems (e.g., NAVAIDs) are addressed in 5.1.2. Specification of flight path is addressed in 5.1.3, such as is applicable to defining an RNAV, LNAV, or VNAV path to be followed by an aircraft. Specific airborne equipment requirements for Category I or II authorizations are addressed in 5.2 and 5.3.
5.1.1. Airborne Systems.
a. Airworthiness criteria for aircraft systems intended to meet requirements of this AC are specified in paragraph 5.1.3 through 5.19 below, or Appendix 2 or 3 for demonstration of airborne systems for eligibility for Category I or II minima respectively.
b. For aircraft which completed an airworthiness demonstration applicable to Category I or II using earlier versions of this AC, or previous applicable ACs, new operational authorizations may be requested or may be continued only as provided for in standard OpSpecs.
5.1.2. Non-Airborne Systems (e.g., NAVAIDs or equivalent GNSS capability). Unless otherwise specified by FAA, NAVAID/landing system characteristics to be used should have been addressed using an acceptable means of facility or capability classification (e.g., For a U.S. ILS facility, and example of a typical classification would be “II/E/2”).
a. The classification should be specified in a manner suitable to address:
(1) Intended NAVAID performance level (or an equivalent capability for GNSS),
(2) Signal or capability coverage with respect to the intended flight path(s) and runway, and
(3) NAVAID or capability “availability and integrity” (e.g., considering standby capability and power, as applicable).
b. This classification schema should at least be provided for any xLS capability (e.g., ILS, MLS, or GLS).
Typically this is done by use of FAA or ICAO criteria such as specified by FAA Order 6750.24 as amended, or ICAO Annex 10 Criteria, as suited to the applicable NAVAID facility or capability. NAVAID facility or capability operational use is then predicated on suitable facility or capability classification respectively for ILS, MLS, or GLS
(e.g., for ILS, III/E/2).
c. NAVAID classifications or equivalent capability classification schema should be consistent among ILS, MLS or GLS to the maximum extent possible.
d. At non-U.S. facilities, consideration of equivalence to U.S. classification may be necessary for operational authorizations.
e. For GLS, classification schema are evolving and are expected to continue to do so as new GNSS elements or augmentation methods become operational. Nonetheless, an appropriate classification method equivalent to that used for ILS, or as otherwise specified by FAA or ICAO, should be used (e.g., addressing “Performance Level”/”Coverage”/”Integrity” such as “PL2/T/1”).
f. NAVAID facility or capability classification schema or associated airborne system documentation referring to that classification schema for ILS, MLS, or GLS should not be defined or expressed in operational authorization terms (e.g., Category I, II, or III xLS). This is necessary to recognize that operational authorization criteria for Category I, II, or III may change in time, and because authorizations may not be unique to a particular NAVAID classification or capability, and further, may depend on and be a function of evolving airborne system elements, procedures, or other factors.
Page 52 Par 5
5.1.3. Flight Path Specification.
5.1.3.1. Lateral.
a. Category I. The following levels of lateral performance shown in Table 5.1.3-1 are acceptable for Category I and corresponding minima may be applied. Any one or more methods listed below may be demonstrated, but the method(s) used should be identified as the basis for the demonstration.
Table 5.1.3.1-1.
CATEGORY I - LATERAL PERFORMANCE/MINIMA
1) ILS/MLS/GLS (any one xLS) [Minima equivalent to ILS at 200 ft. HAT] [Lateral tracking performance from 1000 ft. HAT to 200 ft.
HAT should be stable without large deviations (i.e., within +50 microamps deviation) from the indicated course or path, or equivalent; using at least 3 different representative facilities for a minimum of 9 total approaches. System performance should be acceptable without undue oscillation.]
2) “ILS Equivalent” (e.g., SCAT I/ MASPS;WAAS/MOPS) [Minima equivalent to ILS at 200 ft. HAT]
3) RNP RNP < .03 .03 <RNP< .3 RNP > .3 [Minima equivalent to ILS at 200 ft. HAT] [Minima typically not lower than a DA(H) of 250 ft. HAT] [Minima restricted to not lower than a DA(H) of 250 ft. HAT]
4) FMS (LNAV/VNAV or LNAV) [Minima restricted to not lower than a DA(H) of 250 ft. HAT]
5) RNAV [Minima as specified by Standard OpSpecs/SIAP]
6) LOC, LOC BCRS, VOR, VOR/DME,
NDB, ASR, PAR [Minima as specified by Standard OpSpecs/SIAP]
b. Category II. The following levels of lateral performance shown in Table 5.1.1-2 are acceptable for Category II. Any one or more methods may be demonstrated, but the method used should be identified as the basis for the demonstration.
Par 5 Page 53 Table 5.1.3.1-2.
CATEGORY II - LATERAL PERFORMANCE/MINIMA
1) ILS/MLS/GLS (any one xLS) [Minima equivalent to ILS at 100 ft. HAT] See Category I Criteria to 300 ft. HAT, and in addition, [Lateral tracking performance from 300 ft. HAT to 100 ft. HAT within +25microamps deviation from the indicated course or path, or equivalent, (for 95% of the time/per approach) using at least 3 representative facilities and for a minimum of 20 total approaches.
System performance should be acceptable without undue oscillation.]* * NOTE: Or using JAA ACJ AWO 231 Method
2) RNP RNP < .01 [Minima equivalent to ILS at 100 ft. HAT]
c. Lateral Performance below or beyond DA(H). For either Category I or II procedures with a DA(H) below 250 ft. HAT*, when guidance is provided (e.g., for autoland, or HUD flare/rollout), the lateral performance should at least be equivalent to that attainable using an ILS Type I/E/1 localizer (or RNP .003) from 200 ft. HAT, or 100 ft.
HAT as applicable, to the end of rollout.
*NOTE: This provision does not apply to systems intended for Category III - see AC120-28D for Category III requirements.
d. From 200 ft. HAT or 100 ft. HAT, as applicable, until returning to an established missed approach segment of the approach procedure, if guidance is provided, performance should be at least equivalent to that attainable using an ILS Type I/E/1 localizer front and back course, or RNP.3 as applicable.
5.1.3.2. Vertical.
a. Category I. The following levels of vertical performance are acceptable for Category I and corresponding minima may be applied. Any one or more methods listed below may be demonstrated, but the method(s) used should be identified as the basis for the demonstration.
Page 54 Par 5 Table 5.1.3.2-1.
CATEGORY I - VERTICAL PERFORMANCE/MINIMA
1) ILS/MLS/GLS Glide Slope/Glide Path (any one xLS Glide Slope) [Minima equivalent to ILS at 200 ft. HAT] [Vertical tracking performance from 700 ft. HAT to 200 ft.
HAT should be stable without large deviations (i.e., within +75 microamps deviation) from the indicated path, or equivalent, using at least 3 different representative facilities and for a minimum of 9 total approaches. System performance should be acceptable without undue oscillation.]
2) “ILS Glide Slope Equivalent” (e.g., SCAT I/ MASPS;
WAAS/MOPS) [Minima equivalent to ILS at 200 ft. HAT]
3) RNP RNP < .03 and ECEF** VNAV .03 <RNP< .3 and BARO VNAV RNP > .3 with or without BARO VNAV [Minima equivalent to ILS at 200 ft. HAT] [Minima typically not lower than a DA(H) of 250 ft. HAT] [Minima restricted to not lower than a DA(H) of 250 ft.
HAT]
4) FMS BARO VNAV [Minima restricted to not lower than a DA(H) of 250 ft.
HAT]
5) RNAV [Vertical performance not applicable*]
6) LOC, LOC BCRS,VOR, VOR/DME, NDB, ASR, PAR [Vertical performance not applicable*; except PAR minima equivalent to ILS] *Note: A procedure addressing a stabilized approach from the Final Approach Fix to MDA(H) is recommended for these procedures (except this note does not apply to PAR).
**Note: ECEF VNAV - VNAV referenced to “Earth Center Earth Fixed Coordinates,” or geometric height above the “earth reference surface” based VNAV.
b. Category II. The following levels of vertical performance are acceptable for Category II. Any one or more methods may be demonstrated, but the method used should be identified as the basis for the demonstration.
Par 5 Page 55 Table 5.1.3.2-2
CATEGORY II - VERTICAL PERFORMANCE/MINIMA
1) ILS/MLS/GLS (any one xLS Glide Slope/Glide Path) [Minima equivalent to ILS at 100 ft. HAT] See Category I Criteria to 300 ft. HAT, and in addition, [Vertical tracking performance from 300 ft. HAT to 100 ft. HAT within +35** microamps deviation from the indicated course or path, or +12 ft, which ever is greater, or equivalent, (for 95% of the time/per approach) using at least 3 different representative facilities and for a minimum of 20 total approaches. System performance should be acceptable without undue oscillation.]* * NOTE: Or using JAA ACJ AWO 231 Method ** NOTE: When this provision is applied to path tracking in conjunction with Category III, momentary excursions up to + 75 microamps during test demonstrations may be acceptable if flight guidance system touchdown and landing performance is otherwise shown to be satisfactory.
2) RNP RNP < .01 with ECEF** VNAV [Minima equivalent to ILS at 100 ft. HAT]
c. Category I or Category II.
(1) Vertical (VNAV) performance at altitude constraints prior to a Final Approach Fix (FAF) or Final Approach Point (FAP), or at an FAF or FAP. For procedures with VNAV segment(s) prior to an FAF or FAP, at an FAF or FAP (e.g., intercepting an FAS from an en route segment, STAR, Profile Descent, initial approach or intermediate approach segment), vertical performance should normally be based on use of a vertical “Fly by” path rather than a “Fly over” path. The small vertical displacement which may occur at a vertical constraint as a result of using a vertical “Fly by” waypoint rather than vertical “Fly over” waypoint is considered operationally acceptable, and desirable, to ensure asymptotic capture of a new (next) vertical segment. This momentary deviation below the published minimum procedure altitude is acceptable provided the deviation is limited to no more than 100 ft. and is a result of a normal VNAV capture. This applies to both “level off” or “altitude acquire” segments following a climb or descent, or vertical climb or descent segment initiation, or joining of climb or descent paths with different gradients.
NOTE: A “Fly By” vertical waypoint is a WP for which an aircraft may initiate a vertical rate change and depart the specified vertical path to the active WP prior to reaching that WP, in order to asymptotically capture the next vertical path. A “Fly Over” vertical waypoint is a WP for which an aircraft must stay on the defined vertical path until passing the active WP and may not initiate the necessary vertical rate change to capture the next vertical path until after passing the active WP. Hence, after passing the active WP, as the next WP becomes active, and if there is a vertical path change, the aircraft must re-adjust vertical rate to re-capture the vertical path after having already overshot the first opportunity for an asymptotic capture of that new path.
(2) Vertical (VNAV) performance at waypoint altitude constraints near the point at which DA(H) or MDA(H) may occur. For procedures with waypoints at or near the point at which DA(H) may occur, vertical (VNAV) performance should not preclude continuous descent of the aircraft to the runway, following the established VNAV path to the runway (e.g., VNAV should not initiate inappropriate capture of a missed approach segment and
Page 56 Par 5 automatic level off (at MDA(H)) or initiation of MAP climb, without pilot confirmation that a missed approach or go-around is intended (e.g., TOGA initiation).
(3) Vertical (VNAV) performance below or beyond DA(H) or MDA(H). For procedures with a DA(H) below 200 ft. HAT* (e.g., for autoland, or HUD flare/rollout), the glide path/glide slope vertical performance should at least be equivalent to that attainable using an ILS glide slope at a facility classified as Type I/E/1, between 200 ft.
HAT and 50 ft. HAT.
*NOTE: This provision does not apply to systems intended for Category III - see AC120-28D for Category III requirements.
5.1.3.3. Longitudinal. Longitudinal (along track) requirements for Category I or II operations are as specified below.
a. Category I. The following longitudinal (along track) requirements are acceptable for Category I. Any one or more methods listed below may be demonstrated, but the method(s) used should be identified as the basis for the demonstration.
Par 5 Page 57 Table 5.1.3.3-1.
CATEGORY I - LONGITUDINAL PERFORMANCE/MINIMA
1) ILS/MLS/GLS (any one xLS, or any combination provided by MMR) Use of VHF OM/MM Marker Beacons Use of VOR/TACAN Fixes (other than for MM) Use of LOM/LMM NDBs Use of suitable DME Distance Information Use of FMS RNAV Fixes (other than for MM) Use of Distance to “Runway Threshold WP” Other methods (e.g., Radar fixes, Fan Markers) No specific method of assuring along track position [Minima equivalent to ILS at 200 ft. HAT] [Minima equivalent to ILS at 200 ft. HAT] [Minima equivalent to ILS at 200 ft. HAT] [Minima equivalent to ILS at 200 ft. HAT] [Minima equivalent to ILS at 200 ft. HAT] [Minima equivalent to ILS at 200 ft. HAT] [Restricted minima may apply - DA(H)>250 ft. HAT] [Restricted minima may apply - DA(H)>250 ft. HAT]
2) “ILS Equivalent” (e.g., SCATI/MASPS;WAAS/MOPS) [Same as for ILS/MLS/GLS described above
3) RNP* RNP < .03 .03 <RNP< .3 RNP > .3 [Minima equivalent to ILS at 200 ft. HAT] [Minima typically not lower than a DA(H) of 250 ft. HAT] [Minima restricted to not lower than a DA(H) of 250 ft.
HAT] *Note: RNP Systems/Procedures that do not provide for display of distance to a “Runway Threshold WP” may have minima additionally restricted.
4) FMS (LNAV/VNAV or LNAV) [Minima restricted to not lower than a DA(H) of 250 ft.
HAT]
5) RNAV (Op-Specs Part C; Para C063) [Minima as specified by Standard Op-Specs/SIAP]
6) LOC, LOC BCRS,VOR, VOR/DME, NDB, ASR, PAR [Minima as specified by Standard Op-Specs/SIAP]
b. Category II. The following levels of longitudinal (along track) performance are acceptable for Category II.
Any one or more methods may be demonstrated, but the method used should be identified as the basis for the demonstration.
Table 5.1.3.3-2
CAT II - LONGITUDINAL PERFORMANCE/MINIMA
1) ILS/MLS/GLS (any one xLS, or any combination provided by MMR) Same as for Category I, except that an IM or suitable distance readout to a “Runway Threshold WP” is also required.
2) RNP RNP < .01 [Same as for ILS/MLS/GLS above.]
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5.1.3.4. Typical Wind and Wind Gradient Disturbance Environment. The lateral and vertical performance described in paragraph of 5.1.3 above should typically be expected to be achievable in conditions at least as described below. Performance may be estimated, assessed analytically, demonstrated in simulation, or demonstrated in flight. Relevant associated information on demonstrated winds encountered or estimated wind gradient capability may be included in the AFM, as desired by the applicant.
a. Systems intended for use with procedures for either Category I or Category II should be capable of coping with at least the following wind, wind gradient, and turbulence conditions:
• Reported Surface Headwind Component - 25 kts
• Reported Surface Tailwind Component - 10 kts
• Reported Surface Crosswind Component - 15 kts
b. Wind Gradients/Shear - at least 4 kts per 100 ft. from 500 ft. HAT to the surface;
c. Recommended Capability - Ability to cope with 8 kts per 100 ft. for 500 ft., moderate turbulence, knife edge shears of at least 15kts over 100 ft., 20 kts lateral directional vector shears of 90 degrees over 100 ft., and ability to cope with a 20 kt logarithmic shears between 200 ft. and the surface.
5.2. Airborne Equipment for Category I. The following equipment (along with any additional equipment specified by 14 CFR for IFR flight) is the recommended aircraft equipment for an authorization for Category I.
a. For ILS, GLS, or MLS approach capability:
• Two navigation receivers, or equivalent type of device, of each type intended for use, NOTE 1: The navigation receivers specified above may be provided as two or more integrated multi-sensor units (e.g., MMR), NOTE 2: For GLS, at least one data link receiver capable of receiving GBAS uplinked corrections for GNSS position fix correction data may be considered acceptable, when used with dual navigation receiver capability (e.g., dual GPSSU sensors) receiving GPS SV ranging information. Dual data link receivers capable of receiving GBAS uplinked corrections for GNSS are recommended.
NOTE 3: Installation of only one navigation receiver may be authorized by FAA for special circumstances, considering the particular facilities and routes to be used, such as if suitable minima restrictions and requirements for alternate navigation capability are applied (e.g., one GLS receiver if two ILS receivers are installed).
• Suitable navigation displays, attitude, vertical speed, and airspeed displays for each pilot (see paragraph 5.9 for details)
• Suitable failure annunciation visible to each pilot
• One or more Marker Beacon systems (unless an approved RNAV substitute is available, or if not necessary for the route of flight, including alternates)
• One or more DMEs (unless an approved RNAV substitute is available, or if not necessary for the route of flight, including alternates)
• One or more ADFs (unless an approved RNAV substitute system is available, or unless ADF is not required for the intended route of flight, including alternates). Note that two ADFs may be required IAW paragraph 121.549 for certain international operations, and for certain obstacle or terrain critical departure, approach, or missed approach procedures
• For aircraft intended for approval of landing minima below RVR 3000, at least one flight director or one autopilot