ss. METAR, ICAO Routine Aviation Weather Report tt. MFD, Multifunction Flight Display uu. ND, Navigation Display vv. NOM, Nominal ww. PFD, Primary Flight Display xx. PFI, Primary Flight Information yy. POH, Pilot's Operating Handbook zz. RAIM, Receiver Autonomous Integrity Monitoring (used with GPS) aaa. RT, Right bbb. SAE, Society of Automotive Engineers ccc. STC, Supplemental Type Certificate ddd. SVS, Synthetic Vision Systems eee. TAS, Traffic Advisory System fff. TAWS, Terrain Awareness Warning System ggg. TFR, Temporary Flight Restrictions hhh. TC, Type Certificate iii. TCAS, Traffic Alert and Collision Avoidance System jjj. TSO, Technical Standard Order kkk. UL, Underwriter’s Laboratories lll. VOR, Very High Frequency Omni-Directional Range mmm. VFR, Visual Flight Rules nnn. VMC, Visual Meteorological Conditions ooo. VFE, Maximum flap extended speed 11
ppp. VMO, Maximum operating limit speed qqq. VNE, Never-exceed speed rrr. VNO, Maximum structural cruising speed sss. VS0, The stalling speed or the minimum steady flight speed in the landing configuration ttt. VS1, The stalling speed or the minimum steady flight speed obtained in a specific configuration uuu. WAAS, Wide Area Augmentation System
6.2 Definitions. This section contains definitions for terms in this document.
a. Accuracy: A degree of conformance between the estimated or measured value and the true value.
b. Adverse Operating Condition: A set of environmental or operational circumstances applicable to the airplane, combined with a failure or other emergency situation, that results in a significant increase in normal flight crew workload.
c. Component: Any self-contained part, combination of parts, subassemblies, or units that perform a distinct function necessary to the operation of the system.
d. Continued Safe Flight and Landing: This phrase means the airplane can continue controlled flight and landing, possibly using emergency procedures, without requiring exceptional pilot skill or strength. On landing, some airplane damage may occur as a result of a Failure Condition.
e. Conventional: A system is considered “Conventional” if its function, the technological means to implement its function, and its intended use are all the same as, or closely similar to, that of previously approved systems that are commonly used. The systems that have established an adequate service history and the means of compliance for approval are generally accepted as "Conventional."
f. Critical: Usually a function whose loss would prevent the continued safe flight and landing of the airplane.
Note: The term “critical function” is associated with a catastrophic failure condition.
Newer documents may not refer specifically to the term “critical function.”
g. Criticality: Indication of the hazard level associated with a function, hardware, software, etc., considering abnormal behavior (of this function, hardware, software, etc.) alone, in 12
combination, or in combination with external events. Criticality is a failure classification that could be no safety effect, minor, major, hazardous, and catastrophic. See AC 23.1309-1E for more guidance.
h. Design-Eye Box: A three-dimensional volume of space surrounding the design eye reference point that designers and evaluators use to determine the acceptability of display and control locations.
i. Design-Eye Reference Point: A single reference point in space selected by the designer where the midpoint between the pilot’s eyes is assumed to be located when the pilot is properly seated at the pilot’s station.
j. Development Assurance: All those planned and systematic actions used to substantiate, to an adequate level of confidence, that errors in requirements, design, and implementation have been identified and corrected such that the system satisfies the applicable certification basis.
k. Enhanced Vision System: An electronic means to provide a display of the forward external scene topography (the natural or manmade features of a place or region especially in a way to show their relative positions and elevation) through the use of imaging sensors, such as a forward looking infrared, millimeter wave radiometry, millimeter wave radar, low light level image intensifying.
l. Equipment Essential to Safe Operation: Equipment installed to comply with the applicable certification requirements of 14 CFR part 23 or operational requirements of 14 CFR parts 91 and 135.
m. Error: An omitted or incorrect action by a pilot or maintenance person, or a mistake in requirements, design, or implementation.
n. Failure: An occurrence that affects the operation of a component, part, or element such that it can no longer function as intended (this includes both loss of function and malfunction.
o. Failure Condition: A condition affecting either the airplane or its occupants, or both, either direct or consequential, caused or contributed to by one or more failures or errors considering flight phase and relevant adverse operational or environmental conditions or external events.
Failure conditions may be classified according to their severity. See AC 23.1309-1E for more information on definitions of failure conditions.
p. Field-of-View: The angular extent of the display that can be seen by either pilot with the pilot seated at the pilot’s station. See section 15 for more information on the field-of view.
q. Fix: A generic name for a geographical position. A fix may also be referred to as a waypoint, intersection, reporting point, etc.
r. Flight Plan: Refers to any sequence of fixes that are interconnected by the desired path. Flight plans may range from the simplest that include only the aircraft’s present position, the active waypoint, and the desired path between them, to more complicated plans that include departure and destination airports with multiple intermediate fixes.
s. Function: The lowest defined level of a specific action of a system, equipment, and pilot performance aboard the airplane that, by itself, provides a complete recognizable operational capability (for example, an airplane heading is a function). One or more systems may contain a specific function or one system may contain multiple functions.
t. Functional Hazard Assessment: A systematic, comprehensive examination of airplane and system functions to identify potential minor, major, hazardous, and catastrophic failure conditions that may arise as a result of a malfunction or a failure to function.
u. Hardware: An object that has physical being. Generally refers to circuit cards, power supplies, etc.
v. Hazard: Any condition that compromises the overall safety of the airplane or that significantly reduces the ability of the pilot to cope with adverse operating conditions.
w. Head-Up Display: A transparent optical display system located level with and between the pilot and the forward windscreen. The HUD displays a combination of control, performance, navigation, and command information superimposed on the external field of view. It includes the display element, sensors, computers, and power supplies, indications and controls. It is integrated with airborne attitude, air data and navigation systems, and as a display of command information is considered a component of the flight guidance system.
x. Independent: A component, part, element, or system that is not relying on some other component, part, element, or system for accomplishing its function. This design concept ensures that the failure of one item does not cause a failure of another item. For redundancy, each means of accomplishing the same function need not necessarily be identical.
y. Indicator: A means for displaying information of a parameter. More than one indicator could be depicted on one display. Fo r example, a primary flight display may have indicators for attitude, altitude, airspeed, heading, and navigation.
z. Instrument: An electrical or mechanical measurement device. In § 23.1311 it is defined as: Devices physically contained in one unit and devices composed of two or more physically separate units or components connected together. (One example is a remote indicating gyroscopic direction indicator that includes a magnetic sensing element, a gyroscopic unit, an amplifier, and an indicator connected together.)
aa. Map Orientation: Refers to the rule that determines the directional relation of the map to the upper part of the display depiction. Using a north-up rule, the north side of the map would be toward the top of the display and the south side of the map would be at the bottom. Using 14
a desired path-up rule, the map would be oriented so the desired path would be vertical on the map and pointing straight up toward the top of the display.
bb. Map Range: The geographic extent of the map region (for example, the distance covered by the map representation in either the vertical or horizontal direction).
cc. Malfunction: Failure of a system, subsystem, unit, or part to operate in the normal or usual manner. A condition whereby the operation is outside specified limits.
dd. Multi-Function Display: Any physical display unit, other than the PFD, used to present various information, on which the layout may be reconfigured.
ee. Navigation: The process of planning, tracking, and controlling the course of an airplane from one place to another.
ff. Navigation Display: The display or suite of instruments by which navigation data is presented to the pilot.
gg. Navigation Information: Information that aids the flightcrew in determining the aircraft’s location in a given environment (for example, on flight plans, VORs, GPSs, features on the airport surface including taxiway, signage, etc.).
hh. Primary: As used for instruments, it is defined in § 23.1311(c) as the “display of a parameter that is located in the instrument panel such that the pilot looks at it first when wanting to view that parameter.”
ii. Primary Flight Display (PFD): A single physical unit that always provides the primary display of all the following: altitude, airspeed, aircraft heading (direction) and attitude located directly in front of the pilot in a fixed layout in accordance with § 23.1321. It may provide other information pertinent to guidance and fundamental control of flight of the airplane, such as critical engine parameters.
jj. Primary Flight Information (PFI): A PFI refers to those functions or parameters required by the airworthiness and operational rules, such as airspeed, altitude, attitude, and heading (direction), that are on the PFD.
kk. Primary Function (PF): This definition is applicable in the case when there is more than one function available for same function. A function that is installed to comply with the applicable regulations for the required function, and one that provides the most pertinent controls or information instantly and directly to the pilot. For example, the PFD is a single physical unit that always provides the primary display and it complies with the requirements of all the following:
altitude, airspeed, aircraft heading (direction) and attitude. This PFD is located directly in front of the pilot and used instantly and first by the pilot. A standby (additional) PFD that is intended to be used in the event of failure of the PFD is an example of a secondary system.
ll. Primary Navigation: Where the pilot looks first for a display of navigation information such as on an HSI or CDI. It displays vertical and lateral deviation and it may have the digital distance indication to/from the selected fix.
mm. Redundancy: The presence of more than one independent means for accomplishing a given function. Each means of accomplishing the function need not necessarily be identical.
nn. Reversionary Display: A secondary means to provide information initially presented on the PFD or MFD by the transfer of information to an alternate display.
oo. Scale: The relative proportion of the linear dimensions of objects on a display to the dimensions of the corresponding objects and distances being represented (for example, 1 inch = 100 nautical miles).
pp. Secondary Display: A means to present information on another display. A display that can be used for backup or secondary purposes, such as in the event of a failure of another display.
qq. Standby Instrument: A dedicated instrument that is always available that presents primary flight information.
rr. Supplemental Function: A function that is not required or intended to meet all the airworthiness and operational requirements. It is usually installed for additional situational awareness.
ss. System: A combination of components, parts, and elements that is interconnected to perform one or more functions.
tt. Synthetic Vision System: A computer-generated image of the external scene topography from the perspective of the flight deck that is derived from aircraft attitude, high precision navigation solution, and database of terrain, obstacles and relevant cultural features.
Note: “Topography” defined as maps or charts of natural and man-made features of a place or region especially in a way to show their relative positions and elevations, as applicable whenever deemed appropriate and practicable.
uu. Track: The projection on the earth’s surface of the path of an aircraft, the direction of which is usually expressed in degrees from north (true, magnetic, or grid). A track is the actual flight path of an aircraft over the surface of the earth.
Note: For more definitions related to safety assessments, refer to AC 23.1309-1E for the appropriate definitions.
vv. Warning. A clear and unambiguous indication to the pilot of a failure that requires immediate corrective action. An inherent characteristic of the airplane or a device that will give 16
clearly distinguishable indications of malfunction or misleading information may provide this warning.
7.0 Display Description. The following paragraphs give a brief description of an electronic display. They do not cover all the capabilities and details of these displays or the information presented on them.
7.1 General. Electronic displays have replaced many of the traditional electromechanical and analog instruments. These displays also augment and/or combine the functionality of conventional systems, such as radios and navigational systems. The major display technologies now used are multicolor CRTs, LCDs, electro luminescence, plasma, and LEDs. The initial electronic displays mimicked the traditional mechanical and electromechanical flight and powerplant instruments. The colors, symbols, and formats on these initial electronic displays are similar to those on traditional conventional instruments. Modern electronic displays provide integration and formats that often differ from traditional instruments.
7.2 Display Configuration. Electronic displays may be installed in several configurations. A basic electronic display may provide only one flight or powerplant parameter, while more sophisticated systems integrate many parameters on one electronic display. One of the major design goals for these systems is eliminating separate conventional gauges, instruments, and annunciators. Recent installations show a trend toward a higher degree of integration. For example, an integrated primary flight display provides several parameters such as attitude, heading (direction), airspeed, and altitude. Integration of various systems should include analysis to ensure that complexity and workload are compatible with general aviation pilots' capabilities. For more guidance on IMA that implement TSO authorized hardware elements, see TSO-C153 and AC 20
170.
8.0 Flight Displays.
8.1 Instrument Requirements.
a. Sections 23.1303, 23.1305, 23.1311, and 23.1321, with the applicable operating rules (14 CFR parts 91, 121, and 135), incorporate flight and powerplant instrument requirements for part 23 airplanes. The navigation equipment requirements are given in operational rules specified in §§ 91.205, 121.303, 121.305, 121.307, 135.143, 135.149, 135.159, 135.161, and 135.165. Display requirements for navigation information are dependent on the navigation system installed in the aircraft. Instruments and equipment required for flights under parts 91, 121, and 135 may be affected by the electronic display installation. These instruments and equipment include:
gyroscopic bank and pitch, gyroscopic direction, gyroscopic rate-of-turn, slip-skid instruments, and other required communication and navigational equipment.
b. There have been applications to install equipment, such as flight and navigation displays, as non-required. These applications request approval for these installations as situation awareness (SA) only. It is not acceptable to label a display as “SA-Only” and assume that its failure condition is acceptable. Installing displays that provide PFI that are more compelling than 17
the required primary PFI displays, but they do not meet the appropriate operational and airworthiness requirements, and labeling them as “Supplemental” or “SA-Only" is not acceptable.
Section 13.6 provides more guidance.
c. The basis for certification has been that the equipment should perform its intended function and not present a hazard. Instruments that aid situation awareness should be certified under the part 23 requirements, including § 23.1301 and § 23.1309. These displays could provide hazardous misleading information. PFI is essential for safe operation. An instrument that provides PFI should meet the minimum standards of applicable TSOs or an equivalent standard. It also should meet the guidance in AC 23.1309-1E, AC 23-17C, and the guidance in this AC.
8.2 Primary Flight Information (PFI). PFI refers to those functions or parameters that are required by the airworthiness and operational rules, such as airspeed, altitude, attitude, and heading (direction). It may provide other information pertinent to guidance and fundamental control of flight, such as critical engine parameters. Attitude, airspeed, altitude, and heading (direction) are the PFI required in § 23.1311(a)(3) and (5), and they must be arranged according to § 23.1321 in the “basic T” arrangement. Direction should be heading with track presented, if available as a selectable option. The horizon reference line on the PFD should be at least 3.25 inches wide in straight and level flight for integrated displays. This recommendation is not intended to prevent replacement of mechanical instruments with an electronic display of a similar horizon reference line. When the true horizon is no longer on the display, the artificial horizon line should provide a distinctive demarcation between sky and ground (or the background). Display of PFI on reversionary or standby displays should be arranged in the basic T-configuration, but it is not required. The standby instrument or displays of PFI location should meet the FOV guidance criteria in section 15.
8.2.1 Acceptable Methods for Compliance with § 23.1311(b). There are three acceptable methods for meeting the attitude requirements which is considered information essential for continued safe flight and landing. Compliance can be accomplished by using dedicated standby instruments, dual PFDs, or reversionary displays that present primary flight information. Electronic display systems without dedicated standby instruments should have at least two independent displays able to provide PFI to the pilot. These displays should be powered such that any single failure of the power generation and distribution systems cannot remove the display of PFI from both displays. Section 23.1311(b) in Amendment 23-62 st ates: “The electronic display indicators, including their systems and installations, and considering other airplane systems, must be designed so that one display of information essential for continued safe flight and landing will be available within one second to the crew by a single pilot action or by automatic means for continued safe operation, after any single failure or probable combination of failures.”
8.3 Standby Instruments. The purpose of standby instruments or another independent PFD is to ensure that PFI is available to the pilot during all phases of flight and during system failures.
Individual indicators should be a minimum of 2 inches in diameter or, if combined, a minimum diameter of 3 inches (or equivalent) displayed.
8.3.1 Dual PFDs. Electronic display systems with dual PFDs should incorporate dual, independently powered sensors that provide primary flight parameters such as AHRS with 18
comparators and dual ADC. Dual PFDs with dual AHRSs and ADCs, which include checking and are powered by multiple power sources and distribution systems, are significantly more reliable than presently certified mechanical systems.
8.3.2 PFD and Autopilot with an AHRS. For normal operation, when using a single AHRS to drive the PFD and the autopilot simultaneously, the installation must mitigate hazardous or catastrophic system level failures. An example configuration supporting proper mitigation would include all of the following:
a. A dedicated standby attitude instrument within the primary maximum FOV or independent reversionary attitude display.
b. An AHRS with appropriate comparator or monitor of equivalent performance.
c. Appropriate system warning/caution annunciation associated with an AHRS malfunction.
d. If an aircraft is equipped with multiple AHRS, it may be acceptable, when one AHRS fails, to drive both the autopilot and the PFD from a single AHRS as long as an AHRS independent attitude display (required for some aircraft classes) is located in the primary maximum field of view. The failure must be annunciated to the pilot, and the pilot must be able to select the non-failed AHRS. For aircraft that do not have an independent attitude indicator, when one AHRS fails, the autopilot should be manually or automatically disengaged. The autopilot may be reengaged if appropriate mitigation is available (for example, see a. through c. above). The AFM or supplemental AFM should contain the appropriate procedures applicable to the equipment installed. See section 11.0 for additional guidance. AC 23.1309-1E guidance should be considered for these configurations.
e. Displays not meeting FOV guidance criteria may require additional human factors airworthiness evaluation by the certification authority. See section 15 for additional guidance.
8.4 Reversionary Flight Displays Instead of Standby Instruments or Dual PFDs.
8.4.1 General Requirements.
a. Reversionary flight displays provide a secondary means to provide PFI through alternate display formats on another PFD or MFD by the transfer of information to an alternate display or by some other means. The function of an MFD system is to provide the pilot access to various data, or combinations of data, used to fly the aircraft, to navigate, to communicate, and/or to manage aircraft systems. The MFD would also present PFI as needed to ensure continuity of operations. 14 CFR part 23, § 23.1311(b), Amendm ent 23-62, states the electronic display indicators, including their systems and installations, and considering other airplane systems, must be designed so that one display of information essential for continued safe flight and landing will be available within one second to the crew by a single pilot action or by automatic means for continued 19
safe operation, after any single failure or probable combination of failures. To meet the requirements of § 23.1311(b), a full-time standby display, another independent PFD, or an independent reversionary attitude display, must be installed. Reversionary modes could be automatically and manually selected or only manually selected.
b. Reversionary configurations are significantly more reliable than presently certified mechanical systems, and the skills required while flying in reversionary mode are identical with those used when flying in primary mode. Traditional external standby flight instruments (either electronic or mechanical) offer potential safety problems associated with delay in pilot reaction. The pilot may delay a decision to transition to standby instruments and to transition to partial panel techniques, as opposed to the simple action the pilot would take to switch displays. A nearly identical format on the reversionary display of all PFI that is also shown on the PFD provides a significant safety enhancement over standby instruments. This is especially true when the size, location, arrangement, and information provided by the standby instruments are significantly different from those on the PFD.
c. Reversionary display modes should provide consistent display formats to the PFD. The reversionary flight information should be presented by an independent source and display to prevent complete loss of PFI due to a single failure. The reversionary configuration should have two independent displays that incorporate dual-independently powered AHRS and dual ADC subsystems that provide PFIs. The reversionary system response time should provide flight critical information on the MFD in less than one second after a single pilot action or an automatic operation.
d. A reversionary configuration should have a single pilot action that would force both the PFD and MFD displays into reversionary mode operation. However, the PFI should be presented in similar format and sufficient size in the reversionary mode as it is in normal mode to allow the pilot to enhance the control of the airplane. This reversionary configuration should provide backup information essential to continued safe flight and landing with an intuitive control that allows instant, simultaneous access to reversionary mode on both the PFD and MFD displays.
The single pilot action should be easily recognized, readily accessible, and have the control within the pilot’s primary optimum field of view. An acceptable method for the single pilot action is the red color and/or lighted red “halo” ring that announces its position on the panel at all times.
8.4.2 Reversionary Methods.
a. One method is to have an automatic reversionary display with a single pilot action that would force both the PFD and MFD displays into reversionary mode operation. If PFI on another display is not provided, provide automatic switching to ensure PFI is available to the pilot. Automatic reversion must provide a complete display of PFI on the remaining display within one second if a fault is detected.
b. Most possible faults should be covered by this automatic reversionary capability. Only a total loss of the display may not be reliably detected automatically, but such a failure condition would be obvious to the pilot. Faults that result in automatic switching should be extensive enough to ensure PFI availability meets the requirements of § 23.1309. If such a 20
malfunction occurs, a single pilot action should provide a full display of the essential information on the remaining display within one second. All modes, sources, frequencies, flight plan data, etc., should be similar as they were on the PFD before the failure.
c. Another reversionary method would include a means to access the reversionary mode manually through a single pilot action. Manual activation of the reversionary mode on the MFD through single action by the pilot is acceptable when procedures to activate the PFI on the MFD are accomplished before entering critical phases of flight. The PFI would be presented continuously on the reversionary display during critical phases of flight (for example, takeoff, landing, and missed or final approach).
8.5 Display of Attitude. For flights under IFR conditions in part 91 and part 135 operations, and under VFR at night for part 135 operations, attitude information is required. The loss of all attitude information or the presentation of misleading attitude information could result in a catastrophic failure condition where the pilot could not continue safe flight and landing of the airplane. It is recommended that the display of attitude follows the guidelines (below) that are also in GAMA Publication #12.
a. The pitch ladder should be caged to the center of the display.
b. At pitch attitudes when the true horizon line would not normally be displayed, some sky or ground should be indicated on the PFD pitch display (minimum 3/8 inches and maximum of
11.5 percent of the display), and the horizon line should indicate off-scale.
c. With the airplane symbol on the horizon line, the range of visible pitch attitude should be at least + 25 to -15 degrees, but not to exceed a total pitch range of 50 degrees.
d. Bank angle presentations should use a roll pointer; however, roll pointers and skypointers should not be mixed in the same flight deck/cockpit.
e. Roll scale indices should be placed at 10, 20, 30, 60, and 90 degrees. An index may also be placed at 45 degrees.
8.6 Display of Direction (Heading or Track).
8.6.1 General.
a. The loss of direction (heading or track) information could result in reduced capability of the pilot to cope with adverse operating conditions. The orientation of any secondary navigation display is optional (for example, Track-up, North-up, Heading-Up). For flights under IFR conditions, a stabilized heading indicator must provide the primary display of the direction parameter. A magnetic direction indicator or track may provide the reversionary display of direction.
b. The heading display should provide a clear and unmistakable display of aircraft symbol and heading. HSI should provide a clear and unmistakable display of aircraft position, heading, and track (an option, if available) relative to the desired course/track. Section 17 contains more guidance on symbology. Direction should be heading when track is presented, if available as a selectable option, with the data source clearly indicated. On the primary display, the heading scale should have a mode that presents at least 120 degrees of arc. Other display formats may be acceptable and have been previously approved, but they need to be evaluated from a human factor perspective.
8.6.2 Hazardous Misleading Heading Information.
a. The FHA for the failure effects of hazardous misleading heading information from an AHRS is clarified in AC 23-17C. This policy is specifically about the application of AC
23.1309-1E for an airplane with the certification basis of Amendments 23-41 or later. This clarification is limited to installations approved for operation in IMC under IFR. For operations limited to VFR, a misleading heading indication is not considered hazardous.
b. Develop an FHA, and the related safety assessments, for the specific airplane type and configuration since there can be many combinations of failures, various mitigating factors, and other functions available to a pilot. These many factors affect the criticality of the heading indication; therefore, use a safety assessment process from AC 23.1309-1E to classify the failure conditions for misleading heading information.
c. A hazardously misleading heading is usually when the accuracy error is greater than 10 degrees on the primary heading instrument and it is an undetected error. The safety assessment process should consider appropriate mitigating factors. For Class I part 23 airplanes, the failure condition for misleading hazardous heading is usually considered major.
8.7 Display of Altitude, Airspeed, and Magnetic Compass Information. The original requirements of CAR 3 were adopted and later recodified into part 23, § 23.1303, paragraphs (a),
(b), and (c). At that time, pneumatically driven displays provided airspeed and altitude functions.
Since then, the FAA envisioned airspeed, altitude, and magnetic compass information would remain available to the pilot with the loss of the airplane's primary electrical power. For electronic displays, § 23.1311(a)(3) requires the primary display of attitude, airspeed, and altitude to be uninhibited in any normal mode of operation. Section 23.1311(a)(5), as amended by Amendment 23-62, requires an independent magnetic direction indicator and either an independent secondary mechanical altimeter, airspeed indicator, and attitude instrument or electronic display parameters for the altitude, airspeed, and attitude that are independent from the airplane's primary electrical power system. Primary altitude or airspeed displays that require electrical power are acceptable if means are provided for their continued operation upon loss of the airplane’s primary electrical power, or if pneumatically driven instruments are available for the pilot’s use. A standby or reversionary integrated display of altitude, attitude, and airspeed, instead of individual electronic display indicators for airspeed altitude and attitude, is acceptable under one condition. The condition is that the standby or reversionary integrated display and the primary display are powered such that at least one integrated display with attitude, altitude, and airspeed is available after failure of any power source or distribution path.