Avionics & Instruments

Avionics and flight instruments aid the pilot to control the aircraft and maintain situational awareness.


Introduction

Introduction
  • Aircraft became a practical means of transportation when accurate flight instruments freed the pilot from the necessity of maintaining visual contact with the ground
  • Flight instruments are crucial to conducting safe flight operations and it is important that the pilot have a basic understanding of their operation
  • Various types of air navigation aids are in use today, each serving a special purpose
    • These aids have varied owners and operators, namely: the Federal Aviation Administration (FAA), the military services, private organizations, individual states and foreign governments
    • The FAA has the statutory authority to establish, operate, maintain air navigation facilities and to prescribe standards for the operation of any of these aids which are used for instrument flight in federally controlled airspace as tabulated in the Chart Supplement U.S.

Basic "Six-Pack" Flight Instruments

Basic "Six-Pack" Flight Instruments
  • Six Pack: Aircraft Instruments Explained
    Mid-Continent Instruments and Avionics
  • The core instruments in an aircraft center around "the six-pack."
  • These instruments enable the pilot to maintain spatial orientation during flight.

  • Airspeed Indicator:

    • The Airspeed Indicator (ASI) displays the aircraft's airspeed, typically in knots.
    • The airspeed indicator measures the differential pressure between the impact/dynamic pressure and static pressure by utilizing the Pitot-static system.
    • The instrument's design translates pressure to mechanical movement through the airspeed dial.
    • Airspeed indications, usually displayed in knots, display or reference different types of airspeed, referred to as "V-speeds."
    • Airspeed indicators are considered critical instrumentation, and before a flight, pilots must consider the regulations and conduct preflight actions to ensure performance and reliability.
    • Newer aircraft often maintain backup airspeed indicators but are equipped with modern Inertial Reference Unit (IRU), Inertial Navigation System (INS), and Attitude Heading Reference System (AHRS) systems for glass displays.
    • As with any system or instrument, anomalies and malfunctions are possible, requiring detailed knowledge of the indicator and related systems.

  • Altimeter:

    • An altimeter is a type of barometer which measures the vertical distance to the surface, necessary for a pilot to maintain the desired or assigned altitude during flight
    • Maintaining a current altimeter setting is critical because the atmosphere pressure is never constant
      • That is, in one location the pressure might be higher than the pressure just a short distance away
    • Altimeters function by measuring pressure differences which are displayed in terms of feet (or meters)
    • Different types of altimeters measure different types of altitude
    • Altimeters however, are not without their inaccuracies and errors
    • Taking these errors into consideration, a set of cold temperature and altimeter procedures standarize operations under extreme conditions
    • As technology matures, new instrumentation including encoding altimters are better sharing altitude information
    • No matter the case, pilots conduct their preflight actions which include inspections, tests, and regulatory compliance to mitigate inaccuracies altimeter
    • Altimeter technology has not remain static and the advent of Inertial Reference Units (IRU), Inertial Navigation Systems (INS), and Attitude Heading Reference Systems (AHRS)
    • As with any system or instrument, anomalies and malfunctions are possible, requiring detailed knowledge of the indicator and related systems.

  • Attitude Indicator:

    • The attitude indicator, originally called the Artificial Horizon Indicator, is an instrument that references the aircraft's pitch and bank against an artificial horizon utilizing a gyroscopic system.
    • Although electric versions are available, the instrument generally uses the vacuum/gyroscopic system to spin the gyroscopes.
    • It operates on the principle of rigidity in space, which gives an immediate and direct indication of the aircraft's orientation.
    • Attitude indicators, however, are not without their inaccuracies and errors.
    • Preflight actions minimize the chance of inaccurate information.
    • As with any system or instrument, anomalies and malfunctions are possible, requiring detailed knowledge of the indicator and related systems.

  • Heading Indicator:

    • The heading indicator, also called a directional gyro, is an instrument designed to determine aircraft direction to aid the pilot in navigation
      • When set properly, heading indicators indicate primary heading and indirect bank (due to heading change)
    • Functions using the vacuum system and operates on the principle of torque-induced precession (gyroscopic precession)
    • Although very reliable, a magnetic compass has so many inherent errors, such as magnetic dip, that it has been supplemented with gyroscopic heading indicators
      • The heading of the aircraft is shown against the nose of the symbolic aircraft on the instrument glass, which serves as the lubber line to display directional (heading) information in reference to 360°
    • Senses rotation about vertical axis
    • Because airplane does more than yaw, additional gimbal is needed to allow free rotation (2 gimbals total)
    • Gyro heading indicators, with the exception of slaved gyro indicators, are not north seeking, therefore they must be manually set to the appropriate heading by referring to a magnetic compass
      • Rigidity causes them to maintain this heading indication, without the oscillation and other errors inherent in a magnetic compass
    • Older directional gyros use a drum-like card marked in the same way as the magnetic compass card
      • The gyro and the card remain rigid inside the case with the pilot viewing the card from the back
      • This creates the possibility the pilot might start a turn in the wrong direction similar to using a magnetic compass
    • Heading indicators like the one in Figure 3-31 work on the same principle as the older horizontal card indicators, except that the gyro drives a vertical dial that looks much like the dial of a vertical card magnetic compass
    • As with any system or instrument, anomalies and malfunctions are possible, requiring detailed knowledge of the indicator and related systems.

  • Turn Coordinator:

    • Turn coordinators display the rate of turn and roll information.
    • Designed to function off an electrically or vacuum/pressure driven gyroscope, indicating the quality and coordination of a turn.
    • Pilots monitor the instrument's performance on startup and taxi to ensure proper function.
    • Newer aircraft utilize modern Inertial Reference Unit (IRU), Inertial Navigation System (INS), and Attitude Heading Reference System (AHRS) systems for glass displays.
    • As with any system or instrument, anomalies and malfunctions are possible, requiring detailed knowledge of the indicator and related systems.

  • Vertical Speed Indicator:

    • The Vertical Speed Indicator (VSI) is an instrument that displays the rate of climb and descent to the pilot by measuring rate-of-pressure changes.
    • Pressure changes provide vertical speed indications for the pilot to determine the aircraft's trend before the altimeter registers changes.
    • While not required to function or be calibrated for flight, the vertical speed indicator does contain inherent errors for pilots to consider as part of their preflight actions.
    • Newer aircraft utilize modern Inertial Reference Unit (IRU), Inertial Navigation System (INS), and Attitude Heading Reference System (AHRS) systems for glass displays.
    • As with any system or instrument, anomalies and malfunctions are possible, requiring detailed knowledge of the indicator and related systems.
  • Six Pack: Aircraft Instruments Explained
    Mid-Continent Instruments and Avionics

User Reports Requested on NAVAID Outages

User Reports Requested on NAVAID Outages
  • Users of the National Airspace System (NAS) can render valuable assistance in the early correction of NAVAID malfunctions or GNSS problems and are encouraged to report their observations of undesirable avionics performance
    • Although NAVAIDs are monitored by electronic detectors, adverse effects of electronic interference, new obstructions or changes in terrain near the NAVAID can exist without detection by the ground monitors
    • Some of the characteristics of malfunction or deteriorating performance which should be reported are: erratic course or bearing indications; intermittent, or full, flag alarm; garbled, missing or obviously improper coded identification; poor quality communications reception; or, in the case of frequency interference, an audible hum or tone accompanying radio communications or NAVAID identification
    • GNSS problems are often characterized by navigation degradation or service loss indications
  • Pilots conducting operations in areas where there is GNSS interference may be unable to use GPS for navigation, and ADS-B may be unavailable for surveillance
    • Radio frequency interference may affect both navigation for the pilot and surveillance by the air traffic controller
    • Depending on the equipment and integration, either an advisory light or message may alert the pilot
    • Air traffic controllers monitoring ADS-B reports may stop receiving ADS-B position messages and associated aircraft tracks
  • GPS testing can be found here
  • Malfunctioning, faulty, inappropriately installed, operated, or modified GPS re-radiator systems, intended to be used for aircraft maintenance activities, have resulted in unintentional disruption of aviation GPS receivers. This type of disruption could result in unflagged, erroneous position-information output to primary flight displays/indicators and to other aircraft and air traffic control systems. Since Receiver Autonomous Integrity Monitoring (RAIM) is only partially effective against this type of disruption (effectively a "signal spoofing"), the pilot may not be aware of any erroneous navigation indications; ATC may be the only means available to identify these disruptions and detect unexpected aircraft positions while monitoring aircraft for IFR separation
  • Pilots encountering navigation error events should transition to another source of navigation and request amended clearances from ATC as necessary
  • Pilots are encouraged to submit detailed reports of NAVAID or GPS anomaly as soon as practical. Pilot reports of navigation error events should contain the following information:
    • Date and time the anomaly was observed, and NAVAID ID (or GPS)
    • Location of the aircraft at the time the anomaly started and ended (e.g., latitude/longitude or bearing/distance from a reference point)
    • Heading, altitude, type of aircraft (make/model/call sign)
    • Type of avionics/receivers in use (e.g., make/model/software series or version)
    • Number of satellites being tracked, if applicable
    • Description of the position/navigation/timing anomaly observed, and duration of the event
    • Consequences/operational impact(s) of the NAVAID or GPS anomaly
    • Actions taken to mitigate the anomaly and/or remedy provided by the ATC facility
    • Post-flight pilot/maintenance actions taken
  • Pilots operating an aircraft in controlled airspace under IFR shall comply with CFR 91.187 and promptly report as soon as practical to ATC any malfunctions of navigational equipment occurring in flight; pilots should submit initial reports:
    • Immediately, by radio to the controlling ATC facility or FSS
    • By telephone to the nearest ATC facility controlling the airspace where the disruption was experienced
    • Additionally, GPS problems should be reported, post flight, by Internet via the GPS Anomaly Reporting Form at http://www.faa.gov/air_traffic/nas/gps_reports/
  • To minimize ATC workload, GPS anomalies associated with known testing NOTAMs should NOT be reported in-flight to ATC in detail; EXCEPT when:
    • GPS degradation is experienced outside the NOTAMed area
    • Pilot observes any unexpected consequences (e.g., equipment failure, suspected spoofing, failure of unexpected aircraft systems, such as TAWS)

Other Instruments

Other Instruments

  • Automatic Dependent Surveillance-Broadcast:

    • The Automatic Dependent Surveillance-Broadcast (ADS-B) is the most recent leap in Next Generation (NextGen) modernization technology
    • "Real-time precision, shared situational awareness, advanced applications for pilots and controllers alike – these are the hallmarks of ADS-B NextGen surveillance"

  • Emergency Locator Transmitter:

    • Safety is the primary concern with everything aviation
    • The Emergency Locator Transmitter (ELT) was designed with safety in mind, when luck is at its worst, allowing pilots to broadcast their position when in distress

  • Angle of Attack Indicator:

    • An angle of attack indicator is a more accurate measurement of the aircraft's performance
    • These systems incorporate a numeric value to be read in flight while also using stick shakers to avoid the pilot putting the aircraft into an unsafe situation
  • Transponder

  • Magnetic Direction Indicator:

    • The Earth is a huge magnet, spinning in space, surrounded by a magnetic field made up of invisible lines of flux
      • These lines leave the surface at the magnetic North Pole and reenter at the magnetic South Pole
    • Lines of magnetic flux have two important characteristics:
      • Any magnet that is free to rotate will align with them, and
      • An electrical current is induced into any conductor that cuts across them
    • Most direction indicators installed in aircraft make use of one of these two characteristics
    • One of the most common types of magnetic direction indicators is the Magnetic Compass

Instrumentation: Moving into the Future

Instrumentation: Moving into the Future
  • Until recently, most GA aircraft were equipped with individual instruments utilized collectively to safely operate and maneuver the aircraft. With the release of the electronic flight display (EFD) system, conventional instruments have been replaced by multiple liquid crystal display (LCD) screens
    • The first screen is installed in front of the pilot position and is referred to as the primary flight display (PFD)
    • The second screen, positioned approximately in the center of the instrument panel, is referred to as the multi-function display (MFD)
  • These solid state instruments have a failure rate far less than those of conventional analog instrumentation. [Figure 3-18]
  • With today's improvements in avionics and the introduction of EFDs, pilots at any level of experience need an astute knowledge of the onboard flight control systems, as well as an understanding of how automation melds with Aeronautical Decision-Making (ADM)

  • Training for avionics:

    • Companies often create simulators which can be downloaded on their websites:
  • Whether an aircraft has analog or digital (glass) instruments, the instrumentation falls into three different categories:
    • Performance
    • Control
    • Navigation
  • Airspeed Indicator
    Performance Instruments
  • Airspeed Indicator
    Performance Instruments

  • Performance Instruments:

    • The performance instruments indicate the aircraft's actual performance. Performance is determined by reference to the altimeter, airspeed or vertical speed indicator (VSI), heading indicator, and turn-and-slip indicator. The performance instruments directly reflect the performance the aircraft is achieving. The speed of the aircraft can be referenced on the airspeed indicator. The altitude can be referenced on the altimeter. The aircraft's climb performance can be determined by referencing the VSI. Other performance instruments available are the heading indicator, angle of attack indicator, and the slip-skid indicator [Figure 2]
  • Airspeed Indicator
    Control Instruments
  • Airspeed Indicator
    Control Instruments

  • Control Instruments:

    • The control instruments display immediate attitude and power changes and are calibrated to permit adjustments in precise increments. The instrument for attitude display is the attitude indicator. The control instruments do not indicate aircraft speed or altitude. In order to determine these variables and others, a pilot must reference the performance instruments [Figure 3]

Avionics Frequencies

Avionics Frequencies
  • The 960-1164 MHz band is part of the 960-1215 MHz band allocated on a primary basis to the Federal Government for the aeronautical radionavigation service (ARNS)
  • The Federal Aviation Administration (FAA) domestically manages the 960-1164 MHz band
  • Ground-based and airborne systems that operate in this band control civilian and military aircraft in the National Air Space (NAS)
  • The Distance Measuring Equipment (DME) system and its military version, the Tactical Air Navigation (TACAN) system operates throughout the band
  • The Air Traffic Control Radar Beacon System (ATCRBS) and the Mode Select (Mode S) system have a ground-based and airborne component and operate on the frequencies of 1030 MHz and 1090 MHz
  • Identification Friend or Foe (IFF) system is the primary positive means of aircraft identification in air defense operations
  • An IFF transponder receives interrogation pulses at one frequency (1030 MHz), and sends the reply pulses at a different frequency (1090 MHz)
  • Proper use of IFF facilitates rapid engagement of enemy aircraft, conserves air defense assets, and reduces risk to friendly aircraft
  • The Traffic Alert and Collision Avoidance System (TCAS) operates at 1030 and 1090 MHz and is independent of any ground system
  • The International Telecommunication Union 2007 World Radiocommunication Conference allocated the band 960-1164 MHz to aeronautical mobile (route) service (AM(R)S)
  • The Automatic Dependent Surveillance-Broadcast (ADS-B) system and the Universal Access Transceiver (UAT) operate on the frequencies of 978 MHz and 1090 MHz
  • In addition to the ARNS and AM(R)S systems, the Department of Defense (DOD) operates a communication system, the Joint Tactical Information Distribution System (JTIDS) in this band on a coordinated basis

Conclusion

Conclusion
  • Avionics are tools, not crutches
  • While very useful, they can be rendered less so by not maintaing software versions or obstruction databases
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References

References