AC 27-1B, Chg 7 2/4/2016 Independent: A component, part, element, or system that does not rely on another 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.
Indicator: A means for displaying information of a parameter. One display could depict more than one indicator. For example, a primary flight display may have indicators for attitude, altitude, airspeed, heading, and navigation.
Integrated Modular Avionics (IMA): Both AC 20-170 and RTCA Document DO-297 provide the following definition of an IMA system:
Shared set of flexible, reusable, and interoperable hardware and software resources that, when integrated, form a platform that provides services. These services are designed and verified to a defined set of safety and performance requirements, to host applications performing aircraft functions."
Instrument: A device that is physically contained in one unit, or a device 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).
Map Orientation: The relationship between the directions on a map to the compass depiction. Thus, using a North-up depiction, 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 a track-up depiction, the map would be oriented so that the aircraft's track would be vertical on the map and pointing straight up toward the top of the display.
Map Range: The geographic extent of the map region (for example, the distance covered by the map representation in either the vertical or the horizontal direction).
Multifunction Flight Display (MFD): Any physical display unit, other than the PFD, with a reconfigurable layout that presents a variety of information.
Navigation: The process of planning, recording, and controlling the movement of an aircraft from one place to another.
Navigation Display: A suite of instruments that shows navigation data to the pilot.
Navigation Information: Information that aids the flightcrew in determining the aircraft's location in a given environment (for example, with respect to flight plans, VORS, NDBs, features on the
- Primary Display: As defined in § 23.1311(c) when used for instruments, it is "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."
Primary Flight Display (PFD): A single physical unit that always provides the primary display of all of the following: altitude, airspeed, aircraft heading (direction), and attitude located directly in front of the pilot in a fixed layout in accordance with § 27.1321. It may include primary navigation information in a navigation section of the same display such as an HSI, navigation source and waypoint data, wind vector, and other basic navigation data. It may also provide other information pertinent to guidance and fundamental control of flight of the aircraft, such as engagement of flight guidance mode, flight director cueing, or other information.
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- Primary Flight Information (PFI): Functions or parameters, such as airspeed, altitude, attitude, and heading (direction), required by the airworthiness and operational regulations.
- Primary Function: An installed feature that provides the most pertinent controls or information instantly and directly to the pilot.
Primary Navigation Display: Display containing the most critical navigation information, such as on an HSI or CDI. It has the capability of displaying vertical and lateral deviation and may have the digital distance indication to/from the selected fix.
Redundancy: The presence of more than one independent means for accomplishing a given function.
Reversionary Display: A secondary means to provide information initially presented on the PFD or MFD by the transfer of information to an alternate display, usually as the result of a failure of a primary display.
Reverse Video (Inverse Video): Visual alert or status indication presented with the inverse of the normally displayed alert. For example, for a visual alert normally displayed with yellow letters on black background, the "reverse video" presentation would be a yellow background with black letters.
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).
Secondary Display: A means to provide display of information on a display other than the Primary Display.
Standby Instrument: A dedicated instrument that is always available, which presents primary flight information.
- Supplemental: Any additional function beyond those operationally required.
System: A combination of components, parts, and elements that are interconnected to perform one or more functions.
- Synthetic Vision System: A system used to create a synthetic image representing the environment external to the aircraft. An image display based entirely or partially on an internal database carried on the aircraft.
- Time-Critical Warning: The highest level of warning for conditions that require immediate flight crew response to maintain the immediate safe operation of the aircraft. Examples of Time-Critical warnings are:
• Overspeed Warnings.
• Low Energy Warnings.
• Helicopter Terrain Awareness Warnings (HTAWS).
• TCAS Resolution Advisory.
• Predictive and Reactive Windshear Warnings.
- Track: The flight path of an aircraft over the surface of the earth, also known as true course.
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AC 27-1B, Chg 7 2/4/2016 Note: For additional definitions related to safety assessments, refer to section 27.1309 and MG 21 (FHA) of this AC.
c. Display Description.
(1) General.
(i) EDS displays and installations range from individual representations of ADI and HSI to fully integrated display suites combining primary flight and navigation information on a single display, a PFD and powerplant/system information on another display, or EICAS display. The flexibility allowed by the technology provides display designers wide latitude in how and where to display information to the pilot. Other displays or MFD of supplementary information may also be included in the installation.
(ii) The display layout and format of information may range from digitally rendered representations of conventional "round-dial" electromechanical gauges and instruments to tape displays to hybrid "round-dial" representations. Regardless of the format, the information displayed must be easily accessible and understandable by the pilot.
(iii) Retrofitting EDSs into existing "round-dial" or analog cockpits can create challenges due to interfaces with previously installed avionics and autopilot systems. There should be an evaluation of these installations to ensure the pilot-system interface does not increase or significantly change the focus of pilot workload in order to manage and operate the system.
(iv) EDSs have the capability to combine the display of multiple flight, navigation, and powerplant parameters on to a single display, resulting in the loss of independence provided by individual gauges or instruments. As a result, considerations regarding loss of required information must account for a possible single failure leading to the loss of all flight, navigation, or powerplant information on a display.
(2) Basic flight and navigation information.
(i) 14 CFR 27.1303 and Appendix B to part 27 define required flight and navigation instruments.
(il) Flight Instruments: There are different instrument requirements for VFR and IFR rotorcraft (see Appendix B to part 27, VIll). Consult operational regulations (e.g., parts 91 and 135) for any additional flight instrument requirements. Flight instruments that are not required by § 27.1303 but are installed to satisfy either an operational requirement or to enhance safe operation of the rotorcraft should be located as close as possible to the pilots' center line of vision. For example, radar altimeters should be installed where pilots can easily incorporate the gauge into their airspeed and altitude scan. Placing a radar altimeter or other flight instruments at the maximum extent of the pilots' secondary field of view makes the instrument difficult to incorporate into an efficient scan and increases pilots' workload.
(ili) Navigation information.
(A) The display of navigation information can be either on the PFD or on an EHSI.
Supplemental navigation information, such as moving maps, can be displayed on MFDs. However, the EHSI or PFD should provide the pilot with course and heading adherence, coupled with the information required for the pilot to attain and maintain awareness of the rotorcraft's position relative to navigation (B) Navigation equipment requirements are also given in operational rules (For example, §§ 91.205 and 135.143). Display requirements for navigation information depend on which navigation system is installed in the rotorcraft. Electronic display installations may affect the instruments and equipment required for flights under part 91 and part 135. These instruments and equipment include Page MG 19 -12
gyroscopic bank and pitch, gyroscopic direction, gyroscopic rate-of-turn, slip-skid instruments, and other required communication and navigational equipment.
(iv) Arrangement and visibility of primary flight and navigation information. Place the primary flight and navigation information in the pilot's primary field of view. Figure AC 27 MG 19-1 illustrates the primary field of view. Due to rotorcraft instrument panel design, the display of some information may be located below -15° and will need flight evaluation to confirm that pilots can see the information easily without extensive eye movements.
LT 15 CYL UP Horiz 15 ° +15 ° RT Horizontal Vertical •15 ° → NOM DN Figure AC 27 MG 19-1 Primary Field of View
(3) Powerplant.
(1) 14 CFR 27.1305 defines the powerplant and associated instruments information that should be displayed continuously.
(ii) Powerplant indicators and information necessary to set and monitor power should display in the pilot's primary field of view (Figure AC 27 MG 19-1).
(ili) However, the required powerplant information and indications that show engine health and ability to produce power (e.g., oil temperature and pressure) can be displayed in the pilot's secondary field of view, depicted in Figure AC 27 MG 19-2. Position this information within the secondary field of view where pilots can easily see it during their routine scans. A cross-cockpit location may not be acceptable, depending on cockpit and instrument panel width.
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AC 27-1B, Chg 7 2/4/2016 UP LT Horizontal Vertical 30° 40 Horiz 30° 15° 20 ° → RT NOM DN Figure AC 27 MG 19-2 Secondary Field of View
(4) System.
(i) Electrical system information required by § 27.1351 and other system information, like integrated caution and warning messaging that may be included in an EICAS display, may also be displayed in the secondary field of view.
(ii) EDSs provide the ability to present system information on separate pages of a display.
System architecture should not allow deselecting of the PFD, thereby not allowing access to system pages on MFDs.
(ili) The EDS design should inhibit access to configuration and maintenance pages in flight.
However, pilots should have access to all information they need to perform their normal and any nonnormal procedures.
(iv) The EDS design and installation should inhibit any pilot or manually initiated built-in-test of the EDS in-flight.
d. Display of Information.
(1) Format.
(i) See SAE ARP 4102-7 for examples of display formats. If new or novel formats are developed, coordinate with the certificating authority early in the certification project. Issue papers and, possibly, equivalent level of satety findings may be required.
(ii) Information format should allow the pilot quick access to the information presented without confusion or concentration. The format of the information is influenced by the type of information it should relay to the pilot.
(A) There needs to be graphical display of parameters for information containing rate or that can be dynamic in nature. Additionally, graphical display of parameters provides both discrete and spatial information to the pilot. It shows the pilot where the parameter is relative to limits as well as the specific value. Additionally, graphical displays allow the pilot to see changes spatially, as opposed to relying on remembering a numerical value and comparing it to the present numerical value.
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(B) Numerical display of information is useful for static information that does not change or for pilot-selected discrete parameters. Additionally, if the parameter does not need to convey information regarding rates of change or position relative to a limit, then it may be acceptable to display it numerically.
(iii) Failure indications of loss of information should be clear, unambiguous, and not misleading. For example, it has been effective to use a red "X" with failure indication or the graying out of a failed parameter with failure indication. Removal of the indication upon failure without other symbology can cause confusion. Regardless of the method used to indicate a failed parameter, it should be intuitively obvious that the information is neither available nor misleads the pilot.
(iv) The format should inform the pilot with indications of flight guidance, attitude, airspeed, and altimeter information sources. For systems with redundant sources, where the system monitors and compares data between the systems, indications should alert the pilot of a mismatch and an indication to the use of whether the data sources are "offside" or "onside." Switch position alone should not be used to indicate selection of the system.
(2) Colors.
(i) Develop the color philosophy early and apply it consistently throughout the instrument displays. SAE ARP4102-7 contains information regarding color schemes.
(ii) Color should not be the sole method of coding to account for pilot color vision deficiencies.
Use of redundant coding such as shape, outline, flashing, reverse video, or auditory is encouraged.
However, flashing use should be limited. If applied, the use of flash coding should be consistent. For example, flashing should not be a caution for one parameter and a warning for another.
(iii) Colors used to alert pilots must follow the requirements in § 27.1322. Also, consider AC 25.1322-1 regarding color use guidance. However, coordinate with applicable certificating authority prior to adopting AC 25.1322-1 guidance.
(A) The color red must be reserved for alerting functions requiring immediate pilot awareness and action. Red is required to be used when marking limits on instruments and gauges. See section 27.1543 and subsequent sections of this AC for further guidance on the use of colors.
Additionally, red may not be used to alert the pilot that a system is functioning normally in an emergency
(1) Red should not be used as an outline for instruments or gauges, or to define areas or "windows" on displays.
(2) Graphical displays of powerplant parameters should not present red bands or arcs. The marking of limits must comply with § 27.1547.
(B) The color scheme on moving map displays, navigation displays, and terrain displays should be the same. This is important to decrease pilot confusion and the possibility of providing misleading information.
(iv) Consider using the color schemes shown in the below tables.
Recommended Colors for Certain Functions Feature Color Warnings Red Flight envelope and system limits, exceedances. Red or Yellow / Amber as appropriate (see above) Cautions, non-normal sources. Yellow / Amber Page MG 19 - 15
AC 27-1B, Chg 7 2/4/2016 Feature Color Scales, dials, tapes, and associated information White elements.
Earth Tan / Brown Sky Blue / Cyan Engaged Modes/normal conditions. Green Glide path and course deviation indicators. Magenta/Green Flight directors or "fly-to" indicators Magenta Divisor lines, units and labels for inactive soft buttons. Light Gray Specified Colors for Certain Display Features Display Feature Color Set 1 Color Set 2 Fixed reference symbols White White* Current data, values White Green Armed modes White Cyan Selected data, values Green Cyan Selected heading Magenta* Cyan Active route/flight plan Magenta White * Use of other colors for this function may be acceptable as long as they are not flightcrew alerting colors used for conditions that may require pilot action or indicate abnormal conditions.
(3) Symbology.
(i) One benefit of symbol standards versus other information formats is the compact encoding of information, which minimizes clutter. With careful planning, base the use of symbols upon established industry standards. SAE ARP 4102/7 and ARP 5289 standards provide examples of accepted symbols and symbol sets for PFDs and MFD-navigation displays.
(A) Symbolic encoding of information should remain sufficiently simple for pilots to learn and recall (see section AC 27 MG 20, Human Factors, of this AC). To minimize confusion or misinterpretation, symbols should be easily distinguishable, consistent within the cockpit, and learned with minimal training.
(B) Symbols should not have shapes, colors, or other attributes that are ambiguous or could be confused with the meaning of similar symbols.
(C) The function of symbology should be clear definition and appropriate classification for pilot understanding. Symbols representing the same functions on more than one display should be the same.
(il) HTAWS, automatic dependent surveillance-broadcast (ADS-B), TCAS, and other applications each have their own defined symbol sets. If these features are included in the installation and will use the EDS displays to show information, then the EDS should use each application's (HTAWS, ADS-B, TCAS, etc.) defined symbol set. Assess the symbol sets to ensure they do not contain similar symbology with different meanings.
(iii) The EDS design and integration should provide a means to reduce or "declutter" the EDS of non-essential symbology.
(4) Clutter.
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(i) Computer generated displays provide the ability to present a multitude of information. As a result, numerous formats are possible with an electronic display system. However, excessive information on a limited display size can result in clutter, resulting in reduced efficiency of pilot cues, pilot scan, and detection.
(A) The density of information on the display should be compatible with the pilot's ability to recognize essential information and to minimize misinterpretation. At times, pilots may wish to reduce clutter by removing the display of symbols otherwise used during specific phases of flight.
(B) There should be an information prioritization scheme established to ensure the clear presentation of essential information.
(C) If anticipating clutter, there should be a means provided for manual de-cluttering.
Automatic de-cluttering, such as during specific phases of flight, or during certain alerts, may also be appropriate.
(ii) Clutter should be a major consideration during the reversionary or compacted display modes. When combining essential information on a display after another display or unit fails, the display format should not be confusing and the information should still be usable, including ability to display unusual attitudes.
(iii) Unusual attitude and de-cluttering of the PFD.
(A) All primary attitude displays should provide an immediately discernable attitude recognition capability that fosters a safe and effective unusual attitude recovery capability. The display should provide sufficient cues to enable the pilot to maintain full-time attitude awareness and minimize potential for spatial disorientation.
(1) The display should support the initiation of recovery from unusual attitudes within 1 second with a minimum correct response rate of 95 percent.
(B) Annunciations and Indications.
(1) General. Annunciations and indications include annunciator switches, messages, prompts, flags, and status or mode indications, which are on the flight deck display itself or control a flight deck display. Refer to § 27.1322 for specific annunciations and indications such as warning, caution and
(1) Annunciations and indications should be operationally relevant and limited to minimize the adverse effects on flightcrew workload.
(I) Annunciations and indications should be clear, unambiguous, and consistent with the flight deck design philosophy. When providing annunciation for the status or mode of a system, the annunciation should indicate the actual state of the system and not just the position or selection of a switch. Annunciations should only be indicated while the condition exists.
(2) Location. Annunciations and indications should also be consistently located in a specific area of the electronic display. Annunciations that may require immediate flightcrew awareness should be located in the flightcrew's forward, primary field of view. There may be CAS messaging presentation in the pilot's secondary field of view if there is a Master Caution/Warning indicator.
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AC 27-1B, Chg 7 2/4/2016
(3) Attention-getting cues: When selecting the type of attention-getting cue, a text change by itself is typically inadequate to annunciate automatic or uncommanded mode changes.
(i) Use audio tones or voice messages. Keep the number of different tones to a minimum to decrease the possibility of confusion. Aircrew alerts are more noticeable when a combination ot audio tone/audio message and a visual cue is used.
(i) Blinking or Flashing. Blinking information elements such as readouts or pointers can be effective methods of annunciation. However, the use of blinking or flashing should be limited because it can be distracting, and excessive use reduces the attention-getting effectiveness. Use blinking rates between 0.8 and 4 hertz, depending on the display technology and the compromise between urgency and distraction. If blinking of an information element can occur for more than approximately 10 seconds, there should be a means provided to cancel the blinking.
(5) Flight and Navigation Display of Information on the PFD.
(i) Flight. At a minimum, the primary flight display portion of the PFD should display the attitude, airspeed, altitude, and heading. Most EDS flight displays also include navigation guidance in the form of course deviation, and if applicable, vertical glide path deviation. They can also include information on vertical speed indications, radar altitude, and flight guidance mode. If synthetic vision (SV) is incorporated, it should be on the flight display as a "pilot-view out the window" (egocentric) format. If incorporating SV into the flight display, it should provide the same level of accuracy and validity as the other navigation sources. If displayed on the PFD, describing the SV's intended function as "situational awareness only" or "not required" to justify a lower design assurance level is not acceptable.
(A) Information.
(1) PFI refers to those functions or parameters that are required by the airworthiness and operational regulations such as airspeed, altitude, attitude, and heading (direction). 14 CFR part 27 only requires airspeed, altitude, and heading (direction) as PFI unless the rotorcraft will be certificated for IFR. IFR certifications require instrumentation defined in 14 CFR 27 Appendix B. Most EDS designs include attitude, altitude, airspeed, and heading display in the basic "T" arrangement defined in § 29.1321. There are specific requirements contained in TSOs for the display of each of these parameters.
TSO approval does not authorize installation of a system or instrument into a rotorcraft. The installation of an instrument or system must meet the certification requirements for the rotorcraft.
For example, some attitude indicators carry TSO-C4 approvals but are not qualified for installation in rotorcraft where an ADI is required by the certification rules.
(2) Part 27 rotorcraft certificated to operate under VFR only may require secondary sources of PFI depending:
(1) On the operational rules for the rotorcraft (i.e., part 91 versus part 135).
(I) Whether the failure hazard assessment and system safety assessment (FHA/SSA) show that the failure condition classification warrants redundancy.
3) PFI for FR Rotorcraft.
1) For IFR rotorcraft, the PFI requirements are contained in Appendix B to Part 27, VilI (refer to Appendix B of this guidance for more information). If using an integrated electronic display as a secondary source or standby instrument, there should be arrangement of the PFI in the basic T-configuration on the display. Additionally, PFI is considered essential for safe operation and should meet minimum standards of applicable TSOs or equivalent and must meet the requirements of § 27.1309 Page MG 19 -18
and Appendix B to part 27, if applicable. There should be clustering and arrangement of the electromechanical standby instruments to allow the pilot use of them without undue concentration.
(i) Gyroscopic pitch and bank ADI presentation should meet the requirements of § 29.1303(g)(1) regardless of whether or not they are considered standby ADIS. Appendix B of this AC and AC29-2, section 29.1303 explains the requirements for an ADI to comply with § 29.1303(g)(1).
(B) Arrangement.
(1) 14 CFR 27.1321 specifies placement of information relative to the pilot's field of view. Refer to section 27.1321 of this AC for further guidance.
(2) Most EDS displays follow the traditional "T" arrangement described in Appendix B of this AC and § 29.1303. Deviations from this arrangement should be coordinated early with the certification authority.
(3) Depending on design, addition of information normally found on EICAS or other MFDs, such as power instruments or CAS messages, may be included. If this is the case, early human factors evaluation for clutter, information density, and format and function of non-flight information should be accomplished on bench tests and in a simulator (if available) or on in-flight evaluations.
(C) Format and function.
(1) Display of Attitude:
(j) Most EDS displays format attitude in a conventional manner. Alternate display formats and functions considered should be coordinated early with the CA. Pitch, bank, horizon line and indicators, and the rotorcraft symbol should be clear and easily acquired to allow the pilot quick access to the rotorcraft's attitude in all operating conditions. Regardless of added guidance or navigation cues, there should still be the ability for the accurate assessment of the attitude by the pilot.
(i) Some VFR at night operational rules require an attitude indicator. As a result, depending on whether the rotorcraft is VER or IFR certificated, the design assurance level of the EDS PFD should be commensurate with the assessed FHA failure condition classification for loss of and misleading attitude information. In addition, flight at night in a VFR rotorcraft, especially one without a stabilization system, may require a higher failure condition classification than for day VFR.
(i) Operational rules also require that VER rotorcraft have an ADI for night operations. If an ADI is required, it must meet and be installed in accordance with § 29.1303. Appendix B and section 29.1303 of this AC explains the requirements for an ADI to comply with 14CFR 29.1303(g) (1).
(iv) Additional considerations. 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). 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 does not prevent replacement of mechanical instruments with electronic displays of similar horizon reference line.
(2) Display of Altitude.
(1) Consider primary display of altitude to be barometric altitude. The altitude display format should be clear and easily interpreted by the pilot. If the EDS allow selection of alternate display modes such as switching between feet and meters, then clearly display the active mode to the pilot to avoid confusion. Additionally, if selection between HPa and inches Hg in the Kollsman Window is selectable, the selected mode must be clear and easily interpreted by the pilot.
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AC 27-1B, Chg 7 2/4/2016
(i) Display of Global Navigation Satellite System (GNSS) altitude. The simultaneous display of GNS and barometric altitude is not recommended. If there is a mode to display GNSS or GPS derived altitude, the display of GPS altitude should be distinctly different from barometric altitude so there can be no confusion regarding the source. Additionally, there should be clear labeling of the GNSS altitude. One acceptable label is "GSL."
(iii) Radar or radio altitude (RALT). RALT is required for certain operations. If the integrated display system has the ability to provide RALT displays, there should be consideration given to the intended function of the RALT in rotorcraft. A strictly numerical readout of RALT may not be sufficient to provide the intended function based on operations. Conversely, a graphical display of RALT, depending on the implementation, may create confusion. For example, incorporating a ground reference cue based on RALT into a barometric altitude display could lead to confusion if not supplemented by another cue.
(iv) The use of moving tape displays or graphical representation of traditional round dial altimeters has been equally effective. Linear tape altimeter displays should include enhancements denoting standard 500 and 1,000-foot increments, and they should convey the present altitude unambiguously and at a glance. The combination of altimeter scale length and markings, therefore, should be adequate to allow sufficient resolution for precise manual altitude tracking in level flight, as well as enough scale length and markings to reinforce the pilot's sense of altitude. The scale length should also allow sufficient look-ahead room to adequately predict and accomplish level off. Pilot evaluations have shown that, in addition to the appropriate altitude markings commensurate with rotorcraft performance, the recommended use of an altitude reference bug provides acceptable cues.
(A) A trend indicator should be displayed unless a vertical speed indicator (VSI) is located adjacent to the altimeter. A six-second altitude-trend indicator is typical, but other trend values may be more appropriate depending on the rotorcraft performance and altitude tape scaling.
(B) Some operations require an instantaneous VSI. If installed, ensure it functions correctly and provides the pilot with usable information. Some instantaneous VSI installations may be unusable due to jittery performance.
(il) Navigation. The navigation display (ND) portion of the PFD and a MFD can display navigation information. This section focuses on the navigation information displayed on the navigation display portion of the PFD. Guidance on information presented on the navigation display is contained in SAE ARP 4102-7. Appendix B to SAE ARP 4102-7 provides navigation symbology guidance. Certain information should also be included on the ND. Navigation source (GPS, VOR1, LOC, etc.), waypoint name, and distance-to are types of information the ND should display, particularly if envisioning RNAV approaches. ND displays have also contained primary powerplant information either as individual instruments (torque (TQ), turbine temperature (TOT), or turbine speed (Ng, N1 %RPM)) or as an integrated first limit indicator or power indicator display. Additionally, main rotor RPM (NR), and free turbine speed (Np, NF, N2 %RPM) may be displayed on the ND.
(A) Arrangement.
(1) Normally, the HSI/compass rose is in the middle of the ND with the other information arrayed around it.
(2) Active navigation information (waypoint name, etc.), should be as close to the top of the display as possible to minimize the pilot's scan between the PFD and ND.
(B) Format.
(1) The HSI/compass rose format should have a full 360° display. If an arc feature is included, the arc should display at least 120° of heading. In arc mode, if the heading bug is off the display, there should be a means to indicate to the pilot what heading the bug is set on.
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(2) The rest of the displayed information format should allow for easy assessment and interpretation by the pilot.
(3) Overlays of TCAS, HTAWS, or weather information should not interfere with the use of the ND for primary navigation tasks. There should be definition of the prioritization of overlay popups, if installed.
(6) Powerplant and Systems Information.
(i) Powerplant. EDS display suites may or may not include the capability of displaying powerplant parameters required by § 27.1305 along with electrical system information required by § 27.1351. Displaying powerplant information on a single display, as opposed to displaying the information in separate gauges, decreases the independence of information. As a result, EDS powerplant display (EICAS, IIDS, etc.) design should be robust enough so that information availability and validity is commensurate with the assessed FHA failure condition classification.
(A) Arrangement.
(1) 14 CFR 27.1321 and Appendix B to Part 27 (VIII) specify placement of information relative to the pilot's field of view. Refer to sections 27.1321 and 27.1305 and Appendix B of this AC for further guidance.
(2) Torque, power turbine temperature, power turbine speed, main rotor speed, and free turbine speed should continuously display in the pilot's primary field of view. The format for these parameters can vary and is discussed below.
(3) Display of engine oil temperature and pressure and main gearbox oil temperature (and pressure if required) should continuously display. If positioned in the pilot's secondary field of view, they should be as close to the pilot's primary field of view as possible.
(B) Format. EDS provides the ability to display powerplant information in a variety of formats. For EDS installed to replace analog gauges, the format of the primary powerplant instruments (TQ, N1, TGT) should allow pilots to easily transition from the old analog variant to the digital variant without undue concentration and without training.
(1) Gauge layout and marking should be easy to see and interpret.
(1) If using a similar format such as round-dial representation of a round dial analog gauge, then indices and markings should be similar to the analog gauge the digital display is replacing. This is to ensure there is no negative transfer from reading traditional electromechanical gauges or confusion when reading the digital gauge. There may be improvements made over the existing gauges. For example, an instrument such as a dual tachometer, which provides information on the status of main rotor speed, may also provide information relating to pilot collective input (to correct a deviation in rotor RPM). For example, providing a dual tachometer that places the normal range at the 9:00 position provides the pilot with two types of information. If the rotor RPM is high, the needle is high.
It also gives the pilot a cue that to lower the RPM, the pilot should lower the collective to lower the NR (and bring the needle down to the normal range).
(I) Use of a distinctly different format such as a tape or linear gauge or a distinctly different shaped representation should allow for quick and easy assessment of information. The ease of use should be better or the same upon gauge replacement.
(I) Needles, pointers, or other indicator means should point at the value, not cross or obscure the value. If using multiple needles or pointers on a display, the parameter that they are indicators for should be clear and easily distinguishable from the others on the display.
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