i. Interface to Barometric Altimeter.
(1) If there is an air data s ource select switch, when the pilo t de-selects a n air data source the de-selected source must no longer be used by the GNSS equipment. This becomes important for barometric-aided FDE, since erroneous altitude inputs to the FDE algorithm could lead to improper satellite detection and exclusion.
(2) If the GNSS equipm ent requires barom etric corrected (or pressure) altitude data for certain operations (identified in the GNSS installation ins tructions), the installation should prov ide an auto matic altitu de input from the air data system to the GNSS such that additional pilot actions are not required.
(3) If barometric corrected altitude is required by the GNSS equipm ent and an automatic input of the barometric corrected altitude is not a vailable, an alert for the pilot during approach m ust be provided indicating th e need to e nter the bar ometric pr essure setting in th e GNSS. If the equipm ent requires multiple entries to en ter the co rrection, the workload should be evaluated during an approach.
19. INSTALLATION ISS UES – LP V AND GL S APP ROACHES. This paragraph provides guidance related to the installation of WAAS and LAAS equipm ent supporting LPV or GLS approaches. This guidance applie s to all installations, but is only expected to be spe cifically evaluated as p art of the initial airworthin ess a pproval. GNSS equipment intended for LPV or precision ap proach operation m ust provide for the following:
a. Update Rate. For sensors that support an LPV or precision approach capability (Class 3 equipment of TSO-C145a, LAAS equipment), the position used for the approach must be output at 5 Hz. If the TSO-C145a equipm ent provides a 1 Hz output, the installation must use inertial aiding or other method to obtain deviations at 5 Hz.
b. Differential Group Delay. If the G NSS equipment is ins talled with an antenna that has no t previou sly been de termined to be com patible, verif y that the d ifferential group delay of the antenna is less than or e qual to the requirem ent for the receiver (as specified in RTCA/DO-229C, section 2.1.4.5). The differential group delay of the antenna will be do cumented in th e ins tallation instructions, and the requirem ent for differential group delay will be do cumented in the receiver ins tallation ins tructions.
Antennas h ave filters that cou ld affect the delay. If the antenna instructions do not document the differential group delay, then th e data should be obtained and found to be within the limits specified in the rec eiver installation instructions before approval can be given for approach operations.
c. Performance Monitoring. Suff icient information must be provided in the flight deck to allo w the pilots to m onitor the progr ess and safety of the approach operation.
This in-flight performance monitoring must include:
(1) Unambiguous identification of the intended path for the approach, (e.g. LPV or GLS approach, identifier, frequency or channel number, and selected navigation source), and
(2) Indication o f the positio n of the aircraf t with r espect to th e intended path
(e.g. cross track and vertical deviation information).
Par 18 Page 33
d. System Status. The flig ht crew m ust have a m eans to evalu ate the c apability of the a ircraft equipm ent to ac complish the lo w visibility operation prior to an d af ter departure. The flight crew must be advised of failed ai rcraft sys tems or equ ipment affecting the decision to continue to the destination or divert to an alternate.
e. Annunciations. For installations containing m ore than one approach navigation source, the navigation source (e.g. ILS, GL S) selected for the approach m ust be positively indicated in the normal field of view at each pilot station.
f. Accessibility.
(1) Single equ ipment installations m ust be accessib le and us able by the p ilot.
For aircraft requiring tw o crew members, the equipment should be accessible and usable by either pilot located at a pilot or copilot crew station.
(2) Dual (or more) equipm ent installa tions m ust have a convenient and expedient way to update da ta, infor mation and program s, and a m eans to ensure consistency between the equipm ent (e.g., a “c rossload” capability can ensure identical data) (also addressed under paragraph 18f for stand-alone navigation equipment).
20. INSTALLATION ISSUES – LAAS VDB RECEIVER . This paragraph provides guidance related to the installation of a VDB receiver, including those embedded within a multi-mode receiver. This guidance applies to all installations, but is only expected to be specifically evaluated as part of the initial airworthiness approval.
a. Interference – EMC. The VDB receiver may be susceptible to interference from VHF communications equipment on the aircraft.
(1) For horizontally polarized VDB antenna operating in the presence of a +40 dBm (EIRP) vertically polarized VHF communications transmission, at least 53 dBc of isolation is required to prot ect the VDB rece iver from desensitization. This isolation may be achieved through a com bination of 15 dBc of cross-polariz ation rejection and -38 dBc of antenna coupling.
(2) For aircraft using a vertically polari zed VDB ant enna, the full 53 dBc m ust be achieved through an tenna coup ling. It is not feasible to accom plish this isolation simply due to free space path loss: special considerations will be required.
b. Compatibility with other systems. The VDB receive r may use the loc alizer or VOR antenna. In this case, the performance of the localizer or VOR receivers m ust be re-assessed due to the degradation in sign al strength resulting f rom the splitte r.
AC 23-8A, AC 25-7A, AC 27-1B, and AC 29- 2A provide guidance material on th ese installations.
c. VDB aircraft im plementation loss. The aircraft im plementation loss should be less than 6 dB (gain) and greater than -15 dB (loss) for horizontally polarized antenna, or less than 6 dB (gain) and grea ter than -11 dB (loss) for ve rtical polarized antenna. The total im plementation loss is the algebr aic s um (in dec ibels) of the antenna gain (referenced to an iso tropic radiator) and th e attenuation (as a negative num ber) between the antenna and the VDB receiver. The a ttenuation includes line dissipation and VSWR mismatch losses. The implem entation loss sh ould be verified over the frequency range
108.000 to 117.95 MHz.
Page 34 Par 19
d. The VDB antenna should be installed so that the maximum received power from any on-board transm itter does not e xceed the d esensitization levels of the VDB receive r specified in section 2.2.9.1 of RTCA/DO-253A.
21. INSTALLED PERFORMANCE - DATA SUBMITTAL.
a. General. T his paragraph id entifies docum entation typica lly required by th e aircraft certification au thorities to support installation a pproval. For equipm ent that has not obtained a TSOA, the equipm ent issues described in paragraph 11 through 14 of t his AC must also be addressed as part of th e installation. For equipm ent that has a T SO marking, the item s under paragraph 11 through 14 should be evaluated during the first installation approval in any m ake/model aircraft. The data desc ribed in this paragraph is applicable to obtaining an STC, an amended TC, or an amended STC.
(1) Project Spe cific Cer tification Plan. Provid e a plan tha t estab lishes the certification basis, how the program will be adm inistered, m ethod of com pliance, and schedule. When establishing the certificatio n basis, the plan should identify how the product will m eet the applicable airworthiness requirem ents and any special conditions.
The FAA and Industry Guide to Avionics Approvals provides guidance on developing a project specific certification plan. A dditional infor mation can be found in AC 21-40, Application Guide for Obtaining a Supplemental Type Certificate.
(2) Design Data.
(i) Provide the installation instruction manual from the original equipment manufacturer.
(ii) Provide ins tallation drawings de picting all interface co nnections, switching, wire diagram s, external annunc iations, configurati on programm ing and cockpit layout.
(iii) Provide reliability data or analysis to establish that all probable failures affecting the navigation functi on are detected. Qualitative analysis may be used under AC 23.1309-1C.
(iv) Provide a system safety assessm ent to conf irm that all f ailure conditions have been identified, classified and described in func tional and operational terms. Hardware and software design assurance levels must be substantiated.
(3) Structural Analysis. The insta llation of the GNSS equipm ent, including antenna, m ust be sufficient to m eet all structural m ounting, dynam ic, and em ergency landing loads appropriate to the aircraft. The installer must verify whether antenna installations penetrating the pressure vessel require a damage tolerance assessment of the installation, considering the uni que installation and the aircra ft type certificate basis of airworthiness.
(4) Power Supply. Provide an electrical load analysis to verify that the total electrical lo ad requirem ents are within the capabilities of the aircraft' s electrical generating system. Verify that the supplied elec trical power is consistent with applicable equipment reliability requirements.
Par 20 Page 35
(5) Equipment Com patibility. Provide a da ta f low diagram to identif y which equipment interfaces with the newly instal led GNSS equipm ent. Th e typical interfaces are to a barometric altimeter, flight management system, and Flight Guidance System. If the data flow diagram indicates that there are additional interfaces, the applicant and FAA should develop ground and flight tests to ensure proper functioning of these interfaces.
(6) Environment. Provide qualification da ta subs tantiating th at the a ircraft environment in which the GNSS equipm ent is to b e installed is app ropriate to the environmental categories (or criteria) in RTCA/DO-160(AR) to which the equipment has been tested.
b. Stand-Alone Navigation Equipment Installation.
(1) Pilot’s Guide. An o perations m anual (pilot’s guide) describing the equipment, functions and procedures m ust be provided with the GNSS equipm ent. It is essential that the pilot’s guide be complete, concise, and easy to understand. The pilot’s guide should be reviewed by a flight test pilot familiar with the equipment.
(2) Quick Reference Guide. A quick reference guide must be provided with the GNSS equipment as a training aid for th e operation of the GNSS e quipment. The guide should be evaluated by a flight tes t pilo t fam iliar with the equipm ent. Recommended format and content for this guide is in Appendix 3 of this AC.
(3) Operations m anual or A/RFM(S). An operations m anual or A/RFM(S) containing the limitations and operating procedur es applicable to the equipment installed must be provided. It must address the operation of the equipm ent and the related components as they are installed (e.g., rem ote source selector). If the operations manual does not address the use of the installed equipm ent, if the installation is based on a prior approval that had an A/RFM(S), or if there any limitations associated with the oper ation of the equipm ent, an A/RFM(S) is requ ired. Standard wordi ng for the general and limitations sections of an A/RFM(S) is provided in Appendix 4.
(4) Ground and Flight Test Plans (functi onal and EMI/EMC testing). The applicant must subm it the proposed ground and flight test plans to dem onstrate the equipment performance (as described in paragraphs 22 and 23) and EMI/EMC testing.
22. INSTALLED PERFORMANCE - GROUND TEST.
a. General.
(1) Power Supply. Assess all switching and transfer func tions, including electrical bus switching, pertaining to the GNSS installation.
(2) Accuracy. The accuracy of GNSS e quipment is no t a function of the installation, and should not be evaluated for each installa tion. The accuracy of the equipment will be dem onstrated under the evaluation of the sensor, typically as part of a TSO Authorization.
(3) Interference.
(i) The lack of interference from VHF radio should be demonstrated on the completed GNSS installation by tuning each VHF transmitter to the frequencies listed Page 36 Par 21
below and transm itting for a per iod of 35 seco nds while o bserving the signal status of each satellite being received. Degradation of individually received satellite signals below a point where navigatio n is no longer possibl e is not acceptable and will require that additional isolation m easures be taken. Reevaluation of instal led VHF transceiver performance is not necessary if the filter insertion loss is 2 dB or less.
(ii) Evaluate the following VHF frequencies (25 kHz channels):
121.150 MHz 131.250 MHz
121.175 MHz 131.275 MHz
121.200 MHz 131.300 MHz
(iii) For VHF radios with 8.33 kHz channe l spacing, evaluate the following VHF frequencies:
121.185 MHz 130.285 MHz
121.190 MHz 131.290 MHz
(iv) For ins tallations on ro torcraft, en sure that the roto rblades do no t interfere with the GPS/WAAS received signals . This problem has been experien ced in some rotorcraft and varies with the rotation rate.
(4) Antenna to Aircraft Navigation Refere nce Offset. If applicable, for GNSS equipment supporting precision approach or LP V capability, confirm that the antenna to aircraft center of navigati on offset is appropriate to the insta llation (ref erence RTCA/DO-229C section 2.2.4.3.3).
b. Sensor Installation. No ground tests are recommended for the sensor. Guidance relating to the interface betw een the sensor and the naviga tion system can be found in AC 20-130A.
c. Stand-Alone Navigation Equipment Installation.
(1) Visibility of the controls, displays , and annunciators relating to the GNSS installation should be evaluated during day a nd night lighting conditi ons. No distracting cockpit glare or reflections m ay be introduced and all con trols must be illuminated for identification and ease of use. Night lighting should be c onsistent with other cockpit lighting.
(2) Layout of the installed equipm ent should be evaluated with e mphasis on equipment contro ls, ap plicable circuit brea kers (labels a nd accessib ility), switching arrangement, and related indicators, displays, annunciators, etc.
(3) Navigation parameters displayed on coc kpit instruments such as HSI, CDI, distance display, electronic f light instrum ents system (E FIS), m oving m aps, flight management systems, etc. should be evaluate d against the criteria described in paragraph 18 of this AC.
(4) Failure m odes and associated annunciations, such as loss of electrical power, loss of signal recep tion, GNSS equi pment failure, au topilot/flight d irector response to flags, etc. should be reviewed against the criteria described in paragraph 18 of this AC.
Par 22 Page 37
(5) Manual approach selection or manua l tuning of the approach should override any autom atic selection. Once an approach has been selected, appropriate feedback to the pilot (e.g. display of approach na me (including runway), airport and reference path identifier) m ust be given to in dicate the approach has been correctly selected.
23. INSTALLED PERFORMANCE - FLIGHT TEST.
a. Sensor Installation. Conduct a functional flight te st. Verify continuity of navigation data during norm al aircraft m aneuvering for the navigation m odes to be validated (e.g. bank angles of up to 30 degrees and pitc h angles associated with approaches, m issed approaches and depa rtures, as applicable). A C 20-130A has guidance on the interface between the sensor and the navigation system.
b. Stand-Alone Navigation Equipment Installation.
(1) Continuity of Navigation. Verify c ontinuity of naviga tion data during normal aircraft m aneuvering for the navigati on modes to be validated (e.g., bank angles of up to 30 degrees and pitch angles associ ated with take-off, departures, approaches, landing and missed approaches as applicable).
(2) Equipment Operation. Verify the ov erall operation of the GNSS equipm ent to include at least the following: hold at a de signated waypoint, intercept and track to or from a waypoint on a selected course, turn anticipation, waypoint sequencing, selection of an approach and the general presentation of navigational data (depiction of the “TO” waypoint, distance to waypoint, estimated time of arrival, estimated time en route, ground speed, etc.). Evaluate the overall operation on all of the types of procedures or paths that the equipment supports (e.g., straight legs, DME arcs, and radius to fix legs).
(3) Flight Tech nical Error. Verify that flight technical error (FTE) can be maintained at less than 1.0 NM for en route and approach transition operating modes, and less than 0.25 NM for non-precision approach , both with and without autopilot and/or flight director use, as applicable. This test may not be n ecessary if the FTE has been previously estab lished for the aircraft. One acceptable way of assessing FTE is to monitor the measured cross-track deviation using the navigation display provided.
(4) Interface to Flight Guidance System (FGS). The following issues should be evaluated w hen the eq uipment is interfaced with a flig ht guid ance system . The objective of this paragraph is to en sure that the GNSS equipm ent interface is compatible with the aircraft; the ob jective is not to verify FGS perf ormance. If these issues cannot be addressed for a particular autopilot (e.g., because the autopilot does not respond to flag indications), the GNSS equipm ent m ay still be installed but either should not be connected to the autopilot or, if the discrepancy is consistent with the rest of the aircraft’s navigation capabilities, the issue can be a ddressed in the A/RFM(S) through consistent crew procedures for all types of navigation.
(i) Evaluate steering respons e while flight director and/or autopilot is coupled to the GNSS e quipment during a variet y of different track and m ode changes.
This evaluation should include, as applicable , transition from en route to approach transition to approach to m issed approach m odes and vice-versa. Additionally, evaluate all available display sensitivities.
Page 38 Par 22
(ii) Execute several fly-by turns with va rying wind conditions for flight director and autopilot. Verify the equipm ent accomplishes the turn as a fly-by waypoint and discou rages ove rshoot. Fly-by turns ar e turns where the equip ment initia tes th e turning m aneuver before sequencing the wa ypoint by an am ount equal to the turn anticipation distance.
(iii) Verify that the late ral m aneuver anticipation supplied by the GNSS equipment is appropriate for the aircraft type . Verify that an a ppropriate annunciation of impending waypoint crossing is provided.
(iv) Verify that execution of the Direct-T o function with a re sultant aircraft heading change does not overshoot and cause “S” turns. Reinitialization of the Direct-To function af ter com pletion of most of the requ ired track ch ange m ay be an acceptable means of compliance for equipm ent which does not inherently account for the change in aircraft heading.
(v) Evaluate the autopilot response to a GNSS fault by pulling the circuit breaker for the GNSS equipm ent. This test should be done in all of the GNSS en route and approach modes.
(vi) GLS and LPV Approaches (A) For installations where the autopilot has not been modified and the GNSS equipment provides ILS-like deviations, conduct several approaches while flying raw data, flight director and coupled to the au topilot, as applicable. The objective of this test is to ensure that the GNSS equipm ent interface is com patible with the aircraft; the objective is not to verify approach perfor mance. For aircraft with a potentially large difference between heading and track (e.g., airs hip), evaluate the effects of the offse t between th e GPS antenna or aircraft cente r of navigation during approaches (see paragraph 22a(4) of this AC).
(B) For insta llations where the au topilot has been m odified, the autopilot lateral/vertical control channel perform ance has not been assessed, or nonstandard deviations are provided (not ILS-like), then the approach performance will need to be evaluated per AC 23-17A, 25.1329-1, or equivalent means.
(C) For m anual contro l to the app roach flight path, the appropriate flight display(s) m ust provide sufficient information to maintain the app roach path and make alignm ent with the runway or go-ar ound without excessive reference to other cockpit displays.
(5) Interface to Barom etric Altimeter. If the equipm ent uses barom etric input, verify that the equipm ent properly interprets the barom eter reading. For equipm ent that requires manual entry of barom etric correction, the entry should be accom plished during an approach to evaluate the crew workload.
(6) Switching and Transfer Functions. Veri fy/assess all switching and trans fer functions, including electrical bus switching, perta ining to the G NSS installation .
Evaluate the aircraft system response during switches to all altern ate navigation sources and ensure that the switch is accom plished as expected, that it is clearly annunciated, and that the switching itself does not induce any inaccurate guidance.
Par 23 Page 39
(7) Failure Modes/Annunciations. Review and verify where appropriate various failure m odes and associated annunciations, such as loss of electrical power, loss of signal reception, GNSS equipment failure, FGS response to GNSS flags, etc. Verify that a warning associated with lo ss o f navigati on is accom panied by a visible indication within the pilot’s primary field of view.
(8) Crew Workload. An analysis of cr ew workload when operating the GNSS equipment in association with other piloting requirements should be conducted during all phases of flight, including those non-normal procedures that can be evaluated in flight.
c. LAAS Positioning and Navigation Equipment Installation.
(1) Continuity of Navigation. Verify c ontinuity of naviga tion data during normal aircraft maneuvering for the navigation modes to be validated (e.g. bank angles of up to 30 degrees and pitch angles associated with approaches, m issed approaches and departures).
(2) Interface to Flight Guidance System (FGS).
(i) Evaluate steering respons e while flight director and/or autopilot is coupled to the LAAS equipment during a variety of different mode changes and approach intercepts. Additionally, all available display sensitivities should be evaluated.
(ii) Evaluate the autopilot response to a GNSS fault by pulling the circuit breaker for the GNSS equipm ent. This test should be done in each of th e GNSS modes, if applicable.
(iii) Conduct several approaches while flyi ng raw data, flight director only and coupled to the autopilot, as applicable. The object ive of the test is to ensure that the GNSS equi pment interface is com patible with the aircraft a nd is not a verification of approach perform ance. This objective is va lid only for installati ons with existing and proven performance (e.g. GNSS pr oviding ILS like deviations to replace or supplem ent an existing ILS). For installations w here the autopilot has been modified or the autopilot lateral/vertical control channel perform ance has not been assessed, th en the approach performance will need to be evaluated per AC 23-17A, AC 25.1329-1A, or equivalent means. For aircraft with a potentially la rge difference between heading and track (e.g., airship), evaluate th e effects of the offset be tween the GPS antenna or aircraft cen ter of navigation during approaches (see paragraph 22a(4)).
(iv) For m anual control to the approach f light path, the appropriate flight display(s) must provide sufficient inform ation without excessive reference to other cockpit displays, to en able a suitably train ed pilot to m aintain the app roach path, make alignment with the runway or go-around.
(v) For Part 25 aircraft, the criteria in AC 120-29A, Appendix 2, should also be con sidered. Th e criteria define d for MLS m ay be used to qualify the LAAS functions.
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Appendix 1
d. LAAS VDB Receiver Installation.
(1) To ensure com patibility between the VDB a nd VHF c ommunications equipment, a flight test should b e acco mplished using the highest available V DB broadcast, and transm itting VHF communica tion at 100 kHz above the VDB channel.
For VHF comm unications equipment that cannot transm it below 118.000 MHz, the n
118.000 MHz should be used.
(2) VDB receiving capability should b e dem onstrated in flight. Unlike ILS, where th e ILS facility is always lo cated in front of t he ai rcraft on approach, a LAAS facility cou ld be lo cated anywhere with r espect to the ap proach pa th. Theref ore, the flight test should verify VDB signal reception at all angles relative to the airframe.
Stephen Van Trees Acting Manager, Aircraft Engineering Division Aircraft Certification Service
Page 41 (and 42)
Appendix 1
APPENDIX 1. GPS OCEANIC/REMOTE NAVIGATION
The following criteria define an acceptab le means of compliance for TSO-C129(AR) GPS equipm ent intended for oceanic and re mote operation without reliance on other long-range navigation system s. Equipm ent which previously dem onstrated compliance to Notice 8 110.60 is still eligib le for oceanic and remote operation and need not be reevaluated. Note that GPS/WAAS equipment should not be evaluated against this criteria.
GPS/WAAS equipment is inherently capable of supporting this operation if the operator obtains a fault detection and exclusi on (F DE) prediction program ; no additional evaluation is necessary.
1. APPROVAL PROCESS.
a. TSO Authoriza tion. The cr iteria in this a ppendix is in additio n to the requirements of RTCA/DO-208, Minim um Op erational Perform ance Standards for Airborne S upplemental Navigation Equipm ent Using Global Positioning System , as modified by Technical Standard Order, TSO-C129(AR). The ACO should issue a separate letter of design approval stating th at the equipment (including part num ber) and software prediction program (including revi sion num ber) m eet the criter ia in this appendix.
b. Installation Approval.
(1) The applicant obtains installatio n approval of the GPS navigation equipment.
(2) If the m anufacturer has previously obtained a letter of design approval as described in paragraph 1a of this appendix, fu rther evaluation as described in paragraphs 2 and 3 of this appendix is not required.
(3) If the m anufacturer has not obtained a letter of design approval, then the applicant must demonstrate compliance with the requirements in paragraphs 2 and 3 of this appendix.
(4) The failure of the long-range navi gation function is a m ajor failure condition. For many oceanic/remote operations, this requires equipping the airplane with at least two (or more) independent (i.e., dual control display unit, dual GPS antenna, dual power sources, dual GPS sensors, etc.) navi gation equipment with a m ean time between failures of at least 1000 hours each (for dual equipage).
(5) Once the installation has been appr oved, the A/RFM(S) should be updated to state: "The XXX GPS equipm ent as inst alled has been found to co mply with the requirements for GPS oceanic and rem ote navigation, when used in con junction with the XXX prediction program. This does not constitute an operational approval."
c. Operational Approval. The applicant should be aware that an operational approval m ust be obtained before conducting Class II n avigation (rem ote/oceanic).
Applicants should contact the appropriate F light Standards Distri ct Office to seek approval (reference HBAT 95-09, Guidelines for Operational Approval of GPS to provide the Prim ary Means of Class II Na vigation in Oc eanic and Rem ote Are as of Operation).
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Appendix 1
2. EQUIPMENT PERFORMANCE.
a. TSO-C129(AR). The GPS equipment must meet the criteria of TSO-C129(AR).
b. Fault Detection and Exclusion (FDE).
(1) The GPS equipm ent must be able to detect a nd exclude a GPS satellite failure by means of a f ault detection and exclusion (FDE) algorithm including receiver autonomous integrity m onitoring (RAIM) for detection. The exclus ion of a satellite failure must be autom atic: pilot action is not permitted to accom plish exclusion. The FDE algorithm m ust be aided by b arometric a ltimetry measurements, as requ ired by TSO-C129. Additional augm entations (such as clock aiding ) are no t precluded. F DE terms are defined in RTCA/DO-229C.
(i) Missed alert probability. The probabili ty of missed alert must be le ss than or equal to 0.001 for every geom etry and every navigation m ode. This requirement is on the m issed alert rate external to the GPS equipm ent. W hen related to the in ternal algorithm, it includes both probabilities of missed detection and false exclusion.
(ii) False alert probability. The probability of false alert must be less than or equal to 0.002/hour. This requi rement is on the false aler t rate external to the GPS equipment. When related to the in ternal algorithm, it includes both probabilities of false detection and the failure to exclude the false detection.
(iii) Failed exclusion proba bility. The probability of failed exclusion must be less than or equal to 10 -3 for every geom etry and ever y navigation mode for which exclusion is im plemented. Exclusion m ust be implemented for the oceanic m ode. This requirement is on the alert rate external to the GPS equipment due to failed exclusion.
(iv) Time-to-alert. The tim e-to-alert for oceanic/remote navigation mode is defined to be at least 30 seconds, but must not exceed 5 minutes.
(2) In addition to FDE, the equipm ent must use an acceptable means to detect and exclude from the navigation solution any satellite that experiences a failure wh ich causes a pseudorange step. A ps eudorange step is a sudden change in the m easured distance to a satellite. It can be written as:
PRSTEP = | PRPREDICTED - PRMEASURED | where PRPREDICTED is the predicted pseudorange at the time of measurement, based on previous measurements, and PRMEASURED is the pseudorange at the time of the measurement.
(i) The equipm ent m ust detect a pse udorange step erro r greater than 1000 meters, including steps, which cause loss of lock for less than 10 seconds.
(ii) If a pseudorange step is detected fo r a satellite, that satellite m ust be excluded from use in the navigation algor ithm until its integrity can be verified, and fault detection (RAIM) is available. The m anufacturer is free to choose any m ethod to calculate the predicted pseudor ange. However, any m ethod used should properly take into account satellite m ovement and aircraft dynam ics up to a groundspeed of 750 knots (kts) and accelerations up to 14.7 meters/second/second (1.5 g's).
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