AC 29-2C, Chg 7 2/4/2016
(2) Part 29 category A and non-category A rotorcraft certificated to operate under VFR only may require secondary sources of PFI if the failure hazard assessment and system safety assessment (FHA/SSA) shows that the failure condition classification warrants redundancy. For most installations, there is a requirement for a second attitude, altimeter, and airspeed indicator.
(3) PFI for IFR Rotorcraft
(i) For IFR rotorcraft, part 29 Appendix B (viii) drives the PFI requirements (refer to Appendix B of this AC 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 meet the requirements of § 29.1309 and part 29 Appendix B, if applicable. There should be clustering and arrangement of the electromechanical standby instruments to allow the pilot use of them without undue concentration.
(ii) 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. Section 29.1303 of this AC explains the requirements for an ADI to comply with § 29.1303(g)(1).
(B) Arrangement
(1) 14 CFR 29.1321 specifies placement of information relative to the pilot’s field of view. Refer to, section 29.1321 of this AC for further guidance.
(2) Most EDS displays follow the traditional “T” arrangement described in Appendix B of this AC and 14CFR 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:
(i) 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 aircraft symbol should be clear and easily acquired to allow the pilot quick access to the aircraft’s attitude in all Page MG 19 -22
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.
(ii) For flights under IFR conditions, some VFR at night operational rules, (e.g., 14 CFR parts 91 and 135) require an attitude indicator. The loss of all attitude information or the presentation of misleading of attitude information could result in a catastrophic hazard condition where the pilot could not continue safe flight and landing of the rotorcraft. As a result, depending on the whether the rotorcraft is VFR 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 lead to a higher failure condition classification than for day VFR.
(iii) Additionally, the same operational rules require VFR rotorcraft provides ADI requirements for those operations. If an ADI is required, it must meet and be installed in accordance with § 29.1303. See AC 20-2C and § 29.1303 for guidance on ADI requirements. Section 29.1303 of this AC explains the requirements for an A DI to meet § 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 l ine 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.
(i) 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.
(ii) 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 Page MG 19 - 23
AC 29-2C, Chg 7 2/4/2016 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.
(ii) 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 or compass rose is in the middle of the ND with the other information arrayed around it.
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(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 or compass rose format should have a full 360o display. If an arc feature is included, the arc should display at least 120o 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.
(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 pop-ups, 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 § 29.1305 along with electrical system information required by § 27.1351and hydraulic system information required by § 29.1435. 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 29.1321 and Appendix B (VIII) to part 29 specify placement of information relative to the pilot’s field of view. Refer to section 29.1321 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.
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AC 29-2C, Chg 7 2/4/2016 (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.
(i) 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).
(ii) 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.
(iii) 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.
(iv) Markings must follow requirements of §§ 29.1543 through
29.1555.
(2) Graphical and numerical-only displays of parameters or information should follow the guidance in section d above. Providing a numerical readout along with graphically presented information provides the pilot with complementary data of a specific value coupled with the awareness of where in the operating range that value resides.
(i) There should be graphical display of powerplant pressures and temperatures, fuel levels and pressures, and speeds.
(ii) There should also be graphical presentation of other parameters with a range of normal if the pilot needs to monitor where a parameter is or is changing relative to a limit.
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(C) Part-time vs. full-time display of information.
(1) Powerplant instruments required by § 29.1305 should be displayed full time (i.e., continuous display). However, due to space limitations or display system design, EDS displays that allow for the de-selection of secondary powerplant instruments (e.g., engine oil temperature and pressure, transmission oil temperature, electrical and hydraulic system information) required by § 29.1305, may be acceptable.
There should be continuous display of primary power information (TQ, MGT, Ng, or their equivalents) and Rotor tachometer (Nr and Np).
(i) In order to allow the de-selection or part-time display of these parameters, compensatory features should be designed and provided to alert pilots to select and monitor § 29.1305 instruments prior to the parameter reaching a cautionary or warning limit.
(A) Algorithms and monitoring software can provide the capability to alert pilots about possible anomalies in a parameter’s behavior. Pilots can then select the appropriate display, monitor the situation, and mitigate the situation as required prior to it becoming an abnormal condition.
(B) The monitoring function should automatically provide the same level of monitoring that would exist if there were continuous display of the individual engine gauges.
(ii) To show compliance using part-time display of § 29.1305 required indicators, the applicant needs to show equivalence. Coordinate with engine and powerplant specialists since they will need to assist in the evaluation of the monitoring algorithm parameters. Depending on the strategy employed, the engine manufacturer may also need to be involved. Additionally, coordinate early with the FAA/AUTHORITY since there will need to be an equivalent level of safety.
(ii) System displays. Display of system information (e.g., hydraulic system information, electrical system information), other than powerplant information, may be combined onto an EICAS or IIDS display or displayed on separate displays.
(A) Crew Alerting System (CAS) and Caution Advisory Warning System (CAWS). EDSs may include CAS message windows or CAS messages may display on a separate display. CAS messages must be easily seen and legible in all lighting conditions. The messages or labels must be easily understandable and use standardized acronyms or labels. Display of CAS messages should be located as close to the pilot’s central line of vision as possible unless there is a Master Caution or Master Warning indicator in the pilot’s primary field of view.
(1) Managing Messages and Prompts. The following general guidance applies to all messages and prompts:
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AC 29-2C, Chg 7 2/4/2016
(i) There should be an indication when there are additional messages not displaying that are in a message queue.
(ii) Within levels of urgency, messages should display in logical order.
(iii) If the length of the information for the message, prompt, or response options does not display on a single page, there should be an indication that additional message information exists.
(2) The CAS display should be large enough to generate a display of all possible warnings that are in a worst-case scenario. The design should provide for the sufficient space to display all possible warnings on the screen at once. To decrease the amount of cascading warnings, use algorithms to suppress subsequent cascading warnings that would appear because of an event. For example, loss of an engine could lead to cascading messages of warning-level conditions that resulted from the engine loss. Unless the pilot has to perform separate procedures to correct subsequent warnings from the procedures needed to handle the engine loss, there is no need to present them to the pilot.
(3) CAS message priority.
(i) If displaying CAS messages in a window within an EDS display, prioritize how they will appear. Normally, the presentation of warning messages takes precedence over caution and advisory messages. There can be prioritization of new warnings by importance, recency, or other prioritization scheme.
(ii) Caution message priority should be defined and easily understood by the pilot. Scrolling and paging-over to read overflow Caution messages is allowed. The scrolling function and control must be easily identified and used without undue concentration.
(7) Mission or ancillary displays.
(i) Displays added to the cockpit for specialized uses by a mission crewmember and not the pilot, such as FLIR displays, should be located outside of the pilot’s secondary field of view, if possible, so as not to distract the pilot from flying the rotorcraft.
(ii) Displays of non-required information not integrated into an EDS but intended to be used by the pilot should have all of the attributes and characteristics of an EDS. These displays can be located within the pilot’s secondary field of view but not in the primary field of view and should not displace the display of required information.
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(A) Display of non-required information should be assessed to ensure it does not provide misleading information to the pilot or information contrary to that provided by a required source. For example, an enhanced vision display should not display cues regarding rotorcraft position relative to hazards or navigation waypoints that are contrary to other information provided on the EDS.
(B) The intended function of a non-required information display should be specific and defined. For example, “Increase pilot situation awareness” is not an acceptable statement of intended function. A better statement of intended function is “Increase pilot awareness of hazard location relative to the rotorcraft.”
(8) Reversionary Modes.
(i) General. Because EDS displays can integrate numerous required flight, powerplant, and system information into single displays, there is a greater opportunity for a fault to lead to the loss of the display of multiple parameters. To mitigate this, the use of reversionary modes and displays can ensure the continued display of required parameters. Reversionary modes are sometimes referred to as “compressed displays” or “composite displays.”
(ii) Methodology.
(A) IFR. Refer to 14 CFR Appendix B to part 29 and Appendix B of this AC for information on the IFR requirements. Per Appendix B to part 29, the display of information essential for continued safe flight (i.e. attitude, altitude, airspeed, and heading) must be immediately available to the pilot flying without crewmember action after any single or combination of failures not shown to be extremely improbable. In IFR designs, it is expected that the first display failure should have no impact on the ability of the pilot to continue safe IFR flight to the planned destination.
(1) Unlike normal category rotorcraft (certificated under 14 CFR part
27), transport category rotorcraft with a certificated dual pilot installation, the design should not rely on the pilot’s use of the copilot’s instruments as a standby source of primary information. If there is other information on EDS displays that the pilots access looking at the cross-cockpit display, specific issues should be addressed. Some of the issues are:
(i) Pilots should easily see and interpret the displays from their normal seated position with minimal head movement.
(A) The copilot’s systems should be within the pilot’s secondary field of view.
(B) The display characteristics should support off-angle viewing in all lighting conditions.
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AC 29-2C, Chg 7 2/4/2016
(ii) If required, pilots should easily manipulate the displays with one hand from their normally seated position. Pilot access of the displays and controls must meet the requirements of § 29.777 when used by the pilot-flying as primary flight information.
(2) Automatic reversion is one means to meet the requirement on § 29.1333(b) that allows required information to remain visible to the pilot flying without crewmember action. The format and arrangement of the reversionary mode is discussed below.
(i) Automatic reversion should provide the required information within one second of the detected failure of a display or the display’s inability to provide the information.
(ii) For undetectable loss of the display resulting from a backlight failure or a broken display screen, then a single button push by the pilot is acceptable.
The pilot should be able to recover the lost display of information within one second.
However, the design of the display should be such that these failures are extremely improbable.
(iii) Arrangement. Arrangement of information in a compressed or composite mode must follow the requirements of § 29.1321.
(A) Presentation of primary flight information should remain the same.
(B) Presentation of navigation information should provide for required information in as similar a location as possible as a normal display.
(C) Powerplant and required system information should be arranged in a manner that is easily accessed and readable.
(D) CAS messaging should be displayed with the ability to display all possible warnings without overflow.
(iv) Reversionary mode display format.
(A) Format of the primary flight information should not change.
(B) HSI presentation in a reversionary mode should provide the same usability and function as the non-reversionary mode. Navigation information should still be available and as close to the same format as possible.
(C) Presentation of primary powerplant information the pilot uses to set and monitor power should be prominent and graphically displayed.
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(D) Presentation of powerplant information pilots use to assess the health and ability of the powerplant to develop power can revert to numerical displays if needed. Display of these parameters numerically should include secondary cueing for the pilot in the event a parameter exceeds a cautionary or limit value. For example, the numerical digit or field should provide a visual cue regarding its status as it would in a normal display (see § 29.1322).
e. System Requirements.
(1) All parameters in EDS displays are to be designed in accordance with the relevant TSOs. TSOA does not mean that the function or hardware meets the certification requirements for the rotorcraft in which it is to be installed.
(2) A safety assessment should be provided as part of finding compliance with § 29.1309. The following sections of this AC contains guidance on safety assessments:
Section 29.1309, paragraphs c. (Failure Analysis), d. (Safety Assessment),
f. (Software), and g. (Airborne Electronic Hardware).
MG 21 (FHA)
(3) Special Considerations when determining failure condition classifications.
Consideration should be given to the type of operation that the system is intended to support. For example, failure condition classifications for IFR installations are generally higher than VFR. Information contained on a PFD is usually more critical, in most cases, than information on a MFD.
(i) VFR.
(A) In a VFR-only certificated rotorcraft misleading information will typically have a higher hazard categorization than loss of information. The design should provide mitigation to both as much as feasible, particularly for transport category rotorcraft, since night VFR can be flown in areas that do not provide pilots with good visual cues regarding the horizon or ground features.
(B) PFD. Display of any non-required information such as synthetic vision should not display misleading information. Loss of non-required information should not lead to confusion or affect the ability of the pilot to access or assess required flight information.
(C) Display of powerplant information. 14 CFR 29.1305 contains the required powerplant instrument data to be displayed. Although each item is required, care should be taken with the loss of the following, as applicable: low fuel warning, oil pressure warning for each gearbox, tachometer, and OEI power levels.
(ii) IFR. Regulations for rotorcraft certificated for IFR operations are found in Appendix B to part 29.
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AC 29-2C, Chg 7 2/4/2016
(iii) Field-Loadable Software (FLS) as part of the TC, STC, ASC, and ASTC installation. FLS is software that can be loaded without removal of the equipment from the rotorcraft installation. FLS can refer to either executable code or data. FLS might also include software loaded into a line replaceable unit (LRU) or hardware element at a repair station or shop. When obtaining certification approval for utilization of the FLS capability, refer to the guidance in FAA Order 8110.49.
(iv) Navigation Database Qualification. For area navigation equipment, the navigation database is an essential component of the ability of the equipment to perform its intended function. RTCA Document DO -200A, Standards for Processing Aeronautical Data, contains guidelines pertaining to the navigation database. .
Consider obtaining a Type 2 Letter of Authorization for databases used for Localizer Performance with Vertical Guidance in addition to the required documentation. See AC 20-153A for additional information. See AC 20-153A for additional information.
(4) Environmental qualification. EDS displays should meet the appropriate RTCA Document DO-160G environmental qualifications for rotorcraft. Rotorcraft environments can be more hostile than fixed-wing environments. Give special attention to the temperature and vibration qualifications. See section 29.1309 of this AC for more guidance.
(i) Cooling.
(A) Perform cooling evaluations for the installed components.
(B) Temperature Survey to Determine Proper Cooling of EDS Components.
(1) Equipment Requiring Cooling Test. As with any avionics equipment, good engineering judgment may deem that all components of the EDS should have an in-flight temperature survey performed to ascertain that the thermal environmental tolerance of the system components is not exceeded. Usually, the following general guidelines may be used to aid in determining when an in-flight temperature survey is warranted.
(i) Equipment specified by the manufacturer to require forced air cooling (by an airframe-mounted system) usually requires a temperature survey.
(ii) Equipment that is not specified as requiring forced air-cooling may usually have its critical thermal environment substantiated by laboratory testing.
(2) Temperature Survey Testing. The temperature tests for the EDS units should consist of a short-term test of approximately 30 minutes, which accounts for a rotorcraft that has heat-soaked on the ramp. A factor of 25° F should be added to the maximum corrected temperature to account for “greenhouse effect.” A long-term Page MG 19 -32
test should be accomplished at various altitudes and limiting (low and high) airspeeds.
All avionic equipment should be turned on during the long-term tests, and the cockpit panel lights should be operated at full intensity. The environmental control unit or air-conditioning system should not be operated during the short-term and long-term tests; however, any windows or vents, which are part of the basic TC of the rotorcraft, may be utilized to ventilate the pilot’s stations during the long-term test. Both of these tests should be corrected to the maximum temperature for which the rotorcraft is certificated (maximum outside air temperature) and a standard lapse rate for altitude
(i.e., 3.6° F/1,000 feet), as specified in this guidance (refer to section 27.1309 of this AC). This lapse rate should be applied regardless of the hot day sea level temperature the applicant chooses to certificate for operation. If an airframe cooling s ystem is necessary to keep the display units within acceptable temperature limits, then the pilot(s) must be made aware of a failure or malfunction of this required cooling system.
Some type of cockpit visual annunciation with the capability to perform a preflight test is usually utilized to fulfill this requirement.
(ii) HIRF. Perform HIRF testing in accordance with § 29.1317 and the guidance in section 29.1317 of this AC.
(5) Night vision imaging system (NVIS) lighting. If the EDS is designed with night vision goggle (NVG) compatibility for installation in a NVIS lighting modified cockpit, refer to MG-16 of this AC and RTCA Document DO-275 for lighting performance guidance. Modifications to EDS displays should preserve color uniformity across the cockpit. Most EDSs incorporate color, as a result, in order to preserve the EDS colors close to the rotorcrafts designed colors, the NVIS lighting system should be modified to be compatible with Class B NVGs. Lighting compatible with Class A NVGs may not provide the correct color hues (e.g., red colors tend to look orange or amber, yellow colors tend to have a green tint in daylight, etc.).
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