Appendix 1 S-N data. Plot the data as shown in Figure APX1-1. Utilize the S-N data and loading spectrum of Paragraph 6b in substantiating a crack-free life or in arriving at a replacement time by cumulative damage analysis means. Where practical (as allowed by the number of damaging cycles in the loading spectrum), spectrum testing may be used for fatigue substantiation in lieu of S-N testing followed by analysis. The replacement time established should be included in the airworthiness limitations section of the document established under § 29.1529.
(ii) Fail-Safe Crack Growth (Fracture Mechanics) Substantiation. Test two or more specimens to obtain crack propagation data using either a realistic load spectrum or an accelerated load (spectrum or single) associated with the use of propagation theory and data after cracks have been initiated. Unless a more rational method with an equivalent level-of-satety is applied for, the tollowing methods of setting inspection intervals should be applied. In all cases, the inspection methods and intervals should adequately consider variables such as inspectability, type of inspection, crack growth behavior, and other scheduled maintenance considerations.
(A) For single element (load path) structure, plot the data and set the inspection as shown in Figure APX1-2.
(1) Set the initial inspection at L1/3.
(2) Set the repetitive inspection intervals at L2/4.
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Appendix 1
FLAW SIZE CRITICAL CRACK LENGTH FOR LIMIT LOAD
FIELD DETECTABLE FLAW SIZE
FLAW SIZE CONTROLLED I
BY MANUFACTURING QUALITY LIFE FIGURE APX1-2 CRACK GROWTH FOR SINGLE ELEMENT STRUCTURE Page A1- 18
Appendix 1 (B) For multi-element load path structure:
(1) Test all paths simultaneously with a 0.05-inch thick crack (or size detectable by manufacturing quality control procedures) in the critical element at the start of tests.
(2) Note when field detectable cracking occurs.
(3) Note when one element fails.
(4) Note when the residual strength of the remaining elements decreases to limit load due to crack growth.
(5) From Figure APX1-3, set initial inspection at L, /3.
(6) Set repetitive inspection intervals at (L2 + Lp)/3.
NOTE: If partial failure of the critical element is not detectable, then L2 becomes zero.
Page A1-19
Appendix 1
FLAW SIZE
FAILURE OF
CRITICAL CRACK LENGTH FOR LIMIT LOAD CRITICAL MEMBER
FOR REMAINING MEMBERS I- OR ELEMENT
AFTER FAILURE OF CRITICAL MEMBER MEMBER ELEMENTS
DETECTABLEFLAWSIZE FLAW GROWTH IN CRITICAL REMAINING
FLAW GROWTH LIFE FIGURE APX1-3 CRACK GROWTH FOR REMAINING ELEMENTS
OF MULTIPLE ELEMENT STRUCTURE Page A1- 20
Appendix 1
(iii) Other test and inspection programs may be used rather than those of Paragraphs 7g(5)(i) and 7g(5)(ii), if shown to have comparable or better probability of assuring that a catastrophic fatigue failure will not occur.
(6) The flaw tolerance characteristics can also be shown analytically by rellable or conservative methods such as the following:
(i) By demonstrating quantitative relationships with structure already verified as damage tolerant;
(Il) By demonstrating that the damage would be detected before it reaches the value for residual strength evaluation; or
(iii) By demonstrating that the repeated loads and limit load stresses do not exceed those of previously verified designs of similar configuration, materials, and inspectability.
h. Inspection. Detection of flaws before they become dangerous is the ultimate control in ensuring the flaw tolerance characteristics of the structure. Therefore, the applicant should provide sufficient guidance information to assist operators in establishing the frequency, extent, and methods of inspection of the critical structure, and this kind of information should, under § 29.571(a)(2), be included in the maintenance manual required by § 29.1529. Due to the inherent, complex interactions of the many parameters affecting flaw tolerance, such as operating practices, environmental effects, load sequence on flaw growth, and variations in inspection methods, related operational experience should be taken into account in establishing inspection procedures. Comparative analysis can be used to guide the changes from successful past practice, when necessary. Therefore, maintenance and inspection requirements should recognize the dependence on experience and should be specified in a document that provides for revision as a result of operational experience, such as the one containing the operator's FAA/AUTHORITY-approved structural inspection program developed through the Maintenance Review Board (MRB) procedures for FAR Part 121 operators.
COMBINATION OF REPLACEMENT TIME AND FLAW GROWTH EVALUATION.
It may be possible to extend the replacement time of safe-life components that exhibit limited flaw tolerance capability by using a combination of the safe-life and flaw growth characteristics as described elsewhere in this Appendix and by assigning both a replacement time and inspection period to these components. The replacement time may then be based on the combined probability of not initiating a fatigue crack at or before the replacement time and the probability that the crack, if initiated, will be detected prior to catastrophic failure or loss of limit load (or maximum attainable load, whichever is less) carrying capability. The probability of detection should be based on consideration of the inspection effectiveness, the inspection intervals, and the fatigue life remaining after an obvious partial failure. A lower strength reduction factor Page A1-21
Appendix 1 commensurate with this probability of detection may then be used in the determination of the replacement time.
Page A1-22
Appendix 1 Attachment 1 - FLIGHT STRAIN PROGRAM CONDITIONS TO BE INVESTIGATED
1. GROUND CONDITIONS.
a. Normal start.
b. Rapid increases of RPM on ground to maximum power-on RPM of main rotor.
c. Taxiing with full cyclic control.
d. Landing run (if applicable).
e. Braking (if applicable).
f. Normal shutdown.
g. Special ground checks (if applicable).
2. IN-GROUND-EFFECT (IGE) MANEUVERS.
a. Hovering.
(1) Steady with rotor at maximum side of RPM tolerance.
(2) Steady with rotor at minimum side of RPM tolerance.
(3) 90° right turn.
(4) 90° left turn.
(5) Control reversal.
(i) Longitudinal.
(ii) Lateral.
(iii) Rudder.
(6) Sideward flight.
(1) Right.
(її) › Left.
(ili) Rearward flight.
b. Maneuvering.
(1) Jump takeoff.
(2) Normal takeoff and accelerate to climb airspeed.
(3) Normal approach and landing.
(1) Multiengine.
(ii) One-engine-inoperative.
(4) Full autorotational landing.
Page A1-23
Appendix 1
3. FORWARD FLIGHT-POWER ON.
a. Level flight.
(1) 40 percent VH.
(i) Minimum side of main rotor RPM tolerance (RPM +)
(il) Maximum side of main rotor RPM tolerance (RPM -)
(2) 60 percent VH.
(i) (RPM +)
(il) (RPM -)
(3) 80 percent VH.
(i) (RPM +) (I!) (RPM -)
(4) V
(i) (RPM +)
(ii) (RPM -)
(5) VNE:
(1) (RPM +) (i1) (RPM -)
b. Maneuvers.
(1) Full power climbs.
(i) All engines operative.
(ii) One-engine-inoperative.
(2) Cyclic pull-ups.
(i) 60 percent VH.
(ii) 90 percent VH.
(3) Normal acceleration from climb airspeed to 90 percent VH.
(4) Turns.
(1) Right at 60 percent Vu and 90 percent VH.
(ii) Left at 60 percent Vu and 90 percent VH.
(5) Control reversals at 90 percent VH.
(1) Longitudinal.
(il) Lateral.
(ili) Rudder.
(6) Deceleration from 90 percent Vu to descent airspeed.
(7) Part power descent.
(i) All engines.
(il) One engine out.
4. POWER TRANSITIONS.
a. All engines operating to one engine out.
(1) In full power climb.
(2) At 90 percent VH.
Page A1- 24
Appendix 1
b. One engine out to all engines operating in powered descent.
c. All engines operating to autorotation.
(1) At 60 percent VH.
(2) At maximum forward transition speed.
d. Stabilized autorotation to all engines operating at normal autorotation airspeed.
5. AUTOROTATION.
a. Stabilized.
(1) At 70 percent VNE:
(2) At NE•
b. Turns at 70 percent and 100 percent VNE:
(1) Right.
(2) Left.
c. Cyclic pull-up.
d. Control reversals.
(1) Longitudinal.
(2) Lateral.
(3) Rudder.
The flight and ground conditions of this table may be used as practical in developing operating load spectra for the range of projected aircraft usage such as:
(1) Short missions with high-power cycles and ground-air-ground (GAG) cycles (such as used in logging operations).
(2) Medium range missions of 1 to 2 hours that include three or more GAG or LO-HI power cycles per mission.
(3) Long range missions that consider the longest practical range of the aircraft and consider two or more GAG (or high power) cycles per mission (such as used for remote offshore drilling platforms).
If aircraft usages that produce a large number of high-power cycles (approximately 50 per hour) or high GAG cycles (approximately 25 per hour) such as logging operations are not included in the fatigue tolerance substantiation, this should be noted in the RFM and Maintenance Manual airworthiness limitations section (reference Paragraph 6a).
Page A1-25
Appendix 2 APPENDIX 2
ROTORCRAFT ONE-ENGINE-INOPERATIVE POWER ASSURANCE
1. PURPOSE.
The purpose of this document is to establish an approach for an engine power assurance procedure which will assure that the required OEI power level can be achieved.
2. GENERAL.
The data and methods described herein are intended to be utilized as a guide and not necessarily the only means of achieving the desired result.
3. APPLICABILITY.
The applicability of the document is intended to be primarily in support of the new 30-second and 2-minute OE rotorcraft engine rating scheme.
4. PARTIAL POWER ASSURANCE (ENGINE "RUN-LINE").
a. Fundamental to the concept of limited-use one-engine-inoperative (OEI) ratings is the requirement to be certain that the rated OE power will indeed be available when needed. Conventional periodic power-assurance and topping checks are impractical with the limited-use rating concept because of the rapid expenditure of useful life during exposure at the engine speeds and temperatures consistent with limited-use ratings;
therefore, we require a means of assuring the power available, other than by actual demonstration on each service engine. The advent of more sophisticated controls and engine developments catering to the 30-second/2-minute OEI rating concepts can provide the means to determine: (1) that the thermodynamic/mechanical capability of the engine as tested at the prevailing ambient conditions, will permit reaching a specified power level at any other ambient condition and (2) the fuel system and the various limiters will not prevent the engine achieving OEI power on demand. Pending availability of these new methods, the "parallel run line check" approach is recommended.
b. The method commonly called the "parallel run-line check" that has been in use for two decades may require refinement for application to the new rating structure where the degree of extrapolation to the OEI power level is more extensive and the slope of the individual engine characteristic is important. As in any power assurance method, success is strongly dependent on the validity of the data base, the maintenance of the engines and sensor/indicating systems, and the care taken during the conduct of the power check. In addition, trending of individual engine pertormance Page A2-1
Appendix 2 by the operator and associated analyses can be used to avoid unnecessary flight delays and engine removals.
c. Thermodynamic/mechanical capability can be addressed by test stand mapping of development engines over a range of ambient conditions to establish an adequate data base of engine characteristics. This will address characteristic slope variations between engines and establish correction factors necessary for extrapolation of data from a power assurance checkpoint to the 30-second OEI rating. Statistical verification and/or modification of the data base may be necessary during production by mapping of sample production engines. Performance data, at the 30-second OEI condition, taken during the supplementary block test and also during the "overhaul test" will demonstrate the capability of an engine and its control system near the end of an overhaul period to produce the required power. This will demonstrate capability with a deteriorated base-performance engine.
d. The question of fuel system limitations and other various limiters, which could prevent the engine from achieving OEI power on demand, may be addressed by use of more sophisticated control systems, for example, electronic controls utilizing several engine parameter limiters each with automatic datum reset capability. Such control systems can sense an engine failure and automatically reset the operating limiters upward from "normal" to "OEI" limits. Conventional flow and electronic bench testing can be used to verify the function and limit setting of the units when new or after overhaul or repair. The reset features can be extended in function to include a fixed magnitude pulldown type reset for use in verifying new and field production engine/control combination function ability. Pulldown type resets are currently in use today for verification of limiter settings on some engines and can be utilized in this application to avoid unneeded exposure of the engine to the rapid life expenditure conditions.
e. While the above is envisioned as the probable means in which assurance of capability will occur early in the application of such engines, there will be other means developed. One such means would be utilization of modern electronic engine condition or health monitors to display "go" or "no go" conditions relative to the ability of the engine and its control system to produce 30-second OEI power if required. In this application the device would be a "power assurance meter" and could be used with electronic, hydro-mechanical, and pneumo-mechanical control systems. It is entirely reasonable to expect that self-taught or self-programmed power assurance meters can be used that continually program the actual performance slope of the subject engine and extrapolate to the 30-second OEl with continuous engine monitoring.
Self-programming occurs by sampling engine temperature, speed, torque, other characteristics (such as fuel pressure), and ambient conditions, resulting in the reflection of an actual characteristic for the installed engine. The availability of this information permits treating engines individually, whether it is a new or deteriorated engine or one with either minimum or maximum slope, without the necessary compromises to "best" engines that necessarily occurs using the earlier statistical Page A2-2
Appendix 2 approach. The question of instantaneous fuel system capacity could be addressed by fuel pump/control systems incorporating bypass systems equipped with flow meters.
The health monitor or power assurance meter can continually integrate the fuel flow increment available in terms of power increment required in the event of OEl and would include this intelligence in its pass-fail judgment criteria. Systems of this type would further be conducive to in-service ground checks by overt by-pass deactivation from low power settings to assure satisfactory mechanical function.
f. Power assurance for the limited-use OEl ratings depends on a complete understanding of the engine model's operating characteristics. Two approaches have been discussed, one where, with the aid of a sophisticated fuel control system, the engine "learns" its own characteristics, and the other where the performance extrapolation is compared with a known minimum standard. The establishment of the standard is obviously a vital part of the procedure, which depends to a large extent on the existence of a reliable data base. In a mature program this is relatively easy to maintain, since it is possible to use the new production engine acceptance data to establish engine-to-engine variation and also to test engines prior to overhaul to determine the effects of deterioration. Thus, an up-to-date minimum or worst-engine characteristic can be maintained and service engines would be compared with this minimum engine.
g. When the engine in question is a completely new design, or a remote derivative of an existing design, establishing the initial data base presents some problems which must be resolved. New production engines will eventually establish engine-to-engine variation, but initially an estimated worst variation must be assumed.
The rate of deterioration and its impact on the base standard must be accounted for from the first engine delivered, yet it may be some time before an acceptable number of engines can be tested after service.
h. A partial solution lies in the development and qualification cycle of the engine.
A typical new-design program requires several development engines, of which more than half can be expected to be used for endurance or accelerated endurance testing.
Furthermore, by the time certification is completed and production deliveries have commenced, these engines will normally have amassed several thousand hours of running usually to a schedule far more rigorous than normal service. The information gathered during these tests will provide the necessary data base for the assessment of in-service engines, and it can be progressively enlarged, and the derived data refined, as further production and service data are obtained.
ENGINE CONSIDERATIONS. This section describes the potential causes of an engine not delivering specification OEI power levels in spite of passing a parallel run-line power assurance check. Possible solutions are discussed in the context of one time use 30-second and 2-minute ratings.
a. Eue Flow.
Page A2-3