Avionics & Instruments


  • 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.

User Reports Requested on NAVAID or Global Navigation Satellite System (GNSS) Performance or Interference:

  • 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
  • In addition, 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 GNSS receivers
    • This type of disruption could result in un-flagged, 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 for identification of these disruptions and detect unexpected aircraft position while monitoring aircraft for IFR separation
  • Pilots reporting potential interference should identify the NAVAID (for example, VOR) malfunction or GNSS problem, location of the aircraft (that is, latitude, longitude or bearing/distance from a reference NAVAID), magnetic heading, altitude, date and time of the observation, type of aircraft (make/model/call sign), and description of the condition observed, and the type of receivers in use (that is, make/model/software revision)
  • GNSS problems are often characterized by navigation degradation or service loss indications
  • Reports can be made in any of the following ways:

    1. Immediately, by voice radio communication to the controlling ATC Facility or FSS
    2. By telephone to the nearest ATC facility controlling the airspace where the disruption was experienced
    3. Additionally, GNSS problems may be reported by Internet via the GPS Anomaly Reporting Form at
  • In aircraft equipped with more than one avionics receiver, there are many combinations of potential interference between units that could cause erroneous navigation indications, or complete or partial blanking out of the display
    • GPS interference or outages associated with known testing NOTAMs should not be reported to ATC
Airspeed Indicator
Airspeed Indicator

Basic Six Pack:


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
    Figure 1: Performance Instruments
    Airspeed Indicator
    Figure 1: 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 1]
  • Airspeed Indicator
    Figure 2: Control Instruments
    Airspeed Indicator
    Figure 2: 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 1]
  • Navigation Instruments:

    • The navigation instruments indicate the position of the aircraft in relation to a selected navigation facility or fix. This group of instruments includes various types of course indicators, range indicators, glideslope indicators, and bearing pointers. Newer aircraft with more technologically advanced instrumentation provide blended information, giving the pilot more accurate positional information. Navigation instruments are comprised of indicators that display GPS, very high frequency (VHF) omni-directional radio range (VOR), nondirectional beacon (NDB), and instrument landing system (ILS) information. The instruments indicate the position of the aircraft relative to a selected navigation facility or fix. They also provide pilotage information so the aircraft can be maneuvered to keep it on a predetermined path. The pilotage information can be in either two or three dimensions relative to the ground-based or space-based navigation information. [Figures 3-21 and 3-22]