(10) Additiona Reference Material. Additional procedures for marking powerplant instruments are contained in Advisory Circular 20-88. Where conflicts for rotorcraft exist between AC 20-88 and this document, the more recently dated publication should be utilized.
781A. § 29.1549 (Amendment 29-34) POWERPLANT MARKINGS.
a. Explanation. Amendment 29-34 introduces the optional ratings of 30-second/2-minute OEl. Paragraph 29.1549(e) has been revised to show that the limits for the 30-second OE rating are not required to be marked. Use of the 30-second OEI rating is limited to critical phases of operation after a failure or precautionary shutdown of an engine. During this critical stage of operation the crew should not be required to monitor engine instruments to avoid exceedances. Automatic control of the 30-second OEl limits are required by Paragraph 29.1143(e), therefore the 30-second OEI limits are not required to be marked.
b. Procedures. The method of compliance is unchanged except the marking of 30-second OE limits is unnecessary.
782. BOTORCRAFT AND SYSTEMS CERTIFICATION FOR CATEGORY I| OPERATIONS.
a. Explanation.
(1) Category Il instrument approach and landing minimums variations are based on ground facilities and environment, aircraft equipment, crew training, crew proficiency, and maintenance programs. For the pilot, the approach and landing minimums final consideration is the runway visibility which can be, and usually is, related to a cloud ceiling, although the concept is that if there is a runway visibility of 4,000 feet, as an example, there is a very high probability that the ceiling will be at least 300 feet. Therefore, Category I minimums are weather conditions of not less than a 200-foot ceiling and ½-mile visibility or runway visual range (RVR) of 2,400 feet.
Category Il minimums permit approaches at less than 200 feet decision height/RVR 2,400 to as low as 100 feet/RVR 1,200. Category III approach minimums are less than Category Il but will not be discussed here.
(2) The ground facilities required for a Category Il approach and landing include specific approach lighting extending more than 3,000 feet from the runway, thus eliminating any present heliports from being approved for Category Il operations.
Therefore, the following Category Il approvals procedures for rotorcraft assume an approach to a runway at airspeeds at or above MINI
(3) The regulations and advisory material covering the approval for IFR Category Il operations are included in Part 91, Appendix A, and AC 91-16, Category Il 1224 Par 781
Operations - General Aviation Airplanes. Those references address airplanes;
however, the concept is also suitable for the approval of rotorcraft for Category Il operations. The equipment to be required and the procedures to be followed are basically the same for a rotorcraft as for an airplane. Additional reference material concerning Category I approval is contained in FAA Order 8440.5A, General Aviation Operations Inspection's Handbook, and AC 120-29, Criteria for Approving Category I and Category II Landing Minimum for FAR 121 Operations.
(4) Authority for rotorcraft to use Category A airplane minimums is contained in § 97.3(d)(1). FAA Order 8440.5, §§ 97.3, 91.6, and Appendix A of Part 91 provide authority to consider the rotorcraft as a small, Category A aircraft and relief from the requirement for two pilots and two sets of instruments and equipment. Any rotorcraft that is presented for Category Il certification must first meet the requirements for rotorcraft instrument flight (Appendix B, Part 29, Paragraph 781 of this AC).
(5) In addition to the ground facilities and environment noted above, there are requirements in three other general areas to obtain Category Il approval. These are certification of the aircraft and systems, certification and continuation training of flightcrews, and a continuing maintenance program for the aircraft and Category II required systems. The entire Category Il approval requires a Category Il manual that covers all of these areas. FAA/AUTHORITY approval of this manual would normally be the responsibility of the operations and airworthiness inspectors that grant the approval to an operator for Category Il operations.
(6) The additional equipment necessary for a Category Il approval consists of the flight control guidance system. This system can be either a flight director system or an automatic approach coupler. A flight director system needs only to present computed steering data for the instrument landing system (ILS) localizer and should present at least raw glideslope data on the same instrument as the localizer steering commands. A single-axis steering autopilot could be used if it coupled to the ILS localizer. In a practical sense, however, contemporary rotorcraft flight director and automatic pilot systems use at least two-axes command guidance or coupling, and some provide coupling or guidance in three axes; localizer, glidepath, and airspeed. A marker beacon system or a radio altimeter is required for operations with decision heights of 150 feet or less. A rotorcraft flight manual (RFM) supplement is required to define the configuration limitations and procedures for Category Il operation.
b. Procedures.
(1) Instrumentation. Test instrumentation is required to provide a time history of the following parameters throughout each approach:
- Localizer deviation.
- Glideslope deviation.
Par 782 1225
- Radar altitude (if available).
These parameters can be acquired from the cockpit display for each one. The localizer and glideslope deviations are normally recorded as a microampere deviation from the centerline on a continuous strip recording. The radar altitude is continuously recorded as feet above the ground on the same recording device. Any type of recorder that produces a time history of these parameters throughout the approach would be satisfactory. However, a recorder that can be read during, or immediately after, each approach is recommended. This will allow the acceptability of the tracking during the approach to be determined immediately after each approach.
in addition to the above data, cockpit data should be hand recorded on a format similar to that shown in AC 91-16, Attachment 3 (Figures 782-1 and 782-2).
(2) Systems Evaluation.
The major portion of a Category Il approval is the evaluation of the flight guidance system. To certify the flight guidance system for a specific model rotorcraft, a demonstration of 50 LS approaches with a 90 percent success rate (as defined in Part 91) must be accomplished. If the flight guidance system has not been previously certificated in the rotorcraft, a certification program should be completed for the system before the Category Il evaluation is started. It should be determined that the flight guidance system does comply with all the certification requirements before 50 ILS approaches. This is particularly true of an autopilot system where hardover malfunctions must be considered.
(її) The equipment to be installed for Category Il operations must meet the performance criteria specified in AC 120-29, Appendix 1. This material details the criteria for approval of airborne equipment and its installations to meet Category Il performance. This appendix covers the rotorcraft flight manual, the systems ground tests, and the installation requirements and tests. Transport category rotorcraft should meet the same systems performance requirements as transport category airplanes.
(iii) The flight demonstration required for Category Il system approval is explained in Part 91, Appendix A, Paragraph (e). The accuracy requirements for the tracking equipment are included in Appendix 1 of AC 120-29. The usual method of determining the tracking accuracy is by measuring the localizer and glideslope deviations in microamperes and printing them on a continuous strip recorder. The observed cockpit date should also be recorded on a form similar to that in AC 91-16, Attachment 3 (Figures 782-1 and 782-2). Each approach made during the evaluation should have a complete set of data.
(iv) Coupler systems that require manual trimming by the pilot to center the AFCS actuators should be carefully evaluated, especially in turbulent conditions or 1226 Par 782
gusty crosswinds. These systems may not meet the trim requirements at the 100-foot decision height or may not provide sufficient tracking accuracy without excessive pilot attention and workload.
(V) The effects of coupler system hardover malfunctions should be evaluated in all axes to determine the minimum decision height. The altitude loss that would occur from a nose down hardover at the decision height should be determined.
This altitude loss should be included in the rotorcraft flight manual with the appropriate limitation on the minimum height above the ground for operation with the coupler engaged.
(vi) It is recommended that the demonstration approaches be made to Category II ILS facilities, although this is not required by either Part 91, Appendix A, or AC 91-16. Many Category I ILS installations do not provide good enough signals at the lower altitudes for the precise tracking required for Category Il operations. In many cases, this is due to the effects of terrain or buildings off the approach end of the runway. Nevertheless, if satisfactory accuracy can be attained, all the approaches required for a Category Il approval may be made at Category I facilities. During the flight test, especially if simulated IFR conditions are used in good weather, the approach control and control tower of the tacility being used should be advised that Category Il operations are being conducted. The Category II ILS clear areas must be kept unobstructed to allow satisfactory ILS signals. The air traffic control agencies should assure that taxiing aircraft, airfield maintenance trucks, and other airfield traffic are kept out of the critical areas during the data-gathering approaches. These agencies can also monitor the ILS facility for proper operation to Category Il standards and can advise the test aircraft if abnormal operation occurs.
(3) Rotorcraft Flight Manual. Upon satisfactory completion of an engineering inspection and test program, the FAA/AUTHORITY Rotorcraft Flight Manual (RFM), or supplements thereto, should reflect the following:
(1) The limitations, if any.
(il) Revision to the performance section, if appropriate.
(ill) A statement of Category Il approval to the effect that iThe airborne instruments and equipment meet the performance standards for Category Il approaches" and the following note:
"NOTE: Compliance with the performance standards referenced above does not constitute approval to conduct Category Il operations.
Par 782 1227
CATEGORY II APPROACH EVALUATION Pilot in Command Second in Command Date Registration No. Airport_ Runway _ Weather Wind FAA Inspector This form will be completed whenever an approach is attempted utilizing the airborne low approach system, regardless of whether the approach is abandoned or concluded succesfully.
APPROACH EVALUATION MPLI
1. Was the approach successful? YES NO
2. Flight control guidance system used
a. Auto-coupler SA
b. Flight director
c. If equipped and used, did a and b agree? YES NO Second in Command? YES NO FAA Inspector? YES NO
3. Airspeed at middle marker + _at 100' ‡ _from programmed speed?
4. If unable to initiate or complete approach (indicate which), was reason due to:
a. Airborne equipment Identify and describe nature of deficiency.
b. Ground equipment Identify and describe nature of deficiency.
c. Approach control or tower request
d. Other State reason.
5. Was airplane in trim at 100' for continuation of flare and landings?
YES NO
6. If approach and landing abandoned, state altititude above runway:
feet (State reasons)
7. Quality of overall performance: Good L Acceptable _ - Unacceptable L Pilot in Command's Signature FIGURE 782-1 1228 Par 782
CATEGORY II APPROACH EVALUATION (cont.)
INDICATE GLIDESLOPE AND LOCALIZER DISPLACEMENT AT MIDDLE MARKER AND 100 FT. A.G. POINT
MIDDLE MARKER 100 FT. A.G.
INDICATE AIRPLANE DISPLACEMENT & ORIENTATION WITH
RESPECT TO RUNWAY CENTERLINE AT MIDDLE MARKER AND 100 FT. A.G. BY SYMBOL AT AIRPORTS AND RUNWAYS LISTED.
THRESHOLD
RUNWAY WIDTHS SAMP
1.5 | 1. | 0.5| 10.5 11.0 11.5 0 1 100 FT. A.G.
MIDDLE MARKER REMARKS:
CL OF RUNWAY EXTENDED
TOUCHDOWN WAS FEET FROM THRESHOLD AND
FEET LEFT RIGHT OF CENTERLINE FIGURE 782-2 Par 782 1229
783. STRUCTURAL CONDITION INDICATORS.
a. Related Sections. § 29.301 - Loads; § 29.305 - Strength and Deformation;
§ 29.571 - Fatigue Evaluation of Flight Structure; § 29.1301 - Function and Installation;
§ 29.1309 - Equipment, Systems and Installations; § 29.1321 - Arrangement and Visibility; § 29.1322 - Warning, Caution, and Advisory Lights; § 29.1355 - Distribution System; § 29.1503 - Airspeed Limitations: General; and § 29.1529 - Instructions for Continued Airworthiness.
b. Background.
(1) Structural condition indicators have been used on rotorcraft for several years in two main programs: as part of the basic type design and as part of airworthiness directive (AD) action. When approved as part of the basic type design, only limited "credit" has been given for the installation of structural condition indicators;
i.e., components provided with a structural condition indication system were required to be designed to § 29.571 "safe-life" criteria considering the structural condition indicator system inoperative. So-called "nonhazard" approvals were granted. When used as part of the mandatory actions of ADs, structural condition indicators have had a degree of "credit" recognized, primarily in the recognition of "fail-safety" provided by the indicator system.
(2) Since structural condition indicators have been used during both original type design and AD issuance, and since there is movement toward increased damage tolerance in rotorcraft design, policy concerning condition indicator use is considered appropriate.
c. At present, the use of structural condition indicators alone on new type designs is not considered an acceptable substitute for providing the necessary safe life for each component. However, areas which may be considered when approving these indicators for fail-safety credit are delineated in the following paragraphs.
d. What, how, when, where, and who of structural condition indicators.
(1) Indication of what?
Previous structural condition indicators have primarily been used for crack detection. Several types of through-the-thickness crack detection systems are currently in use. Two types which detect changes in pressure in an instrumented chamber due to gas movement through a cracked wall are known as the blade inspection method (BIM) system and the integral spar inspection system (ISIS). These systems can only detect full-depth cracks which are large enough to allow loss (of gain) of pressure from the instrumented chamber. This presents a limitation since full-depth cracks may be fast growing before detection. Another through-the-thickness crack method is a pressurized, dyed fluid or oil system to detect through cracks in specially 1230 Par 783
designed bolts (NASA patent), spindles, pins, or other closed chamber mechanical equipment.
(ii) Surface cracks can be found by systems such as surface-mounted crack detection wires. These systems would allow a greater safe crack growth period for assuring safe landing after detection than the through-crack-detection systems, but they have been used little in operations because of significant limitations; e.g., complexity of installation, durability problems, limited areas of coverage, and strain level limitations.
(™) Some aircraft have had mast moment indicators or other load indicators to help prevent the pilot from inadvertently applying a high load to the instrumented system or to help the pilot reduce the load by control movements. These load indicators only indirectly give indications of structural condition; therefore, only limited "credit" is allowed for this use. "Credit" is limited in that the fatigue life substantiations of § 29.571 should consider a reasonable number of excursions into the higher ranges established for the load indicator, and special inspections, rework, or replacement instructions should be provided for any strength degradation associated with high range excursions.
(2) How indicated?
Current BIM systems use two types of indicators. The visual blade inspection method (VBIM) uses a gauge mounted on the blade which must be read visually by maintenance personnel while the aircraft is parked. The cockpit blade inspection method (CBIM) uses lights mounted in the cockpit which may be monitored by the crew. Other pressurized chambers have used dyes or oils to improve visual inspection effectiveness. Mast moment indicators and other load indicators use instruments with marked ranges and needles.
(ii) No specific types of load indicators are required by the FAA/AUTHORITY but the type used should be evaluated for accuracy, readability, and overall effectiveness. Paragraphs 783(e) and (t) cover, in more detail, the use of structural condition indicators.
(3) When indicated? Structural condition indicators are used before flight, during flight, and for normal maintenance inspections. Paragraphs 783(e) and (f) contain guidance for cockpit-mounted instruments which are monitored during flight.
Indicators used for normal maintenance inspections are the preferred type since they can be scheduled to allow the most effective use of available maintenance personnel of well-equipped maintenance facilities and of parts available.
(4) Where indicated? Indications on the component are provided by VBIM systems and by systems utilizing dye or colored oil leakage. Cockpit-mounted lights and gauges may be used for certain critical structures which require frequent, but Par 783 1231
АС 29-2B 7/30/97 simple, checks. Maintenance panel locations (cabin, equipment bay, etc.) are the preferred locations for use in routine maintenance.
(5) Who reads indicators? The flightcrew, of necessity, monitors indicators mounted in the cockpit for use during flight. Gauges with ranges of values representing mast bending moments or other structural loads are monitored by the flightcrew, as necessary, to reduce or to prevent control operations from imposing excessive loads or to prevent too many high load applications. Maintenance personnel are generally responsible for reading component-mounted indicators and for monitoring indicators which are mounted on maintenance panels. The before-flight checks may be conducted by maintenance personnel or by flightcrew in certain cases (i.e., cockpit-mounted gauges or "push-to-test" checks).
e. Actions required by indicators.
(1) On-ground indications. Indications noted on the ground should be followed by a functional check of the indication system as provided for by its design. If indications persist after the system has been checked and found to be functional, further inspection of the affected component(s) should be conducted for damage assessment. Any damage found as a result of the detailed inspections should be repaired or replaced as appropriate.
(2) In-flight indications.
Indications used for in-flight monitoring have in the past been used for two main reasons: to provide a structural load display (such as mast bending moment) and to help resolve a service problem (CBIM systems have been used to supplement conventional inspection methods in blind areas.
(її) Structural load display systems should not be used instead of correcting deficient designs. Structural load display systems are appropriate for use in locating control positions, such as the cyclic stick, under transient conditions such as slope landings and hover in sidewinds, but structural load display systems are not considered appropriate for routine operations such as climbout or cruise with constant attention required by the flightcrew. If the load indicator provides a needed tool to the pilot in limited types of operations and does not significantly add to pilot workload otherwise, its use can be considered.
(lI) In the past, certain service problems have been solved by adding in-flight indicators such as CBIM systems. When retrofit of the affected structure is impossible or impractical, and when conventional inspection techniques are shown to be inadequate by themselves, CBIM or similar systems may be the only practical solution, despite the increase in pilot workload and the potential for problems caused by overreaction by the pilot to a structural fault indication. When used for correction of service difficulties, the structural condition indicator system should be accompanied by 1232 Par 783
clear, concise crew directions to prevent possible catastrophic overreaction. Load reduction measures such as rotor speed changes, airspeed reductions, altitude changes, etc., should be clearly provided, if needed. Crack propagation time from indication should be sufficient to allow continued safe flight to a safe landing area. For new designs, CBIM or similar systems which add to the pilot's workload are considered inappropriate. Proper redesign to provide the needed safe life, fail-safety, and inspectability is considered the appropriate action.
f. Complementary considerations of structural condition indicator use.
(1) Two basic programs are commonly used for approval of structural condition indicators. Basic type certification procedures are used for mast moment indicators and similar systems, and AD's (with appropriate type design changes) are used for CBIM systems which require pilot attention and corrective action when an indication of a structural fault is detected.
(2) The fatigue substantiation required by §§ 27.571 and 29.571 should consider a conservative number of excursions into the high load range monitored by a structural condition indicator such as a mast moment indicator. Static strength should not be adversely affected by a single excursion into the high load range monitored by the indicator.
(3) Complementary design provisions should accompany the use of a structural condition indicator system. Redundancy of load paths and inspection systems and indicator system failure analyses should be provided, as necessary, to meet the requirements of § 29.1309. The life remaining after the indicator system detects a structural failure should be calculated (with test verification), and compatible inspection and/or overhaul programs should be provided.
(4) The FAA/AUTHORITY approval of a structural condition indicator system requires evaluation by the airframe, systems and equipment, and flight test specialists.
The airframe specialist has the responsibility to review effects of structural condition indicator system use on aircraft loads, strength and deformation, and structural fatigue evaluation as well as the instructions for continued airworthiness. The systems and equipment specialist needs to evaluate the system for function and installation as well as the reliability requirements of § 29.1309. Flight test evaluation of the instruments' arrangement and visibility, effect on crew workload, and possible changes for RFM is also needed. Care should be exercised to assure that responsibilities are not given to the flightcrew which would be more appropriately handled by a redesign or by the maintenance personnel. Early coordination between all specialists is necessary to prevent delays from last minute design changes.
Par 783 1233
784. EULL AUTHORITY DIGITAL ELECTRONIC CONTROLS (FADEC) FOR
INSTALLATIONS WITH CATEGORY A ENGINE ISOLATION
a. Explanation. The advent of "microprocessor technology" has resulted in rotorcraft engine controls being implemented by digital process control rather than by conventional means. These digital, processor-based full authority engine controls offer many performance advantages (such as isochronous governing) which were not feasible with conventional technology pneumatic or hydromechanical controls.
Because of the incorporation of this advanced technology, some additional considerations must be made of the engine installation to ensure regulatory compliance.
b. Procedures. The following is a discussion of some special attention areas for a Part 29 Category A FADEC engine installation. Paragraph 621(b)(3)(ii)(D) of this AC contains a general definition of what constitutes a "full authority" control.
(1) Software Qualifications.
Paragraph 621(f) contains a general discussion of the use of the recommended RTCA document DO-178A which is utilized for the approval of system software. When utilizing that document, one might arrive at the conclusion that the engine control as a required function is essential and thus level 2 software would be appropriate for the control. However, for this level 2 category software, errors are presumed to exist, and since a software error in a full authority control could result in simultaneous unacceptable malfunctions in all engines, the provisions of § 29.1309(b)(2)(i) for continued safe flight and landing and the engine isolation rule, § 29.903(b), would generally preclude the use of this classification.
System designs which provide redundant distinctive software or an alternate technology control which is automatically selected and meets all of the minimum regulatory requirements would reduce the impact of software errors and may allow the level 2; i.e., essential software classification. At level 1, it is accepted that the software is sufficiently error free that the software does not require further verification in the installation evaluation.
(2) Lightning Strike Protection. A complete discussion of an acceptable method of demonstrating that the FADEC, as installed, is adequately protected against the catastrophic effects of lightning is contained in Paragraph 621b(3) of this AC.
(3) Electrical Power System Considerations.
Normal Operation. The system should be evaluated with all power sources operating normally. If additional power source capability is being provided that is above the minimum required for certification, a certain portion of the evaluation 1234 Par 784
7/30/97 АС 29-2B should be conducted while operating in the minimum configuration. The minimum power source configuration should consider the provisions of § 29.903(b).
(її) Malfunction Conditions. Beginning with the minimum configuration that is required for certification, electrical power system malfunctions should be introduced and the impact on continued FADEC operation determined.
(iii) Circuit Protection Location. The circuit protective devices for the FADEC should be located in the cockpit such that they can be readily reset or replaced in flight. The operation of the FADEC system is considered to be essential to safety in flight. Reference § 29.1357(d).
(iv) System Separation. On multiengine applications, each system should be separated from the other system to the maximum extent practical. Wiring should be routed separately. Power should be taken from independent busses and grounds, and system components should be independent of one another.
(V) Periodic Checks. Where periodic checks are appropriate, they should be made at reasonable intervals. This would normally range from preflight checks for certain items of greater concern to a tie-in with normal aircraft maintenance intervals for other items. If a crew check is specified, it should be evaluated to ensure it is a reasonable check. If items to be checked are located in an area that can be covered by interior upholstery, for example, a crew check would not be considered reasonable, and further design considerations may be in order.
(4) Powerplant Insta lation Considerations.
A demonstration of compliance with § 29.901(c) would generally include a failure mode and effects analysis (FMEA) of the powerplant systems as installed. When a FADEC is utilized, the analysis would consider the control's failure modes, the installed engine reaction, the effect on the aircraft, and the crew response to the situation. Combinations of undetected failures should be considered. Engine failures which may be escalated in severity by the FADEC's response to the initial failure should be analyzed. Potentially hazardous failures should be evaluated during flight testing. The requirements of §§ 29.903(b)(2) and 29.1309(b)(2)(i) should be reviewed in determining acceptability of failures.
(ії) Section 29.903(b)(2), Category A engine isolation, is intended to ensure that a failure will not prevent the continued safe operation of the remaining engine(s) or require immediate action of the crew to ensure continued safe operation.
The FADEC's of the individual engines should be independent. Where communication between FADEC's is required (for example, for torque sharing), care should be exercised to ensure that failures which may occur will not result in a power loss to the extent that total power available is less than would be available under OEI conditions.
The no-required immediate-crew-action provision would preclude credit for manually Par 784 1235