Sufficient flight tests of the installation should be conducted to verify that these values can be maintained. Smaller values for flight technical errors should not be expected, unless the Loran-C system is to be used only when coupled to an autopilot; however, at least the total system 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) method. The result should be less than the values listed below.
Flight Condition Total CrossTrack Error Random RNAV Routes +4.0 nmi En route, on Airways ·3.0 nmi Terminal +2.0 nmi Approach +0.6 nmi
10. IFR AIRWORIHINESS APPROVAL. There are two types of approval which differ greatly as to test requirements and data analysis.
First-Time Airworthiness Approval. This type of approval refers to the very first time an applicant presents a particular model Loran-C equipment for FAA airworthiness installation approval and certification for an IFR navigation system. Any new models of Loran-C equipment by the same manufacturer should undergo the same approval process as the original equipment unless it can be shown 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:
(1) Lab/Bench Tests and Equipment 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 documentation in accordance with the guidelines of RICA/DO-178A where the system performs navigational functions.
(ii) Verification of compliance with appropriate environmental qualification standards such as RICA/DO-160B.
(iii) Examination of the equipment's display capabilities with emphasis on warning, caution, and advisory annunciations.
(iv) Analysis of failure modes.
(v) Review of reliability data to establish that all probable failures are detected.
(vi) Evaluation of the ease of use of the controls and of the viewing ease of the displays and annunciations from a human factor point of view.
(vii) Review of installation and maintenance manuals.
Par. 9 13
(viii) Evaluation of operator's manual (pilot's guide).
(2) Aircraft Installation Data Evaluation. Normally the manufacturer of the Loran-C equipment 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 model. The following assessments are to be made:
(i) Review of installation drawings, wiring diagrams, and descriptive wiring routing.
(ii) Evaluation of the cockpit layout of the installed equipment with emphasis on equipment controls, applicable circuit breakers (labels and accessibility), switching arrangement and related indicators, displays, annunciators, etc.
(iii) Analysis of a data flow diagram in order to review which equipment transmits what data to which other equipment.
(iv) Review of a structural analysis of the equipment installation in order to ascertain whether all Loran-C components 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 Loran-C installation will not cause overloading of the aircraft's electrical generating capacity.
(vi) Evaluation of the antenna installation. A critical aspect of any Loran-C installation is the installation of the antenna. The Loran-C signal is quite weak, typically only one-third the value of the background noise.
Electrical noise in the vicinity of the antenna can render the Loran-C equipment useless.
(A) E-Field antenna (whip, plate, or blade type). Precipitation static has an adverse effect upon the signal 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 lastic nonconducting suriaces. The manufacturer's installation or maintenance manual usually describes "good" E-Field antenna installation practices.
NOTE: Each aircraft should be subjected to a careful ohmic survey of bonding Tan electrical bonding limit of 10 milliohms is considered acceptable). The P-static protection is a required part of the Loran-C installation and must be maintained for proper system operations.
(B) H-Field antenna (loop type). The signal receiving quality of this type of antenna 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 mapping" is normally employed to determine a good mounting location. It 14 Par. 10
should be noted that shifting major aircraft electrical components to different locations within the aircraft may render a previously determined skin map location unsuitable.
NOTE: The following is a simple test to verify the effectiveness of an H-Field 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 Loran-C equipment and record signal-to-noise values (or quality factors) for all receivable stations. Repeat this process of recording signal-to-noise values (or quality factors) with engine(s) running and all electrical/electronic equipment operating on aircraft significant degradation in signal-to-poise ratio values or quality factors. If the antenna installation is satisfactory, there should not be any
(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 Loran-C equipment.
(B) Examination of the interface (function) of other equipment connected to the Loran-C equipment.
(C) Review of various failure modes and associated annunciations such as loss of electrical power, loss of signal reception, loran-C equipment failure, etc.
(D) Evaluation of steering response while autopilot is coupled to the Loran-C equipment during a variety of different track changes.
(E) Evaluation of displayed Loran-C navigation parameters on interfaced flight deck instruments such as HSI, CDI, etc.
(F) Assessment of all switching and transfer functions pertaining to the Loran-C installation including high-power electrical loads and electrical bus switching.
(G) Evaluation to determine whether there exists any electromagnetic or radio frequency interference between the Loran-C installation and other onboard equipment, or vice versa.
(H) Evaluation of the acessibility of all controls pertaining to the Loran-C installation.
(I) Evaluation of the visibility of the displays and annunciators pertaining to the Loran-C installation during day and night lighting conditions. No distracting cockpit glare or refections may be introduced.
(J) Analysis of crew workload when operating the Loran-C equipment.
Par. 10 15
AC 20-121A 8/24/88
(ii) Determination of Navigation Error Flight Test. The initial certification of each Loran-C system to be used for IFR operations should be based on a demonstration of system performance by recording the Loran-C equipment position and comparing it to the actual position of at least 100 locations distributed throughout the Loran-C operational area. These measures should be recorded in flight by overflight of a known ground reference point at low altitude (less than 3,000' above ground level (AGL)) or comparison with a good multiple DME fix. The data should demonstrate that the appropriate accuracy criteria of paragraph 9 are met on a 95 percent probability basis.
Flights into known poor signal areas should be conducted to verify that the caution indications for bad geometry and poor signal quality function properly.
A ground or flight test for P-static protection, if appropriate, should be conducted. Normal flight manuevers should not cause loss of the Loran-C signal and the system dynamic response should be confirmed. Any unusual flight technical errors or errors resulting from use of the autopilot and flight director should be evaluated and examined. For receivers that track only one chain at a time, at least 50 percent of the accuracy measurements should be accomplished at or near the extremes of each defined LOA. For master independent, cross chain, and multi-chain receivers, at least 50 percent of the accuracy measurements should be accomplished at or near the extremes of the combined chain coverage area. At these points, the system should also demonstrate its ability to acquire the Loran-C signal after power interruption.
b. Follow-On Airworthiness Installation Approvals. This type of approval refers to installation approvals in any model or type of aircraft after a firsttime airworthiness approval of the particular Loran-C equipment has been issued.
Follow-on approvals may use the first-time airworthiness approval, which was either a IC or an SIC, as a basis for installation approval. Follow-on installation approvals may be accomplished by IC or SIC, or may be in the form of a field approval on an FAA Form 337. The applicant or installing agency requesting a follow-on Loran-C installation utilizing this method of data approval should:
(1) Contact either the manufacturer or organization responsible for obtaining the first-time airworthiness approval in order to:
(i) Obtain a sample airplane flight manual (AFM) or rotorcraft flight manual (RFM) supplement (or supplemental flight manual, as appropriate).
(ii) Obtain verification of the equipment approval status, including the model of the antenna and software program identification.
(iii) Discuss any problem areas and seek assistance in their solution.
(2) Conduct a similar data evaluation as outlined in paragraph 10a(2).
(3) Conduct flight evaluations similar to the flight tests outlined in paragraph 10a(3)(i).
(4) Verify that the ohmic bonding check of the aircraft has been conducted and that appropriate numbers and types of static dischargers are 16 Par. 10
8/24/88 AC-20-121A installed if an E-Field antenna is used, or that a skin map has determined the appropriate location for the antenna if an i-Field antenna is used.
(5) Verify that the maximum expected groundspeed of the aircraft is less than the maximum operating speed for which the Loran-C equipment is qualified.
(6) Spot-check navigation accuracy and verify proper system operation by conducting an evaluation flight. The flight test should be of sufficient length and should follow a plan which permits proper functional evaluation of the Loran-C installation. Accuracy should be verified by conducting at least two low-level overflights of known landmarks (i.e., a VOR station). (A DME-DME position fix may be substituted for one of the low-level overflights.) The receiver should demonstrate the ability to properly acquire the Loran-C signal under varying conditions, including at least five acquisitions in flight and five on the ground. Acquisition demonstrations should encompass a variety of chains (for single chain receivers) and, if possible, poor signal quality areas.
If possible, this flight should include areas of poor coverage to observe proper operation of appropriate annunciations. The purpose of this test flight is not to validate navigation error values, but rather to verify that in the course of this installation nothing was done to compromise the accuracy of the system as determined by the first-time approval. Errors in excess of the values listed in paragraph 9 should be evaluated to determine possible causes. If a logical explanation is not available, additional flight test data points should be collected in the area(s) where the excessive error occurred. If such error (s) persists, approval of the installation should be withheld.
11. OPERATIONAL CONSIDERATIONS.
Operation in the National Airspace System (NAS). The aircraft should have navigational equipment installed and operating appropriate to the ground facilities to be used (not including Loran-C systems). Within the conterminous United States, this requirement may be met with the installation of a VOR receiver in addition to the Loran-C system approved for IFR operation.
b. Loran-C Operational Area. Operators and their flightcrews should consult the approved flight manual supplement for their aircraft to determine approved operational areas that apply to their aircraft. Flightcrews must be aware that operational areas may be different for different Loran-C systems, and the appropriate operating area (s) for a particular system can only be determined by reference to the approved flight manual or other FAA approved documents.
M. C. Beard Director, Aircraft Certification Service Par. 10 17
Appendix 1 APPENDIX 1. PROCEDURES FOR OBTAINING FAA APPROVAL FOR IFR/VER OPERATIONS BY SUPPLEMENTAL TYPE CERTIFICATE OR FAA FORM 337 (FIELD APPROVAL FOR FOLLOW-ON INSTALLATIONS.
1. APPROVAL OF TECHNICAL DATA BY SUPPLEMENTAL TYPE CERTIFICATE (SIC).
a. The STC Applicant:
(1) Makes an application for an STC at the nearest FAA aircraft certification office. Farly contact is wise, since scheduling may be critical. FAA evaluates the data submitted by the applicant, issues a Type Inspection Authorization (TIA), and participates in ground/flight tests outlined in paragraph 10. An SIC is issued when all airworthiness requirements are met.
If the submitted data is adequate, the STC authorizes identical installations in the same aircraft type.
(2) Designs and installs the Loran-C system to the criteria set forth in applicable paragraphs of this advisory circular, or consistent with ocher data acceptable to the Administrator.
(3) Obtains an authorization from the equipment manufacturer to reference the original data for equipment accuracy (per paragraph 9), or conducts the necessary tests.
(4) Makes an aircraft available (with the Loran-C system installed) for ground inspection and flight test. The applicant is responsible for furnishing a qualified flightcrew for the required flight tests.
Should Submit the following kinds of data for FAA airworthiness evaluation:
(1) Equipment data such as:
(A) Equipment schematics and system wiring diagrams.
(B) Equipment manufacturer's operating instructions and installation instructions.
(C) Equipment manufacturer's quality control procedures (not required if manufacturer's quality control is FAA-approved).
(D) Environmental test data.
NOTE: Equipment data need not be submitted if the equipment has been manufactured under a technical standard order authorization.
(ii) Fault analysis covering installation.
(iii) Installation information and/or photographs, including antenna and P-static protection devices.
(iv) Structural substantiation as necessary.
Appendix l
(v) Installation wiring diagrams.
(vi) Flight manual revision or supplement, or placard drawings as required (see paragraph 2c of this appendix).
(vii) Evidence of previously approved data.
(viii) Electrical load analysis.
b. The Equipment Manufacturer Can Certify (to the applicant and FAA) that the performance criteria in paragraph 9 by reference to the original STC have been satisfied, a TSO has been obtained, and that the appropriate environmental tests have been conducted.
APPROVAL OF TECHNICAL DATA INSTALLATTON FOR IFR OPERATIONS BY FAA FORM 337 (FIELD APPROVAL).
Data Submitted by the Applicant. Alteration data for the equipment installation will be submitted with a properly executed FAA Form 337, and a certification from the manufacturer to confirm that the system performance requirements of paragraph 9 have been met.
b. Additional Data Which May Be Required. If required for FAA airworthiness evaluation by the FAA district office approving the technical data/installation, the applicant may also be required to furnish a copy of the equipment data (for equipment not produced under a technical standard order authorization), manufacturer's operating and installation instructions fault analysis for installation, installation details and/or photographs, substantiation of structural changes, and system wiring diagrams.
SUPPLEMENT. An AFM/REM supplement (or supplemental flight manual) prepared by the applicant and containing the following information must be presented for FAA Airplane Flight Manual (AFM) or Rotorcraft Flight Manual (RFM) approval.
(1) Equipment operating limitations.
(2) Emergency/abnormal operating procedures (if applicable).
(3) Normal procedures for operating the Loran-C system and any interfaced equipment.
(4) Procedures for verifying proper operation after power outages.
d. The applicant makes an aircraft available (with the Loran-C system installed) for ground and flight tests, and is responsible for furnishing a qualified flightcrew for the required flight test. The results of the flight test should made a part of the data submitted. The FAA approving inspector will request to observe the flight test.
NOTE: The FAA inspector will evaluate and sign the airplane flight manual supplement or rotorcraft flight manual supplement (or supplemental flight manual) presented by the applicant as part of a field approval. Generally, FAA
Appendix 1 inspectors should have sufficient understanding of the AFM or the RFM to approve a supplement for the Loran- installation without the need for engineering assistance. However, if engineering assistance is needed, then the inspector should request it early in the program.
e. Field approvals of Loran-C installations for IFR should be limited to follow-on installations where the original approval was through the IC or STC process and where the system installation is either of the stand-alone kind or where the interface with autopilot, flight director, and aircraft equipment is of a simple nature. For example, a simple interface is one which provides a switching arrangement to substitute the Loran-C deviation and flag signals for the comparable outputs of one VOR receiver. Field approvals without engineering assistance should not be made when:
(1) The Loran-C equipment transfers or accepts data from other navigation systems or computers such as inertial, Omega, or flight management systems;
(2) The aircraft has numerous sources of navigation information installed with a complex switching system; and
(3) The Loran-C equipment incorporates a software configuration that has not been FAA approved.
APPROVAL OF INSTALLATION FOR VER OPERATIONS. Approval of Loran-C installations for operations under VFR may be obtained by TC, STC, or data field approved by the FAA on an FAA Form 337. If previously approved data is available or the installation can be accomplished by utilizing provisions provided by the airframe manufacturer for standard avionics equipment installations, the installation then be approved for return to service by one of the entities noted in FAR 43; i.e., repair station, manufacturer, holder of an inspection authorization, etc., provided the installation:
Conforms to the acceptable methods, techniques, and practices contained AC 43.13-1A, Acceptable Methods, Techniques and Practices - Aircraft Inspection Repair and AC 43.13-2A, Acceptable Methods, Techniques, and Practices - Aircraft Alterations.
b. Does not interfere with the normal operation of other equipment installed in the aircraft. This is accomplished by a ground test and flight test to check that the Loran-C equipment is not a source of objectional electromagnetic interterence (EMI), is functioning properly and safely, and operates in accordan with the manufacturer's specifications.
c. Does not involve complex switching for integration with other aircraft systems; e.g., flight directors, electronic flight instrument system (EFIS) displays, etc. The Loran-C may be coupled to the radio nav function of an autopilot provided it has a course deviation indicator output that is compatible with the autopilot and the same installation procedures normally used for the VOR coupling are used.
Appendix 1
d. Provides a navigation source annunciator if the Loran-C installation supplies any information to displays such as an HSI or CDI which can also display data from other equipment normally used for aircraft navigation.
Except for items c and d of this paragraph, is completely isolated from all IFR systems.
Has an approval recordation contained in an FAA Form 337 and that a placard is in clear view of the pilot which indicates Loran-C Not Approved For IFR. " NOTE: Helicopters approved only for VER operations do not need placarding.