Note: Extensive service experience should not be considered as a basis for level of criticality without accomplishing RTCA Document DO-178 procedures.
(20) Rotorcraft Health and Usage Monitoring Systems (HUMS).
(i) General. HUMS can be divided into two major categories: health monitoring systems and usage monitoring systems. The provisions of § 29.1301 are used to determine that the system performs its intended function. The provisions of § 29.1309(a) and (b) are used to look at the impact of environmental conditions and malfunctions. There have been very few HUMS approved to replace service life or other specific physical limits but several systems are now in the process of seeking approval. We consider health monitoring systems the serious applications of this technology, and it will probably be some time before the necessary database is available to allow full reliance on this technology. There have been numerous approvals of usage monitoring systems as optional equipment, and a good example of this technology is a condition monitoring system described in paragraph b.(19) above.
Refer to section AC 29 MG 15 of this AC for guidance on the certification of HUMS.
(ii) Health Monitoring Systems.
(A) We anticipate that these systems will begin as “optional” systems in order to build a database to support expansion of the approval to achieve credit for extension of maintenance intervals, and so forth. Systems range from low to high integrity requirements depending on the determined criticality of application.
(B) Some systems under consideration will utilize off aircraft processing of data. If pursuing this, it should be assumed that the aircraft data will be lost or misplaced at the processing center, and the aircraft system design should consider this possibility. Some on-board data storage is one way to account for this lost data. The integrity of the processing center’s software should be equal to that of the aircraft software. In addition the intervals for processing the data from each flight should be specified as part of the approval.
(C) Due to the limited experience with these systems, we suggest using the issue paper process to record the progress of the approval, and to provide information for later updating of this guidance material.
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CHAPTER 3
AIRWORTHINESS STANDARDS
TRANSPORT CATEGORY ROTORCRAFT
MISCELLANEOUS GUIDANCE (MG) AC 29 MG 2. STANDARDIZED TE ST PROCEDURE FOR ROTORCRAFT DC ELECTRICAL SYSTEM TESTS.
a. Test Requirements.
(1) General. The following functions and characteristics are to be evaluated:
(i) Normal System Operation.
(ii) Parallel Load Division.
(iii) Excitation.
(iv) Stabilization.
(v) Systems Malfunction.
(vi) Environmental Capability.
(vii) Electromagnet ic Compatibility.
(viii) Cooling Capability.
(ix) Surge Characteristics, Ripple Voltage, and Voltage Spikes.
(2) Instrumentation. Calibration records should be available for all instrumentation. Current and voltage vs. time should be recorded in a permanent form.
Enough specific currents and voltages should be recorded to allow reconstruction of any sequence of events that would happen as a result of any system testing described herein.
(3) Regulatory References. Sections 29.1301, 29.1307(c), (d), (e), 29.1309,
29.1351, 29.1353, 29.1355, 29.1357, 29.1363.
(4) Miscellaneous. The assigned FAA/AUTHORITY systems and equipment engineer normally witnesses these tests and should be notified as far in advance of the testing as possible to minimize scheduling problems. Conformity of the test setup must be established prior to conducting any testing. Most of the above test categories can be conducted on a bench test setup. A bench test setup is especially recommended in the case of the system malfunction tests. It is the applicant ’s option to demonstrate his Page MG 2
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AC 29-2C, Chg 4 5/1/2014 equipment either on the bench or installed for ground tests. When a bench setup is used, it should represent the actual aircraft installation to the extent that components and wiring (type, gage, and length) are duplicated. Some retesting may be necessary on the aircraft to verify the bench test results.
b. Ground and Bench Test Procedures.
CAUTION: Prior to disconnecting the batte ry and removing or adding large loads, either isolate the avionics systems or assure that transients induced are within limits of the avionics equipment.
(1) Normal System Operation.
NOTE: Equipment should be operat ed for at least 10 minutes prior to each test as a warmup.
(i) Minimum electrical load for paralleling and minimum engine RPM.
(ii) Vary RPM of all engines from low to high and back to low.
(iii) Repeat b(1)(ii) for maximum and 50 percent of maximum electrical loads.
(2) Parallel Load Division (if parallel system).
(i) Minimum electrical load for paralleling and minimum engine RPM.
(ii) Fifty percent of maximum electrical load and minimum engine RPM.
(iii) Maximum electrical load and minimum engine RPM.
(iv) Minimum electrical load for paralleling, vary No. 1 engine RPM from low to high and back to low while holding the RPM of the other engine at minimum (low).
(v) Repeat above b(2)(iv) for each other engine on the rotorcraft.
(vi) Repeat above b(2)(iv) and b(2)(v) procedures with 50 percent of maximum electrical load.
(vii) Repeat above b(2)(iv) and b(2)(v) procedures with a maximum electrical load.
(3) Excitation.
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NOTE: All of these tests are to be conducted with the battery OFF since the purpose of the tests is to determine if the ship’s battery is necessary for excitation of the alternator(s)/generator(s).
(i) Minimum anticipated electrical load, low engine RPM, and alternator(s)/generator(s) OFF. Demonstrate that when an alternator/generator is turned ON, it will come on the line. Repeat for any other alternators/generators in the system.
(ii) Maximum electrical load, low engine RPM, and alternator(s)/generator(s) OFF. Demonstrate that each alternator/generator will individually come on the line.
(iii) Minimum anticipated electrical load, high engine RPM, and alternator(s)/generator(s) OFF. Demonstrate that each alternator/generator will individually come on the line.
(4) Stabilization.
NOTE: All of these tests are to be conducted with the ship’s battery OFF, since the purpose of the tests is to determine if the ship’s battery is necessary for stabilization of the alternator/generator. In each case, if the ship’s battery is not necessary for stabilization, the alternator/generator should be on the line and remain there at a satisfactory voltage level.
(i) Minimum anticipated electrical load, low engine RPM, alternator(s)/generator(s) ON. Switch on the heaviest electrical load that is anticipated to be installed on the aircraft.
(ii) Repeat b(4)(i) for a maximum electrical load and low engine RPM.
(iii) Repeat b(4)(i) for a minimum anticipated electrical load and high engine RPM.
(iv) Repeat b(4)(i) for a maximum electrical load and high engine RPM.
(5) System Malfunctions.
(i) Overcurrent faults (faults to airframe ground that are less than
5.0 Milliohms) should be applied to buses and feeders as necessary to demonstrate that the system’s overcurrent circuit protective devices are properly coordinated and provide adequate protection/fault isolation.
(ii) Simulate an overvoltage condition on each alternator/generator to demonstrate satisfactory operation of the overvoltage sensing network. On a Page MG 2 - 3
multiengine configuration, the faulty alternator/generator should be removed without affecting operation of the remainder of the system.
(iii) The annunciation circuitry should be checked for indication of failures such as overvoltage, tripped generators, overcurrent, open feeders, open tie breakers, etc.
(6) Aircraft Ground Tests. If the above tests (reference b(1) through (4) inclusive) are conducted on a bench setup, enough tests should be repeated on the aircraft to validate the bench test results. The following tests should be conducted on the aircraft:
(i) Normal Battery Starts. Start all engines on the aircraft following the normal procedure prescribed in the flight manual. Record starter volts and amperes, time, and any other parameters deemed necessary.
(ii) Ground Power Cart Starts. If the aircraft is equipped with a plug for a ground power cart, use the procedure described in the flight manual and start all engines. Record starter volts and amperes, time, and any other parameters deemed necessary.
(iii) Emergency Battery Operation (if provided). The emergency battery mode of operation should be tested to assure at least proper switching, annunciation, and battery capacity. In some instances, an analysis of battery capacity may be adequate.
(iv) Other Tests. Conduct other tests as necessary to demonstrate proper operation of the specific design being evaluated.
(v) Distribution System Tests. With all systems operating individually, open and close feeder circuit breakers and system circuit breakers and assure separation of power sources for essential systems. For example, removing power from one bus by opening a feeder should not result in loss of both NAV 1 and NAV 2 or both COMM 1 and COMM 2 or both attitude gyros, or for example, opening NAV 1 circuit breaker should not affect NAV 2, etc. If the opening of the feeder protection has been satisfactorily demonstrated on a bench test facility, it should not be necessary to repeat that demonstration on the actual aircraft. The effect of loss of power sources should also be demonstrated on the aircraft. Reference §§ 29.1357(e) and 29.1309.
(7) Environmental Qualification. Each component of the system, such as relays, switches, alternator, generator, sensor, regulator, diode, etc., should be qualified to the critical environmental parameters. The temperature, altitude, humidity, and vibration expected in the approved aircraft operational envelope should fall within those limits the applicant substantiates for the electrical system components. (Refer to paragraph AC 29.1309.)
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(8) Electromagnetic Compatibility. At no time during any of the qualification testing described herein should objectionable interference in the aircraft’s radio, navigation, cockpit instrument, autopilot, or interphone system be considered acceptable.
NOTE: The quantitative type testing used for Items (7) and (8) above is outside the scope of this document. The latest re vision of RTCA Document DO-160 is an acceptable standard.
(9) Transient Tests. The D.C. system should be tested and shown to exhibit surge, ripple, and spike voltages within the limits of the latest revision of RTCA Document DO-160.
(i) The surge and ripple voltage tolerance of avionic equipment is defined by the latest revision of RTCA Document DO-160. Category Z is considered applicable to rotorcraft D.C. systems.
(ii) The voltage spike tolerance of avionic equipment is defined by the latest revision of RTCA Document DO-160.
(10) Ground and Bench Test Report. At the conclusion of the ground and bench test program a report should be prepared and submitted that contains at least the following:
(i) System schematic (including instrumentation tie-in).
(ii) Instrumentation list (including calibration records).
(iii) Test result recordings.
(iv) Detailed procedures and results obtained.
(v) Conformity inspection records.
(vi) Other data, photographs, etc., to describe the test setup.
(vii) Summary of the test results. This summary should show the maximum load to which each bus, alternator/generator, etc., has been tested.
(viii) Analysis of test results. This should describe how compliance with the regulations has been shown. It should inclu de consideration of the critical failure modes. Refer to this AC’s sections AC 29 MG 1 paragraph a.(4)(ii) and AC 29.1309 paragraph b.(9)(iii)(D)(4) for further information on failure analyses.
c. Flight Test Procedures.
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(1) Alternator/generator cooling tests should be conducted in accordance with paragraph AC 29.1351.
(2) On multiengine rotorcraft, single-engine air starts should be conducted using the manufacturer’s recommended procedures. This should be accomplished for each engine individually.
(3) A cockpit evaluation of the electrical system should be conducted to evaluate:
(i) Switch, circuit breaker, and annunciator identification.
(ii) Visibility of placarding, switches, etc., during bright sunlight and night operation.
(iii) Color of annunciators as related to the function/malfunction annunciated.
(iv) Load meter readability.
(v) Access to essential switches, circuit breakers, etc.
(vi) Electromagnetic interference.
(vii) Compatibility of the electrical system with the rotorcraft flight manual and the need for additional procedures in the RFM.
(viii) Clarity of functions such as opened feeder breakers, tie breakers, related annunciation, and necessary corrective action in the event of malfunction.
(ix) Absence of undesired functions in relation to switch combinations.
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CHAPTER 3
AIRWORTHINESS STANDARDS
TRANSPORT CATEGORY ROTORCRAFT
MISCELLANEOUS GUIDANCE (MG) AC 29 MG 3. ROTORCRAFT AND SYSTEMS CERTIFICATION FOR CATEGORY II OPERATIONS.
a. Explanation.
(1) Category II 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 II 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 II but will not be discussed here.
(2) The ground facilities required for a Category II 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 II operations.
Therefore, the following Category II approvals procedures for rotorcraft assume an approach to a runway at airspeeds at or above VMINI.
(3) The regulations and advisory material covering the approval for IFR Category II operations are included in Part 91, Appendix A, and AC 91-16, Category II Operations - General Aviation Airplanes. Those references address airplanes;
however, the concept is also suitable for the approval of rotorcraft for Category II 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 II 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 II certification must first meet the requirements for rotorcraft instrument flight (Appendix B of Part 29 and paragraph AC 29.1543).
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(5) In addition to the ground facilities and environment noted above, there are requirements in three other general areas to obtain Category II approval. These are certification of the aircraft and systems, certification and continuation training of flight crews, and a continuing maintenance program for the aircraft and Category II required systems. The entire Category II approval requires a Category II 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 II operations.
(6) The additional equipment necessary for a Category II 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 II 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.
- 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 AC 29 MG 3-1 and AC 29 MG 3-2).
(2) Systems Evaluation.
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(i) The major portion of a Category II approval is the evaluation of the flight guidance system. To certify the flight guidance system for a specific model rotorcraft, a demonstration of 50 ILS 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 II 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.
(ii) The equipment to be installed for Category II 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 II 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 II 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 met hod 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 AC 29 MG 3-1 and AC 29 MG 3-2). 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 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 II 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 Page MG 3 - 3
required for a Category II 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 facility being used should be advised that Category II 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 II 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:
(i) The limitations, if any.
(ii) Revision to the performance section, if appropriate.
(iii) A statement of Category II approval to the effect that “The airborne instruments and equipment meet the performance standards for Category II approaches” and the following note:
“NOTE: Compliance with the performance standards referenced above does not constitute approval to conduct Category II operations.
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CATEGORY II APPROACH EVALUATION Pilot in Co mand Second in Command Date Registration No. Airport - Runway - - Weather Wind FAA Inspector This form will be completed whenever an approach is attempted utilizing the airbome low approach system, regardless of whether the approach is abandoned or concluded succesfully. APPROACH EVALUATION SAMPLE
1. Was the approach successful? YES NO
2. Flight control guidance system used
a. Auto-coupler
b. Flight director
c. If equipped and used, did a and b agree? YES NO Second in Comm and? YES NO FAA Inspector? YES NO
3. Airspeed at middle marker + - at 100' + - from program med 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 Acceptable Unacceptable Pilot in Command's Signature FIGURE AC 29.MG 3-1 Page MG 3 - 5