Airplane Instruments Study Guide

MAGNETIC COMPASS

• The magnetic compass is the only self-contained direction-seeking instrument in the airplane.
• Primarily used to set the heading indicator before flight and to verify its accuracy during flight.
• Contains two steel magnetized needles fastened to a float, with a compass card mounted around the edge.
  • Needles are parallel, with north-seeking ends pointed in the same direction.
  • One segment of the floating compass card is visible through the instrument face.
• The compass card has letters for cardinal headings (N, E, S, W).
  • Each 30° interval is represented by a number, omitting the last zero (e.g., “3” represents 30°, “30” represents 300°).
  • The card is graduated for each 5° between these numbers.
• The float assembly (needles, card, and float) is mounted on a pedestal and sealed in a chamber filled with white kerosene.
  • The pedestal is the mount for the float assembly.
  • The float assembly balances on a pivot, allowing free rotation and tilting up to 18°.
  • The kerosene decreases oscillations and lubricates the pivot point. The float's buoyancy reduces weight on the pivot.
• A diaphragm at the rear of the compass bowl allows for expansion/contraction of the fluid, preventing bubbles or case bursting.
• A lubber line (reference line) is mounted behind the glass face for reading compass indications.

Magnetism Basics

• A magnet attracts metal, with the strongest attraction at the poles and weakest at the midpoint.
• Lines of force flow from each pole in all directions, bending around to the opposite pole to form a magnetic field.
• The Earth has a magnetic field with lines of force oriented approximately to the north and south magnetic poles.

Magnetic Variation

• Magnetic variation is the angular difference between true north and magnetic north.
• The Earth’s magnetic poles do not coincide with its geographic poles, used in aeronautical charts.
• Magnetic compass needles point to magnetic north, not true north.
• Local magnetic fields from mineral deposits can further distort the Earth’s magnetic field.
• Isogonic lines connect points of equal magnetic variation on aeronautical charts, showing degrees of east and west variation.
• The agonic line connects points of zero variation.
• These lines are periodically replotted to correct for shifts in the poles or local disturbances.
• During taxi, check that the compass swings freely and indicates known headings.

Compass Errors

• Compass errors include:
  • Compass deviation
  • Magnetic dip
  • Compass card oscillation

Compass Deviation

• Compass deviation is the difference between the compass heading in an airplane and the airplane’s actual magnetic heading.
• Caused by localized magnetic fields from the airplane's metal components, electrical equipment, and engine.
• Deviation values are determined for every 30° of heading and displayed on a compass calibration card.
• Metallic and electrical equipment changes position relative to the compass needles as the airplane turns, altering their influence on the needles.
• Deviation depends on the airplane's heading and the strength/cycles of electrical components in use.
• Compasses are checked and compensated periodically to reduce deviation error (compass swing).
• Remaining errors are recorded on a compass correction card near the compass.
• Airport ramp compass roses are used for maintenance and pilot testing, located away from local interference.
• To fly compass headings, refer to the compass correction card for corrected headings to steer.

Magnetic Dip

• Magnetic dip is the tendency of compass needles to point down towards the magnetic pole.
• Dip error is greatest at the poles and zero at the magnetic equator.
• Lines of force in the Earth’s magnetic field are parallel to the Earth’s surface at the magnetic equator and curve downward closer to the poles.
• A magnetic needle aligns with the line of force, becoming parallel at the equator and pointing downward near the pole.
• The compass card responds only to the horizontal plane of the Earth’s magnetic field.
• Compasses are considered accurate only during straight-and-level flight at constant airspeed.
• During turns and acceleration/deceleration, the fluid level and compass card do not remain level, causing magnetic force to pull “down” as well as toward the pole.
• The course limits the dip errors to the Northern Hemisphere only, where errors are reversed in the Southern Hemisphere.

Acceleration/Deceleration Error

• Acceleration/deceleration error is due to the dip of the Earth’s magnetic field, occurring on easterly or westerly headings in the Northern Hemisphere.
• The aft end of the compass card tilts upward during acceleration and downward during deceleration.
• The compass indicates a turn toward north when accelerating and toward south when decelerating.
• Remember ANDS: Accelerate North, Decelerate South.
• Acceleration/deceleration error does not occur on northerly or southerly headings.

Northerly and Southerly Turning Error

• The card banks due to centrifugal force, causing the north-seeking ends of the compass to dip to the low side of the turn, giving erroneous turn indications.
• Most apparent on northerly and southerly headings.
• On a northerly heading, the compass lags or indicates a turn in the opposite direction when turning east or west. The lag diminishes as the turn progresses.
• On a southerly heading, the compass needle shows a greater amount of turn than is actually made, diminishing as the turn progresses.
• When turning to a northerly heading, the rollout is indicated before the desired heading is reached (compass lags).
• When turning to a southerly heading, the rollout is indicated after the desired heading is passed (compass leads).
• Remember UNOS: Undershoot North, Overshoot South.
• The amount of lead or lag is approximately equal to the latitude of the locality.
  • When turning to north, include the degrees of latitude in the lead for rollout, plus the normal lead.
  • When turning to south, maintain the turn until the compass passes south by the degrees of latitude, minus the normal rollout lead.
• Turning errors do not occur when turning from or through easterly or westerly headings.
• Magnetic dip errors diminish as acceleration/deceleration or turns are completed.

Compass Card Oscillation

• Compass card oscillation results from erratic movement of the compass card due to turbulence or rough control technique.
• During oscillation, the compass is affected by all previously discussed factors.

PITOT-STATIC SYSTEM

• The pitot-static system provides atmospheric air pressure for the:
  • Altimeter
  • Vertical speed indicator
  • Airspeed indicator
• The two major parts are:
  • The pitot pressure chamber and lines
  • The static pressure chamber and lines

Pitot Pressure

• Pitot pressure (ram, impact, or total pressure) is taken from a pitot tube, normally mounted on or beneath the leading edge of the left wing.
• The pitot tube is aligned with the relative wind in a location with minimal disturbance or turbulence.
• The pitot line is connected only to the airspeed indicator.
• Some pitot tubes have an electric heating element to prevent ice blockage.
• Pitot tubes also have a drain opening to remove water.

Static Pressure

• Static pressure (pressure of still air) is usually taken from the static line attached to a vent mounted flush with the side of the fuselage.
• In some airplanes, the static source is found on the back of the pitot tube.
• The static pressure lines provide static air pressure to the altimeter, vertical speed indicator, and airspeed indicator.

Airspeed Indicator

• The airspeed indicator is a pressure differential gauge that displays the difference between pitot and static pressures.
• Dynamic pressure is the difference between ambient static pressure and total ram air pressure.
• As an aircraft moves through the air, dynamic pressure results from increased pitot pressure or decreased static pressure, causing the airspeed diaphragm to expand or contract and move the indicator needle.
• Color coding on the instrument face facilitates instrument scan and cross-check.
• Glass cockpits provide trend indication for comprehensive scanning.

Types of Airspeed

• Indicated airspeed (IAS) is the direct instrument reading from the airspeed indicator, uncorrected for variations in air density or installation and instrument errors.
• Calibrated airspeed (CAS) is IAS corrected for installation and instrument errors.
  • CAS is needed to maintain a certain true airspeed (TAS) and can be determined with a flight computer using altitude and temperature.
  • Example:
    • To maintain a TAS of 180 kt at an altitude of 12,000 ft with an outside air temperature of +5°C, use a CAS of 147 KCAS, calculated using a flight computer.
• True airspeed (TAS) is CAS corrected for density altitude.
  • TAS is the true speed of an airplane through the air.
• Airspeed limitations can be seen on an analog instrument, ASI provides true airspeed mechanically by setting the pressure altitude against the air temperature in the top window via the adjustment knob, and the TAS is indicated in the lower left window.

Alternate Static Source

• An alternate source of static pressure is provided in most airplanes in case the static ports become clogged.
• This source is selected manually with a valve and is usually vented inside the flight deck.
• The alternate static pressure is usually lower than the normal static air source due to the venturi effect around the flight deck.
  • Accelerated air flow results in lower pressure.
  • Instrument indications differences when using the alternate static source:
    • The altimeter may indicate a higher-than-actual altitude.
    • The vertical speed indicator will initially indicate a climb, then level off.
    • The airspeed indicator will indicate a greater-than-actual airspeed.

Blockages in the Pitot-Static System

• During the visual inspection, ensure the pitot tube and static vents are not blocked. Clear any blockages by a certificated maintenance technician.
• If the pitot tube becomes clogged with ice during flight, only the airspeed indicator is affected.
• If the static ports are iced over, the vertical speed indicator will not reflect climbs and descents.
• When both the airspeed indicator pitot tube and the drain hole are blocked, the airspeed indicator acts as an altimeter.
  • Changes in airspeed do not change the indicated airspeed at a given altitude.
  • During climbs, the indicated airspeed increases.
  • During descents, the indicated airspeed decreases.
  • This results from the differential between the pressure of the air locked in the pitot tube and the static air vent pressure.
• If the vertical speed indicator is not calibrated correctly, it can still be used for IFR flight by adjusting for the error.
• The vertical speed indicator is not a required instrument for IFR flight. However, you are required to report the inability to climb/descend at least 500 fpm by the FAA.
• If the outside air temperature increases during a flight at constant power and a constant indicated altitude, TAS and true altitude will increase.

ALTIMETER

• The altimeter measures the height of the airplane above a given level.
• It's one of the most important instruments because:
  • Ensures the airplane is high enough to clear terrain or obstructions.
  • Maintains altitudes per air traffic rules to reduce midair collision risk.
  • Allows selecting altitudes to take advantage of favorable winds and weather.
  • Provides altitude for calculating true airspeed.

Principle of Operation

• The pressure altimeter is an aneroid barometer that measures atmospheric pressure to display altitude in feet.
• The altimeter uses static pressure as its source of operation.
• Altitude is determined in terms of air pressure.
• The basic component is the aneroid wafer.
  • A stack of sealed aneroid wafers expands or contracts with atmospheric pressure changes and rotates the pointers on the dial through a shaft and gearing linkage.
• Most altimeters have three pointers (or “hands”).
  • 10,000-ft. interval (thin needle with a flared triangular tip)
  • 1,000-ft. interval (short, thick needle)
  • 100-ft. interval (long, medium-thickness needle)
• A cross-hatched flag is displayed for flight altitudes below 10,000 ft.
• An example: The altimeter indicates an altitude of 14,500 ft.
• The altimeter is calibrated using the International Standard Atmosphere (ISA) table, which has specific values for each altitude.
  • ISA sea level temperature and pressure are 15°C (59°F) and 29.92 in. Hg.
  • Atmospheric pressure decreases about 1 in. Hg for every 1,000-ft. altitude gain.
• The altimeter can be adjusted to compensate for nonstandard pressure.
  • Adjust the altimeter to a barometric scale located on its face.
  • The area where the scale is displayed is known as the Kollsman window.
  • The altimeter setting adjustment knob allows adjustment for nonstandard pressure.
    • Rotating the knob changes the scale and the hands simultaneously by 1,000 ft. per 1 in. Hg.
    • Example: Changing from 29.92 in. to 30.92 in. increases indicated altitude by 1,000 ft., or from 30.15 in. to 30.25 in. increases indicated altitude by 100 ft.
  • The aneroid wafer expands to a definite size, indicating height above the pressure level set in the Kollsman window.

Altimeter Setting and Altitude

• Prior to takeoff, the altimeter should be set to the current local altimeter setting.
  • With the current setting, the indicated altitude on the ground should be within ±75 ft. of the airport elevation for acceptable accuracy.
• If the current local setting is unavailable, use the departure airport elevation.
• Pressure altitude is the indicated altitude when the altimeter setting is adjusted to 29.92 in. Hg.
  • Pressure altitude is used in computations of density altitude, true altitude, and true airspeed.
  • Pressure altitude will equal true altitude when standard atmospheric conditions exist.
  • Pressure altitude and density altitude are the same at standard temperature.
• The altimeter must be set to pressure altitude when flying at or above 18,000 ft. MSL to guarantee vertical separation.
• When flying in colder-than-standard air, the airplane will be at a lower-than-indicated altitude.

Vertical Speed Indicator

• The vertical speed indicator is a rate-of-pressure change instrument providing trend and rate information.
• It compares static air pressure vented from the same source against itself.
• Static air is delivered directly to the diaphragm from the static system and simultaneously to the instrument case through a metered leak.
• When the aircraft climbs or descends, the diaphragm expands or contracts with the change in static pressure.
• The calibrated leak allows static pressure to remain higher or lower for a time.
• The difference in these pressures deflects the needle, reflecting the speed vertically on the instrument face.

GYROSCOPES

• The turn indicator, the heading indicator, and the attitude indicator contain gyroscopes.
• Gyroscopic instruments are operated by either a vacuum or an electrical system.
• In most light airplanes, the vacuum system powers the heading and attitude indicators, and the electrical system powers the turn indicator.

Vacuum System

• The vacuum system spins the gyro by drawing air against the rotor vanes to spin the rotor at high speeds.
• A vacuum pump creates the required vacuum.
• Some airplanes use a pressure pump instead, pushing air through the gyros.
• A typical vacuum system includes an engine-driven vacuum pump, a vacuum relief valve, an air filter, and necessary tubing.
• A suction gauge on the instrument panel indicates the amount of vacuum in the system.
  • Some airplanes have a low-vacuum warning light.
    • When the light is on, check the suction gauge and prepare for erroneous readings on vacuum-driven gyro instruments.
  • Some airplanes also have a standby vacuum system driven by the manifold induction system.
• Listen to your electric gyroscopes for unusual noises after the battery is turned on but before the engine is started.

Gyroscopic Principles

• Any spinning object exhibits gyroscopic properties.
• A wheel designed and mounted to utilize these properties is called a gyroscope.
• The two fundamental properties of gyroscopic action are:
  • Rigidity in space
  • Precession

Rigidity in Space

• A gyro is resistant to deflection of the spinning wheel, based on Newton’s laws of motion:
  • A body at rest will continue at rest, and a body in motion will continue in motion in a straight line, until acted on by an outside force.
    • An example is the rotor of a universally (freely) mounted gyro. When the wheel is spinning, it remains in its original plane of rotation regardless of base movement.
    • The attitude and heading indicators use rigidity for their operation. Their rotors must be universally mounted.

Precession

• Deflection of a moving body is proportional to the deflective force applied and inversely proportional to the body’s mass and speed.
  • Precession is the deflection of a spinning wheel when a deflective force is applied to its rim.
    • The deflection is 90° ahead in the direction of rotation and in the direction of the applied force.
    • The wheel’s precession rate is directly proportional to the deflective force.
    • The turn indicator operates using precession.

Design Characteristics

• Two important design characteristics of an instrument gyro are:
  • Great weight or high density for size
  • Rotation at high speeds with low friction bearings

Gimbals

• The mountings of the gyro wheels are called gimbals. They may be circular rings, rectangular frames, or part of the instrument case itself.

HEADING INDICATOR

• The heading indicator (HI) is a gyroscopic instrument commonly used as the primary source of heading information.
• The HI is not affected by the forces that make the magnetic compass difficult to interpret.
• In most light airplanes, the HI is powered by the vacuum system.
  • The Heading Indicator runs on the gyroscopic principle of rigidity in space
    • Fixed to the rotor there is a compass card.
    • Since the rotor remains rigid in space, the points on the card hold the same position in space relative to the vertical plane
• Must be set to the heading shown on the magnetic compass.
  • As the instrument case and the airplane revolve, the card provides heading information.
    • The compass card has letters for cardinal headings (N, E, S, W):
      • N represents heading $360°$ or $0°$.
      • E represents $90°$.
      • S represents $180°$.
      • W represents $270°$.
    • Each $30°$ interval of direction is represented by a number, the last zero of which is omitted.
    • Between these numbers, the card is graduated for each $5°$.
• The HI may creep or drift due to precession, chiefly from bearing friction or improper vacuum pressure.
  • The amount of drift depends on the condition of the instrument.
    • Consider worn, dirty, or improperly lubricated bearings the cause of drift.
• Prior to takeoff, check that the HI maintains the correct heading after taxi turns.
• The HI should be compared to the magnetic compass every 15 min. for accuracy during straight, level, and unaccelerated flight.
• Bank and pitch limits vary:
  • Approximately $55°$ of pitch and $55°$ of bank for heading indicators found in light airplanes
  • When either of these are exceeded the instrument will tumble
  • After tumbling, it should be reset with the adjustment knob at the edge of the instrument.
  • Some heading indicators avoid tumbling.

Remote Indicating Compass

• The remote indicating compass (RIC) combines the functions of the magnetic compass and the HI.
• RICs compensate for the errors and limitations of older HIs.
• The two panel components of a typical RIC are the pictorial navigation indicator and the slaving control and compensator unit.
• The pictorial navigation is commonly referred to as a horizontal situation indicator (HSI).
• The slaving meter needle indicates the difference between the displayed heading and the actual magnetic heading.
  • When the aircraft is turning, the slaving meter shows a full deflection to one side or the other.
  • A right deflection (+) indicates a clockwise (right) error in the HI compass card (i.e., the correct magnetic heading is to the right of the indicated heading).
    • Depressing the right (counterclockwise) heading drive button will move the HI compass card to the left, increasing (+) the indicated heading toward the correct value (e.g., from $180°$ to $190°$).
  • A left deflection (–) indicates a counterclockwise (left) error in the HI compass card (i.e., the correct magnetic heading is to the left of the indicated heading).
    • Depressing the left (clockwise) heading drive button will move the HI compass card to the right, decreasing (–) the indicated heading toward the correct value (e.g., from $190°$ to $180°$).
• The slaving control and compensator unit has two manual heading drive buttons for selecting either the “slaved gyro” or “free gyro” mode.
  • To make corrections to the RIC, put the system in free gyro mode.
  • After correction, return to the slaved mode (normal mode).
• A magnetic slaving transmitter is a separate unit mounted remotely to eliminate magnetic interference:
  • Contains the flux valve, which is the direction-sensing device of the system.
    • A concentration of lines of magnetic force, after amplification, becomes a signal relayed to the HI unit, which is also remotely mounted.
    • This signal operates a torque motor in the HI unit that precesses the gyro unit until it is aligned with the transmitter signal.
  • The magnetic slaving transmitter is connected electrically to the RIC or HSI.

ATTITUDE INDICATOR

• The attitude indicator (AI), with its miniature airplane and horizon bar, depicts the attitude of the airplane.
• The relationship of the miniature airplane to the horizon bar is the same as the relationship of the real airplane to the actual horizon.
• Provides an instantaneous indication of even the smallest changes in attitude.
• In most light airplanes, the AI is powered by the vacuum system.
• The gyro in the AI is mounted on a horizontal plane and depends on rigidity in space.
• Horizon Bar:
  • Fixed to the gyro
  • It remains in a horizontal plane as the airplane is pitched or banked about its lateral or longitudinal axis.
  • The dial (banking scale) indicates the bank angle.
• Adjustment knob: Moves the miniature airplane up or down to align with the horizon bar to suit the line of vision.
  • Wings overlap the horizon bar during straight-and-level cruising flight.
• Prior to IFR flight, check that the horizon bar is erect and stable within 5 min. of engine warm-up.
  • The horizon bar should not tilt more than $5°$ when making taxi turns.
• Though the position of the miniature airplane can be adjusted, it is the horizon bar that moves to indicate attitude in flight.
  • The horizon bar remains parallel to the horizon as the airplane’s attitude changes.
    • Movements of the horizon bar above or below the miniature airplane should not exceed one-half bar width.
    • Additional inputs should not result in more than a one-half bar width correction.
• Precession errors (pitch and bank) on attitude indicators are greatest when rolling out of a $180°$ steep turn in either direction.
  • As the airplane returns to straight-and-level coordinated flight, the miniature airplane will show a slight climb and a turn in the opposite direction to the turn just made.
    • Pitch and bank indication should be accurate to avoid descending and turning in the direction of the turn that was just made
  • These precession errors during turns (including coordinated turns) are caused by centrifugal force acting on the pendulous vanes (erection mechanism in the attitude indicator).
    • This results in the precession of the gyro toward the inside of the turn.
  • AI reflects an error during skidding turns, which processes the gyro toward the inside of the turn.
    • As the airplane returns to straight-and-level coordinated flight, the miniature airplane shows a turn in the direction opposite to the skid. Pitch indication is not affected.
  • Deceleration precession makes some altitude indicators incorrectly indicate a descent.
    • Conversely, acceleration precession may result in attitude indicators incorrectly indicating a climb.
• The AI is highly reliable and the most realistic flight instrument on the instrument panel.
  • Refer to the AI often during flight into areas of restricted visibility or any time the actual horizon is not visible.

TURN-AND-SLIP INDICATOR

• The turn-and-slip indicator (T&SI) is another type of turn indicator used in some older airplanes.
• The T&SI has a needle instead of a miniature airplane and indicates movement only around the vertical (yaw) axis, not the longitudinal (roll) axis.
• Prior to engine start, the T&SI should indicate the needle centered, the tube full of fluid, and the ball approximately centered.
  • The turn needle will deflect in a wings-level yaw or during a turn while taxiing.
• During taxi turns, the needle should deflect in the direction of the turn, and the ball should move freely opposite the turn due to centrifugal force.
• The inclinometer in the T&SI works in the same manner as in the turn coordinator.
• Senses rotation about the vertical axis only, whereas the turn coordinator operates on precession with the gimbal frame canted at an angle $30°$ from the longitudinal axis.
  • The canted gimbal frame allows for sensing of both roll and yaw.

TURN COORDINATOR

• The turn coordinator (TC) indicates rate and quality of turn and serves as an emergency source of bank information if the attitude indicator fails.
• The TC is actually a combination of two instruments: a miniature airplane and an inclinometer (or ball).

Miniature Airplane

• Indicates rate of roll and rate of turn.
  • Indicates the rate of roll along the longitudinal axis when the bank is changing.
  • Indicates the rate of turn along the vertical axis when the bank is constant.
  • Only provides an indirect indication of bank angle.
• During taxi turns, the miniature airplane indicates a turn in the direction of the taxiing turn, and the ball moves to the outside of the turn due to centrifugal force.
• The miniature airplane is connected to a gyro (usually driven by electricity).
  • Due to the tilt around $30°$ the gimbal axis of the gyro precesses:
    • Vertical (yaw)
    • Longitudinal (roll)
    • Allows TC to show both
  • The view of the miniature airplane is from the tail, when rolling to the right the miniature airplane banks to the right proportionally to the roll rate.
  • When the airplane is stabilized it shows the rate of turn. When beginning a turn it first shows the rate of bank indirectly.
  • During a turn, the TC first shows the rate of bank indirectly and, once stabilized, the rate of turn.

Rate of Turn

• For any given airspeed, a specific angle of bank is necessary to maintain a coordinated turn at a given rate.
  • The faster the airspeed, the greater the angle of bank required to obtain a desired rate of turn.
• In a standard-rate turn, when the turn needle points to one of the small side marks, it indicates that the airplane is turning at a rate of $3°$ per second.

Inclinometer

• The inclinometer of the TC consists of a sealed, curved glass tube containing kerosene and a ball that is free to move inside the tube.
  • The fluid provides a dampening action, ensuring smooth movement of the ball.
• A rate of $3°$ perSecond is considered a standard-rate turn, and completing $360°$ of turn requires 2 min.
• The tube is curved so that the ball tends to seek the lowest point, which is the center of the tube during coordinated flight. Two reference markers aid determining when the ball is in the center. Coordinated Turn:
  • Turning forces are balanced, the ball remains centered in the tube.
    Uncoordinated Turn:
  • Turning forces are unbalanced, excess force. The ball moves away from the center of the tube in the direction of the excessive force.
    Skid:
  • The rate of turn is too great for the angle of bank.
  • Excessive centrifugal force moves the ball to the *outside of the turn.
    • To achieve coordinated flight: Increase the bank angle or reduce the rate of turn by reducing the rudder force.
      Slip:
  • The rate of turn is too slow for the angle of bank.
  • The lack of centrifugal force moves the ball to the inside of the turn.
    • To achieve coordinated flight: Decrease the bank angle, increase the rate of turn by applying rudder pressure.

Memory Aid for Ball position:
* Apply rudder pressure on the side where the ball is exposed, step on the ball.
Quality of Turn:
* If the airplane has the correct rate of turn to the angle of bank

GLASS COCKPITS

• Glass cockpit instrumentation and automation of basic flight indications are common in general aviation airplanes.
• All major aircraft manufacturers now have a full glass cockpit as standard or optional equipment.

Glass Cockpit Definition

• A glass cockpit is a system of electronic flight displays (EFDs) and associated components that display information, such as:
  • Aircraft flight attitude and direction
  • Location via a moving map
  • Pertinent engine information

Functionality and Benefits

• Glass cockpits integrate many flight instruments with aircraft performance data on one or more screens to give flight status in a convenient, easy-to-read format.
• These systems display information from electronic sources instead of traditional pitot-static and vacuum systems.

Benefits:
* Increased internal error-monitoring capability.
* More reliable.
* Reduces maintenance.

• Integrated avionics systems pair glass cockpits with communication and navigation radios, transponders, autopilots, weather and traffic display systems, and even cabin controls.
• These systems are designed to:
  • Decrease pilot workload
  • Enhance situational awareness
  • Increase the safety margin

Components

• Two central components found in glass cockpit systems:

Primary Display Flight

• A primary flight display (PFD) usually consists of the six basic flight instruments (displayed electronically).

Additional Capabilities:
* Navigational instruction can also be displayed.
* Various insets of traffic, terrain, and moving map information can be selected.
* Other flight status information:
* Distance and bearing to the next waypoint,
* Ground track
* Outside air temperature
* Navigation instruments
* Communication frequencies.
* Instrument sensor systems used to display information on a PFD are more sensitive and reliable than traditional gyroscopic instruments.

Benefits:
* The PFD presents all necessary flight information in one central location with trend displays.
* The pilot is not only aware of what is happening with the airplane at any given time but also what will happen in the immediate future.

Multi-Function Display

• A multi-function display (MFD) usually includes a large moving map (several map pages may be available) and engine instrumentation.

Additional Capabilities:
* Interfaces with weather radar, traffic avoidance systems, terrain warning systems, and various forms of navigational charts and/or instrument approach plates.

Benefits:
* The MFD provides the pilot with the “big picture,” greatly increasing situational awareness.
* From the MFD, the pilot can monitor:
* The nearest airports
* Wind drift
* Terrain and landmarks
* Weather and traffic information (if equipped)

• EFDs utilize an air data computer (ADC) that receives the pitot and static inputs.
  • Computes the difference between the total pressure and the static pressure,
  • Generates the information necessary to display the airspeed, altitude, and vertical speed on the PFD.
• An attitude and heading reference system (AHRS) provides information typically given by gyroscopic instruments, such as:
  • Attitude (pitch/bank)
  • Heading
  • Rate of turn
  • Turn coordination

Components:
* Replaces free-spinning gyros with solid-state laser systems.
* Capable of flight at any attitude without tumbling.
* AHRS sends attitude information to the PFD to generate the pitch and bank information of the attitude indicator.
* Heading information is derived from a magnetometer that senses the earth’s lines of magnetic flux.

• These devices are typically referred to as line replaceable units (LRUs) because of their stand-alone nature and the ease with which they can be replaced.

Safety Systems

• Glass cockpit systems promote safety through internal, automatic error-monitoring and alerting systems.
  • A typical system will alert a pilot if any operational tolerance is exceeded in any system component.

PFD and MFD Failure response:
* Information from both displays can be shown on a single screen, called reversionary mode.
* Troubleshooting a malfunctioning glass cockpit system is as easy as:
* Plugging a computer into the system
* Determining the error code
* Replacing the malfunctioning unit

• Failures in these systems are rare, but they do happen.
  • The time between errors in the systems is measured in thousands of hours rather than hundreds of hours for traditional instrumentation systems.

Workload and Situational Awareness

• Glass cockpit systems can reduce pilot workload and increase situational awareness.
• Pilots with incomplete knowledge of advanced avionics systems will find that their workload is actually increased and their attention is shifted from flying the airplane.
• Complete system knowledge is essential to use a glass cockpit system effectively.
• Combining that knowledge with experience and flight requirements will encourage safe and successful flights.
• Much more initial and recurrent training is needed to acquire and retain the knowledge and skills to accomplish a flight safely using glass cockpits.
  • Pilots flying with advanced avionics or glass cockpits must continually learn their system’s functions, capabilities, and limitations.
  • Safety can be compromised if the pilot is not aware of what data is being presented or if the electronic data is used as a substitute for required preflight planning.
• As with flying conventional instruments, you must maintain a correct instrument scan to correctly interpret instrument indications and avoid fixation.

Automation

• Although most of the aviation community believes automation has made flying safer, there is a fear that pilots fail to see automation as a double-edged sword.
  • Technologically advanced avionics can both increase and decrease pilot awareness.
    • Humans are characteristically poor monitors of automated systems. When passively monitoring an automated system for faults, abnormalities, or other