t ‘) c/ U.S. Department of Tronsportatron Federal Aviation Administration Advisory Circular Subject: AIRG33EzMINESS APPROVALOF IMe: g/12/88 AC NO: 20-1()1c OMJSG&/VLJ? NAVSWION SYSTEMS IFOR USE lnitiated by: xR-12() Change:
IN THE U.S. NATIONAL AIRSPACE sYsm MASS AND ALASKA 1 PURPOSE. This advisory circular establishes an acceptable ws, but not tie only means, of obtaining airworthiness approval of an mga/Very mw Frequency (VLF) navigation system for use under VFR (visual flight rules) and IFR (instrument flight rules) within the conterminous United States, Alaska, and surrounding United States waters. Like all advisory material, this advisory circular is not, in itself, mndatory and does not constitute a regulation. It is issued for guidance purposes and to outline one method of compliance with aimrthiness requirements. As such, the terms "shall" and "must1 used in this advisory circular pertain to an applicant who chooses to follow the method presented. The guidelines provided in this advisory circular supersede those of AC 90045A, Approval of Area Navigation Systems for Use in the U.S.:National Airspace System, for ma/VLF navigation equipt. 2.
2 CANCELLATION.
canceled.
Advisory Circular (AC) 200lOlB, dated December 1, 1980, is 3 and RELATEDFAR. Federal Aviation Regulations (FAR) Parts 23, 25, 27, 29, 43, 91 0 4 0 RELATEDREADINGMA!TERIALS,
a. Federal Aviation Administration (FAA)/Technical Standard Order (TSO) C94a, Qnega Receiving Equipment Qxrating Within the Radio Frequency Range 10.2 to 13.6 Kilohertz, and TSO C120, Airborne Area Navigation Equipment Using ma/VLF Inputs. Copies nay be obtained from the Deparmt of Transportation, FAA, Aircraft Certification Service, Aircraft Engineering Division (AIR-1201, 800 Independence Avenue, SW., mshington, DC 20591.
b Radio Technical Cammission for Aeronautics (RICA), Document No.
E?TCA&6OB, Environmental Conditions and Test Procedures for Airborne Quipment, lBcument No. RX@&164A, Airborne &ga Receiving Equipnt, bcu.ment No. RTCA/DO-178A, Software Considerations in Airborne Systems and EQuipnt Certification, and writ No. RICA/DO-190, Minimum Operational Performance Standards for Airborne Area Navigation Equipment using Omega/vr;F Inputs. Ccpies may be purchased from RTCA Secretariat, One McPherson Square, Suite 500, 1425 K Street, WV., Wshington, DC 20005.
c. Advisory Circular 90-82, Random Area Navigation Routes. Copies may be obtained fromthe Department of Transportation, Utilization and Storage Section, M-443.2, Washington, DC 20590.
AC 204OlC g/12/88
d. Advisory Circular 27-1, Certification of Normal Category Rotorcraft.
This documnt should be referenced to determine if considerations beyond those contained in this advisory circular are necessary when installing an W/W navigation system in a nom1 category rotorcraft. If necessary, AC 27-1 will address those item peculiar to rotorcraft installations. Copies my be ordered from: Superintendent of mcuments, U.S. Govermt Printing Off-ice, FJashington, DC 20402, or from any of the Government Printing Office bookstores located in major cities throughout the United States, Identify the publication as AC 27-1, Certification of Norm1 Category Rotorcraft, Stock Number 050-007-00708-6.
e. Advisory Circular 29-2, Certification of Transport Category Rotorcraft.
This document should be referenced to determine if considerations beyond those contained in this advisory circular are necessary when installing an Omega/VL,F navigation system in a transport category rotorcraft. If necessary, AC 29-2 will address those it- peculiar to rotorcraft installations.
5.BxKGR0UND.
a. System Description: Omega is a radio navigation system which uses low frequency, precisely timed pulsed signals from eight round transmitting stations sL&ed thou&r& of miles apart around the mrld. The VW commications system is comprised of a series of high power very low frequency transmitters comprising the U.S. Naval VLF Telecmmn ications Network. Omega stitions transmit in a very precise phase stable format and are synchronized with each ' other using atomic clocks. The VW signals are transmitted similarly, hover, are not synchronized with each other as with Vega signals. Position data is derived by measuring the phase changes of signals being received. The system solves the continuously changing georrretry problem and converts the phase changes being measured fram several stations into distance and direction of rrw>vement since the last phase meilsurmts were taken. The increTllenta1 changes in distance and direction are continuously combined with previously calculated positions to determine the present position. Navigation values such as distance and bearing to a waypoint are computed from the aircraft latitude/longitude and the location of the waypoint. Course guidance is generally provided as a linear deviation from the desired track of a great circle course. The desired course my be pilot selectable or my be determined by the navigation computer by cqutations based on the locations of succesive waypoints.
b . System Availability and Reliability.
(1) The Ortega station netmrk was created solely for the purpose of providing long-range navigation. &ega system status itiomtion is available on a telephone recording fram U.S. Naval Observatory, telephone (703) 866-3801.
-a status -sages are also broadcast by the Esational Bureau of Standards on stations WWV and WWH at 16 minutes wt each hour (WWV) and 47 minutes past each hour MWVEiL
(2) Unlike the ddicated Cxrrega netmrk, the VW -ications system operated by the U.S. Navy is hot primarily intended for navigation use. The
g/12/88 AC 20401C mvy my shut stations down, add new stations, change frequencies, etc., with no advancewarning. Information on current W system status is not published for the aviation user.
(3) The Omga/VLF navigation system, while it my use VLF mmmmications stations to supplmt and enhance the ma system (increase'areas of coverage, irrprove performance, etc.), should be capable of accurate navigation using Wga signals alone.
c. Omega Position Errors. The accuracy of Omega/VLF navigation can 'be degraded by errors due to phase disturbances of the signals as they propagate from the station to the aircraft, improper mdeling of the signal propagation changes caused by diurnal shift, errors due to poor station/aircraft geometry, surface conductivity, etc.
d. General Operational Limitations.
(1) En Route National Airspace System (NAS) Use. An Qmqa/VLF system my be approved for en route navigation VFR or IFR within the conterminous United States and Alaska. Other navigation equipnt (i.e., Very High Frequency Range (WR), distance measuring equipmnt (IIMEjf tactical air navigation (Tm)) appropriate to the ground facilities along the intended route to be flown shouldbe installedandoperable.
(2) Terminal and Approach Use in the NAS. An ma/VW .system my not be approved for terminal and approach operations.
(3) IFR kvigation EQuipment. Aircraft employing Qrqa/VLF for IFR navigation should also be equipped with an approved alternate means of navigation.
6 . DEFINITIONS.
a. En mute Operations. En route operations are those flight phases conducted on charted WR routes designated as high or low altitude routes (Jet or Victor), direct point-to-point operations between defined waypoints, or along great circle routes as descriw in AC 90-82.
b, Precipitation Static (P-Static). P-static is electromagnetic noise generated by the dissipation of an electrical charge from an aircraft into the atmsphere. The aircraft becorcles charged by flight through particles suspended in the atmsphere such as dust, ice, rain, or sno&. Unprotected aircraft my create so much noise that the Qqa/VLF receiver can no longer detect the transmitted signal.
c. Synchronization. Synchronization is the process of determining which Qnega station transmits which segmnt of the Qxga format at a specific tim.
7 AIRKMIXINESS ~NSIDERATIONS. Orrega/VLF navigation system have been certificated for VFR and IFR use as an area navigation system for en route navigation in the NAS. This paragraph establishes acceptable criteria for Omga/VLF - system, Par. 5 3
I I
g/12/88 AC 200101C
(1) Flightcrew Inputs of: m.------ - - - - - --
(i) Aircraft present position in terms of latitude and longitude to at least the nearest 0.1 minute.
(ii) At least three (for to-from equip&) or four (for to-to equipment) mypoint positions in ternrrs of latitude and longitude to at least the nearest 0.3, minute.
(iii) A means to confirm correctness of input data prior to utilization of the new data by the system.
(iv) A "direct to" function to define a route segment from present position to any waypoint.
(VI The capability for operator deselection and reselection of any station or combination of stations.
(vi) A mns for mnual update of system position by the pilot to permit insertion of a known present position.
(21 The S tern Disola fi Information and Should Provide:
(i) Present position in te- of latitude and longitude to at least the nearest 0.1 minute and in terms of magnetic bearing and distance to or from a waypoint to the nearest 0,l nautical mile (ti) (distance to the nearest 1.0 rxni is acceptable for equipment previously approved under TSO% C94 and C94a) and nearest degree. Distances of at least 260 nmi should be capable of being displayed, but distances greater than 99.9 nmi need only be displayed to the nearest nautical mile.
(ii) Waypoint position designation in terrors of latitude and longitude to at least the nearest 0.1 minute or in texms of rrragnetic bearing and distance from present position or another waypoint. Way;?oint designation in term of magnetic bearing and distance should 'be to the nearest degree of bearing and to at least 0.1 nmi for distances up to 100 nmi then at least 1.0 nmi for distances of 100 nmi or TTY3re.
NOTE: Information should be provided to the flight crew to prevent the designation of waypoints by a sequence of bearings and distances (i.e., the reference position for a wypoint designated by bearing and distance should be designated -by latitude and longitude).
(iii) A display of active waypoint identification (not necessarily waypoint position) used to define the navigation track being flown.
NOTE: Only systems which define the desired navigation track in tenors of its endpoints can be used to navigate on published airways due to changes in mgnetic variation after the commissioning of the ground facility.
Par. 7 5
AC 20401 g/12/88
(iv) A display of the desired track in terms of the appropriate magnetic course to atleastthe nearest 1.0 degree. Display of the appropriate mgnetic course should not require the flightcrew to input the magnetic variation corresponding to the present position.
(VI A display of the distance to the active waypoint-to the Ewest
0.1 nmi (distance to the nearest 1.0 ti is acceptable for equipnt previously approved under TSO% C94 and C94aL Distances of at least 260 nmi should be capable of being displayed, but distances greater than 99.9 nmi need only be displayed to the nearest 1.0 nmi.
(vi) A continuous analog (i.e., non-nurrreric) display of crosstrack deviation with a minimum full-scale deflection of +5.0 nmi, readability of 1.0 - ti or less, and minim discernable event of 0.1 nmi or less.
(vii) .A display of crosstrack deviation to the nearest 0.1 nmi up to
9.9 nmi and 1.0 nmi beyond, with a range of at least +20 ti. This my be a digital display, IMY be pilot selectable, andneed noF be part of the course deviation indicator.
(viii) A display of the distance and magnetic bearing (at the rrfromW' end of the segment) between way@nts to the nearest 1.0 nmi and 1.0 degree.
(ix) The capability to indicate, on d-d, the specific ckllega/VW stations currently used in the navigation calculations as well as the status of all stations being tracked. 6;.
(x) An annunciation of i-ding waypoint crossing.
(3) Caution Indication(s) for the System Should Be Located on or near the indicator specified in paragraph 7b(2)(vi) and should provide a readily discernible caution indication(s) to the pilot(s) for any of the following:
. (1)
(ii)
(iii)
(iv) (VI Inadequate or invalid navigation signals or sources.
The absence of primary power.
Inadequate or invalid navigation displays or output sources.
Equipment failures.
Reversion to a secondary dead reckoning rmde of navigation.
WIE: -These failure/status indications shall occur independently of any operator action, Power or navigation equipnt failures may be indicated in a mn manner, The lack of adequate navigation signals or sources (considering sigmlto-noise ratio (SNR) as well as geomtry) should be annunciated when compliance with the navigation accuracy specified in paragraph 9 cannot be assured.
(4) The system shall be capable of autmtic synchronization within 6.0 minutes after the application of power. Synchronization should be possible with a SNR or one station/all frequencies of at least 0 & in a 100 Hz bandwidth with no coherent interference.
6 Par. 7
g/12/88 AC 200101~
(5) data input.
Navigation Guidance Should Be Available within 5 seconds of waypoint
(6) The Equipment Should Have the Capability to meet the criteria outlined in paragraph 7b(l) through 7b(6) throughout the range of environmntal conditions which will be encountered in actual service. Exposure of the equipmt to the environmntal test conditions'of TSOX120 my be used to demnstrate this capability. Environmental testing to obtain a TSO-C94 or TSO-C94a authorization my be used, provided that the test results demnstrate corrpliance with ' the criteria'of paragraphs 7bU) through 7b(6).
(7) The Equipnt Should Provide a Pkans for the Fliqhtcrew to determine system status prior to flight.
(8) The Equivt Should Provide the WiqationAccuracy specified in paragram 9 for all groundspeeds up to a maxim value 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 @pnt rmnufacturer.
(9) The IQuiwnt Should Provide mans to Alert the Flightcrew prior to arrival at a Fiaypoint 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 nw the indicator specified in paragraph 7b(2)(vi)- For ckrrega/vLF systm which are not coupled to a flight director or autopilot, a procedural mans based on a continuous and properly located distance to waypoint display my be used for waypoint lateral maneuver anticipation. System which provide steering signals for flight directors or autopilots should provide automtic turn anticipation and a waypoint alert which occurs prior to the initiation of the turn by the flight director or autopilot.
(10) If a Capabiltiy for Parallel Offset Tracks is Provided, track selection should be in incrmmts of at least 1.0 nmi left or right up to an offset of at least 20 nmi. &ans should be provided to continuously indicate that an offset track has been selected. Waypoint alerting and turn anticipation should be provided prior to arrival at the point where the offset intersects the angle bisector of the ,oarent track. These functions sho-uld operate as described in paragraph 7bt9L
c. Software Changes. The provisions of this paragraph apply to &ga/VLF quipmnt which utilizes a digital corquter to provide navigation information or system monitoring. The computer program (software) operates the computer and provides the basic functions of these system. The software for navigation functions of Qqa/VLF equipnt described in paragraph 7b (for 0mga/VLF used for IFR operations) should be verified and validated to at least the level 2 requirments as defined by R!KA/DO-178A, Software Considerations in Airborne System and Equi,mnent Certification. Any changes to software which affects navigational functions are considered to be major changes to the equipmnt.
Unless software partitioning has been previously established, any change to level 1 or level 2software of ckru3ga/VLF navigation equipnt should be verified and validated to the appropriate level and should be demonstrated as not having inadvertently affected the ramining navigational functions. changes to software used for ma/VW quipnt limited to VF'R use or equipment having Par. 7 7
AC 204OlC established partitioning from software IFR system are considered to 'be minor FM, providing the manufacturer of the - configuration mnagment and quality assurance plan approved by the FAA.
Software status must be identified on the outside of the associated line g/12/88 which provides navigational functions in and do mt require prior approval by the onutga/V~F equipnt has a software replaceable unit in accordance with the criteria of RTcA/DO-178A.-- Software changes in TSO approved equipment must be reported to the cognizant Aircraft Certification office. If the equipmnt 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 epment already installed in an aircraft my 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 EQUIPMEW INSTALLXTION CONSIDERA!TIONS FOR USE UNDER IFR.
a. Location of the mqa/VLF Display. Each display element, used as a primry flight instrumnt in the guidance and control of the aircraft, for maneuver anticipation, or for failure annunciation, should be located where it is clearly visible ticable looking to the pilot (in the pilot's primary field of view) with the least pracl deviation from the pilot's norm1 position and line of vision when forward along the flight path.
b l Failure Protection. Any probable failure of the airborne Omega/VIZ navigation system should not degrade the normal operation of other required equipmnt or create a flight hazard. Norml operation of the Wga/VLF installation should mt adversely affect the performanc e of other aircraft equi-t.
c. Enviromntal Conditions. The aircraft envirorxwnt in which the &ega/W system is installed should be found to be mpatible with environrrrental categories to which the eguipment was tested.
d. Electromqnetic Interference. The ma/W navigation system should not be the source of objectionable electmmgnetic interference, nor be adversely affected by electromgnetic interference from other equi,wru3nt in the aircraft.
e. P-Static Protection. If an E-Field antenna (whip, plate, or blade type> is used, the aircraft should -be protected by acceptable bonding techniques and installation of static discharger;. These protective devices should be specified as part of the approved design data for the Omega/VW installation. The capability to provide satisfactory P-static protection for the mga/VLF system should be derrronstrated as part of the initial certification program and for each subsequent installation using an E-Field antenna. This testing may be accowi lished by ground or static testing if sufficient data is provided to detwnstrate that the proposed technique is equivalent to flight testing- If a flight demnstration is selected, it must be conduct& at speedy UP to Vne, Vm, or k through known P-static conditions such as a cloud of ice crystals. mmntary loss of signal when encountering heavy P-static conditions my be acceptable provided the eguipnt is capable of providing acceptable navigation information during such conditions.
8 Par. 7
g/12/88 AC 20401c
(1) P-Static Charqinq/Discharqinq. P-static charging of the aircraft can cause degradation of the signal-to-noise ratio by one of three rrvajor mechanisms: sparkover of isolated metal panels, corona discharge, and strearrrer currents, Sparkover of isolated metal 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 be evaluated by a-careful ohmic survey (an electrical bonding limit of 10 milliohms is considered acceptable) of each aircraft in which the ma/VU? system is installed or by other suitable techniques. The effects caused by streamer currents can be reducd by placing the receiving antenna as far as possible from any nonconductive surfaces such as windshields. The nonconductive surfaces may be coated with a conductive coating. Tarporary spray coatings are not satisfactory. mrona discharge can be reduced by the appropriate placing of orthodecoupled static dischargers on the &r&ties 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 resistance rod and rrretal pins are recmmmded although other types may also be used if they can d-n&rate ability to provide protection from radio frequency U?EY coupling to the &ga/W antenna. The number, type, and location of these static dischargers to be installed on a particular aircraft model should be determined by following the instructions provided by the manufacturer of the static discharger for ?-static protection.
f Anti-Ice Protection. If the aircraft in which the &ga/vLF 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 ma/VW system can 'be shown to operate satisfactorily when the antenna is subject to icing, or if the system is limited via placard or d flight mual to indicate that it is not to be us&l for navigation during flight in icing conditions, then anti-ice protection is not required.
9 Dynamic Responses. The system shall continue to indicate aircraft posi- tion to the accuracy specified in paragraph 9 during aircraft maneuvering or changes in attitude encountered in nonrral operations, assuming secondary inputs are not lost during the maneuver.
h System Controls. The system controls should 'be arranged to provide adqu&e protection against inadvertent system turnoff. The controls for system operation should be radily accessible to, and usable by, the flightcrew and 'be visible under all expected lighting conditions, including night and direct sunlight.
i. system Tests. The initial approval of an &tzga/VLF system for IER use involves extensive testing to demxstrate system performance, operational areas, enviromntal qualifications, etc., as described in paragraph 7b(6). Subsequent installations in other aircraft need o&nly be tested to the extent necessary to d-n&rate proper operation of interfacing aircraft equipxant such as autopilots, flight directors and instrument displays, satisfactory antenna installations as evidenced by the reception of Orrega/VLF signals during normal flight maneuvers (including P-static conditions for E-Field antennas), satisfactory clearance of EMI, and functional check of the Ort~ga/V'U? equipment.
Par. 8
AC ZO-101C g/12/88 . I Manufacturer's Instructions. Wga/VLF equipnt should be installed in accordance with instructions and limitations provided by the manufacturer of the equimnt.
9 . SYSTEM ACCURACY.
a. En route IFR Operation Along Random (Off Airways) RNU7 Routes with Radar Coverage. The error of the airborne Orrrega/VLF equipnt should be less than +3.8 nmi of crosstrack error on a 95 percent probability basis and +3.8 rxni of glong-track error on a 95 percent probability basis. - b En route IFR @eration on Airways in the NAS.
Onega;VW equipnvtnt The error of the airborne sh ould be less than +2.8 nmi of crosstrack error on a 95 percent probability basis and +2.8 nmi OF along-track error on a 95 percent probability basis for approval-of en route IFR operations on airways.
c. Flight Technical (Pilotage) ELrrors. With satisfactory displays of crosstrack position, the FAA has determined that flight technical errors can be.?
expected to be less than the values shown below on a twosigma 'basis.
Flight Condition Flicrht Technical Error En route +l.O nmi - Sufficient flight tests o Lc the installation should be conducted to verify that these values can be maintain& Smiler values for flight technical errors should not be expected, unless the Qxxzga/VLF system is to be used only when coupled to an autopilot; however, at least the total systm crosstrack accuracy shown below should be maintained.
If an installation results in larger flight technical errors, the total crosstrack error of the system should be determined by combining equipment and flight technical errors using the root sum square (RSS) rr&hod. The result should be less than the values listed below.
Flight Condition Total Crosstrack Error Random RNAV Routes En route, on Airways +4.0 nmi T3.0 nmi -
10. IFK AIRWWHIhBS APPROVAL There are two types of approval which differ greatly as to test requirents and data analysis.
a. First-Time tirworthiness Approval. This type of approval refers to the very first tim an applicant presents a particular rcw>del orrU;ga/W equiprrsent for FAA airworthiness installation approval and certification for an IFR navigation system. Any new .&els of Wga/W? equipixnt by the same mufacturer should undergo the same approval process as the original eauipment unless it can be shawrl by analysis and tests that the new model will-function as well or better than the approved equipment. A first-time approval is conducted in three phases:
10 Par. 8
g/12/88 AC 20401c
(1) Lab/Bench Tests and -parrent Data Evaluation. This phase consists of the following:
(i) Analysis of the manufacturer's procedures for verification and validation of software and review of supporting documntation in accordance with the guidelines of R!KA/Do-178A where system performs navigational functions. . -.
(ii) Verification of compliance with appropriate enviro~nmental qualification standards such as RKA/DO-16OB.
(iii) Examination of the quimnt's display capabilities with emphasis on warning, caution, and advisory annunciations.
(iv) Analysis of failure mdes.
(v) Review of reliability data to establish that all probable failures are detected.
(vi) Evaluation of the mse of use of the controls and of the viewing ease of the displays and annunciations from a humn factors point of view.
(vii) Review of installation and mintenance manuals.
(viii) Evaluation of operator's manual (pilot's guide).
(2) Aircraft Installation Data Evaluation. Normlly the mnufacturer of the -a/W? equipnt will provide an aircraft as a test bed for a first-time installation approval. This first-time installation approval will serve as a basis for any subsequent installation approvals regardless of aircraft type or mdel. The following assessments are .to be made:
(i) Review of installation drawings, wiring diagram, and descriptive wiring routing.
(ii) Evaluation of the cockpit layout of the installed equipment with emphasis on equipmnt controls, applicable circuit breakers (labels and accessibility), switching arrangemnt and related indicators, displays, and annunciators.
(iii) Analysis of a data flow diagram in order to review which equipnznt transmits what data to which other equipment.
(iv) Review of a structural analysis of the equipnt installation in order to ascertain whether all ma/VU' coponents are satisfactorily attached - to the basic aircraft structure.
(v) Examination of an electrical load analysis in order to verify that the added electrical power requirements of the -a/W? installation will not cause overloading of the aircraft% electrical generating capacity.
(vi) Evaluation of the antenna installation. A critical aspect of any Q-tqa/VLF installation 1 l s the installation of the antenna. The Omqa/VJLF Par. 10
AC 20401C g/12/88 signal is quite weak, typically much less than one-third the value of the background noise. Electrical mise in the vicinity of the antenna can render the ortlega/vLF equip& useless.
A E-Field antenna (whip, plate, or blade type). Precipitation static has an ad;ferse effect upon the sigml receiving capability of this type of antenna. The adverse effects of precipitation static can be minimized by use of the proper antenna type and location, by installation of high-quality static dischargers, by proper bonding, and by application of anti-static paint on all plastic nonconducting surfaces. The manufacturer's installation or maintenance manual usually describes "good" E-Field antenna installation practices.
J5UL-E: Each aircraft should be subjected to a careful ohmic survey of bonding (an electrical bonding limit of 10 milliohm is considered acceptable). The P-static protection is a fequired part of the &aga/VLF installation and must be maintained for proper system operations.
B H-Field antenna (loop type). The signal receiving quality of this type of ant&a is adversely affected by aircraft electrical skin currents, particularly by 400 Hz ac. P-static has no appreciable effect on an H-Field antenna, and its effects can usually be ignored. A procedure called "skin mpping" is normally employed to determine a good munting location. It should be noted that shifting major aircraft electrical mmponents to different locations within the aircraft my render a previously determined skin mp location unsuitable.
NOTE: The following is a simple test to verify the effectiveness of an HiField antenna installation located by skin mapping. Park the aircraft away from any external electrical noise source. Using only the aircraft's battery, and with all other electrical equipment off, activate the Omega/VU? equipment and record signal-to-noise values (or quality factors) for all receivable stations. Itepst this process of recording signal-to-noise values (or quality factors) with engine0 running and all electrical/electronic equipment operating on aircraft power. If the antenna installation is satisfactory, there should not be any significant degradation in signal-to-noise ratio values or quality factors.
(3) Flight Test Evaluations. Flight tests are conducted in two stages:
(i) Functional Flight Tests Consist of:
A Evaluation of all operating modes of the mga/VW equipmnt. - B lamination of the interface (function) of other equipmnt connected to the-mga/VLF.
C Review of various failure r&es and associated annunciations such as loss of &ctrical power, loss of sigml reception, &ga/VW quip=nt failure, etc.
D Evaluation of steering response while au\opilot is coupled to the -a/VW eqzipment during a variety of different track changes.
12 Par. 10