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(4) Class II Navigation NAVAIDs. Class II navigation does not automatically require the use of LRNS. In many instances, you can conduct Class II navigation with conventional NAVAIDs if special navigational techniques supplement these NAVAIDs. Any portion of an en route operation in controlled or uncontrolled airspace, with any navigation system or any navigation technique, is Class II navigation for that portion of the route that is outside the operational service volumes of ICAO standard en route NAVAIDs.
10-2. IRS/INS AND LONG-RANGE NAVIGATION PROCEDURES.
a. Background. Recently, an aircraft deviated approximately 60 miles from an assigned NAT track and came within a few feet of colliding with an aircraft assigned to an adjacent track.
Following the near miss, the aircraft that had deviated from its track did not follow established contingency procedures for aircraft experiencing navigational uncertainty, thus creating the potential for further conflict with other aircraft as it returned to its assigned track. The crew’s failure to operate the navigation equipment in a disciplined systematic manner during all phases of flight caused the incident. The crew’s failure to comprehend the relationship between navigation performance, contingency procedure, and collision avoidance further complicated the incident.
(1) Navigation and Human Errors. Although navigation errors are infrequent, human errors account for a majority of the errors attributed to aircraft equipped with automated systems.
Most inadvertent navigation errors have occurred when the equipment was functioning normally, but the operating procedures prescribed were either inadequate or the operator did not follow them. Experience indicates that the increased accuracy and reliability of modern automatic navigation systems can induce a degree of complacency on the part of flightcrews, and may result in failure to routinely cross-check system performance. Under these circumstances, human errors may remain undetected for excessive periods. A common error associated with automated systems is incorrect programming of the oceanic waypoint latitudes by multiples of 1° (60 NM).
In an organized track system (OTS), this can result in the flight maintaining a wrong track with high precision and thereby constituting a serious threat to other aircraft properly occupying that track and FL. Vigilance and diligence in properly applying established procedures are essential to safe oceanic navigation. Although operational procedures may differ among navigation systems, many good practices and procedures are basic to all automated and semi-automated systems.
(2) Practices and Procedures for IFR Long-Range Navigation Operations. IFR long-range navigation operations using pilot-operated electronic long-range navigation equipment should use the practices and procedures recommended in this document. Prior to issuing operations specifications (OpSpecs) authorizing operations requiring long-range navigation equipment, the FAA principal operations inspector (POI) should ensure that the operator’s training program, manuals, and check airman program include and emphasize these practices and procedures. For operations currently authorized by OpSpecs or a letter of authorization (LOA), review the operator’s navigation program to ensure that it follows the guidance contained in this AC. The Flight Technologies and Procedures Division, AFS-400, must approve any deviation from these requirements.
b. Weather. In addition to the normal review of weather information concerning terminals, crews should be alert for hazardous weather that may require a flight plan change or in-flight re-routing. It is important to obtain a copy of the wind flow chart (constant pressure chart or the equivalent) for the FL and the route flown. This information may be valuable when evaluating wind forecasting errors or if DR operations become necessary due to equipment failure. As the flight progresses, give consideration to plotting actual wind information on the plotting chart as a means of evaluating the accuracy of the forecast.
c. Notices to Airmen (NOTAM). Besides checking NOTAMs for departure, destination and alternate airports, check NOTAMs concerning NAVAIDs or special airspace restrictions along the planned route.
d. Waypoint Management. The navigation program should include a standard system for indicating waypoint status as detailed below. The specific procedures recommended are in the list below. Variations in specific symbols may be necessary to accommodate the individual operator’s program.
• The crew stores the waypoint coordinates in the computer. (Enter the waypoint number next to the relevant waypoint coordinates.)
• A second crewmember independently cross-checks the coordinates and zone distances. (Circle the waypoint number.)
• The second crewmember cross-checks the coordinates and zone distances during the approaching waypoint check. (Draw a diagonal line through the waypoint number.)
• Waypoint passage has occurred. (Draw a second diagonal line through the waypoint number.)
• Cross-checking during all phases of flight. (Flight planning, preflight, en route.)
• Official (master) document.
• Plotting.
e. Plotting Procedures. Use of plotting procedures has had a significant impact on the reduction of gross navigation errors (GNE). All flights using long-range navigation equipment as the sole means of navigation require the use of this technique to plot the flight route on a plotting chart and to plot the computer position approximately 10 minutes after waypoint passage. Routes of shorter duration that transit airspace where special conditions exist, such as reduced lateral separation standards, high density traffic, or proximity to potentially hostile border areas may require the use of plotting procedures. All turbojet operations where the route segment between the operational service volume of ICAO standard NAVAIDs, VOR, VOR/DME, and NDB exceed 725 NM and all turboprop operations where the route segment between the operational service volume of ICAO standard NAVAIDs exceeds 450 NM require plotting procedures. The operational service volume is that volume of airspace surrounding a NAVAID which is available Par 10-2 Page 117
for operational use, within which a signal of usable strength exists, and where co-channel interference does not operationally limit that signal. You can determine the operational service volume for a specific NAVAID by contacting the Frequency Management Section within each regional Airway Facilities Division. Operational service volume includes the following:
• The officially-designated standard service volume excluding any portion of restricted standard service volume.
• The extended service volume.
• Within the United States (including offshore control areas (CTA)) by published instrument flight procedures (Victor or jet airways, standard instrument departures (SID), Standard Terminal Arrival Routes (STAR), Standard Instrument Approach Procedures (SIAP) or instrument departure).
• Outside the United States, any designated signal coverage or published instrument flight procedure equivalent to U.S. standards.
f. Flight Planning. Many operators use a computerized navigation flight plan. Take care to verify that all en route waypoints are correct and legibly shown on the flight plan. It is good practice to select a waypoint loading sequence and number each waypoint accordingly. If using more than one copy of the flight plan, designate one copy as the official copy. To eliminate possible confusion, ensure that all necessary information, routing changes, estimated time of arrival (ETA), and waypoint loading sequence is on this flight plan, and use the official copy for all reports to ATC. Additionally, if the flight is within the North Atlantic Organized Track System (NAT OTS), obtain a copy of the current track message and be alert for conflict between the flight plan and the track message. Track messages are issued approximately every 12 hours and describe the NAT routes, gateways, and FLs available for eastbound and westbound flights during the period indicated. While planning an over-water flight, pilots should review NOTAMs for any condition that may affect the operation and accuracy of LRNSs. Approach the use of heading information for cross-checking with caution. In steering a given route segment with a navigation computer, the true heading required to maintain a Great Circle course will change.
For example, the true heading to maintain the Great Circle course from 50°N. 30°W. to 50°N. 40°W. will be 274° at 30°W., 270° at 35°W., and 265° at 40°W. Differences in variation along the route will further change the magnetic heading required to maintain course. The flightcrew must have a thorough understanding of the flight plan heading information and DR technique in order to use this check with any degree of certainty.
g. Navigation Preflight (at Aircraft). Verify navigation system software identification and modification status codes. Cross-check inputs to navigation computers. One crewmember should carry each insertion out in its entirety and another should recall and verify it. Cross-check computer flight plan zone distances with zone distance displayed in navigational computers.
Perform the cross-check of coordinates and zone distances on all computer systems individually when using the remote loading feature. For INS, after placing the systems in the navigation mode, check the groundspeed while the aircraft is stationary. A reading of more than a few knots may indicate an unreliable system.
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• Cross-check computer flight plan, waypoint coordinates and identifiers with source documents (airfield diagrams, en route charts, and NAT track messages, if applicable).
• Plot the flight route on a chart of appropriate scale. Operational experience has demonstrated that a scale of 1 inch to 120 NM provides the most benefit for plotting purposes.
• Compare routing information on ATC flight plans, computer flight plans, NAT track messages, plotting charts, aircraft observations and Aircraft Report (AIREP) forms.
• It is advisable not to copy waypoint coordinates from source documents (track message, en route charts, etc.) to the flight plan for subsequent insertion into the navigation computers. To avoid errors in transcription, insert waypoint coordinates into the computers directly from the source documents.
• Since the initial stage of the flight can be very busy, give consideration to ensuring the navigation system waypoint transfer switches are in the “auto” position to facilitate outbound tracking and waypoint changeover during this period.
• With systems such as INS that navigate during ground operations, it is advisable to cross-check present position, taxi distance or groundspeed (as appropriate) prior to takeoff to confirm proper system operation and to ensure that the present position remains accurate.
h. Equipment Preflight. In addition to operating procedures such as checklists for confirming proper system operation, take care to ensure the proper programming of the navigation equipment. This is a very important procedure and you should not rush it. All navigation information, coordinates, or courses and distances should be programmed by one crewmember and verified by another. In addition, crews should verify that each system uses the same waypoint loading sequence and indicate on the flight plan that the crew entered cross-checked the present position, if applicable, and waypoints. If time becomes a factor, it is more important to verify that the first two or three waypoints are correct than to rush through the procedure to insert as much information as possible. Give consideration to using another cross-check that compares the flight plan or charted distance between waypoints and the distance computed by the navigation system to detect programming or flight planning errors. This serves as a double check on waypoint verification and will also reveal any error in the flight plan. A difference of more than 2 NM may indicate a programming or flight planning error.
i. Pre-Takeoff and Coast Out. Before takeoff, cross-check the computer present position to confirm proper system operation. At least two crewmembers should copy and confirm the oceanic clearance. Perform accuracy check to compare navigation computer position with VOR, VOR/DME or NDB. Direct overflight of a NAVAID and for cases when you do not directly overfly the NAVAID apply the NAV accuracy check. Record the gross error in the flight log.
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j. Within Range of the Outbound Gateway. Flights should not continue beyond the outbound gateway unless the required long-range navigation equipment is functioning properly.
To confirm proper operation, certain cross-checks should be performed while within range of the gateway NAVAID. Since this may be the last positive position cross-check until the inbound gateway, the following practices may also provide valuable information for resolving any later navigation difficulties.
(1) ATC Clearances. Two crewmembers should cross-check all ATC oceanic clearances to ensure the clearance is copied correctly. Cross out any flight plan waypoints that were revised in an ATC clearance and enter the revised coordinates in a legible manner. Prior to proceeding outbound from the gateway, compare the current ATC clearance to the flight plan and the information in the navigation computers for the gateway and verify the subsequent waypoints. Verify and change (if necessary) the clearance track on plotting chart.
(2) Gross Error Check. A gross error check is a position accuracy cross-check using normal airway facilities such as VOR, VOR/DME or NDB. The operator usually accomplishes the gross error check by flying directly over the gateway (if possible) and subsequently establishing the aircraft on the outbound course using the gateway NAVAID. This check detects errors that may have accrued in position information since takeoff, provides information used to determine the most accurate system for use as a steering reference, and provides an opportunity to correct position information. The gateway check also confirms that the operator establishes the aircraft on the outbound course and is tracking toward the next waypoint.
(3) Flight Instruments Used for Display. When operators use flight instruments for the display of either airways (VOR) information or information from the LRNS, they should leave the “radio/nav” switches in “radio” position after passing over the gateway NAVAID until the radio information becomes degraded. Operators should then place switches in the “nav” position.
(4) Compass Deviations. Give consideration to performing a compass deviation check on systems such as INS that use true heading information from sources independent of the aircraft compass system. You can determine the compass deviation by comparing the INS derived data later in the flight to determine the most accurate system should a divergence between systems occur. You can apply the compass deviations to the respective compasses to determine the actual magnetic heading. Operators can apply local variation to the true heading of each INS to obtain the derived magnetic headings. The most accurate INS should be the one with a magnetic heading that compares the most favorably with the actual magnetic heading.
k. After Passing the Gateway. Select the system determined to be the most accurate during the gross error check as the autopilot (AP) steering reference. When not used for other purposes, this system should display present position. Routinely check cross-track, track angle error (TKE) and distance-to-go. Display computer position coordinates and compare with ATC clearance to confirm that you maintained track CL.
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l. Approaching Waypoint. Within 2 minutes of each waypoint, both pilots should verify that the subsequent waypoint in the ND agrees with the current ATC clearance. Cross-check coordinates of the approaching waypoint and subsequent waypoints. Compare zone distance on the flight plan to that displayed on the navigation computer for the next leg. Compare computer flight plan ETA with ETA information displayed in navigation computers. (On some systems, you may accomplish this cross-check more easily during waypoint passage.)
m. After Passing Each Waypoint. Approximately 10 minutes after passing each waypoint, plot the present position information on the NDs on a navigation chart to confirm that the ATC clearance is satisfied. Confirm that the navigation systems have switched to the next flight segment (leg change). Verify that the aircraft is tracking along the next flight segment (tracking outbound).
n. Approaching the Inbound Gateway. Make certain preparations for the transition from long-range navigation to airways navigation. The FAA recommends the following practices:
• As soon as feasible, set up the navigation radios to receive the inbound gateway NAVAID.
• When the gateway NAVAID is providing reliable information, place the “radio/nav” switch in the “radio” position and steer the aircraft to acquire and maintain the proper inbound radial/bearing.
• Unless otherwise directed by ATC, fly the aircraft directly over the gateway.
• When over the gateway, record the position information from the navigation displays (ND). You can use this information to confirm system accuracy. Compare VOR, VOR/DME, NDB course and distance information with that displayed in navigation computers. The FAA recommends that you make system accuracy computations after arrival to avoid conflicts with other cockpit duties during the critical periods of descent, approach and landing.
o. After Arrival. Compute and record the individual navigation system errors and error rates (if applicable) for future reference. It is desirable to record this information in a document that remains aboard the aircraft to provide subsequent flightcrews with a recent history of system performance. This information may be used with most systems to predict individual system performance for future flights under similar circumstances. Additionally, this information may prove valuable to subsequent flightcrews for resolving navigation abnormalities, such as divergence between systems.
10-3. LRNS PROBLEMS AND RECOMMENDED ACTIONS. Although the accuracy and reliability of the newer navigation systems are excellent, malfunctions and failures occasionally occur. When a malfunction occurs, flightcrews should guard against jumping to conclusions since hasty actions are seldom necessary and may further complicate the situation. Experience has shown that successful resolution of navigation difficulties in oceanic areas usually requires a thorough, thoughtful process that normally begins during preflight planning.
The training program manuals and check airman program for air carrier operations should emphasize procedures followed in the event of partial and total instrument failure. Non-air carrier operators should be able to demonstrate this emphasis in their training programs if requesting an LOA for oceanic operations in special airspace. The following guidance is for consideration when encountering or suspecting navigation difficulties.
a. Navigation Errors. Monitoring procedures used during oceanic operations indicate the frequency and course of navigation errors. Considering that operators make thousands of flights, errors are actually rather infrequent. Navigation systems are generally so reliable that there is some concern about overconfidence. Therefore, crews should guard against complacency.
(1) Frequent Causes of Errors. Frequent causes of errors include the following:
• Making a mistake of 1° of latitude when inserting a forward waypoint.
• The crew received re-clearance by ATC but forgot to re-program the navigational system.
• The operator left the AP in the heading or de-coupled position after avoiding severe weather or they left it in the VOR position after departing the last domestic airspace VOR. In some cases, this occurred after distractions by selective calling (SELCAL) or flight deck warning indications.
• The controller and crew had different understandings of the clearance because the pilot heard what he/she wanted to hear rather than what they actually said.
(2) Rare Causes of Errors. Rare causes of errors include the following:
• The latitude/longitude coordinates displayed at the gate position were incorrect.
• Because of a defective chip in an aircraft system, and although the crew inserted the correct forward latitude, it “jumped” 1°. (INS only.)
• The aircraft has an advanced system that includes all waypoint coordinates already in the database equipped. The crew assumed the coordinates were correct, but one was not.
• Although the crew had the correct coordinates available, the information inserted into the system was from an incorrect company flight plan.
b. Detection of System Failure. In general, we usually consider system failure to have occurred when one of the following situations develop:
• Activation of a warning indicator that cannot be reset;
• Self-diagnostic or built-in test equipment (BITE) indicates that the system is unreliable;
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• The position error over a known geographic location exceeds the maximum permissible tolerance established for a particular navigation system; or
• The system’s operation is so abnormal that, despite the absence of warning or malfunction indications, the flightcrew considers the system no longer useful for navigation.
c. Detection of System Degradation or Malfunction.
(1) Identifying a Faulty System. While system failures are usually straight forward, malfunctions or gradual system degradations are usually more difficult to detect. This is particularly true when only two systems are onboard. A divergence between the navigation systems, a situation that often occurs gradually, usually detects navigation difficulties of this type. This factor may reduce the possibility of identifying the faulty system unless operators diligently use periodic cross-checking practices. Consider the following factors when attempting to identify a faulty system:
• Check the BITE codes for indications of system fault.
• Review the gateway gross error check for indications of the most accurate system.
• If you maintain a regular record of system performance and it is available, a review of the record may give a clue as to which system is faulty.
• If possible, use VOR, automatic direction finder (ADF), DR, airborne radar, or other NAVAIDs to obtain a position fix.
• Cross-check heading, groundspeed, track, and wind information between systems and compare this information with the best known positive information such as position over a fix.
• Attempt to contact nearby aircraft to obtain wind or groundspeed and drift correction information that may identify the malfunctioning system.
• The compass deviation check may provide a clue as to which system is faulty for systems such as INS.
(2) Determining a Faulty System. Even though you take these steps, a divergence between systems may occur, but the flightcrew may be unable to determine which system is at fault. When this occurs, use the practices described in the following paragraph.
d. Recommended Actions Following System Failure. After detecting a system malfunction or failure, inform ATC that the flight is experiencing navigation difficulties so that you can adjust the separation criteria, if necessary. Reporting malfunctions to ATC is an ICAO requirement and 14 CFR part 91 requires compliance. If you can identify the failed system with a high degree of confidence and the other system appears normal, the best course of action may be Par 10-3 Page 123
Page 124 Par 10-3 to fly the normal system and carefully monitor its performance using any additional NAVAIDs available. In the unlikely event that a total navigation failure occurs and other aids are unavailable, the only action may be to fly by contingency DR using the flight plan headings and times. Under these circumstances, flightcrews should continue to use all means available to obtain as much navigational information as possible. Flightcrews should be alert for visual sightings of other aircraft, since a hazard may exist due to an inadvertent deviation from the assigned track. In some cases, it may be possible to establish and maintain visual contact with another aircraft on the same track.
e. Recommended Action Following a Divergence Between Systems. Since a small divergence between systems may be normal, evaluate the significance of the divergence. In general terms, if the divergence is less than 10 NM, the best course may be to closely monitor system performance and continue to steer the system considered most accurate. If the divergence between systems is greater than 10 NM, it may degrade one of the systems. Therefore, make attempts to determine which system may be faulty. If you cannot determine the faulty system using the practices described in this section, and both systems appear normal, the action most likely to limit gross tracking error may be to position the aircraft so that the actual track is midway between the cross-track differences for as long as the position uncertainty exists. Advise ATC that you are experiencing navigation difficulties so that you may adjust separation criteria as necessary. Give consideration to abandoning this “split-the-difference” practice if the divergence exceeds the separation criteria currently in effect on the route of flight. If a divergence of this magnitude occurs and you cannot isolate the faulty system, the best course may be to fly by contingency procedures using the best known wind information. However, in some cases, the best known information may be flight plan headings and times.
10-4. PROVING TESTS AND VALIDATION FLIGHTS. Title 14 CFR parts 121 and 135 require evaluation of an operator’s ability to conduct operations safely and in accordance with the applicable regulations before issuing an operating certificate or authorizing a certificate holder to serve an area or route. The testing method used by the FAA to determine an operator’s capabilities are validation flights. Sections 121.93, 121.113, and 135.145 require an operator to demonstrate the ability to conduct operations over proposed routes or areas in compliance with regulatory requirements before receiving FAA authority to conduct these operations. The FAA requires validation flights for authorization to add any areas of operation beyond the continent of North America and Mexico, and before issuing authorization for special means of navigation.
Though proving tests and validation flights satisfy different requirements, it is common practice for operators to conduct both tests simultaneously. However, validation flights are important to consideration of oceanic operations (14 CFR part 119, § 119.59).
a. Validation Flights. Sections 121.93, 121.113, and 135.145 require operators to show the capability to conduct line operations safely and in compliance with regulatory requirements before receiving authorization to conduct those operations in revenue service. The most common method of validating an operator’s capability is to observe flight operations. The FAA normally requires validation flights before issuing OpSpecs granting authority to conduct operations beyond the populated areas of the North American (NAM) continent. When the FAA conducts a validation flight, they conduct an in-depth review of the applicable portions of the operator’s proposed procedures, including flight following, training programs, manuals, facilities, and maintenance programs. There are four situations that require validation flights in association
with approval of Class II navigation: initial approval; addition of an LRNS or a flight navigator;
operations into new areas; and addition of special or unique navigation procedures. Validation flights are required when an operator proposes to conduct operations that require confirmation of the ability to operate an aircraft type within specified performance limitations. These limitations are based on the character of the terrain, extended over-water, the type of operation, and the performance of the aircraft. Validation flights are also required when an operator proposes to conduct in-flight or ground maneuvers that require special operational authorizations.
b. Carriage of Revenue Passengers on Validation Flights. Title 14 CFR does not forbid the carriage of revenue passengers on validation flights. The operator may receive FAA authorization to carry revenue passengers during the validation flight when the proposed operation is similar to those in the applicant’s previous experience. However, validation flights do not normally permit the carriage of revenue passengers in the following situations:
• When the operator is seeking initial approval to conduct Class II navigation in any airspace designated as a special area of operation;
• When the operator is seeking approval to conduct Class II navigation by an LRNS or by using a flight navigator not previously approved for that means of navigation;
• When the operator is seeking approval to conduct Class II navigation by means of a long-range navigation procedure not previously approved for that operator; and
• When the operator has not previously operated a specific aircraft type in operations requiring special performance authorization.
c. Special Areas of Operation (SAO). Certain areas of Class II airspace are considered special operating airspace for purposes of validation. These areas include the following:
• Northern Canadian areas of magnetic unreliability;
• NAT/MNPS airspace and Canadian MNPS airspace;
• Central Pacific (CENPAC) composite airspace and Northern Pacific (NOPAC) airspace;
• Arctic Ocean and Antarctic airspace; and
• Politically sensitive areas of operation.
d. Special Navigation Procedures. Validation flights are normally required when an applicant proposes to use navigation procedures not previously demonstrated. These procedures include the following:
• Pilotage, including DR;
• Flight navigator procedures;
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• Celestial navigation;
• Pressure pattern and Bellamy drift DR;
• Free gyro or grid procedures; and
• Any combination of the preceding procedures.
e. Other Situations Requiring Validation Flights. Special operational authorizations and special performance authorizations may also require validation flights. The FAA encourages operators who require additional information on validation flights to contact their local FAA Flight Standards District Office (FSDO).
10-5. INS NAVIGATION—SPECIAL PRACTICES AND PROCEDURES.
a. Preflight. Since INS is a self-contained device and not a position fixing device, it will retain and possibly increment any error induced during alignment throughout the flight unless you remove it through updating procedures. Therefore, during preflight, exercise care to ensure that you insert the accurate present position information into the INS. Although most INSs will automatically detect large errors in present position latitude during alignment, large errors in present position longitude may exist without activating a warning indication. When cross-checking present position coordinates, be alert for the correct hemispheric indicator (that is, N., S., E., W.) as well as the correct numerical values. Since you cannot realign most INSs in-flight, it may require special procedures such as ground realignment to correct a significant error in present position. If the INS in use has the capability of “gang-loading” (simultaneous loading) by use of a remote feature, take care so that you cross-check any data entered by this method separately on each individual INS to detect data insertion errors. Verify the INS software identification and modification status codes to ensure installation of the proper equipment and utilization of the appropriate operating checklist. The operating checklists should include a means of ensuring that the INS is ready to navigate and that the operator activated the navigation mode prior to moving the aircraft. Any movement of the aircraft prior to activating the navigation mode may induce very large errors that only ground realignment can correct.
After placing the system in the navigation mode, check the INS groundspeed when the aircraft is stationary. An erroneous reading of more than a few knots may indicate a faulty or less reliable unit. If this occurs, check the malfunction codes.
b. In-Flight Updating. INS is essentially accurate and reliable, but it is possible to introduce errors in an attempt to improve accuracy by in-flight updating. On the other hand, INS errors generally increase with time and are not self-correcting. If large tracking errors occur, they may significantly degrade aircraft safety and separation criteria. Consider these factors in any decision relative to in-flight updating. As a guide to flightcrews, some operators consider that unless the ground facility provides a precise check and unless the error is fairly significant (for example, more than 6 NM or 2 NM/hour), it is preferable to retain the error rather than update.
10-6. FAA APPROVAL OF GLOBAL POSITIONING SYSTEM (GPS) EQUIPMENT AND OPERATIONS.
a. Portable Units. Handle all portable electronic systems and portable GPS units in accordance with § 91.21. The operator of the aircraft must determine that each portable electronic device they use the aircraft they operate will not cause interference with the navigation and communications systems. Mount yoke mounts usually sold with a portable GPS unit to prevent interference with the operation of the aircraft controls. Install permanent mounts and externally mounted antennas for use with a portable GPS unit in a FAA-approved manner. A critical aspect of any GPS installation is the installation of the antenna. Shadowing by the aircraft structure can adversely affect the operation of the GPS equipment. Electrical noise or static in the vicinity of the antenna can adversely affect the performance of the system. Use portable GPS receivers as a supplemental aid to VFR in conjunction with an approved primary means of navigation.
b. GPS Equipment Classes. GPS equipment is categorized into classes A, B, and C (ref. TSO-C129, TSO-C129A, TSO-C145, and TSO-C146).
(1) Class A. Equipment incorporating both the GPS sensor and navigation capability.
This equipment incorporates receiver autonomous integrity monitoring (RAIM).
• Class A1 equipment includes en route, terminal, and non-precision approach navigation capability.
• Class A2 equipment includes only en route and terminal navigation capability.
(2) Class B. Equipment consisting of a GPS sensor that provides data to an integrated navigation system (i.e., flight management system (FMS), multi-sensor navigation system, etc.).
• Class BI equipment includes RAIM and provides en route, terminal, and non-precision approach capability.
• Class B2 equipment includes RAIM and provides only en route and terminal capability.
• Class B3 equipment requires the integrated navigation system to provide a level of GPS integrity equivalent to RAIM and provides en route, terminal, and non-precision approach capability.
• Class B4 equipment requires the integrated navigation system to provide a level of GPS integrity equivalent to RAIM and provides only en route and terminal capability.
(3) Class C. Equipment consisting of a GPS sensor that provides data to an integrated navigation system (i.e., FMS, multi-sensor navigation system, etc.) that provides enhanced guidance to an AP or flight director (FD) in order to reduce FTE.
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