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ADVISORY AC 120-37 DATE lo/lo/78
CIRCULAR DEPARTMEST OF TR.4XSPORTATIOX Federal Aviation Administration . Washington, D.C.
FAR GUIDANCE MATERIAL Su bjwt : OPERATIONAL AND AIMKXWNESS'APPROVAL OF AIRBORNE oME3GA R?DIONAVIGATION SYSTEMS AS ASOLE MEWS OFOVEZWATER m RANGE NAVIGATION 1 PURPOSE. IMs advisory circular establishes an acceptable means, but m only means, of obtaining airworthiness and operational approval of Airborne OME& Navigation Systems as a sole means of long range navigation for operations cotiucted outside the United States in accordace - with FAR 121, 123 or large aircraft operated under FAR 135.2. ' ' - l ' 2 REFERENCES. Feckral Aviation Regulations (FAR) 121.355, 121.389, 121.103,
121.121, 121.405, 121.411, 121.413, 121.414, 121.433, 123.27,
135.2, 21.111, 25.1301, 25.1309, 37.205 xCI A% 120-3X, AC 120-33.
a. OMEGA is a radio navigation system which uses a worldwide netwrk of very low frequency signals fmn eight groun+based transmitters. 'Ihe principal attributes of the OMEGA system are the high degree of signal stability and low signal attenuation which produce reliable position information over great distances. Experience has shown airborne OMEGA equipent is capable of producing accurate navigation information.
b. Various methods of signal processing are used by different manw facturers to develop position information asid navigation guidance (i.e., rhwrho, hyperbolic, single frequency, 3.4 KC tracker, etc.).. Since these variations in processing methods exist, each design should be evaluated and approved individually. When OMEGA systems meet the provisions described below, they may be used as sole means of long range navigation for operations in oceanic and/or remote land areas where adequate accuracy and reliability have &n demonstrated. U.S. Navy VLF Omnunications stations may be utilized to supplement OMIDGA navigation solutions.
However, the U.S. Navy VLF stations are not dedicated to navigation and their signals may not be available at all times. Therefore, systems approved in accordance with this circular should be capable of operating on OMEG?4 signals alone.
Initiated by: ~~~-130 AFs223
AC 120-3’7 10/10/78 C. This advisory circular is divided int ~WD sections. 91e first section deals with the airworthiness approval under IFAR 25, and the second section deals with operational approval under FAR 121.
d Guidance concerning cmpliance with Fm 91.20 regard- the North Atlantic (NAT) Minimum Navigation Perfomance Specifications (PINIPS), and a description of the applicable airspace, is contained in Advisory Circular 120-33.
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e. 'Ihis circular only addresses dual oMM3A installations. Installations which propose to use one OMBGA system in canbination with one or more other types of sensors or units should be evaluated on an individual basisl considering the performance of the pq~s&I system.
c SEcrIONl -AIRWRZXINESSAPPWAL 4 0 GENERAL. mplicants desiring aimrthiness approval of dual airborne OMMlA navigation systems in accordance with this advisory circular should contact the appropriate FAA Rzgiona Engineering and Manufacturing Office at least 30 days prior to start of the evaluation for processing a supplemental type certificate (SK) or type certificati (TC) amendment. A dual OMEGA installation includes tw3 receiver processor units, tw *control.; - _I display units, and tm antennas. / (f :\ 5 MINIMUM FUNCTIONSNECESSAW t PiD SCE MEANS OF NAVIGATION.
WHENUSEDFVR POSITIUVFIXING u Ixlal independent WlEG?I navigation systems used as a position-fixing device or positiol+-keeping device and sole means of navigation should meet the performance requirements of FAR 37.205 (TSO C-94) titled "Airborne CHEGA Receiving Equip-nent;" particthrly section three of Radio Wchnical Gomnission for &xonautics Exxxnent No. IXH64 entitled "Minimum Performance Standards Airborne oMEx;TA Wceiving Equipent" dated March 19,1976. When installed in aircraft, the system should satisfy the following conditions:
a. System Data Inputs and Functions. The system should provide a means of entry for at least the following data inputs and functions:
(1) Present position (initialization, reinitialization and update)
(2) typoints '
(3) Heading, wind and TAS; or track and ground speed; or other external information required for operation in the secodary mcde (dead reckoning)
(4) Time
(5) Date
(6) Deselection and reselection of any station. Automatic deselection and reselection is acceptable if shown tD be effective and reliable.
(7) Lane ambiguity resolution. Autanatic lane anbiguity resolution is acceptable if shown tL) be effective and reliable.
b Systms Displays The system should provide a means of displaiing to‘the operato; the following information:
(1) Present position
(2) Time
(3) Date
(4) Synchronization Status
(5) Station(s) deselected - station(s) selected
(6) Time and position recall in event of pwer failute for up to 7 minutes
(7) Annunication when system is not operating in the primary OMEG?i navigation mOde
(8) A warning by adequate visual or aural signals of system failure, malfunctions, power interruption, lack of synchronization or operation without adequate signals
(9) Coordinates of waypoints
(10) Bearing and distance.between waypoints
(11) Deviation from desired course
(12) Distance and time to go to selected waypoint
(13) Track angle and/or error
(14) Drift angle
(15) Wind, True Airspeed (TM) and Heading; or Track and . * , . Ground Speed (GS) rr
(16) Stations currently being utilized to determine position
(17) Steering information on the horizontal situation indicator (HSI) or equivalent
(18) Confirmation of data insertion 6 0 EQUIPMENT INSTALLATION.
a. Location of OMEGA Displays and Controls. System controls and data display should be visible to, and usable by each pilot while seated at his duty station if the equipment is to be operated by the pilot.
b Failure Protection. Any probable failure of the airborne @EGJJ navigaiion system should not derogate the normal operation of equipnent connected to it nor should Ix)'EmEI1 operation of oMEK;A result in failure or degraded perfomanee of interfaced equipnent. Likewise, the failure of interfaced equipment should not render an oMM'3A system inoperative.
6. mvironmental Conditions. TheOMM;Aequipnentshould be capable of performing its intended function over the environmental ranges expected to be encountered in actual operations. The RICA Docuanent No. Ix)-160 should be utilized for appropriate guidelines.
d Electromagnetic Interference. like OMEGA navigation system should not be'the source of objectionable electromagnetic interference, nor be adversely affected by electrqnetic interference from other equipment in the aircraft.
AC IS37 lo/lo/78
e.
minimize antes.
Antenna Performance. The antenna design and installation should the effects of precipitation (p) static and other noise or disturbf affect& * Dvnamic ResDonses. The system o=ration should mt be adversely * & by aircraft maneuvering 02 changk in normal operations.
attitude encountered in g System Controls. The system controls adequate protection against inadvertent system should be arranged tr> provide turnoff.
h . Preflight Test. A preflight test capability should be provided to inform the flight crew of system status,
i. Aircraft Electrical Power Source. One OMEGA system should be installed so that it receives electrical pawer frm a bus that provides maximum reliability for operation of the OMEGA equipnmt without jeopardizing essential or emergency loads assigned to that bus. The other OMEGA system should be installed so that it receives pawer from a different bus that provides a high degree of reliability. Any electrical mr transient, including in-flight selection of another source of power for either OMEGA system, should not adversely effect the operation of either OMEGA%ystem' -.
, 3 l pot\Fer Interruption to the Omega System. r ,i
(1) After a power interruption of 7 + 2 seconds, the @lEGA equip ment should automatically resynchronize and re%ne normal operation within 3 minutes without operator intervention.
(2) After a pawer interruption of greater than 7 seconds and up to 7 minutes, the oMM;A equipment should either autcxnatically resee rr0rma.l.
operation (including proper lane resolution) or, retain the last "power-on" OMEGA equipent position and time for display on ccmmnd. A battery, if shown to be of sufficient capacity, may be used to perform this function.
k . Steering Outputs. The OMEGA system should provide steering outputs. to the autopilot and/or horizontal situation indicator or equivti lent so that the equipment interface is compatible.
1 . Airplane Flight Manual. The Airplane Flight Manual should contain the following information on the @IGA equipment:
(1) Normal procedures for oprating the equipment;
(2) Equipment operating limitations;
(3) Emergency/abnormal operating procedures (if applicable).
(4) Procedures for reacquiring the proper lane after p0wer outages.
AC 120-3’7 7 l&g SYSTEM ACCURACY. The system should meet the accuracy stipulated for range navigation systms in FAR 37.205 (TSO C-94) per (KICA EM64 Section III 'para. 3.8), 8 IEMON~TI~OFP~~CE. An applicant for approval of dualnavigation system installation should show that the installed OMEGA system can demonstrate adequate performance by a cmbination of ground and flight evaluations defined below:
a. Ground Evaluation.
(1) After installation, an operational/functional check should be performed to demonstrate compatibility between the oMM;A system and aircraft electrical and electronic systems. This test should be conducted with all electrical/electronic equipent operating no&ly on aircraft mer. A ground location should be selected that minimizes the presence of external electromagnetic.'interference. In addition, it should be demonstrated that the OMEGA equiment will not adversely affect other systems to which it may be connected, i.e., air data, autopilot, flight director, and oorrrpass system.
. (2) The OMEGA velocity and heading (or track) information present4 on the Control/Display Unit and other interfacing instrunents', &ould have reasorxzle comparison to the primary indications on other flight deck instrunents. IXlring these tests the primary velocity and heading inputs to the OMEGA system should be slewed through their operating range TV assure compatibility of input to interfaced equipnent. 'Ihis evaluation may be conducted in flight.
(3) Displays of all data basic to the installed OMEA systems should be demonstrated to show no instability or discontinuity when utilizing those stations identified by the systems as usable and necessary for navigation. This evaluation may be conducted in flight.
b l Flight Evaluation.
(1) The OMEGA navigation system should be checked in flight to determine that the design and installation criteria are met. All mdes of operation should be functionally checked. The Airplane Flight Manual pnocedures should be evaluated in flight including abnormal and emergency procedures. This evaluation should include: reinitialization, lane ambiguity resolution, etc., during normal and adverse conditions.
Interfaced equipment should be evaluated to assure proper operation.
Normal flight maneuvering should include 180* turns for verifying dynamic response.
(2) Tke aplplicant for airworthiness approval should provide data frm sufficient flights in the anticipated area of intended use to show that the OMEN navigation system can be used to meet the accuracy requirements stipulated for long range navigation systems in FAR 37.205 5
AC ED-37 10/10/W (TSO C-94) i.e., RICA Do-164, Section III, para. 3.8. Consideration should be given to time of day, season, station outages, station geometry and poor signal to noise ratio.
(3) It should be demonstrated that operation of the system does not impose an unacceptable workload in a normal in-flight environment on the flight crew. mis aspect should receive careful scrutiny relative ti .
crew w&load during power outages, dead reckoning (DR) aperation and detecting/resolving lane ambiguities.
(4) The Dead Reckoning (DR) tie should be evaluated tcdetermine the maximum period for which interim use is permissible. That information should be included in the Airplane Flight Manual.
under Evaluation of a specific operator's Section II *rational F$proval;
procedures should be
9.49. I?Em?mD.
SECTION 2 -0PERATIoNALAPPIwVAL accomR1
a. The basic requirements under FAR Part 121 for en route navigation facilities are contained in Sections 121.103 and 121.121.
b . wplicants desiring operational approval for use of dual OMEGA systems should contact the Air Carrier District Office, Flight Standards District Office or General Aviation District Office charged with the administration of their oFrating certificate a minimum of 30 days prior to the proposed start of evaluation flights.
21 l FEQUEST FoROPEIRATloNALAPPEIcxrALo me request should contain the follclwing information:
a. Evidence of an FAA Airworthiness Approval of the system, including a description of the system installation.
b 0 Exmrience.
(1) Prior to presenting the initial request, an operator should have accumulated sufficient experience with the equipment to establish a history of the accuracy and reliability of the system proposed for use. The applicant may include previous or related operational experience of other operators, using the same equipment on the same type aircraft, and operational experience gained during type certification or supplemental type certification of the aircraft. Once a particular system has received an 6
equipnenta~roval~ evaluation and approval in subsequent same type aircraft installations may be adjusted to avoid duplication of part of the accuracy and reliability data gathering process involved in the issuance of the original approval.
(2) A cqnprehensive sunmary of any flight experience which will establish a history of adequate signal coverage during day or night operations, accuracy, lane ambiguity detection/resolution, and service reliability should be provided to show ccmpetency in the proposed operation and maintenance of the equipment.
c. proposed revisions to the werations Manual describing all normal and abnormal system operating procedures, flight crew error protection procedures including cross-checking of data insertion, detailed methtis for continuing the navigation function with partial or ca-nplete m system failure and reacquiring the proper lane after any pawer outages, and procedures for continuing operations in the event of a divergence between systems.
d Proposed revisions to the Minimum Equipent List (MEL) concerning @EGA, with appropriate justification.
e. A list of operations to be conducted using the system, cont&ning an analysis of each with respect to signal reception for ground synchronization and en route operation, signal absorption by the Greenland icecap, sufficient redundancy of signal coverage to permit continued operation during station outages, procedures for oprating in areas of magnetic canpass unreliability (if applicable), availability of other en route aids, and adequacy of gateway facilities to support the system. Fbr the purpose of this advisory Circular, a gateway is a specific navigation fix where the use of the long range navigation system corrnnences or terminates.
f Procedures for timely dissemination of OMMzA NoTAM information to crerlmembers.
g A training program curriculum to include initial and recurrent train&g and checking for those crewmnbers who are to operate the OMEA equipent.
h An outline of the maintenance program for the equipment, including train& of maintenance personnel, positioning of spares and test equipment, maintenance manual revision procedures if applicable, and the other means of capliance with the requirements of Subpart L of FAR Part 121.
22 l EQUIPMENT AND ~UIPMDJT INSTALLATION.
a. m navigation systems should be installed in accordance With the airworthiness approved system installation requirements.
b If evaluation flights are made in operations on which a long range navigation system is required, a navigation system already approved for the operator under Part 121 should be used as the primary means of navigation.
23 l TRAINING PROGRAMS.
a. Initial training programs should include the following:
(1) Instruction regarding responsibilities of flight crewngnbers, dispatchers, and maintenance personnel.
(2) FW those crewnembers who are to operate the OMEGA equipment (pilots and navigators, as appropriate), instruction in the following:
(a) Description of the OMEGA network, airborne system description, limitations, and detection of malfunctions.
( w dures and testing, including periodic between systems,
(c) (a if applicable.
Normal operating procedures including preflight proce - data insertion and cross-checking, en route procedures cross-checking of system position display and mparison +' i, <:
Updating procedures, if applicable.
werations in areas of magnetic ccmpass unreliability, Abnormal and emergency procedures including: airborne conditions, procedures for assessing and resolving divergences between systems, and procedures for reacquiring the proper lane in case of pawer.
outages in excess of 7 seconds,
(f) A review of navigation, including flight planning and applicable meterology as necessary, if not addressed in another approved training program.
(g) (Bmpilation of terminal and/or gateway system errors.
b Procedures for operating the OMW4 navigation system should be incor&ated into the recurrent training program for those crewnembers who are to operate the OMEGA equipment (pilots or navigators, as appropriate).
c. Fbr flight crewnembers (pilots or navigators, as appropriate) without previous OMEGA experience, the training and qualification program should include an inflight qualification check based on the training program.
m/10/78 AC 120-37 Accomplisbent of such training during evaluation flights is acceptable.
Sufficient flight crews considered fully qualified by the applicant should be observed in flight by the FAA to determine the overall effectiveness of the training and qualification program. Flight crews possessing current operational experience with the installed OMEM equipnent need only receive training specifying any differences in procedures created by using oMEx;A as a sole means, if applicable.
d Annual line checks as required by FAR 121..440 should include a check if oMM;A operating procedures. Required annual checks of flight navigators should also include a check of WEA operating procedures.
24 . ACCURACYANDREL~ABILITY. The applicant should show:
a. That an adequate inflight service reliability rate, stated in terms of inflight mean time between failures (MIFF), is in existence, with no significant unresolved problems remaining.
b That in the areas of proposed operation the a navigation system meets kcuracy requirements stipulated for OMEGA navigation systems in the airworthiness section of this circular. If the system is proposed to be operated in areas requiring special navigation requirements (i.e., MNPS),.
the accuracy required for those areas must also be demonstrated. Sytit&n& which beccane exceedingly inaccurate without displaying a warning indication should be included in the accuracy accounting. Systems which display a failure warning and are subsequently shut down or disregarded should be included in the accounting of failed systems in paragraph 24a, but excluded from the accuracy accounting.
c. That @EGA navigation systems which are subject to lane ambiguity have a reliable means of reacquiring the proper lane.
d That the OMEGA sole means systems can meet navigation separation requir&ents and have sufficient signal redundancy to continue navigation during oIMM;A station outages, Quipent having the capability to process the U.S. Navy VLF signals may utilize that feature to refine OMEGA information to assist in meeting this stipulation.
e. ?Ihat within the proposed area of operation, navigation capability is not predicated on the dead reckoning (DR) tie, and that any interim operation in DR does not degrade navigation accuracy and reliability beyond that required to comply with ATC requirements.
25 l EWGUATIONPROGRAMANDFINALAPPRWAL,
a. Prior to final approval for the use of OMEGA as a sole means of long range navigation, a thorough evaluation should be made of the operator's training program and a flight evaluation should be conducted by FAA personnel.
A flight evaluation should be requested as a part of the application for operational approval for the use of @EGA as a sole means of long range navigation.
b 'Ihe evaluation should ensure the adequacy of operating pmcedures, training prograansr availability of term&& gateway, area and enroute ground-based navigation aids, operational accuracy, equipent reliability, and acceptable maintenance procedures. @lEGA equipnent operations should be closely analyzed to ensure that an unacceptable m&load is not imposed upon the flight crew by the use of the @!.EM equipment in normal and abnormal operations.
c. The applicant should provide data from sufficient flights which demonstrates the ability to use the particular type of OMEGA as a sole means system in operations so that the requirements of FAR 121,103 and 121,121 for the area of intended operation are met.
d After the evaluation is cqleted, FAA approval is indicated by isskce of operations specifications, or amendments thereto, authorizing the use of dual OMEGA as a sole means of long range navigation in the areas ir? which operations were demonstrated. Approval is limited TV those operations or areas where ccmpiiance with FAR 121 requirements was demonstcatd,.
e. The operations specifications should contain applicable limitations or special rqxr merits needed for particular routes or areas, and, where i 1. ‘i \ necessary, a iisr of a sufficient nunber of OMEGA ground transmitters required to be in operation to provide the necessary amount of signal redundancy.
Acting Director9 Flight Standards Service 10