minimum values for continuous safe operation. Discontinuities in width have been used when normal ranges vary with other parameters. Integrating instruments in place of these markings should be encouraged although there may be no regulatory requirement for them.
(3) Cautionary Ranges. Time limited ranges, precautionary ranges, or ranges for which special operating procedures are required should be marked with a yellow arc or yellow line. If a yellow range is used to indicate a special operating procedure, information describing the special procedure should be included in the Rotorcraft Flight Manual.
(4) One-Engine-Inoperative Markings. One-engine-inoperative (OEI) ratings represent a special challenge for retaining simplicity and clarity in powerplant instrument markings. OE ratings are eligible to be used only during an extremely small portion of total flight time; therefore, they should not dominate the presentation or obscure other markings. They are needed only for reference. Indices for 2½-minute and 30-minute power may be marked above the takeoff power redline on engine power instruments. OE reference markings should be clearly distinct from the normal all-engines operating markings. One acceptable means of marking OEl limits has been narrow dashed radials with yellow for 30-minute, and red for 2½-minute limits. OEI markings should be consistent between gages. For example, a 30-minute marking on an N1 or torque gage should be similar in appearance to the 30-minute marking on the engine temperature gage.
(5) Red Arcs or Ranges. Sections 29.1549(d) and 29.1553 allow the use of red arcs. Experience has proven that when red arcs are used to indicate maximum or minimum values, the meaning of a red line loses its significance. Therefore, the use of red ranges or arcs to indicate limit values should be discouraged. Red is conventionally used to represent a limit (maximum or minimum) for which an aircraft or component has been substantiated. A "range" of limits for a given parameter is not consistent with the definition of the terms "limit," "minimum," or "maximum." In addition, a red arc tends to imply that more than one value is limiting, that a scale is provided to show operation within a range of values, and that an absolute limit may not exist until the extreme of a red range is attained. These implications must be avoided wherever possible by specifying a single limiting value and marking it with a single red line (radial). If readings in excess of that value were indicated, it would then be obvious to the crew that a limit had been exceeded. A red arc may be used to indicate a transient vibration range as indicated in § 29.1549(d); however, if the range is a cautionary range and not a prohibited range, use of a yellow arc is recommended. The fuel gage configuration described in § 29.1553 is considered a special application of red arcs. Occasionally a red arc has been utilized when limits vary with other parameters. Discontinuities in width could conceivably represent limits when other parameters are considered. The use of integrating instruments would alleviate much of the problem and should be encouraged although it is recognized that there may be no regulatory requirement for them.
Par 781 1221
(6) Elight Evaluation. In evaluating gage markings, the final criterion must be, "Are the markings adequate for correct interpretation by the crew?" FAAJAUTHORITY evaluations of gage markings should begin early in a certification program utilizing a cockpit or aircraft mock-up whenever possible. All required gages and gage markings must be readable from each pilot station. Depending on cockpit and window geometry, gages should be evaluated in direct sunlight unless they are located high on the panel underneath a substantial glare shield. Evaluation in direct sunlight is especially important for any displays using light bars of digital lighting segments, such as digital radar altimeter presentations or vertical scale instruments using light segments.
Required gages must be readable without upper body movement or extensive head movement by the crew. Evaluators should be especially alert to any scale markings or range markings which are obscured by parallax, as such features are unacceptable. If the aircraft is to be approved for night operation, each required indicator must also be evaluated during night lighting conditions. The same visibility requirements apply for night; however, the evaluator should particularly look for lighting features which may change or obscure the colored markings. For example, in one case, red gage markings were totally obscured by red instrument lighting. Except for minor changes, lighting should be evaluated in flight in order to correctly evaluate vibration effects and various background lighting conditions.
(7) Digital Instruments.
For purposes of this discussion, two types of digital indicator are considered: (1) an indicator which consists of a column of light segments which illuminate sequentially to display changing values, and (2) an indicator which consists of horizontal and vertical line segments in the configuration of a block "g" to display numerical values. Both indicator types work well for parameters where trend information is generally not needed such as engine oil pressure or temperature.
However, for rapidly changing parameters such as engine exhaust gas temperature, torque, or RPM, trend information may not be attainable. Advisory Circular 20-88 (guidelines on the marking of power plant instruments) specifies that instrument markings are intended to provide necessary information at a glance. Trend information for power indicators is vitally important for safe operation of a rotorcraft, and this information must be obtainable at a glance. For the columnar light segments, the ability to quickly detect trend information is largely a function of the resolution provided by single segments (e.g.; if there are two segments for each percent RPM, the ability to detect trend information is better than if there is only one segment for each percent RPM). For digital indicators displaying numerical values, trend information may be unattainable because rapidly changing parameters produce a blur, and this design may be unsuitable as a single source of information. The evaluator should use a great deal of caution to assure adequate trend information is available in primary power and rotor indicators of digital design.
1222 Par 781
7/30/97 АС 29-2B (її) Another area of concern in digital and moving tape instruments is the ability to determine when limits are being approached. Color code markings are frequently incorporated on the moving face of a tape or digital presentation. In such cases, it is mandatory that limit markings be affixed adjacent to the presentation, or that another means be provided so that the pilot can anticipate approaching a limit. The beginning and end of normal and cautionary ranges should be marked adjacent to the display. The entire range need not be color coded adjacent to the display if the colors are integral on the face of the tape or in the individual digital segments. Marking of limit values solely on the tape or in the colored light segments alone is unsatisfactory.
Marking of digital indicators displaying numerical values is adequately addressed in AC 20-88, Paragraph 3, General.
(iii) Appropriate failure modes should be evaluated during the system analysis. This will ordinarily include portions of the digital display. Such failures should be detectable whenever they affect reading accuracy. As a result of this analysis, the system may incorporate a test feature which assures all digital segments operate satisfactorily. This feature should be encouraged.
(8) Additional Markings. To keep markings standardized and uncomplicated, only the FAA/AUTHORITY-approved ranges and limits should be included. Items such as manufacturer's recommended values or manufacturer's warranty information are inappropriate for instrument markings and should not be included. Such information may be presented elsewhere. Transient limits may be indicated by a small red index such as a dot or triangle. Information defining allowable conditions for each transient index should be in the rotorcraft flight manual (e.g., maximum for starting, 12 seconds).
(9) Airspeed Indicator. While the foregoing information is generally applicable to airspeed indicators, some particular features warrant additional attention.
(i> A red cross-hatched radial line should be located at power-off VNE if that value is less than power-on VNE:
Many rotorcraft have erratic, unreliable, or nonrepeatable airspeed indications at low speed which warrant caution when operating in that speed range. In such cases, a yellow arc on the instrument with appropriate flight manual explanation has been found acceptable.
(ill) Indicated airspeed values should be utilized for all airspeed indicator markings.
(iv) Airspeed "bugs" may be used to highlight important takeoff, landing, or limit speeds. This concept may generally be encouraged; however, there are a maximum number of "bugs" that can be utilized without confusion for any given indicator. Typically, two "bugs" are acceptable; three or more are questionable. "Bugs" may also be used on a variety of instruments other than the airspeed indicator.
Par 781 1223
(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