U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: AIRKXTHINESS -APPlXCXiAL OF lD3AN-C NZ07IGATIONSYSTEMSFORUSE IN THE U.S. NZYTIONAL &AIRSPACE SYSTm (NAS) ANDALASKA Date: 8/24/88 AC No: 20-12-j3 Initiated by: mR-12() Change:
1 PUfXKXE. This advisory circular establishes an acceptable mzans, but not tie only means, of obtaining airworthiness approval of a mran-C navigation system for use under VFR (visual flight rules) and IFR (insmnt flight rules) within the conterminous United States, Alaska, and surrounding United States waters. Like all advisory rraterial, this advisory circular is not, in itself, mandatory and does not constitute a regulation. It is issued for guidance purposes and to outline one m&hod of compliance with aimrthiness requirents. As such, the terms %hall" and "must" used in this advisory , circular pertain to an applicant who chooses to follow the method presented.
The guidelines in this Advisory Circular supersede those of AC 90-45-9, ZXpproval of Area Navigation Systems for Use in the U.S. National Airspace System, for I&ran-C navigation equipment.
2 CANCELLXPION. Advisory Circular (AC) 20-121, Aimrthiness Approval of -A&borne mran-C Systerzls for Use in the U.S. mtional Airspace Systa, dated August 23, 1984, is canceled.
3 &d 4 l -RELATEDFAR. Federal Aviation Regulations (FAR) Parts 23, 25, 27, 29, 43, 91 l RELATED READING -.
a. Federal Aviation Administration (FAA)/Technical Standard Order (TSO) C60b, Airborne Area Navigation Equi&pment Using Loran-C Inputs. Copies array be obtained from the Department of Transportation, FAA, Aircraft Certification Service, Aircraft Engineering Division (AIR-1201, 800 Independence Avenue, S.W., Washington, DC 20591.
b D&16&3, Radio Technical Commission for Aeronautics (RTCA), IBcument No.
Environmental Conditions and Test Procedures for Airborne Fquipmant, IBwnt No. RTCA/DO-178A, Software Considerations in Airborne Systm and Equimt Certification, and m cement &k RTCA/DO-194, Minimum werational Performance Standards for Airborne Area Navigation Quipnt using -ran-C Inputs. mpies may be purchased from RTCA Secretariat, One L!!Pherson Square, Suite 500, 1425 K Street, N.W., Washington, DC 20005.
c. Advisory Circular 90-82, Random Area Navigation Routes. Copies may be obtained from the Departmat of -Transportation, Utilization and Storage Section, M-443.2, Washington, D.C. 20590.
AC ZO-121A 8124188
d. A&isory Circular 27-1, "Certification of Normal Category Rotorcraft."
This do cument should be referenced to determine if considerations 'beyond those contained in this advisory circular are necessary when installing a Loran-C area navigation system in a no&ml category rotorcraft. If necessary, AC 27-1 will address those items peculiar to rotorcraft installations. Copiesrraybeordered from: Sxperintendent of Bcurrrents, U.S. Govex-t Printing Office, 'rrJashington, DC 20402, or from any of the Govermnt Printing Office bookstores located in . r‘Mjor cities throughout the United States. Identify the publication as AC 27-1, Certifimtion of Normal Category %torcraft, Stock Number 050-007-00708-6.
e. Advisory Circular 29-2, Certification of Transport Category Rotorcraft.
-This do cument should be referenced to determine if considerations beyond those contained in this advisory circular are necessary when installing a Loran-C area navigation system in a transport category rotorcraft. If necessaq, AC 29-2 will address those items peculiar to rotorcraft installations. Co& maybe obtained from the Department of Transportation, . Utilization and Storage Section M-443.2, Washington, D.C. 20590.
5. l3AcKGRouND.
a. System Description. Loran-C is a radio navigation system which uses tim synchronized pulsed signals from ground transmitting stations spaced several hundredmiles apart. The stations are configured in chains of three to five stations which transmit with the same pulse group repetition interval (GRI).
Within each chain, one station is designated as master and the r-inder as secondaries. The master has unique pulse and phase transmission characteristics to distinguish it from the secondaries. Loran-C position is derived by measuring the difference in arrival time of pulses from three or more ground stations, The ZS. Coast Guard WSCW presently uses a homogeneous spheroid for theearth model for the Loran-C system based on the 'JJbrld Geodetic System, 1972 Datum (xlay be updated to 1984 Datum), and the Defense Mapping Agency Sea Water Propagation Model for the propagation model. Xavigational values such as distance and 'bearing to a waypoint are cmuted from the aircraft latitude/ longitude and the location of the waypoint. Course guidance is generally provided as a linear deviation frown the desired track of a Great Circle Course.
The desired course rt~y be pilot selectable or may be determined by the navigation ccmputer by computations based on the locations of succesive mypoints.
b l System Availability and Reliability.
(1) Loran-C navigation predicated on hyperbolic lines of position originating from a single chain may not be suitable for IFR use throughout the entire continental 'Jnited States and northern -Alaska. Equipment utilizing Bter independent, cross chain, and/or multiple chain receivers have been approved for IFR use in areas where single chain receivers are unacceptable.
(2) Loran-C system status is available through the Notice to Airmen usDmi!a system.
Par. 4
Loran-C status information is also available by mans of telephone data service (300 or 1200 baud, ASCII) frown the U.S. N=l Wservatory, telephone (202) 653-1079. Loran-C ground transmitter reliability exceeds 99 percent annually.
(3) Expansion of Loran-C coverage and iqxovements in signal integrity are presently being jointly accomplished by the FAA and USCG.
c. Ioran-C Fosition Errors. The accuracy of Loran-C navigation can be degraded by various factors. Errors are caused by the slower signal propagation over land and fresh water than over sea water. These errors appear to be quite constant over distances of up to several miles. The effect of these errors is a shift or bias in the mquted latitude/longitude in the local area. Use of another triad in the same area may produce a different bias value. Areacalibration procedures my reduce the effect of these bias errors. Errors can also *be caused by weather fronts, abrupt changes in terrain, noise, and geometric amsiderations, amng others. Tkse effects can be minimized by incorporation of propagation mdels and other correction factors which substantially reduce these errors automatically.
d. General OPerational Limitations.
(1) En Route and Terminal National ,9irspace System (NAS) Use. A Ioran-C system my be approved for en route and terminal navigation VFR or IFR within the conterminous United States and Alaska. Other navigation equimnt (i.e., Very High Frequency Qmi Range (WR), Distance LN&suring Equipment (IME), Tactical Air Navigation (TACAN), Automatic Direction Finder (ADF)) appropriate to the ground facilities along the intended route to 'be flown should be installed and operable. En route and terminal accuracy requiremmts must be met without the need for operator entry of calibration or correction factors.
(2) %proach Use in the N&S. A Loran-C system my be approved for instnmmt approach operations within the conteminous United States and Alaska provided the installed systm meets the minim performance requirements of TSCXZ6Ob. Operator entry of calibration or correction factors shown on a charted insmnt approach procedure may be used in satisfying approach accuracy requirements.
(3) IFR Navigation Qui~nt, Aircraft eqloying Loran-C for IFR navigation should also be equipped with an approved alternate mans of navigation.
(4) Loran-C Operational Areas. Operational use of the Loran-C system my be limited to specified mran-C Operational Areas (IDA's) because of system characteristics and other factors affecting system performance. Loran-C operation should be limited to those geographic areas where the equipment has 'been d-n&rated to meet the performnce specifications of this advisory circular.
6 l DEE'INITIONS.
a. Amroach Operations.
dxted on charted Instnmmt Approach operations are those flight phases con- Approach Procedures (IZPs) commencing at the Par. 5
initial approach fix (IAF') and concluding at landing or the missed approach holding fix, as appropriate.
b 0 Area Calibration. Area calibration is a procedure where tim rrreasuremt correction factors are input into the -ran-C system to reduce the effect of propagation anoI&.ies, C. Baseline. A line beteen a Loran-C mster station and one of its secondary stations or between two secondary stations.
d . Baseline Extension, The extension of the baseline beyond the mter or secondary station. Navigation in this region may be inaccurate due to geometrical considerations resulting in -igums position solutions.
e. Blink. A mthod of indicating non-standard operation of a Loran-C station be Thing off and on the ninth pulse of an affected master station or the first tw pulses of an affected secondary station. Blinkis used to denote that a station is operating outside of specified tolerances.
f Cycle Slip Erroneous use of an incorrect cycle of the 100 kFlz carrier of the Koran-C signal for time msurmnts. Normally the third cycle of a given pulse is used for time Lmsurement. Each cycle slip will result in a 10 microsecond error in tinre mzas'urant and a corresponding error in navigation.
g En mute Operations. En route operations are those flight phases con- duct2 on charted VOR routes designated as high or low altitude routes (Jet or Victor), direct point-to-point operations 'between defined waypints, or along great circle routes as descr?bed in Advisory Circular 90-82, Random Area Navigation Routes.
h. EnveloAE-to-QQcle Discrepancy (ECD). The discrepancy between the desired and actual zero phase crossing at the end of the third cycle of the Loran-C pulse. U.S. Coast Guard specifications for the Loran-C transmitted signal provide a further definition of ECD.
i. Geomtric Dilution of Precision (GDOP). A factor used to express navigational error at a position fix caused by divergence of the hFbolic lines of position as the receiver's (aircraft%) distance from the baseline increases.
.
3 Group Repetition Interval (GRILL Thetimeinterval (msured intens of microkconds) between one group of pulses and the next from any transmitter within a Iman< chain. -All stations in a specific chain use the SUE GRI.
k. Group Repetition Rate (GRR). The reciprm1 of the GRI bsually Amssured in groups per second), 1 Line of Position (LOP). A hyperbolically curved line defined by successive Gut constant tti difference (TD) msurements using the signals from two mran=C transmitters. TW crossing IxIP's define a receiver's location, thus at 4 least three &ran< stations must be used to establish a position fix.
Par. 6
m. Master Bpendentkbde. A Loran-C operating tie where all tim differenceax2asurenx2nts areexecuted with reference to the master's pulses.
n.
designs station Master Independent Mode. An in which a secondary station signal.
operating Illodie used signal my be substi in som2 receiver tuted for the master
0. Precipitation Static (P-Static). P-static is electromgnetic noise generated by the dissi,oation of an electrical charge from an aircraft into the atmsphere. The aircraft becomes charged by flight through particles suspended in the atmosphere such as dust, ice, rain, or snow. Unprotected aircraft my create so much noise that the Loran-C receiver can no longer detect the transmitted signal.
p. Skywave, Loran-C signal energy traveling such tlhat it is reflected by the ionosphere. Skywaves travel farther than the ground wave to reach a given point and can interfere with ground wave reception at some locations.
cz Tim Difference (TD). The elapsed time, in microseconds, msured at the rkiver (aircraft), between the arrival of a set of pulses frcKn one Loran-C station's signal to the arrival of a set of pulses from another station's signal.
r. Triad. The collective name given to the three stations from a Ioran-C chain fraich navigational information is being derived.
s. Terminal AreaOperations. Terminal area operations are those flight phases conducted on charted Standard Instrwnt Departures (SID* sJf on charted Standard Terminal -Arrivals (STARW, or other flight operations 'bet=en the last en route fix/wapint and an initial approach fix/-mint.
7 . AIRWR!EHI'S CONSIDEWWIc)NS. Loran-C navigation systems have been certificated for VFR and IFR use as an area navigation system for en route and terminal navigation in the MS. This paragraph establishes acceptable criteria for Im3n-C systems,
a. Loran-C Installations Used for Operations Under Visual Fliqht Rules (VE'R) Only. Operators wishing to use bran-C for operations limited to VFR ~lldy obtain approval of the installation by Type Certificate UC), Suppkmntal !Qpe Certificate (STC), data field approved by the FAA on an FAA Form 337, Major Repair and Alteration, or by the use of previously approved data. -The approval for return to service should be signed by one of the entities noted in FAR 43;
i.e., repair station, manufacturer, holder of an inspection authorization, etc.
The installation vwification should ensure, but is not limited to, the following:
(1) The Loran-C Installation Bes Not Interfere with the no& operation of other equimt installed in the aircraft. This is accomplished by a ground test and flight test to check that the Loran-C equimnt is not a source of objectional electromagnetic interference (EMI), is functioning properly and safely, and operates in accordance with the manufacturer% specifications.
Par. 6
(2) The Structural kbuntinq of the Loran-C Quipnt is sufficient to ensure the restraint of the equipment when subjectedto the Wgencylanding loads appropriate to the aircraft category.
(3) A Xaviqation Source Annunciator i- 3 Provided on or adjacent to the display if the -ran-C installation sqplies any information to displays such as a horizontal situation indicator (HSI) or course deviation indicator (CDI) which can also display infomtion from other systems nomrally used for aircraft navigation.
(4) The Loran-C Controls and displays are Installed with a placard(s) which states 'Yoran-C NOt @proved for IFW'
(5) The Loran-C *May Be Coupled to the %adio Nav" Function of an autopilot provided the system has a CD1 or steering output that is copatible with the autopilot, and the same ilrlstallation procedures normally used for the VOR coupling are used.
b. Loran-C Installations Used as an Area Navigation System Under I&nsmnt Flight Xules (IFR), The standards for navigation within the W are mre stringent than the requirements for long-range, overqter navigation. I0ran-C quiptrent produced undo TSO-CGOa is not necessarily appropriate for en route area navigation under inst rument flight rules since this technical standard order was originally written for long-range, over-water navigation. Minimum iperfomce standards for Loran-C equipment to be used in the NAS are specified in TSO-C6Ob. Quipnt previously certified using TSO-CGOa and AC 20012l/AC 90045A may contynue to be approved for en route and terminal operations provided the appropriate performance standards are satisfied. mpnt approved for non-precision approaches must have TS3C6Ob approval and meet specified minimum performance s+adards. Criteria for area navigation EQW7) systerrrs based on Uran-C navigation are amplified in the* following paragraphs. The initial certification of a Loran< system requires an engineering evaluation because of the need to verify accuracy, failure indications, approved oLperating areas, enviromntal qualifications, etc. Subsequent installations of the same~ran=C system in other aircraft I~ELY require additional engineering evaluation, depending u,n the degree of integration of the Loran-C system with other aircraft systm. An engineering evaluation will be necessary to change or increase approved operating areas. Loran-C systems for use under instrmnt flight rules should provide the following:
(1) Flightcrew Inputs of:
(i) Aircraft present position in tenors of latitude and longitude at least to the nearest O.lminute.
(ii) For en route operations, at least three (for to-from equip&) or four (for to-to equipment) waypoint positions in terms of latitude and longitude at least to the naest 0.1 minute.
(iii) For terminal and approach o&perations, at least eight (for to-from equip&) or nine (for to-to equi~nt) waypoint positions in terms-of latitude and longitude to at least the nearest 0.1 minute.
6 Par. 7
(iv) A -s to confirm correctness of input data prior to utilization of the new data by the system.
(VI A WirecttowV function to define a route seqant from present position to any waypint.
(vi) Chain (mster and secondary> and GRI designation if the systa requires manual designation.
(vii) A means for manual update of system position by the pilot to permit insertion of a known present position,
(2) The System Displays Should Give No Operationally Misleading Infomtion and Should Provide.
(i) Present position in terms of latitude and longitude to at least the nearest 0.1 minute and in t- of magnetic bearing and distance to or from a q+@nt to at least the nearest 0.1 nautical mile (nmi) and nearest degree.
Distances of at least 260 ti should be capable of being displayed, but distances greater than 99.9 ti need only be displayed to the nearest 1.0 nmi.
(ii) Waypoint position designation in terms of latitude and longitude to at least the nearest 0.1 minute or in terms of magnetic bearing and distance from present position or another way@nt. * Vikypoint designation in te3zrr~ of magnetic bearing and distance should be to at least the nearest degree of bearing and 0.1 ti for distances up to 100 nmi then at least 1.0 ti for distances of 100 nmi or rm3re.
1’193TE: Information should be provided to the flight crew to prevent the designation of way-points by a seqilence of bearings and distances (i.e., the reference position for a waypoint designated by bearing and distance should be designated by latitude and longitude),
(iii) A display of active waypoint identification (mt necessarily waypoint position) used to define the navigation track 'being flown.
BfCYTE: Only systems which define the desired navigation track in terms of its endpoints can be used to navigate on published airways due to changes in magnetic variation after the cohssioning of the ground facility.
(iv) A display of the desired track in terms of the appropriate magnetic course to at least the nearest 1.0 degree. Display of the appropriate magnetic course should not require the flightcrew to input the magnetic variation corresponding to the present position.
(v) A display of the distance to the active waylsoint to the nearest
0.1 nmi. Distances of at least 260 nmi should be capable of being displayed, but distances greater than 99.9 ti need only be displayed to the nearest 1.0 ti.
. Par. 7
AC 20421A 8/ 24/88
(vi) A continuous amlog (i.e., nonnumeric) display of crosstrack deviation with Zn ~dte/Wnninal Approach blmi) bmi) ~tinimum Full-Scale Deflection Readd~ility Mitim Discernable ~Pbvmznt >5.0
71.0
0.1 - * >1.25
0.25 '
70.05 - * Nmx: Smiler valaes of minirrnmt full-scale deflection for approach my be acceptable provided the proposed value is found satisfactory by an engineering evaluation.
(vii) A display of crosstrack deviation to the nearest 0.1 nmi up to
9.9 nmi and 1.0 mni 'beyond, with a range of at least +20 nmi. This may be a digital display, may be pilot selectable, and need noF be part of the course deviation indicator.
(viii> A display of the distance aLyld magnetic bearing (at the lTfrmV' end of the segrrmt) between waypoints to at least the nearest 1.0 mni and 1.0 degree.
(ix) The capability to indicate, on d-d, the specific I;oran-C stations c-urrently used in the navigation calculations as well as the status of all stations being tracked.
(x1 An annunciation of impending waypoint crossing.
(3) Caution Indication(s) for the System Should be Located on or near the indicator specified in paragraph 7b(2)(f) and should provide a readily discernible caution indication(s) to the pilot(s) for any of the following:
(i) I1mdequate or invalid navigation signals or sources.
(ii) The absence of primary power.
(iii) Inadquate or invalid navigation displays or output sources. In the approach mde, the inability to assure navigation position data accuTate to within +0.3 nmi.
(iv) Equipment failures.
W Reversion to a secondary dead reckoning mde of navigation.
Wl?l3: These failure/status indications shall occur independently of any operator action. Power or navigation equipment fai lures mybeindicated in a commnmanner. The lack of adequate navigation signals or sources (considering signal-to-noise ratio (SNR) as well as geomtry) should be annunciated when compliance with the navigation accuracy specified in paragraph 9 cannot be assured. In the approach mde, the lack of adequate navigation signals or 8 Pax. 7 .
a/24/88 AC 20421A \ sources shall be annunciated by means of a flag displayed on the priory navigation display. In other mdes, an appropriately located annunciator Imv be -L US&i.
(41 When Within an Acceptable LGA, the system shall erly acquire and track signals and provide navigation to the fied in paragraph 9 under the conditions and within the time TSO-CGOb.
(5) Navigation Guidance Should be Available within 5 seconds of waypoint be able to propaccuracies specilimits specified in data input. .
(6) The E&ment Should Have The Capability to met the criteria outlined in paragraph 7bU) through 7b(5) throughout the range of environmmtal conditions which will be encountered in actual service. Exposure of the equipment to the environmntal test conditions of TSO-C60b may be used to demonstrate this capability. Environmental testing to obtain a EXXZCiOa authorization may be used provided that the test results also demnstrate complialnce with the criteria of paragraph 7bU) through 7b(6). ,
(7) The E@lipmnt Should provide a Means for the Flightcrew to determine system status prior to flight.
(8) The Bquimnt Should Not Exceed the Error Values specified in paragraph 9 for all groundspeeds up to a mximrn wlue to be set by the manufacturer and should provide usable navigation information necessary for holding patterns conducted with standard rate turns at speeds up to 250 knots groundspeed or at a less- value specified by the equipnt manufacturer.
(9) The Bqu.ivt Should Provide ~Means to Alert the Flightcrew prior to arrival at a -mint to permit turn anticipation in accordance with the approximate formula of 1.0 nmi for each 100 knots of groundspeed. This indicator should be located on or neaLr the indicator specified in paragraph 7b(2) (f). For Imxn-C system which are not co~@ed to a flight director or autopilot, a procedural ~SW based on a continuous and properly located distance to waypoint display my be used for mmint lateral maneuver anticipation. @stew which provide steering signals for flight directors or autopilots should provide automtic turn anticipation and a waypoint alert tiich occurs prior to the initiation of the turn by the flight director or autopilot.
(10) If a Capability for Parallel Offset Tracks is Provided, track selection should be in increments of at least 1.0 nmi left or right up to an offset of at least 20 mi. I'clans should be provided to continuously indicate that an offset track has been selected. Waypoint alerting and turn anticiption should be provided prior to arrival at the ,rx>int where the off set intersects the angle bisector of the parent track. These functions should operate as descri'oed in paragraph 7b(9),
c. Software Chancres * equipment which utilizes l The provisions of this paragraph apply t0Loran-C a digi .tal computer to provide navigation information or system mnitoring. The coiiuter program (software) operates the computer and provides the basic functions of these systems. The software for navigation Par. 7 9
functions of Loran< equipnt described in paragraph 7b (for Loran-C lused for Ii?R operations) should -be verified and validated to at least the level 2 requirmnts as defined by R!KA/DO-178A, "Software mnsiderations in Airborne Systerrrs and Equip-t Certification." Any changes to software which affects navigational functions are considered to be major changes to the eqtimnt.
Unless software partitioning has 'been previously established, any change to level 1 or level 2 software of -ran-C area navigation equipnt should be verified and validated to the appropriate level and should be dermnstrated as not having inadvertently affected the remaining navigational functions. changes to software used for rx>ran-C q-ui-t limited to VFR use or equimt having established partitioning from software w',?ich provides navigational functions in IFR system are considered to be minor and & not require prior approval by the FAA, providing the rrnanufacturer of t,tle Loran-C equipznt has a software configuration mangmt and quality ass'urance plan approved by the FAA. .
Soft-e status must 'be identified on the o-&side of the associated line replaceable unit in accordance with the criteria of RTcA/DO478A. Software change inTSOapproved equimntmtbereportedtothe cognizant Aircraft Certification Office. If the quipmnt displays a software identifier to the flightcrew, the airplane or rotorcraft flight manual (or appropriate placard) should indicate the approved identifier. Software changes incorporated in equipnt already installed in an aircraft may require additional evaluation and possible flight manual supplement revision prior to returning the aircraft to service, depending upon the scope of the change.
8 0 l!XKUIm INSTALLATION CONSDFRATIONS FOR USE UNDER IFR.
a. Location of the -ran-C Display. Each display elmnt, used as a primary flight inst rumnt in the guidance and control of the aircraft, for imeuver anticipation, or for failure annunciation, should be located where it is clearly visible to the pilot (in the pilot's primary field of view) with the least practicable deviation from the pilot% normal position and line of vision when looking forward along the flight path.
b. Failure Protection. Any probable failure of the airborne Loran-C navigation system should mt degrade the normal operation of other required equipment or create a flight hazard. Normal o,oeration of the -ran-C installation should not adversely affect the perfomrance of other aircraft equimnt.
c. Envirormxxtal Conditions. The aircraft enviromnt in which the Lr>ran< system is installed should be found to be compatible with envirorxental categories to which the equipnt was tested.
d. Zkctromqnetic Interference. The Ioran< navigation system shouldnot be the source of objectionable electrcdnagnetic interference, nor be adversely affected by electromgnetic interference from other quipmnt in the aircraft.
is used, the aircraft should
e. P-Static Protection. If an E-Field antenna (whip, plate, or blade type) be protected by placing the antenna in a suitable location, by acceptable bonding techniques and installation of static dischargers, These protective devices should be specified as part of the approved 10 Par. 7
design data for the Iman-C installation. The capability to provide satisfactory P-static protection for the Ir>ran-c system should be demonstrated as part of the initial certification program. This testing may be accomlished by ground or static testing if sufficient data is provided to dmonstrate that the proposed technique is equivalent to flight testing. If a flight demonstration is selected, it must be conducted at speeds up to Vne, --- Vm, or b through kmwn P-static conditions such as a cloud of ice crystals l I?brrusntary loss of signal when encountering heavy P-static conditions my be acceptable provided the equipnt is capable of providing acceptable navigation information during such conditions.
(1) P-Static Charging/Discharging. P-static charging of the aircraft can cause degradation of the sigLnal-to-noise ratio by one of three major muchanisms: sparkover of isolated metal panelsr corona discharge, and str- currents. Sparkover of isolated xx&al panels can be handled by appropriate bonding. This bonding needs to occur on all control, and trim surfaces as well as isolated access panels. Bonding should'beevaluatedbya carefulohmic survey (an electrical bonding limit of 10 milliom is considered acceptable) of each aircraft in which the Loran-C system is installed or by other suitable techniques. The effects caused by streamr currents can be reduced by placing the receiving antenna as far as possible from any nonconductive surfaces such as windshields. The nonconductive slurfaces may be timted with a conductive coating. Teqorary spray coatings are not satisfactory. Corona discharge can be reduced by the appropriate placing of orthodecoupled static dischargers on the extremities of the aircraft. A number of recent studies have shown that the frayed-wick types of discharger rapidly lose their effectiveness as a result of use. Therefore, dischargers constructed with a high resistaxe rod and ~tal pins are reccxm nded although other types my also be used if they can kuxstrate ability to provide protection from radio frequency (RF) coupling to the Iman% antenna. The number, type, and location of these static dischargers to be installed on a particularaircraft model should be determined by following the instructions provided by the mufacturer of the static discharger for P-static protection.
f, Anti-Ice Protection. If the aircraft in which the 3Aran-C system is installed is approved for flight into known icing conditions, the antenna should have anti-ice protection or be found not to be susceptible to ice buildup.
Alternatively, if the Ioran-C system can be sho-wn to operate satisfactorily when the antenna is subject to icing I or if the system is limited via placard or flight manual to indicate that it is not to be used for navigation during flight in icing conditions, then anti-ice protection is not required.
g Dynamic Responses. The system shall continue to indicate aircraft position to t1he accuracy specified in paragraph 9 within 15 seconds following aircraft mneuvering or changes in attitude encountered in normal operations.
h System Controls. The system controls should be arranged to provide adquke protection against inadvertent system turmff. The controls for system operation should be readily accessible to, and usable by, the flightcrew and be visible under all expected lighting conditions, including night and direct sunlight.
Par. 8 11
AC 200121A S/24/88 . i. System Tests. The initial approval of a I0ran-C system for IFR use involves extensive testing to dmnstrate system performance, operational areas, enviro-ntal qualifications, etc., as described in paragraph 7b0, Subsequent installations in other aircraft need only be tested to the extent necessary to d-n&rate proper operation of interfacing aircraft equimnt such as autopilots, flight directors and instrument displays, satisfactory antenna installations as evidenced by the reception of -ran-C sigmls during no& flight maneuvers, satisfactory clearance of electromagnetic interference E!!4I), and functional check of the Loran< equipment.
.
7 IYanufactuer's Instructions. tiran=C quiprclentshouldbeinstalledin accor&nce with instructions and limitations provided by the -aufacturer of the quipnt.
k. Approach Mbae Limitation. Loran-C equipnt capable of selecting an "approach" mde on the control panel shall be piacarded %pproach Mode N3t Approved for IFR," unless the equipmnt is approved for conduct of Loran-C nonprecision instrurclent approaches.
9 l SYSTEM AccuRAcY.
a. En Route IFR Operation Along Random (Dff Airways) RNW mutes with Radar Coverage. The error of the airborne IAran-C equipnt should be less than +3,8 nmi of crosstrack error on a 95 percent probability basis and +3.8 mi of - - along-track error on a 95 percent probability basis.
b En Route IFR @eration on Airways in the M. The error of the airborne I;oran> equipnt should be less than +2.8 nmi of crosstrack error on a 95 percent probability Sasis and +2.8 nmi-of along-track error on a 95 ipercent prcbability basis for approval-of en route IFR operations on airways.
C. Terminal IFR @eration in the MS. The error of the airborne -ran-C equipment should be less than +1.7 ti of crosstrack error on a 95 percent probability basis and +1.7 m&of along-track error on a 95 percentprobability 'basis for approval of %minal IFR operations.
d Instrumznt -roach @eration in the N&S. The error of the airborne -ran> equipment should be less than +0.3 nmi of crosstrack error on a 95 percent probability hasis and +0.3 ti-of along-track error on a 95 percent probability basis for approval-of inswnt approach operations.
e. Flight Technical (Pilotage) Errors. With satisfactory displays of crosstrack position, the FAA has detextined that flight technical errors can be expected to be less than the values shown below on a twu-sigma basis.
Flight Condition Flight Technical Error m route T&nal Approach +l.O nmi
71.0 nmi To.5 nmi - 12 Par. 8