(v) Applicable procedures and techniques for conduct of hardover tests are contained in Paragraph 637 of this AC. If a quick disconnect device is incorporated, it should be reachable with a finger on the hand operating the appropriate recovery control and should be operable without removing the hand from that control. A quick disconnect system can be used on duplex system if overall reliability of the system is acceptable. All cockpit emergency controls including emergency quick disconnects should be "red." The quick disconnect may be actuated at initiation of recovery. Other disconnects should only be actuated after full aircraft control has been achieved following recovery. Aircraft limits may not be exceeded during malfunction or recovery.
If a monitor device automatically disconnects the SAS, it must be clearly annunciated to the crew.
(vi) Series actuator hardover conditions in some rotorcraft can seriously degrade control margin. Critical loadings, power settings, RPM, and altitudes in conjunction with a SAS actuator hardover in an adverse direction can result in reduction of control travel requiring flight envelope constraints. Flight testing is usually necessary to determine the appropriate flight envelope reductions.
(vii) Subsequent failures and unrelated probable combinations of failures must be considered, including subsequent SAS failures. Systems and equipment section analysis should provide necessary SAS malfunction combinations for flight testing as a result of their system analysis. Minimum requirements for dispatch and procedures following failure should be included in the malfunction analysis. Results of the probability analysis and the resultant malfunction configurations are primarily the responsibility of the systems and equipment section.
(viii) No reasonably probable failure should result in a worse condition than that tested for hardovers. For example, if a magnetic brake force trim system is employed, failure of electrical power to the magnetic brake circuit may cause the cyclic control to fail which may result in a more dangerous flight condition than individual SAS hardovers. The overall control system is to be evaluated for all probable failures to preclude hazardous failure conditions. Other areas for investigation include beep trim and auto trim failures. The delay times of Paragraph 775(6) (ili) are appropriate for all such failures. System malfunctions may also include component failures which result in oscillatory outputs of the actuators). These should be sustainable at least as long as the specified hardover delays, should be manageable thereafter with hands on the controls, and should allow disconnect of the malfunctioning system.
(ix) Engine failure requirements are not entirely consistent with the SAS failure time delays shown in 775b(6)(iii). Engine failure time delays remain as specified in § 27.143(d), and they are lower than corresponding SAS failure delays. Critical engine failure conditions should be reverified during simulated instrument flight with primary reference to flight instruments. Lower time delays for engine failure have been justified on the basis of immediate cues for the critical high powered condition and requirements for engine failure warning systems. Many rotorcraft designs simply 1034 Par 775
cannot endure a 3-second time delay for critical engine failure conditions.
Nevertheless, engine failure, autorotation entries, and autorotation descent (for single-engine rotorcraft and multiengine rotorcraft without Category A engine isolation) should be evaluated in simulated IF conditions, and these flight characteristics must be acceptable.
(7) Controllability.
Control harmony should be present. There should be no objectionable cyclic to collective or roll-yaw-pitch cross coupling.
(¡i) Control forces following a control system malfunction such as a hydraulic system failure should be low enough to allow completion of the intended flight.
It may not be possible to land early during an actual IF flight.
(ії) There should be no tendencies for pilot-induced oscillations; There should be no sustained or uncontrollable oscillations resulting from the efforts of the pilot to control the rotorcraft.
(iv) The control system should have sufficient resolution to permit accurate and precise instrument maneuvers. Some control systems with high breakout forces in conjunction with low control force gradients do not lend themselves to satisfactory instrument flight capability.
(8) Cockpit Arrangement.
The primary flight instrument basic T (or a modified T with VSI above the altimeter) should be located as nearly in front of the pilot as possible. All annunciation necessary for operation of stability systems should be readily in view.
Secondary flight (or navigation) instruments such as radar altimeter and secondary radio course information, DME, etc., should be grouped around the periphery of the T.
Next in priority are primary power instruments such as torque and rotor RPM..
Powerplant instruments and backup attitude information should be placed in the remaining panel areas. Various research and development efforts and previous certification programs have revealed that it is desirable not to locate the standby attitude indicator immediately adjacent to the basic flight instrument T. The standby attitude indicator must be usable and flyable from the primary pilot station (and any other pilot station); however, locating it too close to the primary instruments may be undesirable and should be evaluated. If the standby attitude information is close to the pilot's normal flight instrument scan, he may begin to compare attitude information between the two indicators in his normal instrument scan. Every pilot eye motion to compare these indicators could be a wasted motion that could be more efficiently applied in the normal scan. The pilot should fly either the primary or the backup indicator and it may be an aid if these indicators are noticeably separated. When the standby indicator is located apart from the normal scan and the primary indicator fails, Par 775 1035
the pilot is conscious of a distinctly different instrument scan and is less likely to be continuously coming back to the center of the basic T for attitude reference. Physical separation can assist the transition to standby attitude flight.
(її) All cockpit controls necessary for normal and emergency operations should ideally be located so that they may be actuated without upper body movement.
Moderate head and body movement has been accepted; however, these motions must be evaluated for their vertigo inducing effects. No IFR controls should be located aft of a vertical plane passing left to right (laterally) through the pilot's body.
(ill) If a copilot position is approved, the copilot must have a complete set of flight controls and must be capable of independently flying and navigating the rotorcraft from his position. The copilot must be capable of controlling at least one primary navigation source so that he can operate the rotorcraft during normal conditions without relying on the first pilot to perform needed cockpit functions. Some instruments can be shared between pilots depending on instrument panel presentation. Some examples from previous programs include standby attitude, rotor tachometer (if the aircraft has automatic governing and the crew is provided visual and aural RPM warning), and secondary powerplant instruments such as Ng, oil pressure, and temperature.
(iv) Proper cockpit annunciation is essential for safe operation. SAS and autopilot modes must be properly annunciated. Appropriate annunciator color coding is contained in § 27.1322. There must be no question in regard to the source of navigation information presented to the crew. Where navigation switching is available between individual displays and between pilot positions, the first pilot should have overriding control for his displays.
(9) IMC Evaluation.
(i) As part of the flight test program, new rotorcraft undergoing IFR certification should be flown in the air traffic control system in actual day and night instrument meteorological conditions. Items for consideration during the IMC evaluation include:
(A) Ability of the rotorcraft to safely operate in the National Airspace System, including crew capabilities to cope with probable malfunctions. Examples of failures imposed during this IMC evaluation on previous programs are shown below:
(1) Hydraulic tailure;
(2) Individual COMM, NAV, or intercom failure;
(3) Engine failure;
1036 Par 775
(4) Loss of any power input;
(5) SAS failure;
(6) Trim failure; and (Z) Individual failure of each vertical and directional gyro.
(B) Visibility during low approach conditions in precipitation.
(C) Glare and reflections at night in clouds.
(D) Workload demands on the minimum flightcrew including the failures in Paragraph 775b(9)(A)(1).
(E) Handling qualities in turbulence throughout the IFR approved envelope including typical IFR flight maneuvers;
(1) With reasonably anticipated SAS failures;
(2) With reasonably probable control system failures (hydraulics, force trim, basic ship systems, etc.);
(3) With the typical workload conditions associated with operating in high density traffic areas; and
(4) With other reasonable, probable failures.
(F) Cockpit leaks in precipitation which affect pilot efficiency, safety, or rotorcraft airworthiness.
(ii) Rotorcraft that are an improved, modified, or later model of_previously approved type that have no significant changes in the fuselage and windshield configuration, the aircraft lighting system, and the rain removal systems do not need to be flown in clouds. They may need to be evaluated in clouds if, in the judgment of the flight test personnel, there is some doubt as to the similarity of the configuration.
However, a previously approved rotorcraft undergoing IF certification tests for a different SAS should not require a series of actual FR flights just to determine pilot workload or whether it can be flown in clouds.
(10) Static Position Error. The static position error should be reevaluated to determine altimeter error during instrument approach conditions. This is particularly important when high angle approaches (above 3°) are approved. Static position error for 3° approaches can typically be approximated by the level flight error. The direction of error is important. If the indicated value is lower than actual value, the error is in a Par 775 1037
conservative direction and further investigation may not be required. The direction and magnitude of static position error should be determined for steep angle approach conditions and additional information provided when necessary in the Rotorcraft Flight Manual. An investigation of static system response during the go-around transition should be investigated.
(11) Cross Coupling. IFR handling qualities are enhanced by providing low levels of coupling between axes. During the flight evaluation, pilots should be alert for strong cross coupling tendencies between yaw and pitch, heave (collective) and pitch, heave and roll, or roll and pitch. Any strong coupling effects between these motions may produce unacceptable handling qualities for IFR flight. The rotorcraft should be able to make a smooth transition from any flight condition. As an example, large rolling or pitching moments with collective application would represent questionable handling characteristics for the FR missed approach condition.
(12) Electrical. Avionics, and Instruments. Some aircraft have been certified with different equipment from that suggested in this subparagraph because the certification criteria for IF has evolved in several stages. The following guidance refers to the latest certification requirements:
(i) Additional Avionics/Instruments. The avionics/instrument required for IF certification beyond those required by § 27.1303 should be as follows:
(A) Standby Attitude Indicator. Power for operation and lighting must be independent from the rotorcraft electrical generating/starting system.
Operation must be maintained for 30 minutes after total aircraft electrical power generating system failure. For dual pilot configurations, one pilot's primary indicator may be designated for this purpose, provided standby batteries are provided.
(B) Alternate Static Source. An alternate static source with a means of selecting this source must be provided for single pilot configurations.
(C) Direction Indication. Gyro Stabilized. Magnetic in place of non-magnetic required by § 27.1303(h).
(D) Navigational Systems. Navigational systems required by the applicable operational rules must be provided.
(E) Communication Systems. Communication systems required by the applicable operational rules must be provided.
(F) Other electrical/electronic equipment. Other electrical/electronic equipment required by the applicable operational rules must be provided.
1038 Par 775
7/30/97 АС 27-1A (I) Electrical Power Availability for Avionic and Instrument Systems.
Minimum avionic and instrument systems should remain operative after electrical power failures in relation to IFR operation. The lists that follow suggest the minimum Avionic and Instrument Systems that should remain operational after a single failure of the generating system and after failure of all but the emergency power source. These lists do not address the basic equipment required for non-IFR related operation. These basic equipment requirements are addressed by the appropriate paragraph of this AC.
(A) Avionic and instrument systems that should remain operational for JER approved rotorcraft, after a single failure of the electrical generating system.
The rotorcraft must be capable of IF flight for one-half the maximum cruise duration.
The suggested minimum avionic and instrument systems are as follows:
(1) Flight Instruments. Same as § 27.1303 requirements, except as defined by Subparagraphs 775(12)(i)(A) and (C).
(2) Communications. One VHF radio.
(3) Navigation System. One navigation system, including necessary sensor inputs such as directional gyros.
(4) Transponder.
(5) ICS System. Required for two pilot approval.
(Q) Instrument Lights (or equivalent).
(B) Avionic and instrument systems that should remain operational, for IFR approved rotorcraft, after total failure of the electrical generating system. The rotorcraft must be capable of flight for a minimum of 30 minutes. The suggested minimum equipment is as follows:
(1) Magnetic Compass.
(2) Airspeed-Altitude Attitude Presentation.
(3) Communications One VHF System.
(4) Instrument Lights (or equivalent).
(5) ICS System-For Two Pilot Approval.
(ії) Directional Instruments. A magnetic, gyro stabilized direction indicator is specified because navigation in instrument flight must be precise. In rotorcraft, the nonstabilized magnetic indicator is subject to many errors, particularly in Par 775 1039
turbulence. Therefore, it is inappropriate as the primary source of directional information, but it is adequate as an emergency source. A nonslaved directional gyro is also inappropriate as the primary source of directional information because of drift and the requirement to set it to some other precise reference.
(A) As a minimum for single pilot IFR, a nonstabilized magnetic indicator (such as a "whiskey compass") and a magnetic gyroscopically stabilized direction indicator system (slaved) are required.
(B) The minimum for dual pilot certification includes the instruments required for single pilot, and an additional independent gyroscopically stabilized directional indicator system (slaved or unslaved).
(13) ER Electrical System.
(i) General.
(A) The entire electrical system, both AC and DC portions, should be reviewed with IFR operation in mind. This review is necessary since most of the rotorcraft presently certificated do not include IFR operation as part of their certification.
Many aspects of normal operation and results of failure conditions may be entirely acceptable for VFR operation but unacceptable for IFR operation.
(B) Provisions should be made for a capability to continue flight for one-half the maximum cruise duration in the event of a single failure in the electrical system. Paragraph 652 contains the definition of a "single failure." The evaluation of the system under failure conditions should consider not only the failure itself, but also the recommended cockpit procedure to respond to any failure.
(C) The fault analyses of the electrical system and the results of the system testing to validate that analysis serves as a good starting place for the electrical system review. Failure of each generator, each battery, and each component, such as switches and relays, should be accounted for first since failure of equipment and components are the most probable.
(D) System failure such as tripped circuit breakers, blown fuses, loss of busses, loss of feeders, loss of ground terminals, and failure of electrical disconnect plugs should also be considered.
(E) Routing of all wiring from each power source throughout the distribution system should be reviewed. In all instances feeder wires should be routed separately from small gage control wiring. Also, wiring for each power system should be separated to the maximum extent practical from the wiring associated with other required power systems.
1040 Par 775
(F) A single electrical disconnect plug should not contain wiring for more than one generating system. Many systems incorporate automatic feeder fault protection that disables a power source experiencing a short circuit on its feeder, and in some instances passive protection has been provided for the feeders.
(G) There may be other failures that should be considered that are peculiar to the specific design being evaluated and, if so, an appropriate accounting of these failure should also be made.
(H) Single engine rotorcraft that are being upgraded from VFR to IFR will require careful evaluation of the electrical system. These aircraft normally do not have distribution systems that can tolerate bus or feeder failures, and these failures would result in loss of the entire electrical system. Normally these systems are modified such that distribution system and power supply failures will only result in a partial loss of electrical capability. The power supply problem has been accounted for by the installation of a second generator in some instances or by adding extra battery capacity in others. When an extra battery is added, or a larger battery is substituted, the ampere-hour capacity should be based on one-half the time associated with a worst case maximum flight duration consideration. Additionally, in all instances so far the standby attitude system has been provided a separate power supply capability, in addition to the extra power supply capability described above.
Review of Regulations. The airworthiness regulations concerning electrical systems begin with § 27.1301 (Ref: Subpart F - Equipment) and continue through § 27.1401. Other rules may also concern the electrical system; however, compliance with these sections should have been assured as part of the original VFR approval.
(її) Specific Emphasis Areas. In some previous installations, changes have been necessary in the areas listed below. Future installations should be checked carefully in these areas and other areas that indicate a need for attention.
(A) Systems Affected by Icing. Gross inaccuracies in altitude and airspeed indicators resulting from icing could be disastrous in IFR flight. For rotorcraft not equipped with approved alternate static sources, static ports should be carefully evaluated and should either be heated or an analysis verified by flight test data submitted to substantiate leaving them unheated. Static line routing should be carefully evaluated for low spots. Also, if static ports are on the side of the rotorcraft, the lines should be initially routed upward just behind the static ports, then down to a drain. If the lines are initially routed upward, the lines will not fill with water when the rotorcraft is flown through rain or is washed.
(B) Overvoltage Protection. A few rotorcraft may have this protection, but many do not. Since overvoltage protection is specifically required for Par 775 1041
АС 27-1A 7/30/97 IFR operation, the rotorcraft's basic electrical system should be very carefully reviewed for this capability.
(C) Power Adequacy Indication. Most flight instruments that use a power supply have a visual means integral with the instrument to indicate the adequacy of the power being supplied. For those required flight instruments that are not provided with a visual means, the following should be accounted for:
(1) The visual means provided should be at least adjacent to the instrument.
(2) The visual means should be adequately placarded.
(3) The power should be measured at or near the point where it enters the instrument.
(4) For electrical instruments, the power is considered to be adequate when the voltage is within approved limits. The source of power for the visual means of indication must be independent of the source of power for the instrument itself. Independent, in this case, means a separate circuit protective device and a separate distribution system bus.
(D) Multiple System Separation. Multiple systems performing the same function are required in certain instances because it is probable that a single system will fail. Separation of such systems would preclude a single fault from causing a multiple system failure. The following should be considered:
() When possible, cable routing should be accomplished to ensure the maximum separation; for example, one system routed on one side of the rotorcraft and the other system on the opposite side. Some areas, such as pedestals, junction boxes, and equipment racks bring systems close together, and in these areas physical separation may be minimal.
(2) Systems that are required to be duplicated should not be routed through one electrical disconnect plug.
(3) System grounds should be evaluated to assure wiring for two required systems is not grounded to the same terminal. If a terminal strip contains grounds for multiple systems, it should be grounded to the rotorcraft's airframe in two places from two separate terminals.
(E) Circuit Protective Devices. All systems that are "required" for IFR operation are considered to be necessary for safe IFR operation, and the circuit protective devices for those systems should generally be accessible to the crew in the cockpit so they can be readily reset or replaced in flight. The location of the generator 1042 Par 775
field protective devices has been a problem in some rotorcraft. The protective devices that can result in the loss of a required power system should be accessible in the cockpit. This position is further supported by the occurrence of nuisance opening of circuit protective devices in rotorcraft. Further discussion on this issue is included in Paragraph 655b(4) of this advisory circular.
(F) Intercommunication System. All audio for the entire rotorcraft comes together at this system. An evaluation should be made to ensure that no single failure will result in the loss of all audio for the rotorcraft. Check for common grounds, common connectors, etc. Power inputs should also be disabled.
(14) Rotorcraft Flight Manual Material.
(i) In addition to other required information, the limitations section of the Rotorcraft Flight Manual (RFM) or RFM Supplement must include the approved IFR flight envelope, minimum IFR crew requirements, the minimum required equipment for dispatch into IFR conditions that is not covered by the operating regulations, and the maximum approach gradient which has been approved. If a significant loss of altitude is experienced in any flight regime or maneuver during certification analysis or testing, the emergency operating procedures should include a statement of this altitude loss along with any other appropriate information.
The limitations section of the Rotorcraft Flight Manual should not include restrictions prohibiting external cargo operations. These operations are covered by Parts 91 and 133 and all external load operations conducted under these parts must be approved by the controlling operations inspector. It is the responsibility of the operator to demonstrate, and the operations inspector to confirm, that any external load operation, including en route IFR, can be safely conducted.
(15) Rotorcraft Flight Below Instrument Flight Minimum Speed.
The advent of steep angle, decelerating precision instrument approach procedures will necessitate flying at airspeeds below the instrument flight minimum speed (VINI) established for most rotorcraft under FAR 27 Appendix B, Paragraph 11(c).
(ii) Applications for findings of equivalent safety to approve instrument flight below VMINI, will be considered by the FAA/AUTHORITY for rotorcraft meeting at least the following criteria:
(A) The rotorcraft is certified for FR flight.
(B) For constant airspeed approach approval: a minimum approach airspeed is specified by the applicant, at which the rotorcraft is demonstrated to be safely controllable and capable of instrument flight without undue pilot effort for the Par 775 1043
duration of the approach and transition to missed approach, including acceleration to an airspeed above VMINI- (C) For decelerating approach approval: a two or three cue flight director is provided as required equipment, and the rotorcraft is demonstrated to be safely controllable and capable of instrument flight without undue pilot effort for the duration of the approach and transition to missed approach, including acceleration to an airspeed above VMINI- (D) The rotorcraft is demonstrated to be safely controllable following single failures of aircraft systems not shown to be extremely improbable at the minimum approach airspeed specified by the applicant or encountered during a decelerating approach.
The Rotorcraft Flight Manual Supplement (RFMS) contains the following information in addition to the requirements of Paragraph IX of Appendix B to FAR 27:
(1) Minimum approach airspeed, if applicable.
(2) Additional aircraft equipment requirements for flight below VMINI and/or the minimum approach airspeed, if applicable.
(3) Maximum approach angle.
(4) Maximum allowable surface wind for safe conduct of the approach.
1044 Par 775
Par 775 7/30/97
ACCEPTABLE 15 10
UNACCEPTABLE 5
L L L -0.3 -0.2 -0.1 0.05 0.1 0.15 AC 27-1A DAMPING RATIO (5) 1045 FIGURE 775-1. ROTORCRAFT DYNAMIC STABILITY REQUIREMENTS FOR IFR