1. PURPOSE. This advisory circular (AC) provides an acceptable means, but not the only means, for obtaining and maintaining approval of operations in Category III Landing Weather Minima and low visibility takeoff including the installation and approval of associated airborne systems. This AC is applicable to Title 14 of the Code of Federal Regulations (14 CFR) part 121, 135 and 125 operators.
Certain aspects of this AC are applicable to 14 CFR part 129 operators. Many of the principles, concepts and procedures described also may apply to 14 CFR part 91 operations and are recommended for use by those operators when applicable. Mandatory terms used in this AC such as "shall" or "must" are used only in the sense of ensuring applicability of these particular methods of compliance when the acceptable means of compliance described herein is used. This AC does not change, add or delete regulatory requirements or authorize deviations from regulatory requirements.
CANCELLATION. AC 120-28C, dated March 9, 1984, and AC 20-57A dated January 12, 1971, are canceled.
2. RELATED REFERENCES AND DEFINITIONS.
2.1. Related References. Title 14 of the Code of Federal Regulations (14 CFR) part 23, section 23.1309; part 25, sections 25.1309, 25.1322, 25.1581, and 25.1583; part 91, sections 91.175 and 91.189; part 121, sections 121.579, and 121.651; part 125, sections 125.379, and 125.381; part 129, section 129.11; and part 135, section 135.225.
Unless a specific reference is made to a particular version of a rule or AC, current editions of the following AC’s should be used:
AC 23.1309-1, Equipment, Systems, and Installation in Part 23 Airplanes AC 25-7A, Flight Test Guide for Certification of Transport Category Airplanes AC 25.1309-1, System Design Analysis AC 120-29, Criteria for Approving Category I and Category II Landing Minima for 14 CFR Part 121 Operators Standard Operations Specifications Parts A and C, FAA Order 8400.8, Procedures for Approval of Facilities for FAR Part 121 and Part 135 Category III Operations FAA Order 8400.10, Air Transportation Operations Inspector’s Handbook
2.2. Definitions. A comprehensive set of definitions pertinent to Category III approach and landing and low visibility takeoff is included in Appendix 1.
Within this AC, Runway Visual Range (RVR) values are specified in units of feet (ft.) unless otherwise noted (e.g., meters (m)).
Where visibility minima are stated in both feet and meters (e.g., RVR300 (75m)) using values other than those identified as "equivalent" in standard operations specifications, it is intended that the RVR value in feet apply to minima specified in feet, and the value in meters apply in states specifying their minima in meters.
Minima typically used for low visibility operations including a minima conversion table where applicable are provided in the operations specifications shown in Appendix 7.
In this AC, where the term “RNP Level” is used, it may be considered to be equivalent to the term “RNP Type” typically used in some current ICAO and other authority references. The term “RNP Level” is used in the U.S. to match various RNP approval documents (e.g., AFM’s) already in widespread use, and to reserve use of the term “RNP Type” for future anticipated RNP applications.
3. BACKGROUND.
3.1. Major Changes Addressed in this Revision. This AC includes additional Category III criteria or revised Category III criteria for use in conjunction with Head-up Displays, satellite navigation systems, low visibility takeoff guidance systems, Wide-body Fail Passive operations and use of Category III during certain engine inoperative operations.
This revision also updates and incorporates provisions of the former AC 20-57 into AC 120-28, since provisions of the former AC 20-57 are directly related to and dependent on criteria provided in this AC.
This revision incorporates changes resulting from the first steps toward international all weather operations (AWO) criteria harmonization taken by the Federal Aviation Administration (FAA), the European Joint Aviation Authorities (JAA), and several other regulatory authorities. Subsequent revisions of this AC are planned as additional all weather operations harmonization items (AHI) are agreed and completed by FAA and JAA, or internationally.
3.2. Relationship of Operational Authorizations for Category III and Airborne System Demonstrations. Takeoff and landing weather minima are approved through applicable operating rules, use of approved instrument procedures and issuance of operations specifications. Airworthiness demonstration of airborne equipment and systems is usually accomplished in support of operational authorizations on a one time basis at the time of Type Certification (TC) or Supplemental Type Certification (STC). Since operating rules continuously apply over time and may change after airworthiness demonstrations are conducted, or may be updated consistent with safety experience, additional Category III credit or constraints may apply to operators or aircraft as necessary for safe operations. Airworthiness demonstrations are based on the particular operational and airworthiness criteria in effect at the time a type design certification basis is established for a particular TC or STC.
Subsequent operational authorizations may constrain capabilities originally demonstrated based on current operational regulatory policy and experience. The main body of this AC contains criteria related to operational approval and Appendix 2 and Appendix 3 are the primary source of airworthiness criteria. Nothing in this AC is intended to preclude an operator from proposing and demonstrating to the FAA the ability to operate to Category III minima with a different equipment configuration; or alternatively to an RVR minima lower than that presently described in this document.
3.3. Applicable Criteria. AC 120-28C, dated March 9, 1984, and AC 20-57A dated January 12, 1971 are canceled. Except as described below, new airworthiness demonstrations or operational authorizations should use criteria of AC 120-28D. Airworthiness demonstrations may use equivalent JAA criteria where agreed by FAA through the FAA/JAA criteria harmonization process.
In general, the provisions of the main body of this AC outline concepts, objectives, and provisions necessary for operators. The appendices contain definitions, abbreviations, airworthiness demonstration provisions typically applied in conjunction with type certification, technical information necessary for airworthiness or operational assessments (e.g., atmospheric/wind models, obstacle clearance criteria) and examples of operational authorizations (e.g., sample Operations-Specifications (OpSpecs)). Certain criteria related to airworthiness assessment are included in the main body of the AC primarily to address the status and eligibility of previously certificated in-service aircraft for current authorizations (e.g., status of service bulletin compliance for continued or new authorizations, demonstration provisions applicable to "inservice" aircraft).
Operators electing to comply with this AC's revised criteria may receive the applicable additional credit(s). Aircraft manufacturers, operators or modifiers may elect to demonstrate that their aircraft meet the revised criteria to seek additional credit for any particular operation (e.g., HUD installation) or for all operations addressed by this AC (e.g., incorporation of a general compliance statement related to AC 120-28D, instead of reference to the former canceled criteria of AC 120-28C). However, aircraft demonstrated to earlier criteria may continue to be approved for Category III operations in accordance with that earlier criteria, and applicants may continue to make reference to the fact that an earlier demonstration was based on that previous criteria
(e.g., in the AFM). Aircraft manufacturers, modifiers or operators seeking authorization provided for only in this AC must, however, use applicable criteria of this AC (e.g., for RNP based missed approach obstacle criteria, meet pertinent provisions of Appendix 9). To get a particular authorization cited by this AC, the operator need only meet the provision or provisions applicable (e.g., RVR600 fail passive landing minima may be authorized per 4.3.8 for presently authorized airborne systems meeting previous criteria without regard to Appendix 3 criteria).
4. OPERATIONAL CONCEPTS.
4.1. Classification and Applicability of Minima. Landing minima are generally classified by Category I, Category II and Category III (e.g., see ICAO Annex 6 references, and the associated
ICAO Manual of All Weather Operations DOC 9360/AN910, 2nd Edition, 1991). AC 120-29 (as amended) addresses Category I and II. This AC addresses Category III.
Takeoff minima are usually classified by RVR or meteorological visibility, and other factors (e.g., aircraft characteristics).
Although a wide variety of normal and non-normal situations are considered in the design and approval of systems used for Category III, Category III minima are primarily intended to apply to normal operations.
For non-normal operations, flightcrews are expected to take the safest course of action appropriate for the situation, including consideration of normal landing weather minima. When aircraft systems have been demonstrated to account for certain non-normal configurations (e.g., an approach with an engine inoperative) flightcrew may take into account this information in assessing the safest course of action.
4.2. Takeoff. Takeoff minimums are included in standard operations specifications. This AC addresses criteria for takeoff in low visibility conditions where additional aircraft equipment is provided to assist the pilot in a low visibility takeoff, or is required to assure safe operations when using minima below values acceptable for exclusive use of visual reference.
Standard OpSpecs list minima acceptable to FAA for manual control based exclusively on visual reference.
Authorization of takeoff minima below the level supported by use of visual reference alone requires use of a guidance system which has been demonstrated to provide an acceptable level of performance and satisfactory workload for the minima approved, with or without use of visual reference. The performance and workload assessment of such a system must have considered any compensation that may be introduced by the pilot for particular guidance system characteristics (e.g., coping with a slight localizer signal offset during initial runway alignment) or concurrent pilot use of the guidance system with limited or patchy visual references.
Systems intended to be used at or above the minima authorized for visual reference alone (e.g., as a supplement to manual control) may be used if demonstrated to be:
1) Safe in normal use, and
2) If there is no unacceptable increase in pilot workload or significant adverse effect on crew coordination, and
3) If the system is unlikely to introduce a significant hazard if a failure or degradation of the system itself occurs, and
4) If the system is unlikely to introduce a significant additional hazard if other potential failures in the aircraft occur (e.g., engine failure, electrical component failure), and
5) A failure or anomaly in a NAVAID(s) used does not introduce a significant hazard.
Authorized minima for such systems may be no lower than that specified for manual control using visual reference alone.
If low visibility takeoff operations are predicated on the use of RNP, then the provisions applicable to RNP apply only following liftoff, after passing 35 ft. above the published elevation of the runway.
A proof of concept demonstration is necessary for initial authorization of takeoff minima less than RVR300 ft./75m.
Criteria for demonstration of systems eligible for takeoff minima below the level supported by use of visual reference alone are found in section 5.1.3 for operational authorization or Appendix 2 for systems proposed for airworthiness demonstration.
4.3. Landing.
4.3.1. Concepts and Objectives. Category III landing minima are classified as Category IIIa, Category IIIb or Category IIIc. Definitions of these categories are provided in Appendix 1. Visual conditions encountered in Category III operations range from visual references being adequate for manual control during rollout (e.g., Category IIIa) to visual references being inadequate even for taxi operations without special visual reference enhancements or suitable synthetic references. For any Category III operation, the airplane and external system requirements established (e.g., position fixing) should be compatible with any visual reference requirements that are specified.
Category III operations may be conducted manually using Flight Guidance Displays, or automatically using approved autoland system or with Hybrid Systems which employ both automatic and flight guidance elements. If the particular Flight Guidance Display depicts flight director or other command guidance it may be approved in accordance with this AC, or equivalent. Situational Flight Guidance Displays may be used if the Proof of Concept (PoC) is satisfactorily demonstrated. When an automatic system is to be the primary means of control the use of that system should not require pilot intervention. The means for crew intervention must be provided, however, in the unlikely event the pilot detects or strongly suspects inadequate system performance (e.g., the pilot determines that an automatic landing cannot be accomplished within the touchdown zone). If a Hybrid system is employed, then the primary mode of operation must be automatic to touchdown, with manual control used only as an alternate means to complete the operation.
To be approved for Category III operations, the airplane and its associated systems should be shown to be capable of safely completing an approach, touchdown, and rollout and permitting a safe go-around from any altitude to touchdown following any failure condition not shown to be extremely improbable.
Cockpit design, instrumentation, annunciations and warning systems, should be adequate in combination to assure that the pilot can verify that the aircraft should touch down within the touchdown zone and safely rollout if the controlling visibility is reported at or above applicable minima. Systems based on automatic control to touchdown, or touchdown and rollout and manually flown flight guidance system (e.g., HUD), have been approved by FAA. Other concepts may be acceptable if Proof of Concept [PoC] testing can demonstrate an equivalent or greater level of safety as presently specified for approval of automatic systems (e.g., hybrid systems or vision enhancement systems).
To be approved for Category III operations, the airplane and its associated systems should be shown to be able to perform to the necessary level of accuracy, integrity, and availability. This is typically shown initially during airworthiness demonstration, is confirmed during the operational authorization process, and is monitored by the operator on a continuing basis.
Category III operations are predicated on meeting requirements for Category II, or equivalent, for that portion of the approach prior to 100' HAT (see the current version of AC 120-29 for approval of Category II).
If Category III operations are predicated on the use of RNP, then the provisions of this AC or any subsequent current version of AC120-29A, or other suitable FAA criteria for application of RNP are considered to be acceptable to apply to definition of any instrument approach procedure segment down to 100 ft. HAT.
Below 100 ft. HAT, the provisions of this or any subsequent version of AC120-28 are considered to be the applicable criteria to assure the necessary performance for landing, flare and rollout.
For a go-around and missed approach from DA(H), Alert Height (AH), or the end of the touchdown zone for a rejected landing, RNP provisions may be applied from the point of initiation of a go-around to completion of the applicable missed approach procedure, in accordance with provisions of this version of AC 120-29, any subsequent current version, or any other RNP criteria found acceptable to the FAA.
4.3.2. Fail Operational Category III Operations. A Fail Operational System is a system which after failure of any single component, is capable of completing an approach, flare and touchdown, or approach, flare, touchdown and rollout by using the remaining operating elements of the Fail Operational system. The failure effects of single components of the system, airplane or equipment external to the airplane which could have an effect on touchdown or rollout performance must be considered when evaluating Fail Operational systems. Fail Operational systems may be used to touchdown for Category IIIa (e.g., without a rollout system) or Category IIIb through rollout to a full stop. Use of a failoperational system to touchdown in conjunction with a rollout system that is not fail-operational is acceptable as long as a suitable minimum RVR is specified in the operations specifications, for rollout.
This AC contains criteria for approval of minima as low as RVR150 using a fail-operational system for landing and rollout. Approval of minima less than RVR150 would require a proof of concept [PoC] demonstration.
Note: A landing system is considered to include each of the elements in the aircraft which are necessary to perform the landing and rollout function (e.g., flight control, hydraulic system(s), electrical system(s), sensors).
The required redundancy may be provided by multiple automatic landing systems, by multiple automatic landing and rollout systems, by redundant manual flight guidance systems, or by suitably redundant hybrid systems.
The reliability and performance of the required operational systems should be such that continued safe operation to landing, or landing and rollout, can be achieved following any failure condition occurring below the Alert Height that is not shown to be extremely improbable. Systems identified below and in
4.3.3 through sections 4.3.8, or equivalent, are considered to meet the intent of this provision.
Failure conditions which result in the loss or disconnect of all the redundant landing, or landing and rollout systems, occurring below the Alert Height, are permissible if the occurrence of these failure conditions is extremely remote and the loss or disconnect is accompanied by acceptable warning indications for the pilots. Airplanes which are demonstrated to meet the airworthiness assessments of Appendix 3 for fail operational systems are considered to meet these reliability and performance criteria.
The following are typical arrangements which may be acceptable for Fail Operational Systems:
1. Two or more monitored fail passive autopilots or integrated autopilot flight director systems each with dual channels making up an automatic fail operational system designed so that at least one autoflight system remains operative after the failure of one system, and the failed system is not used or cannot cause unacceptable autoflight system performance.
Note: Following a failure with this configuration, it is not intended that a landing be continued with flight director alone, unless a successful Proof of Concept demonstration has been completed.
2. Three autopilots or integrated autopilot flight director systems designed so that at least two remain operative after failure to permit comparison and provide necessary monitoring and protection while continuing to a landing.
3. A monitored fail passive automatic flight control system with automatic landing capability to touchdown and rollout, if applicable, plus an independent and adequately failure protected manual flight guidance system, suitable for landing and rollout with guidance provided for the flying pilot and monitoring displays for the non-flying pilot. A proof of concept demonstration would be necessary for this arrangement.
4. Two independent and adequately monitored manual flight guidance systems with independent displays for the pilot flying and the pilot not flying, each capable of supporting a landing and rollout. A proof of concept demonstration would be necessary for this arrangement.
Aircraft meeting fail-operational requirements of Appendix 3 of this AC, or equivalent, for landing and rollout may be authorized for fail-operational Category III to the lowest currently applicable minima specified in Operations-Specifications for this type of system. As of the publication of this AC, the lowest authorized minima for U.S. operators are Touchdown, Mid, and Rollout RVR of 300ft within the U.S., or 75m internationally.
Aircraft previously demonstrated to meet acceptable fail-operational criteria of earlier AC’s or alternate criteria (e.g., suitable JAR criteria) may receive additional credit beyond those already authorized, as specified in provisions of this AC, through appropriate showing of compliance with applicable operational provisions of this AC, and subsequent amendment of applicable operations specifications.
An example of aircraft in this category are those B767 or B757 aircraft having statements in the FAA approved AFM indicating they met all fail-op rollout provisions of AC 120-28B or AC 120-28C, except for certain rollout disconnect provisions. Since criteria of AC 120-28D are now revised to alternately address this condition, these aircraft are considered eligible to fully meet Appendix 3 provisions for fail-operational rollout and may be operationally authorized for landing minima accordingly (also see 4.3.8).
Aircraft with a fail operational landing system but without a rollout system, that were originally approved in accordance with AC 120-28, AC 120-28A, AC 120-28B or AC 120-28C, may typically be approved for minima not less than Touchdown Zone, Mid and Rollout RVR600. Eligibility for RVR600 requires compliance with appropriate current service bulletins in accordance with the manufacturer’s recommendations, and a determination by FAA that “in-service” operational performance of the system is acceptable.
Aircraft with a fail operational landing system and a rollout system, or a fail operational landing system and a fail passive rollout system originally approved in accordance with FAA “Special Conditions” for a rollout system, or criteria of AC120-28, AC120-28A, or AC120-28B are now considered to have rollout capability equivalent to fail operational and may typically be approved for minima not less than Touchdown Zone, Mid, and Rollout RVR300. Current models in this group found acceptable include the L1011, A300, DC10-30, certain DC10-10s or DC10-40s with suitably upgraded avionics equipment equivalent to currently FAA approved DC10-10s or -30s, and late model B747-200 or - 300 aircraft with appropriate versions of the triple channel SPZ-1 autopilot and a rollout system. For these aircraft, appropriate current service bulletin compliance should be reviewed and completed, and line operational performance of the system must be shown to be acceptable. However it is important to note that, as with other aircraft types, Category III authorization for some of these aircraft may be restricted to certain runway facilities since landing or rollout performance may not necessarily be
acceptable due to site specific irregular underlying approach terrain, touchdown zone slope, or ILS beam characteristics.
4.3.3. Alert Height. Fail-operational Category III is based on use of an Alert Height (see Appendix I). An Alert Height is the height above a runway based on characteristics of the airplane and its Fail Operational System, above which a Category III approach must be discontinued and a missed approach initiated if a failure occurred in one of the redundant parts of the flight control or related aircraft systems, or if a failure occurred in any one of the relevant ground systems. Use of an Alert Height is consistent with the design philosophy which requires that an aircraft be capable of safely completing a touchdown and rollout (if applicable) following a failure occurring after passing the point at which the Alert Height is specified.
Operational Alert Heights must always be equal to or lower than that specified in the airworthiness demonstration, and may be specified at or below 200 ft. HAT. The Alert Height is specified by an operator of an aircraft and approved by the FAA. The operational Alert Height used must be consistent with the aircraft design, training, ground facilities, and other factors pertinent to the air carriers operation. Typically a minimum usable operational alert height is 50’HAT. However lower Alert Heights may be approved if there is an appropriate reason to do so (e.g., for certain types of hybrid systems).
Airworthiness demonstration of an Alert Height is as specified in Appendix 3. In order to assure the necessary reliability of aircraft systems, airworthiness demonstrations of Alert Height should be from an altitude of at least 200 ft. above the touchdown zone elevation.
4.3.4. Fail Passive Category III Operations. A Fail Passive System is a system which in the event of a failure, causes no significant deviation of aircraft flight path or attitude. The capability to continue the operation may be lost and an alternate course of action (e.g., a missed approach) may be required. A fail-passive system is the minimum capability system acceptable for Category III operation with a Decision Height not less than 50 ft. HAT.
Fail Passive Approach Operations are conducted with a decision height not lower than 50 ft., and are limited to RVR values which provide suitable visual reference to address normal operations as well as failure contingencies. Since a Fail Passive Category III system does not necessarily provide sufficient redundancy to successfully continue the approach and landing to touchdown following any failure in the flight control system not shown to be extremely remote, a DH is specified. A DH is established to assure that prior to passing that point the pilot is able to determine that adequate visual reference exists to allow verification that the aircraft should touchdown in the touchdown zone. If this visual reference is not established prior to passing DH, a missed approach must be initiated. After passing DH, a missed approach will also be initiated if visual cues are lost, or a reduction in visual cues occurs which prevents the pilot from continuing to verify the aircraft is in a position which will permit a landing in the touchdown zone. In the event of a failure of the airborne system at any point in the approach to touchdown, a
missed approach is required. However, this provision does not preclude a pilot's authority to continue an approach if continuation of an approach is considered by the pilot to be a safer course of action.
Such a failure however, does not preclude continuation to a Category I or Category II minima if the necessary remaining elements of the aircraft system are operational and if the crew qualification addresses necessary action to continue such an approach are met. Any adjustments to approach minima or procedures made on final approach should be completed at a safe altitude (e.g., above 500 ft. HAT).
The need to initiate a go-around below 100 ft. AGL due to an airplane failure condition should be infrequent. In addition, an aircraft using a Fail Passive system for Category III should be shown to provide the capability to touch down in the touchdown zone or to complete a safe manual or automatic go-around from any altitude to touchdown following any failure condition not shown to be extremely improbable.
Typical arrangements which may be used to meet the requirements for Category III fail passive operations using a 50 ft. Decision Height include the following:
1. A single monitored automatic flight control system with automatic landing capability.
2. A fail operational automatic flight control system with automatic landing which has reverted to a Fail Passive configuration or has been dispatched in a fail-passive configuration.
3. A monitored flight guidance system (e.g., HUD) designed for manual control by the pilot flying, and for monitoring by the pilot not flying. Aircraft intended for Fail Passive Category III operations should have aircraft systems which meet the criteria specified in Appendix 3. Aircraft previously demonstrated to meet earlier Fail Passive criteria may continue to operate using Category III minima in accordance with approved operation specifications.
4.3.5. Decision Altitude (Height). For Category II and certain Category III procedures (e.g., when using a Fail-Passive landing system) a Decision Height (or an equivalent IM position fix) is used as the controlling minima. The "Altitude" value specified is considered as advisory. The altitude value is available for cross reference. Use of a barometrically referenced DA for Category III is not currently authorized for part 121, 129 or 135 operations at U.S. facilities.
A Decision Height is applied to all Fail Passive operations and is specified at certain locations where fail operational minima is authorized. For Category III, a Decision Height is usually based on a specified radio altitude above terrain on the final approach or touchdown zone. The Decision Height is established to assure that prior to passing that point the pilot is able to determine that adequate visual reference exists to allow verification that the aircraft should touch down in the touchdown zone.
For Category I, a DA(H) is specified as the minimum altitude in an approach by which a missed approach must be initiated if the required visual reference to continue the approach has not been
established. The "Altitude" value is typically measured by a barometric altimeter or equivalent (e.g., Middle Marker) and is the determining factor for minima for Category I Instrument Approach Procedures. The "Height" value specified in parenthesis is typically a radio altitude equivalent height above the touchdown zone (HAT) used only for advisory reference and does not necessarily reflect actual height above underlying terrain. The DA element of a DA(H) is applicable to Category III only in the event that an approach is considered to revert to Category I or Category II minima following airborne equipment failure, ground facility status, or other similar condition permitting an approach to be conducted to pertinent Category I or II minima.
4.3.6. Go-Around Safety. An aircraft approved for Category III should be capable of safely executing a go-around from any point in an approach prior to touchdown with the aircraft in a normal configuration, or specified non-normal configuration (e.g., engine out if applicable). It is necessary to provide for go-around due to Air Traffic Services contingencies, rejected landings, loss of visual reference, or missed approaches due to other reasons. The evaluation of this capability is based on normal, or specified non-normal, Category III operations at the lowest controlling RVR authorized and should account for factors related to geometric limitations during the transition to go around, limited visual cues, auto-pilot mode switching and other pertinent factors. For aircraft in which a go-around from a very low altitude may result in an inadvertent touchdown, the safety of such a procedure should be established considering its effect on related systems, such as operation of auto spoilers, automatic braking systems, autopilot mode switching, autothrottle mode, reverse thrust initiation and other systems associated with, or affected by, a low altitude go-around.
Except for failure conditions shown to be extremely improbable, a safe go-around must be possible from any point on the approach to touchdown.
If an automatic go-around capability is provided, it should be demonstrated that a go-around can be safely initiated and completed from any altitude to touchdown. If the automatic go-around mode can be engaged at or after touchdown, it should be shown to be safe. The ability to initiate an automatic goaround at or after touchdown is not required.
4.3.7. Category IIIa. In accordance with ICAO definitions of Category III, Category IIIa operations may be conducted with either Fail Operational or Fail Passive systems. The lowest approvable landing minima for Category IIIa is RVR700 or a foreign equivalent of 200 meters.
Note: For certain Category III operations using fail passive systems that were formerly limited to RVR700, but now are eligible for authorization to RVR600, see paragraph
4.3.8 (Most Category III operations authorized for RVR700 prior to issuance of this AC are now eligible for authorization to RVR600, upon request of the operator for issuance of a revision to that operator's pertinent OpSpecs).
Category IIIa operations with fail passive systems are conducted using a 50 ft. Decision Height.
Category IIIa operations using a fail operational system with a rollout control system are generally conducted using an Alert Height, and not a Decision Height. Visual reference is not a specific requirement for continuation of the approach or touchdown.
Category IIIa operations using a fail operational system without a rollout control system installed require establishment of suitable visual reference with the touchdown zone prior to touchdown.
For any of the above systems there should be a sufficient combination of information from flight instruments, annunciations, and alerting systems to assure that the pilot can verify that the aircraft should touch down within the touchdown zone, and safely initiate rollout.
Unless otherwise specified by FAA, aircraft having operation specifications authorizing RVR700 as of the effective date of this AC, may continue to use those minima without additional demonstration.
Aircraft demonstrated to meet airworthiness provisions of AC 120-28B or AC 120-28C for Fail Passive systems remain eligible for any previously approved operational authorization under provisions of this AC and do not require additional airworthiness demonstration. Aircraft previously having completed an airworthiness demonstration in accordance with AC 120-28C remain eligible for any operational authorization that was permitted by AC 120-28C.
Aircraft demonstrated to meet airworthiness criteria prior to AC 120-28B, and not currently authorized in operations specifications for Category III may be approved for new Fail Passive Category III operations on a case-by-case basis depending on facilities to be used, service bulletin compliance status and other relevant safety factors.
Aircraft, including wide body aircraft such as the DC-10, L1011 and B 747, which are authorized for fail-operational Category III, but have not been demonstrated to meet the provisions for Fail Passive systems shown in Appendix 3, may be approved for Fail Passive operations with landing minima limited to RVR1000 provided the following criteria are met:
1. The aircraft must be shown to be in compliance with relevant service bulletins for the applicable flight control system and displays.
2. An auto throttle system must be installed and operational.
3. The system must be shown to provide reliable auto land performance in line operations.
4. A demonstration using a simulator or aircraft must be completed for that operator and aircraft type, showing that the system and procedures applicable to Fail Passive operations can be practically applied for that air carrier’s operation.