AC 120-28D Appendix 2 07/13/99 For the use of systems other than ILS or MLS for ‘path in space’ guidance, the assumptions and considerations for the non-airplane elements of the system may be different than applicable to ILS or MLS. If different than ILS or MLS, the applicant shall address these differences and how they relate to the airplane system certification plan.
As applicable, the plan for certification shall describe any new or novel system concepts or operational philosophy to allow the regulatory authority to determine whether criteria and requirements in excess of that contained in this appendix are necessary.
7.1. Performance Evaluation. For new systems and any significant changes to an existing system, the performance of the airplane and its systems must typically be demonstrated by flight test. Flight testing must include a sufficient number of normal and non-normal operations conducted in conditions which are reasonably representative of actual expected conditions and must cover the range of parameters affecting the behavior of the airplane (e.g., wind speed, ILS characteristics, airplane configurations, weight, center of gravity, and non-normal events).
The performance evaluation must verify that the Takeoff System meets the centerline tracking performance requirements and limits of section 6.1.1. of this appendix.
The system performance must be demonstrated in "non-visual conditions" for:
a) normal operations,
b) engine failure cases and,
c) recovery from displacements from non-normal events.
This performance shall be demonstrated to have a satisfactory level of workload and pilot compensation, such as defined by the FAA Handling Quality Rating System (HQRS) found in AC 25-7A, as amended, or equivalent.
The takeoff system shall be shown to be satisfactory with and without the use of any outside visual references, except that outside visual references will not be considered in assessing lateral tracking performance. The airworthiness evaluation will also determine whether the combination of takeoff guidance and outside visual references would unacceptably degrade task performance, require excessive pilot compensation or workload during normal and non-normal operations.
For the purpose of the airworthiness demonstration, the operational concept for coping with the loss of takeoff guidance is based upon availability of some other method for the flightcrew to safely continue or reject the takeoff. The airworthiness demonstration may include a loss of takeoff guidance.
The demonstration of system performance should comprise at least the following, (though more demonstrations may be needed, depending on the airplane characteristics and system design, and any difficulties encountered during testing):
• 20 normal, all-engine takeoffs.
• 10 completed takeoffs, with simulated engine failure at or after the appropriate Vef for the minimum V1 for the airplane. All critical cases must be considered.
• 10 rejected takeoffs, some with simulated engine failure just prior to V1, and at least one run with simulated engine failure at a critical speed less than Vmcg.
AC 120-28D 07/13/99 Appendix 2 For modified systems, credit may be permitted for earlier demonstration(s), but testing up to that necessary for a new system may be required if credit for similarity of design or performance is not appropriate.
Engine failures should be assessed with respect to workload and pilot compensation throughout the entire takeoff phase. In cases where the dynamics of retarding the throttle to idle do not adequately simulate the dynamics of an engine failure, the certifying authorities may require an actual engine shutdown for these demonstrations.
Demonstrated winds, during normal all engine takeoff, should be at least the headwinds for which credit is sought, and at least 150% of the cross winds and tailwinds for which credit is sought, but not less than 15 knots of headwind or crosswind.
The applicant shall demonstrate that operation of the takeoff system does not exhibit any guidance or control characteristics during the operation which would cause the flightcrew to react in an inappropriate manner.
The system shall be demonstrated to have no display or failure characteristics that lead to degradation of the crew’s ability to adequately monitor takeoff performance (e.g., acceleration, engine performance, takeoff speed callouts), and conduct the entire takeoff, and make an appropriate transition to en route climb speed and configuration, for all normal, abnormal and emergency situations.
The system must be evaluated and demonstrated to meet the integrity and failure annunciation requirements of section 6.2, 6.4, and sub-sections of this appendix, as well as the pilot's ability to immediately detect and mitigate non-annunciated failures, as described in section 6.2.
For takeoff systems that use an ILS localizer signal, the airplane system response to loss of the localizer signal shall be demonstrated, and appropriately annunciated to the crew. The airplane system response during a switchover from an active localizer transmitter to a backup transmitter shall be demonstrated (Reference ICAO Annex 10).
For takeoff systems that use MLS, the airplane system response to the loss of the MLS signal shall be demonstrated, and appropriately annunciated to the crew. The airplane system response during a switchover from an active azimuth transmitter to a backup transmitter shall be demonstrated (Reference ICAO Annex 10).
For the evaluation of takeoff systems, the set of subject pilots provided by the applicant should have relevant variability of experience (e.g., experience with or without head-up- display (HUD), Captain or First Officer (F/O) crew position experience as applicable, experience in type). Subject pilots must not typically have special experience that invalidates the test (e.g., pilot's should not have special recent training to cope with HUD failures, beyond what a line pilot would be expected to have for routine operation). The set of pilots provided by the certifying authorities may have experience as specified by the authority appropriate to the test(s) to be conducted. The experience noted above for authority subject pilots or evaluation pilots may or may not be applicable or appropriate for the tests to be conducted.
Failure cases should typically be spontaneous and unpredictable on the subject's or evaluation pilot's part.
7.2. Safety Assessment. In addition to any specific safety related criteria identified in this appendix, a safety assessment of all airplane components of the takeoff system and associated components, considered separately, shall be conducted in accordance with AC 25.1309 to meet the requirements of section 25.1309.
AC 120-28D Appendix 2 07/13/99 In showing compliance with airplane system performance and failure requirements, the probabilities of performance or failure effects may not be factored by the proportion of takeoffs which are made in low visibility conditions.
The responses of the takeoff system to failures of navigation facilities must be considered, taking into account ICAO and other pertinent State criteria for navigation facilities, (for more information see Section 8 of this AC).
Documented conclusions of the safety analysis shall include:
a. A functional hazard assessment (FHA) conducted in accordance with section 25.1309 and a summary of results from the fault tree analysis, demonstrated compliance, and probability requirements for significant functional hazards.
b. Information regarding "alleviating flightcrew actions" that were considered in the safety analysis.
This information should list appropriate alleviating actions, if any, and should be consistent with the validation conducted during testing. If alleviating actions are identified, the alleviating actions should be described in a form suitable to aid in developing, as applicable:
1) Pertinent provisions of the airplane flight manual procedures section(s), or
2) Flight Crew Operating Manual (FCOM) provisions, or equivalent, or
3) Pilot qualification criteria (e.g., training requirements, FSB provisions), or
4) Any other reference material necessary for an operator or flightcrew to safely use the system.
c. Information to support preparation of any maintenance procedures necessary for safety, such as:
1) Certification maintenance requirements (CMR),
2) Periodic checks, or
3) Other checks, as necessary (e.g., return to service).
d. Information applicable to limitations, as necessary.
e. Identification of applicable systems, modes or equipment necessary for use of the takeoff system, to aid in development of flight planning or dispatch criteria, or to aid in development of procedures or checklists for pilot selection of takeoff mode or assessment of system status, prior to initiation of takeoff.
f. Information necessary for development of Non-normal procedures.
8. AIRBORNE SYSTEM.
8.1. General. All general takeoff system requirements are found in section 6.1 of this appendix.
8.2. Peripheral Vision Guidance Systems [PoC]. Peripheral vision systems have not been shown to be suitable as primary means of takeoff guidance. Such systems may be used as a supplemental means of takeoff guidance only if a suitable minimum visual segment is available. A Proof of Concept evaluation program is necessary for Peripheral Vision Guidance systems intended for use as primary means of
AC 120-28D 07/13/99 Appendix 2 takeoff guidance or as supplemental means with visual segments less than the minimum required for un-aided operation.
8.3. Head Up Display Takeoff System. The following criteria is applicable to head up display takeoff systems:
a) The workload associated with use of the HUD must be considered in showing compliance with 14 CFR part 25, section 25.1523.
b) The HUD installation and display presentation must not significantly obscure the pilot's outside view.
c) The entire takeoff operation, through completion of the en route climb configuration, (see section 25.111), is considered to be an intensive phase of flight during which unnecessary pilot workload and compensation should be avoided. Appropriate transition from lateral takeoff guidance (i.e., at about 35 ft. AGL) through transition to en route climb for a takeoff, and from brake release through deceleration to a stop for an aborted takeoff should be ensured. For the entire takeoff and for all normal, and non-normal situations, except loss of the HUD itself, it must not be necessary for the "pilot flying (PF)" to make any immediate change of primary display reference for continued safe flight.
d) Control of Takeoff Flight Path. For the entire takeoff path and for all normal and non-normal conditions, except loss of the HUD itself, the HUD takeoff system must provide acceptable guidance and flight information to enable the PF to complete the takeoff, or abort the takeoff, if required. Use of the HUD takeoff system should not require excessive workload, exceptional skill, or excessive reference to other cockpit displays.
e) The HUD shall provide information suitable for the PF to perform the intended operation. The current mode of the HUD system itself, as well as the flight guidance/automatic flight control system, shall be clearly annunciated in the HUD, unless they can be acceptably displayed elsewhere.
f) Systems which display only lateral deviation as a cue for centerline tracking have not been shown to provide adequate information for the PF to determine the magnitude of the required directional correction. Consequently, with such displays workload and pilot compensation are considered excessive.
A proposed system which displays situation information, in lieu of command information, requires a successful proof of concept evaluation. [PoC]
g) If the system is designed as a single HUD configuration, then the HUD shall be installed for the Captain’s (pilot in command) crew station.
h) Associated cockpit information must be provided to the pilot not flying (PNF) to monitor the PF performance, and perform other assigned duties.
8.4. Satellite Based Systems [PoC]. Currently approved systems are ILS or MLS based. The application of new technologies and systems such as GLS/GNSS requires an overall assessment of the integration of the airplane components with other elements to ensure that the overall safety of the use of these systems is acceptable.
The performance, integrity and availability of any ground station elements, any data links to the airplane, any satellite elements and any data base considerations, when combined with the performance, integrity and availability of the airplane system, should be at least equal to the overall performance, integrity and availability provided by ILS to support equivalent low visibility operations.
AC 120-28D Appendix 2 07/13/99 The role of the satellite based elements in the takeoff system should be addressed as part of the airplane system certification process until such time as an acceptable national, or international standard, for the satellite based system is established.
8.4.1. Flight Path Definition. For Flight Path Definition considerations refer to Section 4.6 of the AC.
8.4.2. On Board Database. Unless there is a means to upload the path definition data via datalink, the required lateral ground path should be stored in an on board database for recall and incorporation into the guidance/control system when required to conduct the takeoff.
The definition, resolution and maintenance of the waypoints which define the required takeoff path should be consistent with the takeoff operation. A mechanism should be established to ensure the continued integrity of the takeoff path designators.
Corruption of the information contained in the on board data base used to define the reference flight path is considered Hazardous. Failures which result in hazardous unannunciated changes to the on board data base must be Extremely Remote.
The flightcrew should not be able to intentionally or inadvertently modify information in the on board data base which relates to the definition of the required flight path.
The integrity of any on board data base used to define takeoff path waypoints for a Takeoff System should be addressed as part of the certification process.
8.4.3. Datalink. Data may be sent to the airplane, via data link, so that the takeoff flight path can be defined with the required accuracy. The required takeoff path may be stored in a ground station database which is uplinked to an airplane, either on request or through continuous transmission. The airplane guidance and control system may incorporate such information to conduct the takeoff.
The integrity of the data link should be commensurate with the integrity required for the operation. The role of the data link in the takeoff system must be addressed as part of the airplane system certification process unless acceptable FAA, or international standards, for the ground system are established. The following items shall be addressed as part of the Takeoff System assessment:
a) Satellite systems used during takeoff must support the required performance, integrity and availability.
This should include the assessment of satellite vehicle failures and the effect of satellite vehicle geometry on the required performance, integrity and availability.
b) The capability of the Takeoff System failure detection and annunciation mechanism to preclude an undetected failure, or combination of failures which are not Extremely Remote, from producing a hazardous condition. This assessment should include failure mode detection coverage and adequacy of monitors and associated alarm times.
c) The effect of airplane maneuvers on the reception of signals necessary to maintain the necessary performance, integrity and availability. Loss and re-acquisition of signals should be considered.
8.5. Enhanced Vision Systems [PoC]. Enhanced Vision Systems which penetrate visibility restrictions to provide the flightcrew with an enhanced view of the scene outside the airplane (e.g., radar) may be considered for airworthiness installation and demonstration. However, this Appendix does not comprehensively address a means of compliance for airworthiness installation approval of such
AC 120-28D 07/13/99 Appendix 2 Enhanced Vision Systems. Performance must be demonstrated to be acceptable to the FAA through proof of concept testing, during which specific airworthiness and operational criteria may be developed.
Criteria for approval of the enhanced vision system must match its intended use. The fidelity, alignment and real time response of the enhanced view must be shown to be appropriate for the intended application. Enhanced Vision Systems also must not significantly degrade the pilot's normal view, when visual reference is available.
9. Airplane Flight Manual. Upon satisfactory completion of an airworthiness assessment and test program, the FAA-approved airplane flight manual or supplement, and any associated markings or placards, if appropriate, should be issued or amended to address the following:
1) Relevant conditions or constraints applicable to takeoff system use regarding the airport or runway conditions (e.g., elevation, ambient temperature, runway slope).
2) The criteria used for the demonstration of the system, acceptable normal and non-normal procedures (including procedures for response to loss of guidance), the demonstrated configurations, and any constraints or limitations necessary for safe operation.
3) The type of navigation aids used as a basis for demonstration. This should not be taken as a limitation on the use of other facilities. The AFM may contain a statement regarding the type of facilities or condition known to be unacceptable for use (e.g., For ILS or MLS) based systems, the AFM shall indicate that operation is predicated upon the use of an ILS (or MLS) facility with performance and integrity equivalent to, or better than, a United States Type II or Type III ILS, or equivalent ICAO Annex 10 Facility Performance Category III facility).
4) Applicable atmospheric conditions under which the system was demonstrated (e.g., demonstrated headwind, crosswind, tailwind),
5) For a Takeoff system meeting provisions of Appendix 2, the AFM (Section 3, Normal Procedures) should also contain the following statements:
"The airborne system has been demonstrated to meet the airworthiness requirements of AC 120-28D Appendix 2 for Takeoff when the following equipment is installed and operative:
<list pertinent equipment>" "This AFM provision does not constitute operational approval or credit for use of the takeoff system."
Examples of general AFM considerations and specific AFM provisions are provided in Appendix 6.
AC 120-28D 07/13/99 Appendix 3 APPENDIX 3
AIRWORTHINESS APPROVAL FOR AIRBORNE SYSTEMS
USED TO LAND AND ROLLOUT IN LOW VISIBILITY CONDITIONS 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.
1. PURPOSE. This appendix contains criteria for the approval of aircraft equipment and installations used for Landing and Rollout in low visibility conditions.
2. GENERAL. The type certification approval for the equipment, system installations and test methods should be based upon a consideration of factors such as the intended function of the installed system, its accuracy, reliability, and fail-safe features, as well as the operational concepts contained in the body of this AC. The guidelines and procedures contained herein are considered to be acceptable methods of determining airworthiness for a transport category airplane intended to conduct a landing and rollout in low visibility conditions.
In addition to the criteria found in this appendix, equipment and installation must also meet the criteria contained in AC 120-29, as amended, an equivalent foreign standard acceptable to the Administrator, or any other criteria acceptable to the Administrator.
The overall assurance of performance and safety of an operation can only be assessed when all elements of the system are considered.
3. INTRODUCTION. This appendix addresses the final approach, landing and the rollout phase of flight. Landing and Rollout Systems may combine various combinations of airplane sensors and system architecture with various combinations of ground and space based elements. This appendix provides criteria which represents an acceptable means of compliance with performance, integrity and availability requirements for low visibility approach, landing and rollout systems to accomplish a landing and rollout in low visibility conditions. Alternative criteria may be proposed by an applicant. With new emerging technologies, there is a potential for many ways of conducting low visibility landings. This appendix does not attempt to provide criteria for each potential combination of airborne and non-airborne elements.
Operations utilizing current ILS or MLS ground based facilities and airborne elements are in use, and the certification criteria for approval of these airborne systems are established. Other operations, using nonground based facilities or evolving ground facilities (e.g., local or wide area augmented GNSS), and the use of some new aircraft equipment require Proof of Concept testing to establish appropriate criteria for operational approval and system certification. The need for a Proof of Concept program is identified in this AC with a [PoC] designator. This appendix provides some general guidelines, but not comprehensive criteria for airplane systems that require a Proof of Concept.
The low visibility landing system is intended to guide the airplane down the final approach segment to a touch down in the prescribed touch down zone, with an appropriate sink rate and attitude without exceeding prescribed load limits of the airplane. The rollout system is intended to guide the airplane to converge on and track the runway centerline, from the point of touch down to a safe taxi speed.
AC 120-28D Appendix 3 07/13/99 The low visibility landing system shall be shown to be satisfactory with and without the use of any outside visual references, except that outside visual references will not be considered when assessing lateral tracking performance. The airworthiness evaluation will also determine whether the combination of guidance and outside visual references would unacceptably degrade task performance, or require exceptional workload and pilot compensation, during normal operations and non-normal operations with system and airplane failure conditions.
For the purpose of the airworthiness demonstration, the operational concept for coping with the loss of guidance is based upon the availability of some other method to accomplish a go-around, landing, or rollout, if necessary. The airworthiness demonstration may include a loss of guidance.
The minimum visibility required for safe operations with such systems and backup means will be specified by FAA Flight Standards in the operational authorization.
The intended flight path may be established in a number of ways. For systems addressed by this appendix, the reference path may be established by a navigation aid (e.g., ILS, MLS). Other methods may be acceptable if shown feasible by a Proof of Concept [PoC]. Methods requiring PoC include, but are not limited to:
• the use of ground surveyed waypoints, either stored in an on-board data base or provided by data link to the airplane, with path definition by the airborne system,
• sensing of the runway environment (e.g., surface, lighting and/or markings) with a vision enhancement system.
On-board navigation systems may have various sensor elements by which to determine airplane position.
The sensor elements may include ILS, MLS, Inertial information, GLS, other Global Navigation Satellite System (GNSS) elements, Local Area Differential GNSS, or GNSS related Pseudolites. Each of these sensor elements should be used within appropriate limitations with regard to accuracy, integrity and availability.
Indications of the airplane position with respect to the intended lateral path can be provided to the pilot in a number of ways.
• deviation displays with reference to navigation source (e.g., ILS receiver, MLS receiver), or
• on-board navigation system computations with corresponding displays of position and reference path
4. TYPES OF LANDING AND ROLLOUT OPERATIONS. The following types of Category III operations typically may be considered:
(1) Fail-operational landing with fail-operational rollout
(2) Fail-operational landing with fail-passive rollout
(3) Fail-passive landing with fail-passive rollout
(4) Fail-passive landing without rollout system capability
(5) The following engine inoperative capabilities may optionally* be demonstrated, for each or any of the cases listed above:
AC 120-28D 07/13/99 Appendix 3
a) Landing with engine failure prior to initiation of the approach
b) Landing and rollout with engine failure after initiation of the approach, but prior to DA(H) or AH, as applicable.
*NOTE: The case of engine failure after passing AH (or DA(H)) through touchdown, or through touchdown and rollout as applicable, is typically addressed as a basic consideration for any system demonstration intended for Category III.
The following definitions may be used for the operations described above.
Landing - for the purpose of this appendix, landing begins at 100 ft., the DH or the AH, to the first contact of the wheels with the runway.
Rollout - for the purpose of this Appendix, rollout starts from the first contact of a wheel(s) with the runway and finishes when the airplane has slowed to a safe taxi speed.
Safe Taxi Speed is the speed at which the pilot can safely taxi off the runway using typical exits, or bring the airplane expeditiously to a safe stop. The safe taxi speed may vary with visibility conditions, airplane characteristics, and means of lateral control.
5. TYPES OF LANDING AND ROLLOUT SERVICES.
5.1. ILS. The ILS is supported by established international standards for ground station operation.
These standards should be used in demonstrating airplane system operation.
The airplane system response during a switchover from an active localizer transmitter to a backup transmitter shall be established. For procedures which do not use a localizer for missed approach, total failure (shutdown) of the ILS ground station may not significantly adversely effect go-around capability.
The Airplane Flight Manual shall indicate that operation is predicated upon the use of an ILS facility with performance and integrity equivalent to, or better than, an ICAO Annex 10 Facility Performance Category III ILS, a United States Type II or Type III ILS, or equivalent.
5.1.1. ILS Flight Path Definition. The required lateral flight path is inherent in the design of the ILS.
Acceptable performance and integrity standards have been established for ILS (see section 8.1 of the AC).
5.1.2. ILS Airplane Position Determination. The airplane lateral position relative to the desired flight path is accomplished by an airplane ILS receiver which provides deviation from the extended runway centerline path when in the coverage area.
5.2. MLS. The MLS is supported by established ICAO Annex 10 international standards for ground station operation. These standards should be used in demonstrating airplane system operation.
The airplane system response during a switchover from an active azimuth transmitter to a backup transmitter shall be established. Total failure (shutdown) of the MLS ground station may not significantly adversely affect go-around capability.
AC 120-28D Appendix 3 07/13/99 The Airplane Flight Manual shall indicate that operation is predicated upon the use of an MLS facility with performance and integrity equivalent to, or better than, an ICAO Annex 10 Facility Performance Category III MLS, or equivalent.
5.2.1. MLS Flight Path Definition. The lateral required flight path is inherent in the design of the MLS.
Acceptable performance and integrity standards have been established for MLS (see section 8.1 of the AC).
5.2.2. MLS Airplane Position Determination. The airplane lateral position relative to the desired flight path is accomplished by an airplane MLS receiver which provides deviation from the extended runway centerline path when in the coverage area.
5.3. GLS/GNSS [PoC]. This appendix section is not intended to provide a comprehensive acceptable means of compliance for airworthiness approval of GLS or GNSS based systems, but it does address key issues pertinent to any applicant who may seek early approval of a GLS (or GNSS based) system. Currently approved systems are ILS or MLS based. The application of new technologies and systems requires an overall assessment of the integration of the airplane components with other elements (e.g., new ground based aids, satellite elements) to ensure that the overall safety of the use of these systems for Category III.
This GLS/GNSS section is also included to identify important differences between conventional ILS/MLS based systems and GLS/GNSS based systems that may affect GNSS or GLS criteria development.
The performance, integrity and availability of any ground station elements, any data links to the airplane, any satellite elements and any data base considerations, when combined with the performance, integrity and availability of the airplane system, should be at least equivalent to the overall performance, integrity and availability provided by ILS to support Category III operations.
5.3.1. GLS/GNSS Flight Path Definition. Appropriate identification of the required flight path for the landing and rollout is necessary to ensure safety of the operation. The required flight path should be established to provide adequate clearance between the airplane and fixed obstacles on the ground, between airplane on adjacent approaches, and to ensure that the airplane stays within the confines of the runway.
The effect of the navigation reference point on the airplane on flight path and wheel to threshold crossing height must be addressed.
In a GNSS based Landing and Rollout System, the required lateral path is established by data, rather than the physical location of an RF signal in space. Earth referenced waypoints define the required path, which is coincident with the runway centerline. The airplane navigation and flight guidance system will require that the appropriate waypoints be provided either from an onboard database or via a datalink.
Certain "special waypoint" definitions, "leg types," and other criteria are necessary to safely implement landing and rollout operations using satellite systems and other integrated multi-sensor navigation systems. Figure 4.6-1 of the AC shows the minimum set of "special waypoints" and "special leg types" considered necessary to conduct landing and rollout operations in air carrier operations.
The required flight path may be stored in an airplane database for recall and use by the command guidance and/or control system when required to conduct the landing and rollout.
The definition, resolution and maintenance of the waypoints which define the required flight path and flight segments is key to the integrity of this type of landing and rollout operation.
A mechanism should be established to ensure the continued integrity of the flight path designators.
AC 120-28D 07/13/99 Appendix 3 The integrity of any data base used to define flight critical path waypoints for a Landing and Rollout System should be addressed as part of the certification process. The flightcrew shall not be able to modify information in the data base which relates to the definition of the required flight path for the critical portion of final approach through rollout.
5.3.2. GLS/GNSS Airplane Position Determination.
The safety of a low visibility landing and rollout operation is, in part, predicated on knowing where the airplane is positioned relative to the required flight path. Navigation satellite systems exist which can provide position information to specified levels of accuracy, integrity and availability. The accuracy, integrity and availability can be enhanced by additional space and ground based elements. These systems provide certain levels of capability to support present low visibility operations and are planned to have additional future capability.
Satellite systems have the potential to provide positioning information necessary to guide the airplane during landing and rollout. If operational credit is sought for these operations, the performance, integrity and availability must be established to support that operation. Ground based aids such as differential position receivers, pseudolites etc., and a data link to the airplane, may be required to achieve the accuracy, integrity or availability for certain types of operation.
An equivalent level of safety to current ILS based Category III operations should be established.
The role of the satellite based elements in the landing system should be addressed as part of the airplane system certification process until such time as an acceptable national, or international standards, for satellite based systems are established.
Basic GNSS (Unaugmented). This is the basic navigation service provided by a satellite system. No additional elements are used to enhance accuracy or integrity of the operation.
Differential Augmentation. The role of the differential station in the landing system should be addressed as part of the airplane system certification process, unless an acceptable national, or international standard, for the ground reference system is established.
Local Area Differential Augmentation. Local Area Differential (LAD) augmentation consists of a set of ground based GNSS receivers that are used to derive pseudo-range corrections and integrity data referenced to a point on or near the airport. This augmentation data is then provided to the airplane via a local, ground based data broadcast signal.
Wide Area Differential Augmentation. Wide Area Differential (WAD) augmentation is not applicable to Category III, except where used in conjunction with other sensors (e.g., to substitute for DME with ILS).
Typically only LAD systems provide a basis for establishing the necessary position fixing accuracy, integrity and availability for the final portion of a final approach segment or rollout. Unaugmented GNSS or WAD are typically only suited for support of initial or intermediate segments of an approach, final approach to restricted DA(H)s, or missed approach. GNSS or WAD may however be used in conjunction with Category III procedures for applications such as equivalent DME distance, or marker beacon position determination, when authorized by the operating rules.