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Computer support in Air Force Maintenance
World Abstracts on Microelectronics and Reliability
311
Planning for complete supportability. CONRAD J. MORGAN. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17 19 January 1978, p. 1. Tailoring the supportability of the prime hardware and the support system to satisfy minimum life cycle cost requirements of the peacetime environment could jeopardize weapon system effectiveness if placed in a wartime environment. Adequate visibility into contingency operations is needed to properly define those characteristics of the prime hardware and support system which permit adequate support in a wartime environment and minimize support costs in the peacetime environment. The author, in addressing this problem, has combined the technique of functional flow diagrams with that of life cycle costing in an attempt to highlight this critical part of the support program.
nucleate boiling ratio or DNBR changes that result with perturbations. Response surface models were developed for relating the input parameters to DNBR. These models were then implemented for establishing reliabilities with two methods: empirical and Monte Carlo. The empirical technique utilized the probability of any pin exceeding a given DNBR value and calculated these for the pins in the hottest bundles. A limit value for the number of pins significantly contributing to the core reliability was established. The Monte Carlo simulations were based on the pins determined to contribute significantly to the reliability of the core. Reactor-corewide fuel pin mean population protection and fuel pin cladding spot extreme DNBR measures of reliability are established. Comparisons with present "maximum design" practices quantify conservatism inherent in the current Babcock & Wilcox procedure.
USAF experience with RIW. DAVID G. NEWMAN and LANCE D. NESBITT. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17-19 January 1978, p. 55. The Air Force is devoting extensive resources to improve the operational reliability of its equipment and to reduce equipment systems Life Cycle Costs. One method being used on a trial basis is the Reliability Improvement Warranty (RIW). RIW is a means of motivating contractors to design and produce equipment with low failure rates and low repair costs. The Air Force has five major applications of RIW. Each application has unique features which influence the risks to the contractor and to the Air Force. The Air Force has made extensive use of Turnaround Time (TAT) and Mean Time Between Failure (MTBF) guarantees. These guarantee features remain controversial. This paper reports on the current Air Force policy for R1W, summarizes the status of the major Air Force RIW applications, identifies some results achieved with use of RIW, and expresses some concerns about the concept.
Models for reliability growth during burn-in: Theory and applications. K. W. FERTm and V. K. MURTHY. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17 19 January 1978, p. 504. This paper consists of two parts. The first part is a summary of an investigation by Fertig (1976) of models for reliability growth of electronic equipment during the burn-in period. Three distinct models for reliability growth based on probabilistic considerations are derived. When the number of components is large, the first model is nearly exponential. The second and third models are more in line with the observed reliability growth during burn-in. In the second part of the paper, the last two models, called, respectively, the competing-risk Weibufi (CRW) and the chance defective exponential (CDE) are applied and compared with examples drawn from diverse types of electronic equipment.
The development of metrics for software R & M. GENE F. WALTERS and JAMES A. MCCALL. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17-19 January 1978, p. 79. This paper describes the derivation and validation of software metrics which provide a means for quantitatively specifying and measuring software quality. This work was part of a study of the factors in software quality conducted in support of the Air Force Systems Command Electronic Systems Division and Rome Air Development Center. The software metrics discussed are those which relate specifically to the quality factors of reliability and maintainability. The swinging door: a first experience in product liability. GARY G. HANSEN. Proc. IEEE A. Reliab. Maintainab. Svmp., Los Angeles, 17-19 January 1978, p. 363. The current climate of product liability litigation evokes strong emotional response from most technical people. What is often overlooked is that in many cases the plaintiff was indeed entitled to some recovery because the product was in some form defective. This paper will present the chain of events reflecting an actual product liability lawsuit while attempting to illuminate the technical and legal issues involved. Reliability prediction for a pressurized water reactor during the design process. A. S. HELLER (Part I) and E. OELKERS (Part ll). Proc. 1EEE A. Reliab. Maintainab. S3mp., Los Angeles, 17-19 January 1978, p. 348. In order to establish operating limits for a pressurized water reactor during the design process, it is important to evaluate the interrelationships and uncertainties among the physical variables to be controlled. A sensitivity study, using known design parameters with simulation through design codes has been completed in order to assess the departure from
Failure rate as a design parameter: Possibilities and limitations. S. N. MARUVADA,K. E. WEISE and M. F. CHAMOW. Proc. 1EEE A. Reliab. Maintainab. Syrup., Los Angeles, 17-19 January 1978, p. 342. This paper examines the availability performance of a fossil-fired generating unit taking into account several derated states. The probabilities of being in the up, down and various derated states are computed using state space techniques and a measure of unit performance derived. The sensitivity of this measure of performance to the failure and repair rates of major components is obtained. The results can be used to aid decision-making during the design of a power generating unit to obtain the most cost-effective reliability improvement. Defining cost-effective system effectiveness and safety programs. W1LLIAM P. MURDEN and WALTER W. HOY. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17-19 January 1978, p. 401. The System Effectiveness and Safety Technical Committee of the American Institute for Aeronautics and Astronautics (AIAA) has addressed the costeffectiveness of SES program elements commonly involved in major system developments. Quantitative costeffectiveness analysis is infeasible for most program elements, but the paper provides a committee consensus on the relative worth of program elements, based on their relative costs, potential for improving system effectiveness, and the timeliness of such improvements. Reliability program elements are emphasized. Computer support in Air Force Maintenance. JOHNY D. DUCKWORTH and RICHARD P. QUINTANA. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17 19 January 1978, p. 11. This paper describes the personal views of the authors concerning plans to modernize the Air Force Maintenance Management Information and Control System
312
\i’orld Abstracts
on MIcroelectronic\
(MMICS). It describes MMICS in a historlcal perspective: it identifies problems which must be addressed in the modernization process; and. it presents II Imaintenance management modernization concept that has been proposed by the author-s. The vleu$ and opinrons expressed in this paper should not in an) way be construed to reflect an) endorsement or confirmation by the Department of Defense or any other agency of the U.S. Government. Quality Assurance for reliable software. PA~u. P. HOWLEY. JK. Proc. IEEE /l. Rrliirb. Mai/rt~ri,~trh. S~np.. Los Angeles. I7 I9 January 1978. p. 73. Concern is being expressed over software reliability b? the aerospace systems agencies procuring large systems with embedded software. While there is disagreement among various advocates about exactly what constitutes software reliability and how it is defined, there is an acl\nowledged need for the application of methods to achieve reliability in software. A number of techniques and tools do exist that are being practiced lo differing degrees among the various firms debeloping large systems software. However. consistency in concept and methodology is not evident. The methodology proposed in this paper is that of Software Ouality Assurance (SWQA). This methodology provides the conceptual and organirational bases for estabhshing and controlling the implementation of software quality goals. It is applied throughout the software life cycle, from the point of system definition through development. extending out through the operaticma life of the software system.
and Reliabilltc
high levels of system ava~lablllty, in the order 01‘ Y).ox”,,. while minimizing system design and operations costs ‘I.116 paper presents the rcliabilitj consideration\ utilired in the design and implementation of the GTE Satellite (‘~~I-~oI-ation (GSAT) earth stations. The design ohlcctl\c of 90.98” (1 system availability was achieved through 111c LISZ ot”: redundant configurations. proven commercial equipmen1, environmental control. equipment accessihillt). ;~nd reliance on equipment supplier< for reliability input da18
Software
Risk reduction by design. PAIJI. F.. IEEE 4. Krlilrh. Mtrinroi,ltrh. Sytnp..
~‘OLNGL~AHI.. Pror~.
Los Angeles. 17- I9 January 107X. p 360. Risk reduction is a goal in many contexts Including risk reduction of personal injury from machines or products. An engineer, using all the tools available, should make a hazard and risk analysis :IS part of an orderly approach to the design of a reasonably safe machine. Several examples in mechanical engineering illustrate the application of the principles. Directed graph techniques for the analysis of fault M,AKTIN F. CHAMOW. 1EEE 7’1~1s. Kelitrb. R-27,
trees.
(1) 7 (April 1978). Since the introduction of the fault tree method for system aafety and reliability analysis more than a decade ago. the method has gained considerable acceptance for qualitative analyses. It has also gained a degree of acceptance for quantitative analyses, despite difficulties encountered in performing the probabilistic evaluations using available methods. Some of the difficulties encountered with previous evaluation methods are avoided by the methods of this paper. The new methods involve the use of directed graphs (digraphs) and related matrix methods, and solutions for paths in a manner similar to that for conventional digrapha. Most of the attractiveness stems from the fundamental philosophy of speedily transforming the graphics into corresponding matrices. This puts the bulk of the solution elfort into the mathematics where it belongs. The ma,jor benefit arises because the mathematical solutions are readily performed by standard matrix techniques, which can be implemented either manually or with the aid of a computer. The neu methods have been used on various hypothetical logic combinations plus actual fault trees of typical sizes. reliability of GSAT Earth Station. WIL.I IAhl J. and GLENN A. ALLFN. Proc. IEEE 4. Relicrh. Mtrimc~imh. Symp.. Los Angeles, 17-19 January 1978, p. 465. Does :I 99.9X”8I 0 system availability design objective for a satellite communications system require an exhaustive and expensive reliability program’? GTE’s experience has indicated that commercially-proven equipment can yield Operational SANKO
An evaluation of two model specification techniques for a lognormal distribution. DIANE I. GIBBONS. IEEE /-~oII,\. Relitrh. R-27, (I) 60 (April 147X). Two frequently used
statistical estimation techniques are applied to the lognormal distribution with unit shape-parameter 1-11~ fbt lechnique involves comparing sample estimates of \he\$ nc~ and kurtosis with their corresponding population value\ in order to determine the suitability of the di\tribution as a model for a set of empirical data. The sample rhcwness and kurtosis for samples of moderate G/c pro\idc biased downward estimates of the population calueh. Thus bias can be considered if this technique IS applied IO ;I data set by using results presented in this paper. The second technique ib probability plotting. .The recommended plotting position is (i - 0.51’1r. An evaluation i>f the praphical eatimatorh sho\\s that they are suhstantiall~ I inferior to the best linear unhlased estlmatorh and Blom’\ estimators. The result3 are applied to ;I data SCI ct)nhisting of automoti\~e emissions.
Reliability
modeling and analysis of fault-tolerant
memories.
W. Cox and B. D. C.\KKOII.. IEEE Trrorc. Relioh. R-27, (I) 49 (April 1978). A memory array rehability model is developed that can be applied to a uide range of including random-acccsa memory organizationa memories (RAM) and read-only memories (ROM). The model is particularly useful for computing the reliability of fault-tolerant memories that employ technlquca vuch as hardware redundancy, error-correcting codes, and auftuarc error-correcting algorithms. The model accommodates the effect of faults masked by data. Reliability models that incorporate the array model arc given for 21 simplex RAM. an N-modular-redundant R4M. a spared RAM, a single-error-correcting RAM. a multipleerror-correcting RAM. and a ROM. Reliabillt) chnracteristics of these memories are compared. The rei;ult\ suggest that memories with error-correcting capability and >pare hit-planes provide the hest reliability. Memories with sparing at the array level are nest best followed b! NMR and simplex organizations. ROM reliability i& shown to be more optimistic when masked faults are conridered GLENN
Optimal reliability allocation under preventive maintenance schedule. T. INAGARI, K. 14o~r. and H. AKASIII. IEEE Trtrrls. Rditrh. R-27, (I) 39 (April 1078). This paper con-
siders a series system of components with time-dependent reliability and gives a nen formulation of an optlmal rehability allocation problem where an optimal preventive maintenance (PM) schedule is determined simlIIt;~neousl~. The importance of this formulation is shown in COIIIparison with a conventional formulation where PM schedule is not taken into account. The optimization problem becomes :I nonlinear mixed-integer programming problem. A simple approximate solution algorithm 15 given on the basis of a nonlinear programmlng (NLP) algorithm. The procedure is illustrated bq use of :I numerical example. Though we restrict out attentmn to the case where a preventive replacement is adopted HIS it PM policy. a similar discussion is possible for the asgood-as-new repair.
311
Planning for complete supportability. CONRAD J. MORGAN. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17 19 January 1978, p. 1. Tailoring the supportability of the prime hardware and the support system to satisfy minimum life cycle cost requirements of the peacetime environment could jeopardize weapon system effectiveness if placed in a wartime environment. Adequate visibility into contingency operations is needed to properly define those characteristics of the prime hardware and support system which permit adequate support in a wartime environment and minimize support costs in the peacetime environment. The author, in addressing this problem, has combined the technique of functional flow diagrams with that of life cycle costing in an attempt to highlight this critical part of the support program.
nucleate boiling ratio or DNBR changes that result with perturbations. Response surface models were developed for relating the input parameters to DNBR. These models were then implemented for establishing reliabilities with two methods: empirical and Monte Carlo. The empirical technique utilized the probability of any pin exceeding a given DNBR value and calculated these for the pins in the hottest bundles. A limit value for the number of pins significantly contributing to the core reliability was established. The Monte Carlo simulations were based on the pins determined to contribute significantly to the reliability of the core. Reactor-corewide fuel pin mean population protection and fuel pin cladding spot extreme DNBR measures of reliability are established. Comparisons with present "maximum design" practices quantify conservatism inherent in the current Babcock & Wilcox procedure.
USAF experience with RIW. DAVID G. NEWMAN and LANCE D. NESBITT. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17-19 January 1978, p. 55. The Air Force is devoting extensive resources to improve the operational reliability of its equipment and to reduce equipment systems Life Cycle Costs. One method being used on a trial basis is the Reliability Improvement Warranty (RIW). RIW is a means of motivating contractors to design and produce equipment with low failure rates and low repair costs. The Air Force has five major applications of RIW. Each application has unique features which influence the risks to the contractor and to the Air Force. The Air Force has made extensive use of Turnaround Time (TAT) and Mean Time Between Failure (MTBF) guarantees. These guarantee features remain controversial. This paper reports on the current Air Force policy for R1W, summarizes the status of the major Air Force RIW applications, identifies some results achieved with use of RIW, and expresses some concerns about the concept.
Models for reliability growth during burn-in: Theory and applications. K. W. FERTm and V. K. MURTHY. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17 19 January 1978, p. 504. This paper consists of two parts. The first part is a summary of an investigation by Fertig (1976) of models for reliability growth of electronic equipment during the burn-in period. Three distinct models for reliability growth based on probabilistic considerations are derived. When the number of components is large, the first model is nearly exponential. The second and third models are more in line with the observed reliability growth during burn-in. In the second part of the paper, the last two models, called, respectively, the competing-risk Weibufi (CRW) and the chance defective exponential (CDE) are applied and compared with examples drawn from diverse types of electronic equipment.
The development of metrics for software R & M. GENE F. WALTERS and JAMES A. MCCALL. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17-19 January 1978, p. 79. This paper describes the derivation and validation of software metrics which provide a means for quantitatively specifying and measuring software quality. This work was part of a study of the factors in software quality conducted in support of the Air Force Systems Command Electronic Systems Division and Rome Air Development Center. The software metrics discussed are those which relate specifically to the quality factors of reliability and maintainability. The swinging door: a first experience in product liability. GARY G. HANSEN. Proc. IEEE A. Reliab. Maintainab. Svmp., Los Angeles, 17-19 January 1978, p. 363. The current climate of product liability litigation evokes strong emotional response from most technical people. What is often overlooked is that in many cases the plaintiff was indeed entitled to some recovery because the product was in some form defective. This paper will present the chain of events reflecting an actual product liability lawsuit while attempting to illuminate the technical and legal issues involved. Reliability prediction for a pressurized water reactor during the design process. A. S. HELLER (Part I) and E. OELKERS (Part ll). Proc. 1EEE A. Reliab. Maintainab. S3mp., Los Angeles, 17-19 January 1978, p. 348. In order to establish operating limits for a pressurized water reactor during the design process, it is important to evaluate the interrelationships and uncertainties among the physical variables to be controlled. A sensitivity study, using known design parameters with simulation through design codes has been completed in order to assess the departure from
Failure rate as a design parameter: Possibilities and limitations. S. N. MARUVADA,K. E. WEISE and M. F. CHAMOW. Proc. 1EEE A. Reliab. Maintainab. Syrup., Los Angeles, 17-19 January 1978, p. 342. This paper examines the availability performance of a fossil-fired generating unit taking into account several derated states. The probabilities of being in the up, down and various derated states are computed using state space techniques and a measure of unit performance derived. The sensitivity of this measure of performance to the failure and repair rates of major components is obtained. The results can be used to aid decision-making during the design of a power generating unit to obtain the most cost-effective reliability improvement. Defining cost-effective system effectiveness and safety programs. W1LLIAM P. MURDEN and WALTER W. HOY. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17-19 January 1978, p. 401. The System Effectiveness and Safety Technical Committee of the American Institute for Aeronautics and Astronautics (AIAA) has addressed the costeffectiveness of SES program elements commonly involved in major system developments. Quantitative costeffectiveness analysis is infeasible for most program elements, but the paper provides a committee consensus on the relative worth of program elements, based on their relative costs, potential for improving system effectiveness, and the timeliness of such improvements. Reliability program elements are emphasized. Computer support in Air Force Maintenance. JOHNY D. DUCKWORTH and RICHARD P. QUINTANA. Proc. IEEE A. Reliab. Maintainab. Syrup., Los Angeles, 17 19 January 1978, p. 11. This paper describes the personal views of the authors concerning plans to modernize the Air Force Maintenance Management Information and Control System
312
\i’orld Abstracts
on MIcroelectronic\
(MMICS). It describes MMICS in a historlcal perspective: it identifies problems which must be addressed in the modernization process; and. it presents II Imaintenance management modernization concept that has been proposed by the author-s. The vleu$ and opinrons expressed in this paper should not in an) way be construed to reflect an) endorsement or confirmation by the Department of Defense or any other agency of the U.S. Government. Quality Assurance for reliable software. PA~u. P. HOWLEY. JK. Proc. IEEE /l. Rrliirb. Mai/rt~ri,~trh. S~np.. Los Angeles. I7 I9 January 1978. p. 73. Concern is being expressed over software reliability b? the aerospace systems agencies procuring large systems with embedded software. While there is disagreement among various advocates about exactly what constitutes software reliability and how it is defined, there is an acl\nowledged need for the application of methods to achieve reliability in software. A number of techniques and tools do exist that are being practiced lo differing degrees among the various firms debeloping large systems software. However. consistency in concept and methodology is not evident. The methodology proposed in this paper is that of Software Ouality Assurance (SWQA). This methodology provides the conceptual and organirational bases for estabhshing and controlling the implementation of software quality goals. It is applied throughout the software life cycle, from the point of system definition through development. extending out through the operaticma life of the software system.
and Reliabilltc
high levels of system ava~lablllty, in the order 01‘ Y).ox”,,. while minimizing system design and operations costs ‘I.116 paper presents the rcliabilitj consideration\ utilired in the design and implementation of the GTE Satellite (‘~~I-~oI-ation (GSAT) earth stations. The design ohlcctl\c of 90.98” (1 system availability was achieved through 111c LISZ ot”: redundant configurations. proven commercial equipmen1, environmental control. equipment accessihillt). ;~nd reliance on equipment supplier< for reliability input da18
Software
Risk reduction by design. PAIJI. F.. IEEE 4. Krlilrh. Mtrinroi,ltrh. Sytnp..
~‘OLNGL~AHI.. Pror~.
Los Angeles. 17- I9 January 107X. p 360. Risk reduction is a goal in many contexts Including risk reduction of personal injury from machines or products. An engineer, using all the tools available, should make a hazard and risk analysis :IS part of an orderly approach to the design of a reasonably safe machine. Several examples in mechanical engineering illustrate the application of the principles. Directed graph techniques for the analysis of fault M,AKTIN F. CHAMOW. 1EEE 7’1~1s. Kelitrb. R-27,
trees.
(1) 7 (April 1978). Since the introduction of the fault tree method for system aafety and reliability analysis more than a decade ago. the method has gained considerable acceptance for qualitative analyses. It has also gained a degree of acceptance for quantitative analyses, despite difficulties encountered in performing the probabilistic evaluations using available methods. Some of the difficulties encountered with previous evaluation methods are avoided by the methods of this paper. The new methods involve the use of directed graphs (digraphs) and related matrix methods, and solutions for paths in a manner similar to that for conventional digrapha. Most of the attractiveness stems from the fundamental philosophy of speedily transforming the graphics into corresponding matrices. This puts the bulk of the solution elfort into the mathematics where it belongs. The ma,jor benefit arises because the mathematical solutions are readily performed by standard matrix techniques, which can be implemented either manually or with the aid of a computer. The neu methods have been used on various hypothetical logic combinations plus actual fault trees of typical sizes. reliability of GSAT Earth Station. WIL.I IAhl J. and GLENN A. ALLFN. Proc. IEEE 4. Relicrh. Mtrimc~imh. Symp.. Los Angeles, 17-19 January 1978, p. 465. Does :I 99.9X”8I 0 system availability design objective for a satellite communications system require an exhaustive and expensive reliability program’? GTE’s experience has indicated that commercially-proven equipment can yield Operational SANKO
An evaluation of two model specification techniques for a lognormal distribution. DIANE I. GIBBONS. IEEE /-~oII,\. Relitrh. R-27, (I) 60 (April 147X). Two frequently used
statistical estimation techniques are applied to the lognormal distribution with unit shape-parameter 1-11~ fbt lechnique involves comparing sample estimates of \he\$ nc~ and kurtosis with their corresponding population value\ in order to determine the suitability of the di\tribution as a model for a set of empirical data. The sample rhcwness and kurtosis for samples of moderate G/c pro\idc biased downward estimates of the population calueh. Thus bias can be considered if this technique IS applied IO ;I data set by using results presented in this paper. The second technique ib probability plotting. .The recommended plotting position is (i - 0.51’1r. An evaluation i>f the praphical eatimatorh sho\\s that they are suhstantiall~ I inferior to the best linear unhlased estlmatorh and Blom’\ estimators. The result3 are applied to ;I data SCI ct)nhisting of automoti\~e emissions.
Reliability
modeling and analysis of fault-tolerant
memories.
W. Cox and B. D. C.\KKOII.. IEEE Trrorc. Relioh. R-27, (I) 49 (April 1978). A memory array rehability model is developed that can be applied to a uide range of including random-acccsa memory organizationa memories (RAM) and read-only memories (ROM). The model is particularly useful for computing the reliability of fault-tolerant memories that employ technlquca vuch as hardware redundancy, error-correcting codes, and auftuarc error-correcting algorithms. The model accommodates the effect of faults masked by data. Reliability models that incorporate the array model arc given for 21 simplex RAM. an N-modular-redundant R4M. a spared RAM, a single-error-correcting RAM. a multipleerror-correcting RAM. and a ROM. Reliabillt) chnracteristics of these memories are compared. The rei;ult\ suggest that memories with error-correcting capability and >pare hit-planes provide the hest reliability. Memories with sparing at the array level are nest best followed b! NMR and simplex organizations. ROM reliability i& shown to be more optimistic when masked faults are conridered GLENN
Optimal reliability allocation under preventive maintenance schedule. T. INAGARI, K. 14o~r. and H. AKASIII. IEEE Trtrrls. Rditrh. R-27, (I) 39 (April 1078). This paper con-
siders a series system of components with time-dependent reliability and gives a nen formulation of an optlmal rehability allocation problem where an optimal preventive maintenance (PM) schedule is determined simlIIt;~neousl~. The importance of this formulation is shown in COIIIparison with a conventional formulation where PM schedule is not taken into account. The optimization problem becomes :I nonlinear mixed-integer programming problem. A simple approximate solution algorithm 15 given on the basis of a nonlinear programmlng (NLP) algorithm. The procedure is illustrated bq use of :I numerical example. Though we restrict out attentmn to the case where a preventive replacement is adopted HIS it PM policy. a similar discussion is possible for the asgood-as-new repair.