Advanced Avionics

Navigation Database Currency (Part Three)

Coupling the FMS to the Navigation Indicator(s)

Every advanced avionics cockpit features one or more navigation instruments used for course guidance. The navigation indicator (e.g., a horizontal situation indicator (HSI) or electronic HSI) may include one or more course deviation indicators (CDIs), as well as one or more radio magnetic indicators (RMIs). When automatic course/ en route/ approach tracking is desired, you must couple (or connect) the FMS to the autopilot and select “navigation” as the source for the autopilot versus “heading” source, for example. With VOR navigation, that was sufficient. Now, with multiple sources of navigation data available, you must also ensure that the proper navigation information source was selected in the FMS. Every advanced cockpit offers buttons or switches that allow you to choose which navigation indications will be shown on which display or instrument.

This situation becomes complicated in aircraft that contain dual FMS/RNAV installations and redundant selectable displays or instruments. The pilot must learn how to configure each navigation instrument to show indications from each possible navigation source.

Figure 3-16 shows an example of a primary flight display (PFD) navigation indicator that combines a course deviation indicator (CDI) and a radio magnetic indicator (RMI), and allows the pilot to display indications from one of two FMS on either indicator.

Figure 3-16. Coupling the FMS to navigation instruments. [click image to enlarge]

Common Error: Displaying the Wrong Navigation Source

The annunciations showing which navigation sources are displayed on which navigation instruments are often small, so there is significant potential for displaying a navigation source other than the one you intended to select. The consequences of losing track of which navigation signals you are following can be significant: you may think you are steering along one course when in fact you are steering along a different one. Be sure to verify these settings prior to departure, and again each time you make changes to any navigation instrument. Some installations compound this potential with automatic source switching. The most common switching mode is a GPS source to be automatically deselected when the VOR is set to an ILS localizer frequency and a signal is present. Typically, that is not a problem since the pilot intends to switch to the ILS anyway. However, the error arises upon missed approach, when the pilot selects another frequency to follow a VOR missed approach routing. At that point, some units revert back to the previous GPS or other RNAV routing selected instead of the VOR frequency that the pilot just picked. This can result in gross navigation errors and loss of obstruction clearances. In some units, this is a shop programmable or jumper selected option. Check your unit’s features. Always check for correct navigation source selection and cross-check against the published procedure. Be ready and able to fly and navigate manually.

Awareness: Mode Awareness

Mode awareness refers to the pilot’s ability to keep track of how an advanced avionics cockpit system is configured. As shown in Figure 3-16, every advanced avionics system offers an annunciation of which mode is currently set—somewhere in the cockpit! There is no guarantee that you will notice these annunciations in a timely manner. The configuration of these systems must remain part of your mode situational awareness at all times. One strategy is to include “mode checks” as part of your checklist or callout procedures. For example, after programming a route into the FMS, verify that the navigation indicator shows course guidance from the desired source, and that the indication agrees with your estimate of the correct direction and distance of flight.

Essential Skills

Determine whether the FMS is approved for the planned flight operation.
Determine if your FMS can be used as a primary navigation system for alternate requirements.
Understand how entries are made and how the entries can be canceled.
Understand how that unit(s) is installed, and how it is programmed or jumpered for optional functions.
Determine which navigation sources are installed and functional.
Determine the status of the databases.
Program the FMS/RNAV with a flight plan, including en route waypoints, user waypoints, and published instrument procedures.
Review the programmed flight route to ensure it is free from error.
Find the necessary pages for flight information in the databases.
Determine which sources drive which displays or instruments, and where the selection controls are located.
Determine and understand how to use and program optional functions and equipment installed with FMS/ RNAV basic unit.

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Navigation Database Currency (Part Two)

Filed Under: Navigation

The Flight Planning Page

Every FMS unit includes a page dedicated to entering a flight plan. Typically, entering a flight plan is a simple matter of “filling in the blanks”—entering the en route waypoints and instrument procedures that make up the planned route.

En Route Waypoints and Procedural Waypoints

Entering a flight route into the FMS unit requires you to enter the waypoints that define your route. FMS distinguish between two kinds of waypoints: (1) waypoints that are published, such as departure, arrival, or approach procedure points; and (2) user defined waypoints. The approved system software (the internal programming) allows the pilot to manually enter airport and en route waypoints. However, you are prohibited by the software from entering (or deleting) individual waypoints that define a published instrument procedure, since misspelling a procedural waypoint name or deleting a procedural waypoint (e.g., final approach fix) could have disastrous consequences. Any changes to the selected database approach procedure will cancel the approach mode. Changing to go direct to a waypoint will not, in most units, cancel the approach mode (such as receiving radar vectors to final and bypassing an intermediate fix).

Entering En Route Waypoints

Looking at the planned route in Figure 3-8, it is apparent that San Carlos airport (KSQL), and SUNOL and TRACY intersections are not part of any instrument procedure that pertains to the planned flight. These waypoints can be entered into the unit, as shown in Figure 3-9.

The remaining waypoints in Figure 3-8, starting with the initial approach fix at ECA, are part of the Oakdale GPS approach procedure. Waypoints that are part of a published instrument procedure are entered by a different technique that will be introduced later. In some cases, you navigate along an airway that contains a string of waypoints, such as the one shown in Figure 3-10.

Figure 3-10. Entering waypoints along an airway.

In this case, it is only necessary to enter waypoints along the airway that represent course changes. In Figure 3-10, REANS intersection is a changeover point that joins the Pomona 073-degree radial and the Twentynine Palms 254-degree radial. For this airway segment, you could enter POM, REANS, and TNP, keeping in mind that the remaining waypoints do not appear in the programmed route.

Entering Airways

More sophisticated FMSs allow you to enter entire airways with a single action into the unit. When an airway and endpoint for that airway are selected, all waypoints that occur along the airway are automatically inserted into the flight plan. Figure 3-11 shows a navigation unit that allows airways to be selected.

Figure 3-11. Inserting an airway into a flight route.

Entering Procedures

Every IFR-capable FMS offers a menu of published instrument procedures, such as departures, arrivals, and approaches. When you choose one of these procedures, the FMS automatically inserts all waypoints included in that procedure into the flight plan. Figure 3-12 illustrates how you might choose an approach procedure using one popular FMS.

Figure 3-12. Inserting published instrument procedures into a flight route. [click image to enlarge]

Risk: Taking Off Without Entering a Flight Plan

The convenience of the FMS, especially the “direct to” feature common to all units, creates the temptation to program only the first en route waypoint prior to takeoff and then enter additional waypoints once airborne. Keep in mind, however, that no matter how skilled you become with the avionics, programming requires “heads down” time, which reduces your ability to scan for traffic, monitor engine instruments, etc. A better strategy is to enter all of the flight data before you take off.

Reviewing the Flight Route

Once a route has been entered into the FMS, the next step is to review the route to ensure it is the desired route. It is particularly important to ensure that the programmed route agrees with the pilot’s clearance, the en route and terminal area charts, and any bearing, distance, time, and fuel calculations that have been performed on paper.

Catching Errors: Using the FMS Flight Planning Function To Cross-Check Calculations

Using the FMS’s flight planning function to check your own flight planning calculations is one example of how advanced cockpit systems can decrease the likelihood of an error. Alternatively, cross-check the computer’s calculations against your own. (Remember the old computer programmer’s adage, “Garbage in, garbage out (GIGO).”)

The flight planning page can also be used to review the route that you entered into the FMS, as illustrated in Figure 3-13. Be sure to check at least four things when reviewing your route.

Figure 3-13. Reviewing the flight route.

Check the Waypoints

On the flight planning page, compare the sequence of waypoints with that prescribed by his or her clearance. Are any waypoints missing? Did you mistakenly include any extra waypoints in the route? Did you misspell any waypoints? Did the computer mistakenly include any extra waypoints in the route?

Check the Distances

On the flight planning page, you can see that the computer has calculated the distances between the waypoints in the route. These distances can be checked against the en route charts. A common error is to misspell the name of a waypoint and, thus, mistakenly enter a waypoint not appropriate to the planned route (e.g., KHEE versus KHEF). Checking the waypoint distances for unusual numbers is a good way to spot these errors.

Check the Desired Tracks

On the flight planning page, you can also see the course that the computer has calculated between waypoints along the route. A desired track between two waypoints represents the shortest path between them. The desired track between two waypoints may differ from the course seen on the aeronautical charts. In fact, there may be a difference of several degrees between the desired track and the airway course. Some of this difference may be due to the method in which the FMS accounts for magnetic variation. Some units use an internal database and interpolate, while others compute all values from tables.

Unlike the world as printed on paper charts, the earth is round, not flat. The shortest distance between two points on the earth is not a straight line; it is an arc, as shown in Figure 3-14.

The shortest route between two points on the surface of the earth is called a great circle route. To find the great circle route that connects two points, imagine a geometric plane cutting through the earth that passes through the two points and the center of the earth.

On the great circle route from SFO to LGA in Figure 3-14, departing SFO, the desired track is a little less than 90 degrees. Upon arrival at LGA, it appears to be greater than 90 degrees. The desired track heading is constantly changing since it is a circle, not a line. If, however, the difference exceeds several degrees, you need to investigate further to determine the cause.

Check for Route Discontinuities

Some FMS units do not automatically assume that you wish to fly between each of the waypoints that have been entered into the flight plan. When there is a question about how to proceed from one waypoint or instrument procedure to the next, some units insert a “discontinuity” in the programmed route. A route discontinuity indicates that the FMS needs further input from you about how two route segments should be connected. A route discontinuity is shown in Figure 3-15. If you wish to proceed directly from the waypoint that appears before the route discontinuity to the waypoint that appears after, you can simply delete the discontinuity, as shown in Figure 3-15.

Figure 3-15. A route discontinuity and deletion.

If the route discontinuity is left in the flight plan, the unit computer will not provide guidance beyond the waypoint that occurs before the discontinuity.

Maintaining Proficiency: Aeronautical Knowledge

It is easy to use an FMS without performing your own calculations for courses, headings, times, distances, and fuel used, but studies have demonstrated that aeronautical skills that are not practiced regularly quickly fade, regardless of experience level or certificates and ratings held. Abnormal and emergency situations (e.g., electrical failure) do occur, so it is important to maintain proficiency in at least making “rule of thumb” calculations on your own.

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Navigation Database Currency (Part One)

Filed Under: Navigation

The navigation database contained in the FMS must be current if the system is to be used for IFR navigation and approaches. Some units allow en route IFR operations if the navigation waypoints are manually verified by the pilot and accepted. The effective dates for the navigation database are shown on a start-up screen that is displayed as the FMS cycles through its startup self-test. Check these dates to ensure that the navigation database is current. Figure 3-7 shows the start-up screen and effective dates for one popular FMS.

Figure 3-7. Checking the navigation database.

Alternative Means of Navigation

To use some GPS-based RNAV units (those certified under Technical Standard Order (TSO) 129) for IFR flight, an aircraft must also be equipped with an approved and alternate means of IFR navigation (e.g., VOR receiver) appropriate to the flight. Ensure that this equipment is onboard and operational, and that all required checks have been performed (e.g., 30-day VOR check).

The avionics operations manual/handbook should state the certification status of the installed system. The supplements to the AFM should state the status of the installed equipment, including the installed avionics. Most systems require that the advanced avionics manuals be on board as a limitation of use.

NOTAMs Relevant to GPS

There are numerous notices to airmen (NOTAMs) that apply specifically to users of navigation aids. For example, when anomalies are observed in the behavior of the global positioning system, or when tests are performed, a GPS UNRELIABLE NOTAM is issued. Similarly, published instrument procedures that rely on RNAV equipment sometimes become “Not Available” when safety concerns arise, such as ground-based interference. It is important to check all NOTAMs prior to IFR flights and, especially, GPS and WAAS NOTAMs before flying. Remember, when talking to a flight service station (FSS)/automated flight service station (AFSS) briefer, you must specifically request GPS/WAAS NOTAMs.

GPS Signal Availability

GPS-based RNAV equipment that uses the DOD GPS relies on adequate signal reception throughout the course of a flight. Signal reception becomes especially critical during instrument approaches when signal reception criteria become more stringent. Signal reception is generally predictable, and you can request information on likely signal reception for the destination airport in the preflight briefing from Flight Service. Many GPS RNAV units include a feature called receiver autonomous integrity monitoring (RAIM) that allows you to view predictions about future signal reception at specific locations. WAAS-enabled receivers do not have this restriction or limitation due to the error corrections available from the WAAS. WAAS is a form of differential GPS (DGPS) providing enhanced position accuracy. Each Wide Area Reference Station (WRS) provides correction data to a Wide Area Master Station (WMS), which computes a grid of correction data to be uplinked to a geostationary satellite (GEO) from a Ground Earth Station (GES). The geostationary satellite transmits the correction data (and also navigation data) to the user on the L1 GPS navigation frequency (1575.42 MHz). The user GPS receiver uses the downlink WAAS data to correct received navigation data. The goal of WAAS is to obtain at least a 7-meter horizontal and vertical accuracy.

Local Area Augmentation System (LAAS), when it becomes available, is another DGPS mode which is designed to provide 1-meter accuracy for precision approaches. It uses a local error VHF transmitter near the runway providing a direct link from the sensor to the aircraft GPS receiver.

Alternate Airports

It is very important to know what equipment is installed in the aircraft. GPS-based FMS/RNAV units certified to TSO-C145A or TSO-146A may be used when an alternate airport is required in the flight plan for the approaches at the destination and alternate airport if the WAAS is operational. No other navigation avionics would be required. Units certified under TSO-C129 are not authorized for alternate approach requirements. The aircraft must have stand-alone navigation equipment, such as VOR, and there must be an approved instrument approach at the alternate airport based on that equipment. (However, once diverted to the alternate airport, the pilot could fly a GPS-based approach there, as long as there is an operational, ground-based navaid and airborne receiver in the aircraft for use as a backup.)

Aircraft Equipment Suffixes

Since air traffic control (ATC) issues clearances based on aircraft equipment suffixes, consult the Aeronautical Information Manual (AIM) Table 5-1-2, Aircraft Suffixes, to ensure that the flight plan includes the correct equipment suffix for a particular aircraft. Use the suffix that corresponds to the services and/or routing that is needed. For example, if the desired route or procedure requires GPS, file the suffix as “/G” or “/L,” as appropriate to that aircraft, and operational equipment installed. (Remember that minimum equipment list (MEL) deferred items can change the status of the aircraft.)

Suitability of an RNAV Unit for VFR Flight

Even when an RNAV receiver is to be used only for supplemental (“supplemental” meaning a situation enhancing source of navigation information, but not the primary or sole source of navigation information) navigation information during VFR flight, you should consider these suitability factors in the interest of safety. The use of an expired navigation database might cause you to stray into airspace that was not yet designated at the time the expired navigation database was published. Some VFR-only GPS units do not alert you when signal reception has faded, which could lead to reliance on erroneous position information. Lack of attention to the “see and avoid” basic principle of every visual meteorological conditions (VMC) flight means too much time spent focused inside the cockpit on advanced avionics versus staying synchronized with the flight events, possibly creating a life-threatening total flight situation.

Programming the Flight Route

The procedures used to program an FMS with your intended route of flight are fundamentally the same in all types of systems, yet many differences are evident. The primary difference between systems lies mainly in the “knob or switchology”—the specific design features, operational requirements, and layout of the controls and displays used to operate the avionics. Be thoroughly familiar with the procedures required for each FMS or RNAV unit to be used.

Suppose you have planned a flight from San Carlos Airport (KSQL) to Oakdale Airport (O27), as shown in the flight plan appearing in Figure 3-8. The planned route proceeds directly to SUNOL intersection, then follows V195 until reaching ECA, the initial approach fix for the GPS Runway 10 approach into Oakdale. The distances, bearings, estimated times en route, and fuel requirements for the flight have all been calculated. The next step is to enter some of these details into the FMS.

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Flight Planning

Filed Under: Navigation

Preflight Preparation

Title 14 of the Code of Federal Regulations (14 CFR) part 91, section 91.103 requires you to become familiar with all available information before beginning a flight. In addition to the required checks of weather, fuel, alternate airports, runway lengths, and aircraft performance, there are a number of requirements unique to the use of avionics equipment. Many of these considerations apply specifically to the use of FMS/RNAV under instrument flight rules (IFR). However, a check of these same requirements before operating under visual flight rules (VFR) enhances safety and enforces good habit patterns, which have been proven to greatly enhance aviation safety.

FMS/RNAV Approval for IFR Operations

Only some FMS/RNAV units are approved for IFR navigation, and it is important to make this determination before flying with any particular unit. Sometimes, this limitation is based on the installation (i.e., method of installation, qualifications of installer), aircraft approval, availability of approved maintenance, and geographic location. No hand-held GPS unit is approved for IFR navigation, and many panel-mounted units are restricted to VFR use only.

Even when an FMS is approved for IFR, the installation of the system in that specific aircraft must also be approved. Even if you have an IFR-approved FMS unit, you may not use it for IFR navigation unless the installation is approved as well. This approval process usually requires a test flight to ensure that there are no interfering inputs, signals or static emanating from the aircraft in flight. RNAV units that do not meet all of these requirements may still be used as situation enhancing navigation resources when operating under instrument flight rules.

The first place to check when determining IFR certification for an FMS is the Pilot’s Operating Handbook (POH) or Aircraft Flight Manual (AFM). For every aircraft with an IFR approved FMS/RNAV unit, the AFM explicitly states that the unit has been approved for IFR navigation and what IFR operations are specifically authorized for that installation.

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Area Navigation (RNAV) Basics

Filed Under: Navigation

RNAV Concept

Area Navigation (RNAV) is a navigation technique that allows pilots to navigate directly between any two points on the globe. Using RNAV, any location on the map can be defined in terms of latitude and longitude and characterized as a waypoint. Onboard RNAV equipment can determine the present position of the aircraft. Using this positional information, the equipment can calculate the bearing and distance to or from any waypoint and permit navigation directly between any two waypoints. In this way, RNAV overcomes a fundamental limitation of conventional navaid point-to-point navigation techniques, which require navigating between electronic navigation transmitters on the ground. The following examples illustrate this limitation.

An aircraft equipped with conventional VOR receivers is positioned at Point A as shown in the diagram at the top of Figure 3-1, and the pilot wishes to navigate directly to Point B. Although there appear to be a few VOR stations in the vicinity of the aircraft, it is not clear whether reception is possible from the aircraft’s present position. If the VOR stations are within reception range, the pilot has two choices: (1) fly to intercept the closest airway, then track it to the intersection; or (2) fly to intercept an extension of the radial that defines Point B (assuming reception is possible). Neither alternative provides the pilot with a means of flying directly to the intersection.

Figure 3-1. Limitations of conventional navigation. [click image to enlarge]

Suppose the same aircraft is positioned at Point A as shown at the bottom of Figure 3-1 and the pilot wishes to navigate directly to Point C, which is neither a VOR station nor airway intersection. This pilot has an even more difficult situation. Assuming the VOR stations are within reception range, the pilot needs to create two makeshift airways using a navigation plotter and chart, fly to intercept one of them, then track to Point C (which the pilot has defined as the intersection between the two courses). Flying a direct course to Point C with any degree of accuracy is not possible. Since RNAV systems are not bound by these limitations, the entire airspace is available for navigational use. The national airspace system can thus accommodate more aircraft. However, when the pilot leaves the established airways, he or she also leaves the guaranteed obstruction clearances designed into the airway system. Always plan flights above the maximum elevation figure (MEF) displayed on sectional charts when flying off airways, and be aware that manmade obstructions such as towers may not be added to charts for some time after construction. If flying a new routing, allow for construction, which may not be published yet.

FMS/RNAV Computer

RNAV is possible through use of a variety of navigation facilities and installed aircraft equipment operated in the U.S. National Airspace System. This handbook focuses on the more common GPS RNAV, a satellite-based radio navigation system available to aircraft equipped with a GPS receiver. In addition to its ability to receive signals from GPS satellites, a GPS receiver also contains a computer processor and a navigation database that includes much of the information found on en route and terminal procedure charts. The newer, more capable units provide map displays, traffic and weather overlays of data, contain VOR/DME/localizer/ glideslope receivers, and can compute fuel usage in addition to the navigation route information. For this reason, the more descriptive term “FMS” is used in this handbook to refer to these GPS receivers.

An FMS allows you to enter a series of waypoints and instrument procedures that define a flight route. If these waypoints and procedures are included in the navigation database, the computer calculates the distances and courses between all waypoints in the route. During flight, the FMS provides precise guidance between each pair of waypoints in the route, along with real-time information about aircraft course, groundspeed, distance, estimated time between waypoints, fuel consumed, and fuel/flight time remaining (when equipped with fuel sensor(s)).

FMS/RNAV/Autopilot Interface: Display and Controls

Every avionics device has a display and a collection of buttons, keys, and knobs used to operate the unit. The display allows the device(s) to present information. The controls allow the pilot to enter information and program the avionics to accomplish the desired operations or tasks. The display and controls for a typical FMS are shown in Figure 3-2.

Accessing Information in the FMS

FMS units contain much more information than they can present on the display at any one time. Information pertaining to some topics often extends beyond what can be presented on a single page. Page groups, or chapters, solve this problem by collecting all of the pages pertaining to the same topic. Each page presents information about a particular topic, and bears a page title reflecting its content. For example, the airport chapter may be divided into several airport pages, each page displaying different information about that airport. One page might be navaids. Another page might be the airport taxiway diagram. Yet another airport page might indicate available services and fixed-base operators. Review the documentation for that specific unit and installation to determine what information and levels of data are available and require updates. Usually, only one page can be displayed at a time. The airport page is displayed on the FMS in Figure 3-3.

Figure 3-3. Pages and page groups (chapters). [click image to enlarge]

Figure 3-3 shows how to access pages and chapters on one manufacturer’s FMS. Different FMS units have different ways of allowing the pilot to switch between chapters and pages, and different ways of informing the pilot which chapter and page is currently displayed.

Making Entries in the FMS

To enter data, you use the FMS buttons (keyboard or individual) and knob controls, or a data source, such as disk media or keypad, as shown in Figure 3-4.

FMS units that do not feature keypads typically require the pilot to make entries using the same knobs to move among chapters and pages. In this case, the knobs have multiple purposes and, thus, have different modes of operation. To use the knobs for data entry, you must first activate what some manufacturers call the “cursor” (or “data entry”) mode. Activating the cursor mode allows you to enter data by turning the knob. In other units, after activating the data entry mode, entries are made by pushing buttons.

Figure 3-5 illustrates the use of cursor mode to enter the name of an airport using one FMS. Pressing the inner knob engages cursor mode. A flashing cursor appears over one of the items on the page, indicating that it is ready for editing. Then, the inner knob is used to dial letters and numbers; the outer knob is used to move the flashing cursor between items on the page.

Figure 3-5. Making entries using cursor mode.

Integrated Avionics Systems

Some systems integrate FMS/RNAV display and controls into existing cockpit displays usually called PFDs and MFDs. In this case, there is no separate display to point to and call the RNAV display. Figure 3-6 shows a system that uses the PFD to provide controls and a display for the FMS. This type of system utilizes the same concepts and procedures described above to access and enter into the navigation computer.

Figure 3-6. An integrated avionics system.

Learning: Simulators for Learning and Practice

Avionics simulators can assist the pilot in developing proficiency in the advanced cockpit. Some manufacturers offer computer-based simulators that run on a personal computer and let the pilot learn how the unit organizes and presents information, as well as practice the buttonpushing and knob-twisting procedures needed to access and enter data. One very important function that every pilot of programmable avionics should learn and remember is how to cancel entries and functions. Turbulent flight conditions make data entry errors very easy to make. Every pilot should know how to revert quickly to the basic aircraft controls and functions to effect recovery in times of extreme stress. These programs are extremely useful not only for initial learning, but also for maintaining proficiency. For more sophisticated training, many manufacturers of flight simulators and flight training devices are now developing devices with advanced cockpit systems. These training platforms allow the pilot to work through realistic flying scenarios that teach not only the operating procedures required for each system, but also how to use the systems most effectively.

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Primary Flight Display (PFD) (Part Two)

Filed Under: Electronic Flight Instruments

Other Flight Status Information

An important feature of the PFD is its ability to gather information from other aircraft systems and present it to the pilot in the integrated display. For example, the PFD in Figure 2-5 presents many useful items about the status of the flight. The top bar shows the next waypoint in the planned flight route, the distance and bearing to the waypoint, and the current ground track. The outside air temperature (OAT) is shown in the lower left corner of the display. The transponder code and status are shown with the current time in the lower right corner. This PFD also allows the pilot to tune and identify communication and navigation radio frequencies at the top of the display.

Making Entries on the PFD

PFDs have evolved and have become more than flight displays in many cases. The amount of data available for display can overwhelm the pilot with data. Therefore, many manufacturers have integrated data control and display controls into the display unit itself, usually around the perimeter of the unit. These data and display controls provide different ways of selecting necessary information, such as altimeter settings, radials, and courses. Figure 2-6 illustrates two different kinds of controls for making entries on primary flight displays. Some PFDs utilize a single knob and button-selectable windows to determine which entry is to be made. Other PFDs offer dedicated knobs for making entries; quantities are sometimes entered in one location and displayed in another. Still other units retain all controls on a separate control panel in the console or on the instrument panel.

Failures and the Primary Flight Display

Instrument System Failure

The competent pilot is familiar with the behavior of each instrument system when failures occur, and is able to recognize failure indications when they appear on the primary flight display. Manufacturers typically use a bold red “X” over, or in place of, the inoperative instruments and provide annunciator messages about failed systems. It is the pilot’s job to interpret how this information impacts the flight.

The inoperative airspeed, altitude, and vertical speed indicators on the PFD in Figure 2-7 indicate the failure of the air data computer. As do all electronic flight displays, navigation units (area navigation (RNAV)/flight management systems (FMS)) and instrumentation sensors rely on steady, uninterrupted power sources of 24 VDC or 12 VDC power. Any interruptions in the power supplies, such as alternator/ regulator failure, drive belt failure, lightning strikes, wiring harness problems, or other electrical failures, can completely disrupt the systems, leading to erratic indications or completely inoperative units. Especially in standard category aircraft not designed or built with the redundancy inherent in transport category aircraft, a proficient and prudent pilot plans for failures and has alternate plans and procedures readily available.

Figure 2-7. A PFD indicating a failed air data computer.

The inoperative attitude indicator on the PFD in Figure 2-8 indicates the failure of the AHRS. By understanding which flight instruments are supported by which underlying systems (e.g., ADC, attitude heading reference system (AHRS)), you can quickly understand the source of a failure. It is important to be thoroughly familiar with the operation of the systems and the abnormal/emergency procedures in the pilot’s operating handbook (POH), aircraft flight manual (AFM), or avionics guides.

Figure 2-8. A PFD indicating a failed AHRS.

PFD Failure

The PFD itself can also fail. As a first line of defense, some systems offer the reversion capability to display the PFD data on the multi-function display (MFD) in the event of a PFD failure.

Every aircraft equipped with electronic flight instruments must also contain a minimal set of backup/standby instruments. Usually conventional “round dial instruments,” they typically include an attitude indicator, an airspeed indicator, and an altimeter. Pilots with previous experience in conventional cockpits must maintain proficiency with these instruments; those who have experience only in advanced cockpits must be sure to acquire and maintain proficiency with conventional instruments.

Awareness: Using Standby Instruments

Because any aircraft system can fail, your regular proficiency flying should include practice in using the backup/standby instrumentation in your aircraft. The backup/standby instrument packages in technically advanced aircraft pro vide considerably more information than the “needle, ball, and airspeed” indications for partial panel work in aircraft with conventional instrumentation. Even so, the loss of primary instrumentation creates a distraction that can increase the risk of the flight. As in the case of a vacuum failure, the wise pilot treats the loss of PFD data as a reason to land as soon as practicable.

Essential Skills

Correctly interpret flight and navigation instrument information displayed on the PFD.
Determine what “fail down” modes are installed and available. Recognize and compensate appropriately for failures of the PFD and supporting instrument systems.
Accurately determine system options installed and actions necessary for functions, data entry and retrieval.
Know how to select essential presentation modes, flight modes, communication and navigation modes, and methods mode selection, as well as cancellation.
Be able to determine extent of failures and reliable information remaining available, to include procedures for restoring function(s) or moving displays to the MFD or other display.

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Primary Flight Display (PFD) (Part One)

Filed Under: Electronic Flight Instruments

A PFD presents information about primary flight instruments, navigation instruments, and the status of the flight in one integrated display. Some systems include powerplant information and other systems information in the same display. A typical primary flight display is shown in Figure 2-1.

Figure 2-1. A typical primary flight display (PFD).

Primary Flight Instruments

Flight instrument presentations on a PFD differ from conventional instrumentation not only in format, but sometimes in location as well. For example, the attitude indicator on the PFD in Figure 2-1 is larger than conventional round-dial presentations of an artificial horizon. Airspeed and altitude indications are presented on vertical tape displays that appear on the left and right sides of the primary flight display. The vertical speed indicator is depicted using conventional analog presentation. Turn coordination is shown using a segmented triangle near the top of the attitude indicator. The rate-of-turn indicator appears as a curved line display at the top of the heading/navigation instrument in the lower half of the PFD.

Cross-Checking the Primary Flight Instruments

The PFD is not intended to change the fundamental way in which you scan your instruments during attitude instrument flying. The PFD supports the same familiar control and performance, or primary and supporting methods you use with conventional flight instruments. For example, when using the primary and supporting method to maintain level flight, the altimeter is still the primary instrument for pitch, while the attitude indicator is a direct indicator and the vertical speed indicator provides supporting information. However, you need to train your eyes to find and interpret these instruments in their new formats and locations.

Common Errors: Altitude Excursions and Fixation

Pilots experienced in the use of conventional flight instruments tend to deviate from assigned altitudes during their initial experience with the PFD, while they adjust to the tape display presentation of altitude information. Another common error is the tendency to fixate and correct deviations as small as one to two feet at the expense of significant deviations on other parameters.

Enhancements to the Primary Flight Instruments

Some PFDs offer enhancements to the primary flight instruments. Figure 2-2 shows an airspeed indicator that displays reference speeds (V-speeds) and operating ranges for the aircraft. Operating ranges are depicted using familiar color coding on the airspeed indicator. One negative human factor concerning this type of presentation should be remembered: while most of the displays are intuitive in that a high indication (such as climb pitch or vertical speed) is corrected by lowering the nose of the aircraft, the situation with the usual airspeed vertical tape is the opposite. In most current displays, the lower speeds are at the lower side of the airspeed indicator, while the upper or higher speeds are in the top portion of the airspeed display area. Therefore, if a low airspeed is indicated, you must lower the nose of the aircraft to increase, which is counterintuitive to the other indications.

Figure 2-2. Vertical airspeed (tape type) indicator.

Figure 2-3 shows an attitude indicator that presents red symbols to assist in recovery from unusual attitudes. The symbols on the display recommend a lower pitch attitude.

Figure 2-3. Attitude indicator with symbols to assist in recovery from unusual attitude.

Other valuable enhancements include trend indicators, which process data to predict and display future performance. For example, some systems generate “trend vectors” that predict the aircraft’s airspeed, altitude, and bank angle up to several seconds into the future.

Primary Flight Instrument Systems

The primary flight instruments that appear on a PFD are driven by instrument sensor systems that are more sophisticated than conventional instrument systems. The attitude of the aircraft may be measured using microelectronic sensors that are more sensitive and reliable than traditional gyroscopic instruments. These sensors measure pitch, roll, and yaw movements away from a known reference attitude. Aircraft heading may be determined using a magnetic direction-sensing device such as a magnetometer or a magnetic flux valve.

Attitude and heading systems are typically bundled together as an attitude heading reference system (AHRS), which contains not only the sensors used to measure attitude and heading, but also a computer that accepts sensor inputs and performs calculations. Some AHRSs must be initialized on the ground prior to departure. The initialization procedure allows the system to establish a reference attitude used as a benchmark for all future attitude changes. As in any navigation system, attitude heading reference systems accumulate error over time. For this reason, AHRSs continually correct themselves, using periods of stable flight to make small corrections to the reference attitude. The system’s ability to correct itself can be diminished during prolonged periods of turbulence. Some AHRSs can be reinitialized in flight, while others cannot. The pilot must become familiar with the operating procedures and capabilities of a particular system.

Information on altitude and airspeed is provided by sensors that measure static and ram air pressure. An air data computer (ADC) combines those air pressure and temperature sensors with a computer processor that is capable of calculating pressure altitude, indicated airspeed, vertical speed, and true airspeed. An air data attitude heading reference system (ADAHRS) combines all of the systems previously described into one integrated unit.

Navigation Instruments

PFDs and multi-function displays (MFDs) typically combine several navigation instruments into a single presentation. The instrument appearing at the bottom of the PFD in Figure 2-1 contains two navigation indicators: a course deviation indicator and a bearing pointer. These instruments can be displayed in a variety of views, and can be coupled to many of the navigation receivers (e.g., instrument landing system (ILS), global positioning system (GPS), very high frequency (VHF) omnidirectional range (VOR)) available in the aircraft. The pilot must, therefore, be sure to maintain an awareness of which navigation receivers are coupled to each navigation indicator.

MFDs may provide the same type of display as installed in the PFD position, but are usually programmed to display just the navigation information with traffic, systems data, radar Stormscope®/ Strikefinder®. However, in many systems, the MFD can be selected to repeat the information presented on the PFD, thereby becoming the standby PFD. The pilot should be absolutely certain of and proficient with the standby modes of operation.

More sophisticated PFDs present three-dimensional (3D) course indications. The primary flight display in Figure 2-4 shows a 3D course indication, called a highway-in-the-sky (HITS) display. This display provides both lateral and vertical guidance along the planned flight path, while simultaneously presenting a 3D picture of the surrounding terrain. Keeping the symbolic aircraft within the green boxes on the display ensures that the flight remains within the selected GPS route and altitude. Consult the AFM and avionics manual for required navigational configuration for this function to be available.

Figure 2-4. An attitude indicator with HITS display symbology.

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How Advanced Avionics Systems Affect the Pilot

Filed Under: Introduction to Advanced Avionics

The third challenge is learning how advanced avionics systems affect the pilot. The additional information provided by advanced avionics systems can affect the way you make decisions, and the ability to automate pilot tasks can place you in the role of system supervisor or manager. These ideas are presented throughout the handbook using a series of sidebars illustrating some of the issues that arise when pilots work with advanced avionics systems. This series is not a complete list; rather, its purpose is to convey an attitude and a manner of thinking that will help you continue to learn.

The Learning series provides tips that can help expedite mastery of advanced avionics. You will learn why taking the time to understand how advanced systems work is a better learning strategy than simply memorizing the button-pushing procedures required to use each system. The importance of committing to an ongoing learning process will be explained. Because of the limits of human understanding, together with the quirks present in computerized electronic systems of any kind, you will learn to expect, and be prepared to cope with, surprises in advanced systems. Avionics equipment frequently receives software and database updates, so you must continually learn system functions, capabilities, and limitations.

The Awareness series presents examples of how advanced avionics systems can enhance pilot awareness of the aircraft systems, position, and surroundings. You will also learn how (and why) the same systems can sometimes decrease awareness. Many studies have demonstrated a natural tendency for pilots to sometimes drift out of the loop when placed in the passive role of supervising an FMS/RNAV and autopilot. You will learn that one way to avoid this pitfall is to make smart choices about when to use an automated system, and when to assume manual control of the flight; how cockpit information systems can be used to keep you in touch with the progress of the flight when automated systems are used; and how some advanced cockpit systems can be set to operate in different modes, with each mode exhibiting a different behavior. Keeping track of which modes are currently in use and predicting the future behavior of the systems is another awareness skill that you must develop to operate these aircraft safely.

The Risk series provides insights on how advanced avionics systems can help you manage the risk faced in everyday flight situations. Information systems offer the immediate advantage of providing a more complete picture of any situation, allowing you to make better informed decisions about potential hazards, such as terrain and weather. Studies have shown that these same systems can sometimes have a negative effect on pilot risk-taking behavior. You will learn about situations in which having more information can tempt you to take more risk than you might be willing to accept without the information. This series will help you use advanced information systems to increase safety, not risk. As much as advanced information systems have improved the information stream to the cockpit, the inherent limitations of the information sources and timeliness are still present; the systems are not infallible.

When advanced avionics systems were first introduced, it was hoped that those new systems would eliminate pilot error. Experience has shown that while advanced avionics systems do help reduce many types of errors, they have also created new kinds of errors. This handbook takes a practical approach to pilot error by providing two kinds of assistance in the form of two series: Common Errors and Catching Errors. The Common Errors series describes errors commonly made by pilots using advanced avionics systems. These errors have been identified in research studies in which pilots and flight instructors participated. The Catching Errors series illustrates how you can use the automation and information resources available in the advanced cockpit to catch and correct errors when you make them.

The Maintaining Proficiency series focuses on pilot skills that are used less often in advanced avionics. It offers reminders for getting regular practice with all of the skills you need to maintain in your piloting repertoire.

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How To Operate Advanced Avionics Systems

Filed Under: Introduction to Advanced Avionics

The first challenge is to acquire the “how-to” knowledge needed to operate advanced avionics systems. This handbook describes the purpose of each kind of system, overviews the basic procedures required to use it, explains some of the logic the system uses to perform its function, and discusses each system’s general limitations. It is important to note that this handbook is not intended as a guide for any one manufacturer’s equipment. Rather, the aim is to describe the basic principles and concepts that underlie the internal logic and processes and the use of each type of advanced avionics system. These principles and concepts are illustrated with a range of equipment by different manufacturers. It is very important that the pilot obtain the manufacturer’s guide for each system to be operated, as only those materials contain the many details and nuances of those particular systems.

Many systems allow multiple methods of accomplishing a task, such as programming or route selection. A proficient pilot tries all methods, and chooses the method that works best for that pilot for the specific situation, environment, and equipment. Not all aircraft are equipped or connected identically for the navigation system installed. In many instances, two aircraft with identical navigation units are wired differently. Obvious differences include slaved versus non-slaved electronic horizontal situation indicators (EHSIs) or primary flight display (PFD) units. Optional equipment is not always purchased and installed. The pilot should always check the equipment list to verify what is actually installed in that specific aircraft. It is also essential for pilots using this handbook to be familiar with, and apply, the pertinent parts of the regulations and the Aeronautical Information Manual (AIM).

Advanced avionics equipment, especially navigation equipment, is subject to internal and external failure. You must always be ready to perform manually the equipment functions which are normally accomplished automatically, and should always have a backup plan with the skills, knowledge, and training to ensure the flight has a safe ending.

Which Advanced Avionics Systems To Use and When

The second challenge is learning to manage the many information and automation resources now available to you in the cockpit. Specifically, you must learn how to choose which advanced cockpit systems to use, and when. There are no definitive rules. In fact, you will learn how different features of advanced cockpit avionics systems fall in and out of usefulness depending on the situation. Becoming proficient with advanced avionics means learning to use the right tool for the right job at the right time. In many systems, there are multiple methods of accomplishing the same function. The competent pilot learns all of these methods and chooses the method that works best for the specific situation, environment, and equipment. This handbook will help you get started in learning this important skill.

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Introduction to Advanced Avionics

Filed Under: Introduction to Advanced Avionics

This section is designed as a technical reference for pilots who operate aircraft with advanced avionics systems. Whether flying a conventional aircraft that features a global positioning system (GPS) navigation receiver or a new aircraft with the latest integrated “glass cockpit” advanced avionics system, you should find this handbook helpful in getting started. The arrival of new technology to general aviation aircraft has generated noticeable changes in three areas: information, automation, and options.

Pilots now have an unprecedented amount of information available at their fingertips. Electronic flight instruments use innovative techniques to determine aircraft attitude, speed, and altitude, presenting a wealth of information in one or more integrated presentations. A suite of cockpit information systems provides pilots with data about aircraft position, planned route, engine health and performance, as well as surrounding weather, traffic, and terrain.

Advanced avionics systems can automatically perform many tasks that pilots and navigators previously did by hand. For example, an area navigation (RNAV) or flight management system (FMS) unit accepts a list of points that define a flight route, and automatically performs most of the course, distance, time, and fuel calculations. Once en route, the FMS or RNAV unit can continually track the position of the aircraft with respect to the flight route, and display the course, time, and distance remaining to each point along the planned route. An autopilot is capable of automatically steering the aircraft along the route that has been entered in the FMS or RNAV system.

Advanced avionics perform many functions and replace the navigator and pilot in most procedures. However, with the possibility of failure in any given system, the pilot must be able to perform the necessary functions in the event of an equipment failure. Pilot ability to perform in the event of equipment failure(s) means remaining current and proficient in accomplishing the manual tasks, maintaining control of the aircraft manually (referring only to standby or backup instrumentation), and adhering to the air traffic control (ATC) clearance received or requested. Pilots of modern advanced avionics aircraft must learn and practice backup procedures to maintain their skills and knowledge. Risk management principles require the flight crew to always have a backup or alternative plan, and/or escape route. Advanced avionics aircraft relieve pilots of much of the minute-to-minute tedium of everyday flights, but demand much more initial and recurrent training to retain the skills and knowledge necessary to respond adequately to failures and emergencies.

The FMS or RNAV unit and autopilot offer the pilot a variety of methods of aircraft operation. Pilots can perform the navigational tasks themselves and manually control the aircraft, or choose to automate both of these tasks and assume a managerial role as the systems perform their duties. Similarly, information systems now available in the cockpit provide many options for obtaining data relevant to the flight.

Advanced avionics systems present three important learning challenges as you develop proficiency:

How to operate advanced avionics systems
Which advanced avionics systems to use and when
How advanced avionics systems affect the pilot and the way the pilot flies