2/5/93: AC 90-92
b. Use Caution! Pilots are cautioned that foreign-operated Loran-C chains may not provide adequate signal coverage when required for air navigation. Pilots are further advised to use extreme caution before committing themselves to an extended ocean crossing. They should also ensure that adequate signal coverage is available throughout the route and be fully prepared to navigate by dead reckoning (DR) or other means in the event of signal loss.
4. APPLICABILITY. Pilots may use Loran-C equipment as a primary means of navigation over certain areas of the Atlantic Ocean, the Caribbean Sea, the Pacific Ocean, and certain other areas, provided that the equipment and software are installed, maintained, and operated in accordance with the prescribed limitations. The following operational guidelines apply:
a. U.S.-Registered Civil Aircraft. Federal Aviation Regulations (FAR), Part 91, Subpart H, governs the operation of U.S.-registered civil aircraft outside the United States.
This subsection requires all such aircraft to comply with ICAO Annex 2 and with FAR §§ 91.117(c), 91.130, and 91.131 when operating over the high seas. In addition, FAR Part 91, Subpart F, and FAR Parts 121, 125, and 135 establish requirements for radio and navigation equipment during over-water or extended over-water operations.
b. VER Operations.
(1) Equipment Requirements. ICAO Annex 2 (to the Convention on International Civil Aviation) entitled, "Rules of the Air," and ICAO Annex 6 entitled, "Operation of Aircraft," require all VFR aircraft to be equipped with the navigation equipment that will enable them to proceed in accordance with their flight plans and the requirements of the various air traffic control (ATC) services. While ICAO Annexes 2 and 6 do not specifically define the kinds of equipment or accuracies required for VFR flight over the oceans and beyond the operational coverage area of conventional land-based VOR, VOR/DME, or NDB NAVAID's, prudence and good pilot judgment both suggest that Loran-C units used as the sole means of VFR oceanic navigation be capable of providing continuous and reliable coverage over the entire route. If Loran-C coverage capability cannot be guaranteed or is unknown, then an alternative means of navigation should be available (see coverage diagrams in appendix 1). DR is an acceptable means; pilotage is not an acceptable means of navigation over large bodies of water because of the absence of prominent landmarks (with the exception of the Gulf of Mexico where there are over 2,000 landmarks offshore). In all cases, Loran-C equipment should be backed up with a DR flight plan progress log or other means so that the pilot knows, at all times, where the aircraft is, since atmospheric phenomena can render a Loran-C receiver useless with almost no advance warning.
(2) Altitude Limitations. ICAO Document 7030, "Regional Supplementary Procedures," also specifies the maximum altitudes that can be flown VFR in specific oceanic Par 3
areas. For example, all pilots must file an IFR flight plan when intending to fly in North Atlantic (NAT) airspace at flight level (FL) 60 (6,000 feet mean sea level (MSL)) and above in New York, Gander, Shanwick, Santa Maria, and Reykjavik Oceanic Control Area/Flight Information Regions (CTA/FIR's), at FL 60 and above in the Bodø Oceanic CTA/FIR beyond 100 nautical miles (nm) seaward from shoreline, and at FL 200 and above in the Søndrestrom CTA/FIR. Since it is extremely unlikely that a NAT crossing can be conducted entirely in visual meteorological conditions (VMC), VFR operations are strongly discouraged.
NOTE: ICAO Annex 6 requires a redundancy of navigation equipment for VFR aircraft operations. For FAR Part 91 VFR operations, this redundancy of equipment may be met by means other than a duplication of navigation equipment. For example, one VOR or NDB (supplemented by DR) and one Loran-C would meet the requirement.
c. IFR Operations.
(1) IPR Operations Outside Minimum Navigation Performance Specifications (MNPS) Airspace. ICAO Annex 2 states, in part, that aircraft operating IFR over the high seas "shall be equipped with suitable instruments and with navigation equipment appropriate to the route to be flown."
(i) Redundancy of IFR Equipment. Annex 6 also requires a redundancy of equipment for IFR operations. FAR Part 91, "General Operating and Flight Rules," is silent on the need for long-range navigation units for operations of small aircraft certificated under FAR Part 23. FAR Part 125 and Subpart F of FAR Part 91, which govern the operation of large and of turbine-powered, multiengine airplanes, require two independent electronic navigation systems. Backup equipment is not required to be identical
• (such as duplicate independent systems). For example, one Loran-C and one Omega system combination is acceptable. Dual temporarily installed long-range navigation (LRN) systems are acceptable for ferry flights, provided that their installation is properly documented and approved.
(il) FAR Part 121, FAR Part 135, and FAA Order 8400.10, Air Transportation Operations Inspector's Handbook," contain specific guidance regarding navigational system requirements for air carrier operations. Specific authorization for equipment and routes is contained in the operations specifications (OpSpecs) for each carrier, as amended by the aircraft's minimum equipment list (MEL).
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215/93 AC 90-92
(il) Offshore Helicopter Operations in the Gulf of Mexico.
(A) IFR offshore helicopter operations are conducted within Houston Center airspace at 7,000 feet MSL and below.
(B) Loran-C equipment may be used for both primary course guidance and approved Loran-C instrument approaches. Use of Loran-C for all IFR offshore helicopter operations in the Gulf of Mexico must be specifically approved by the FAA through issuance of a letter of authorization (LOA). Pilots should refer to FAA Order 8400.10 for further guidance.
(2) IFR Operations Within MPS Airspace. Navigation equipment used in NAT MNPS airspace must meet ICAO accuracy standards as stated in FAR Part 91, appendix C, and be specifically approved by the FAA. In addition, an endorsement must be contained in the "Operating Limitations Section" of the AFM/POH, and each operator and aircraft must have written FAA approval to operate in MNPS airspace. Operational capability should be maintained through recurrent training, periodic equipment inspection, and reliability checks. At present, MNPS airspace is designated over virtually all of the NAT between FL 275 and FL 400 and over certain areas and altitudes over Northern Canada (see figures 5 and 6). ICAO Annex 6 specifically requires all navigation equipment used in MNPS airspace to continuously provide an indication to the flightcrew under all weather conditions of adherence to assigned tracks, within the accuracy required for navigation along that track. For further information on MNPS airspace requirements, pilots should refer to the "North Atlantic MNPS Airspace Operations Manual," and ICAO Document 7030, "Regional Supplementary Procedures."
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FIGURE 5
NORTH ATLANTIC (NAT) MPS AIRSPACE 45° 20° W 70° 60° 50° 40° 30° W 10
FIGURE 6
CANADIAN MPS AIRSPACE Greenland Arctic Sea Ocean 60° Beaufort Sea 55° Gulf of CMPS AIRSPACE Stra Alaska FL 330 TO FL 390 50° Pacific Ocean 45° 40° 35° 120° 110° 100° 90° 80° 70° W 11
AÇ 90-92 2/5/93
5. INSTALLATION AND OPERATIONAL GUIDANCE FOR THE USE OF LORAN-C IN OCEANIC OPERATIONS.
a. Installation Guidance. Loran-C navigation equipment used in oceanic operations should be installed in accordance with AC 20-121, "Airworthiness Approval of Airborne Loran-C Navigation Systems for Use in the U.S. National Airspace System (NAS)," current edition. Loran-C units must be installed under the Type Certificate (TC), a Supplemental Type Certificate (STC) or field approved using an FAA Form 337, "Major Repair and Alteration (Airframe, Powerplant, Propeller or Appliance)." Loran-C units may be susceptible to signal attenuation due to improperly installed antennas. Any temporarily installed Loran-C unit should be connected to an external antenna approved for use by the manufacturer. Pilots should be aware that limited single-chain operation or inappropriate (or obsolete) signal processing software, or a "noisy" antenna system, can all cause loss of navigable signal information with all types of Loran-C units. All temporarily installed or portable Loran-C units must be operated pursuant to FAR § 91.21, "Portable Electronic Devices." This section states, in part, that no person may operate a portable electronic device on a U.S.-registered civil aircraft operated by a holder of an air carrier operating certificate or an operating certificate, or on any aircraft operating IFR. However, the regulations allow for such operations if it has been determined that the portable unit, when operated, will not interfere with either the navigation or communication equipment installed on that aircraft.
b. Oceanic Use. Loran-C navigation equipment for oceanic use should be capable of multiple chain operation and be capable of using any chain necessary for the intended flight.
The unit must also be capable of inputting into memory any latitude/longitude coordinates required for the flight. The manufacturer's most recent software version should be installed, and the appropriate software documentation should be available.
c. Preflight Activities. Pilots should carefully review Loran-C operating limitations and instructions contained in either the AFM or POH (see figure 7 for an example). Pilots should make themselves aware of specific documentation which authorizes the use of this equipment for oceanic navigation and what restrictions and/or limitations, if any, may be placed upon its operational use. An example of a limitation follows: "IFR area navigation of [brand & model name] is limited to the continental United States." Pilots should also review the scope of data within the memory of the Loran-C. For example, are all airport locations stored in memory or are only selected airports stored in memory?
d. Preflight and Continued Airworthiness. During preflight, it is extremely important for pilots to ensure that all flight-control-to-airframe bonding straps (loosely woven metal braid) are secured. In addition, pilots should check each P-static wick for general condition and ensure that adequate bonding exists so that electrostatic discharge does not impede the SNR of the Loran-C. Either of these two conditions could "detune" the Loran-C without warning.
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e. Backup Plans and Equipment. Judgment and plain common sense suggest that it is risky for pilots to attempt a flight over the cold waters of the NAT while relying only on one means of navigation. Pilots should be prudent and always have an alternate plan. They should also have backup navigation equipment available and an up-to-date flight progress log just in case they have to put aside all of their equipment and use DR to their destination.
NOTE: In addition to the need for good judgment and plain common sense, Canadian Air Regulations require specific kinds of backup equipment for aircraft operated over the NAT.
f. Acceptable Signals. If the navigation equipment incorporates a mode for extended range (such as one that uses sky waves), then this mode should not be used when flying in oceanic airspace. Only surface/ground wave signals should be used for oceanic navigation (see figure 10 in appendix 2).
g. MNPS Airspace Approval Documents. Loran-C equipped aircraft approved to fly IFR in NAT or Canadian MNPS airspace, or areas of known magnetic unreliability, should have the basis for each specific approval stated in the AFM or POH, whichever is appropriate. Figure 8 is an example of such an endorsement. In addition, each operator intending to fly an aircraft in MNPS airspace must have separate written authorization from a Flight Standards District Office (FSDO). This LOA should state the geographical or chain coverage limits while using Loran-C to navigate in MNPS airspace (if not explicitly stated in the flight manual supplement section).
h. Minimum Equipment List (MEL) Considerations. Even though a pilot has committed to an ocean crossing, the pilot is still bound to the aircraft's MEL requirements in the event of partial (or complete) failure of any navigation system. Pilots should consult the appropriate MEL for specific guidance.
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FIGURE 7 SAMPLE "PAGE ONE" FROM AFM/POH SUPPLEMENT Oakland, CA
FAA-APPROVED AIRPLANE FLIGHT MANUAL SUPPLEMENT
LORAN-C NAVIGATION SYSTEM AIRCRAFT MAKE: Cessna AIRCRAFT MODEL: T-210F SERIAL NUMBER: T2100014 REGISTRATION NUMBER: N6114R Note! → This document must be carried in the aircraft at all times This document describes the operating procedures for the [make] Loran-C system when it has been installed in accordance with (manufacturer's installation manual) and FAA Form 337 dated For airplanes with a pilot's operating handbook and/or FAA-approved AFM, this document serves as the FAA-approved Imake Loran-C Flight Manual Supplement.
The information contained herein supplements or supersedes the basic AFM only in those areas listed herein. For limitations, procedures, and performance information not contained in this document, consult the basic AFM [if applicable.] FAA APPROVED:
[Inspector's name] Aviation Safety Inspector [Avionics] WP OAK FSDO #123 Federal Aviation Administration
FAA APPROVED 14
FIGURE 8
SAMPLE AFM/POH APPROVAL ENDORSEMENT
TO OPERATE LORAN-C IN MNPS AIRSPACE INSTALLATION CENTER/FAA REPAIR STATION #_ 6114 Earhart Road Oakland, CA 94614
FAA-APPROVED AIRPLANE FLIGHT MANUAL SUPPLEMENT
LORAN-C NAVIGATION SYSTEM
SECTION T
INTRODUCTION A. EQUIPMENT DESCRIPTION Provide a general description of the Loran-C Area Navigation System installed in the aircraft.
Information in → B. GENERAL this section Provided that the Imakel. Loran-C navigation system is receiving adequate usable signals, it has been demonstrated capable of, and has been shown to meet the defines what kinds accuracy specifications of:
of operational use is permitted, and 1. VFR/FR en route, terminal, and approach [if applicable] operation within the conterminous United States and Alaska, in accordance with the criteria of AC any geographica. 20-121A.
limitations to its use. → 2. Flight in the NAT Minimum Navigation Performance Specifications (MNPS) airspace within the following coverage areas:
FAA APPROVED DATE:
I. MINPS Performance Capability. MNPS capability is not solely dependent upon navigation equipment accuracy alone, but also includes the following:
(1) Crew knowledge of the system being used and crew skill at operating the specific navigation equipment. This includes knowledge of basic navigation principles, equipment operating procedures, and MNPS airspace emergency procedures.
(2) Adherence to equipment installation, maintenance and software update standards.
(3) Periodic position accuracy checks using other available NAVAID's along the route of flight.
J. Review Notices to Airmen (NOTAM's). Before attempting any oceanic flight using Loran-C for navigation, operators must review all appropriate Loran-C NOTAM's.
While these are technically NOTAM (D's), they are grouped in a special file entitled, LRN NOTAM's, and listed by chain number. Domestic Loran-C NOTAM's may be accessed under this LRN NOTAM's file. International NOTAM's are issued under the "KNMH" series. NOTAM's for Omega, Loran-C, or GPS must be specifically requested even if the briefer has been informed that the aircraft is RNAV equipped and a standard briefing is being requested. Such a generic request alone is not sufficient to receive Loran-C NOTAM's. In addition, prerecorded telephone answering service messages for selected Loran-C stations are printed in the "Airman's Information Manual" (AIM).
NOTE: Different countries have different ways to disseminate Loran-C NOTAM's. It is the responsibility of the pilot in command (PIC) to obtain all NOTAM's that may affect safety of flight.
Examples LRN 00/000 LRN CHAIN 9960 OTS Explanation: The entire Northeast U.S. chain is out of service.
LRN 00/000 LRN CHAIN 9960 STN Y OTS Explanation: Station Y of the Northeast U.S. chain is out of service.
k. Preprogram Waypoints. The best way to minimize the chances of misprogramming a Loran-C unit is for the pilot to carefully program the various waypoints into the equipment memory before beginning a flight. During this process, it is best to have another person doublecheck waypoint entries to ensure that the unit is properly programmed.
The use of oceanic (such as over-water) plotting charts is a must for effective flight planning 16 Par 5
and flight management when airborne. While it may not be possible for a pilot to use a plotting chart in a small helicopter, alternate position recordkeeping is still a fundamental way for the pilot to stay "position oriented" and on the assigned route/track.
1. Cross-Check Positions. Once airborne and before proceeding beyond the range of standard NAVAID's, flightcrews should cross-check their Loran-C position with ground- or space-based NAVAID's to ensure that all navigation equipment is performing correctly. The flightcrew may use the following methods, as appropriate, to accomplish this:
(1) Flying directly to and over a "gateway" fix and comparing the displayed position data with that derived from the Loran-C equipment;
(2) Navigating precisely to any fix using VOR/NDB bearing and DME or GPS-derived data, then comparing these data with Loran-C derived position data;
(3) Comparing the range and bearing information provided by conventional NAVAID equipment (such as VOR/DME) or GPS-provided data with that obtained from the Loran-C unit;
(4) Plotting a radial/DME fix on a chart and then plotting the Loran-C position for comparison; or
(5) Using any other equivalent procedure that ensures an adequate comparison between standard NAVAID's information and Loran-C derived position information. An example of an equivalent procedure is cross-checking with ground-based ATC radar.
m. Beware of Fatigue! Once committed to an oceanic flight, crewmembers should exercise extreme care to ensure that all waypoints are carefully cross-checked (ideally by another crewmember) to ensure accuracy. Beware of fatigue as a physiological stressor.
Long, oceanic night flights can be tiring. Waypoint insertion errors or the misreading of a clearance are more likely to occur when crewmembers are fatigued.
n. Keep a Waypoint Notebook or DR Flight Progress Log. It is good practice for the pilot or the appropriate crewmember to make written notations of the time each waypoint passage occurs. The aircraft position should then be plotted to ensure that the flight is progressing normally and that the next waypoint has been entered correctly. Routine use of oceanic plotting charts is the most effective way to minimize the chances of performing a gross navigational error. The calculated time to the next fix or checkpoint should be validated. After passing each waypoint, it is good practice for the pilot or the selected crewmember to cross-check the actual outbound heading with the plotted course to ensure that the aircraft is headed in the proper direction, considering the known or forecast winds and Par 5 17
temperatures aloft. Also, if the displayed "distance to go" readout conflicts with where the pilot thinks the actual location is, the pilot should recheck the aircraft's position with another onboard navigation system.
NOTE: The pilot should make sure that navigation is consistent. The actual (and plotted) headings may vary, depending on whether the pilot is navigating along a "rhumb line" or a "great circle" route. A "rhumb line" course appears as a straight line only on Mercator projection charts which are not readily available to the flying community (see Glossary, appendix 2). In any event, the pilot should make sure that the readings on the aircraft's compass system agree with the heading information on the computer-generated flightplan, DR flight log, or plotting charts.
o. Adopt Minimum Standards. Operators and pilots should review and adopt the practices and procedures published in AC 90-79,iRecommended Practices and Procedures for the Use of Electronic Long-Range Navigation Equipment," as their minimum standards. This AC provides guidance for the disciplined and systematic cross-checking of navigation information during all phases of flight.
p. Safeguard Against Signal Loss. Potential interference or loss of Loran-C signal reception is always a possibility. In-flight weather conditions, such as moderate to heavy precipitation and various types of electromagnetic interference, may adversely affect Loran-C signal reception. Such disturbances are unpredictable and could put flightcrews at risk of getting lost over the high seas. Inoperative static wicks or poor antenna bonding may also contribute to loss of signal. If the route takes the aircraft along an extended baseline or outside the Loran-C manufacturer's coverage envelope (see appendix 1 for details), the Loran-C signal may be lost for extended periods. Flight crewmembers should also consider the possibility that the chain transmitter itself may be temporarily out of service or go off the air during an ocean crossing. Under any of the above conditions, a judicious pilot should have an alternate plan of action readily available and be prepared to navigate by other means. If a course is properly plotted and navigation logs are kept up-to-date, a quick conversion to a DR mode will be easier and result in more accurate navigation. If a loss of signal does occur, the pilot flying VFR should be prepared to rely on other available electronic means. Pilots flying IFR in aircraft equipped with multiple, independent navigation sensors may only need to manually switch to their alternate navigation system or DR.
q. Critical Triangle Method. Many professional pilots rely on the critical triangle method to stay out of trouble when flying over the high seas. To minimize risk, experienced pilots rely on three independent navigation systems (as opposed to one or even three Loran-C triads). If one system fails or provides inaccurate position data, the pilot can 18 Par 5