Air University Review, May-June 1971
The weapon systems of the future are dependent on the research being accomplished today, and in many instances they will be dictated as a consequence of this research. An essential aspect of research relative to tactical weapon systems is tactical navigation for airborne weapon systems. A continuing requirement exists to provide the crew of the manned airborne weapon system with a navigational and/or guidance system that will insure the utmost in accuracy and reliability. If the factor of reliability can be achieved at the desired level, mission success can be viewed with a high degree of confidence.
The task of the designer of airborne navigation systems is immeasurably complicated by the demand for ultra highspeed airborne weapon systems with increasing quantities of complex electronic subsystems and a more stringent demand for reduced size and weight of components. Regardless of the infusion of these problems into the research and design effort, scientific and technological capability permits an optimistic view of an attainable goal. Evidence that the goal is in sight is underscored by the design trend toward microminiaturized electronic components, microintegrated electronic circuitry, hybrid circuit elements, new assembly techniques, and simplicity in lieu of complexity.
Coupled with these new design and manufacturing techniques is the increased emphasis on reliability and maintainability. It is my intent in this article to spotlight those functions of design and development that contribute to the major factors of reliability and maintainability. This approach is not intended to detract from the significantly prominent position of capability and performance of the airborne navigation system. Conversely, this approach is intended to complement those elements and at the same time explore the question of reliability and maintainability in such a way as to invite inquiry by the navigation system research, design, and development community of scientists and engineers.
Since World War II the primary emphasis in the design and development of weapon systems has been dictated by the evolving requirement for increased performance capability. The airborne navigation systems have not been an exception to this philosophy. Accuracy and improved performance remain as paramount objectives in the design and development of present and future airborne navigation systems. However, coupled with the performance requirement are the factors of operational and maintenance requirements, which are as significant and essential to mission success as the pinpoint accuracy and capability that have been inherently stipulated. Changing times and changing mission requirements have generated new tactical operations and maintenance concepts that dictate a pattern of design and development of tactical weapon systems that is vastly different from that of the post-World War II era.
Space for location of equipment within an airborne weapon system continues to be at an absolute premium. The requirement for increased numbers of subsystems within the airborne weapon systems escalates at an unprecedented rate. These two factors, in conjunction with the accuracy, performance, reliability, and maintainability requirements in present and future tactical airborne navigation systems, establish the network of criteria that must guide the design and development effort of the industrial complex.
Significant strides have been made in the state of the art, but the scientific and technological surface has merely been scratched in terms of the goals that must be achieved in the design and development of these navigation subsystems. To accommodate the reduced space available for placement of the navigation system within the airborne weapon system, maximum miniaturization of components is mandatory. Platforms, gyroscopes, electronics, computers, and power-supply components must be designed for the ultimate in accuracy and performance but not at the expense of the size, weight, and minimized space available for these vital components. Neither can the navigation system designer succumb to the weakness of previous systems wherein, at best, reliability was questionable, mean time to failure was too short, and the ground support package far exceeded in cost and maintenance requirements those of the basic subsystem installed in the weapon system complex.
The evolution of techniques in the design of navigation systems to meet the confining requirements dictated by present and future tactical airborne weapon systems is in a state of restlessness. For example, research and development have moved ahead in the solid-state technology field. Present programs include work on photoconductive detectors, cadmium telluride devices, and optical transistors. Coupled with this research are the research and development programs producing new chemical processes to provide the setting for the new electronic elements. Successful research programs that produce new materials lead to their use in new devices and systems.
The using agencies can anticipate a host of advantages as these newly developed design techniques find their way into more and more production items. The application of these techniques in the design of new airborne navigation systems for tactical aircraft will be especially significant. Computer programmed memory capacities can be more than doubled through the use of microminiaturized electronics; weight and volume can be reduced by as much as 50 percent through the use of semiconductor integrated circuits; and reliability can be increased by a factor of as much as 75 percent. These newly designed components can and should provide for data processing, malfunction analysis, and function sequencing in addition to the airborne duties of control and/or guidance over a preplanned route to the destination of the weapon system.
The way is clear and the green flag is out to proceed full speed ahead in these investigative areas. It is incumbent upon both military and industrial elements to pursue airborne navigation system development programs commensurate with these evolutionary design and manufacturing techniques. As design and development progress, it is mandatory that the functions of system reliability and maintainability assume the same significant posture that accuracy and performance have occupied in the past. Experience reflects that these functions do not detract from each other. Conversely, they complement each other to achieve a common goal of mission success with a high degree of confidence.
Philosophically, the ideal approach to airborne navigation systems, from both the operational and maintenance viewpoints, would encompass a perfection of design and manufacturing techniques that would result in an infallible system operation. Needless to say, this is not considered an attainable goal within the present capability. Certain attractive aspects of this approach are available, however, and both the producer and the user have recognized this availability. Based on the substantial progress that has been recorded relative to developing increased weapon system reliability and maintainability coincident with system capability, maintenance concepts and requirements are being revolutionized.
The employment and integration of the design and development techniques already discussed inherently provide subsystem equipment items with substantially improved reliability. This favorable fallout is not sufficient, however, to meet the mission demands of tactical weapon systems. Particular effort must be exerted in unison by the industrial and military agencies to specifically design reliability into our tactical weapon systems.
The requirement for deployment and dispersal of tactical assets dictates a high degree of reliability in weapon systems and mobility in support equipment design. Such factors as limited rear-echelon support and limited personnel and skills, coupled with all-weather 24-hour operation, rapid turnaround, and a maximum combat-capability requirement, in effect identify and establish the importance of reliability in the weapon system subsystems. In the search for improved reliability in airborne navigation systems, several areas warrant detailed consideration, including
—refinement and employment in production of design techniques that are tuned to the functions of system reliability. The most important end result of microminiaturization is reliability.
—reduction of the number of interconnections required to complete system functions.
—the continuing requirement for components and subcomponents that provide an extremely high resistance to shock.
—the requirement to reduce thermal stress relative to electronic components.
—improved possibility for inclusion of redundant subsystems through incorporation of microminiaturization techniques.
—reduction of power requirements and the consequent reduced requirement for larger cooling systems.
—on-board built-in self-test and analysis functions, to provide checkout and sequencing and to reduce ground operating time on the system as well as ground support equipment.
—reduction and/or elimination of adjustments to be performed at the field level through designed systems reliability.
—substantial increases in the mean time between failures on all systems and subsystems. Many of the above approaches will contribute to this goal.
—continued aggressive engineering effort to advance and improve electromechanical design techniques and substantially reduce functional degradation and maintenance failures.
These itemized points of departure by no means constitute the whole range of elements that should be subjected to scrutiny when the factor of reliability is under examination. However, these areas are prime candidates for research, development, and refinement toward substantially increasing reliability in future tactical airborne navigation systems.
The present conflict in Vietnam has pointed up many problems in weapon system performance as well as in the areas of reliability and maintainability. We in the tactical weapon system maintenance program have been made acutely aware of these shortcomings, and we have been enlightened on significant improvements that can be achieved through research, design, and development.
Although in this article I have taken a stand for reliability as a major design goal, the fact that reliability cannot be uncoupled from maintainability has been accepted as basic. In order to reflect this fact, I shall underscore some of the salient points that reveal the correlation of reliability /maintainability in any sound design and development program. Then I shall analyze in some detail maintainability as a major function of design.
Regardless of the urgency to design infallible reliability into our tactical airborne navigation systems, the restrictive element of economics still dictates the limit to which the designer is permitted to pursue this goal. Additionally, the state of the art in material and subcomponent development has not advanced sufficiently to be eliminated as an obstacle. Faced with these confining factors, the planners are charged with striking an acceptable balance between increased reliability and superior maintainability characteristics. The obvious approach to resolution becomes a trade-off of reliability factors for improved maintainability factors based on the restraints of the applicable set of criteria stipulated to the research and design community.
Substantial increases in the mean time between failures (MTBF) of components may very well outline a system of “removing and replacing” components, thereby eliminating the requirements for a field repair capability. Conversely, the cost of designing reliability of this magnitude into the navigation system could prove to be prohibitive, and a trade-off for field repair capability may be dictated in order to meet mission requirements. In either event, technological progress to date indicates that the bonus elements of both approaches can be coupled to achieve optimization.
Taking the economic element of the set of criteria, the designer may be enticed into presenting subsystems with built-in test features that show isolation of the anomaly to a module so inexpensive that it can be removed and discarded. Here again maintainability enters the picture, and the trade-off formula must be applied. Where either reliability or maintainability payoffs are achieved, a reduction in requirements for ground support equipment, personnel and skills, and complexity in the logistics support network is inherent.
When reliability and maintainability are welded together as a design goal in the development of tactical airborne navigation systems, a host of advantages will accrue to using agency. The crew’s confidence in the equipment capability will be increased, utilization hours per month for the weapon system can be extended, support equipment and manning requirements both will be reduced, and spares support will be more easily managed.
Performance is a must, and maintenance is indispensable, but if the crew of the manned tactical weapon system is to deliver the payload on the target, the factor of reliability must be incorporated into the triangle. Success in arriving at and returning from the target may very well hinge on a reliable navigation system designed for reliable pinpoint accuracy.
Usually seventy-five percent of the maintenance effort is expended in isolating the malfunction to a manageable component, and the rest is devoted to fixing and returning the item to service, assuming that the component can be repaired at base level. Generally speaking, these percentages apply across the weapon system, including the navigation equipment.
A major complicating factor in the maintenance analysis process is the failure that occurs within the airborne environment but cannot be duplicated or identified on the ground. When this situation arises, neither the operator nor the maintenance technician can justifiably be criticized. During a flight performance, suppose the operator is faced with a function failure confirmed by either a presentation process or something else he has been trained to recognize. In order to call attention to this matter, he must provide the maintenance man with a write-up, which he expands by verbal description. The maintenance technician, armed with these data, his maintenance procedures, and the required items of test equipment, starts his analysis process. In a sequenced, step-by-step analysis utilizing his test equipment items precisely as directed, he fails to confirm the problem and in fact determines that the system functions perfectly during the ground check process. The missing factor is the relationship of system operator in the demanding airborne environment. Technology is presently at the threshold of solving this dilemma.
The road to effective maintenance of airborne navigation systems is presently paved with large quantities of sophisticated and intricately complex test equipment, highly skilled technicians, and long hours of employing proceduralized troubleshooting techniques. Resolution of these obstacles appears to be just over the horizon, and investigation of the problem is worthy of serious consideration. For example, it appears both economical and feasible to design the malfunction analysis, isolation to the module, and recording into the navigation system. This on-board capability can result from joint utilization of the navigation computer system coupled to recording and operator presentation devices.
With a system designed along these lines, several advantages wilt accrue to both the operator and the maintainer. First, the malfunction can be isolated, analyzed, and recorded in the airborne environment. Second, the operator can be presented with the problem immediately and offered alternatives to circumvent possible disaster. Third, the time required to identify and isolate the problem on the ground can be reduced to zero. These are only the primary advantages of such a system. Test equipment quantities can be drastically reduced, maintenance skill levels can be reduced, and the total number of maintenance personnel required will drop substantially.
The recommended on-board concept makes provision for insuring minimized maintenance with reduced amounts of aerospace ground equipment (AGE); effective fault detection, isolation, and analysis; logical maintainability; and maximum assurance of mission accomplishment. The recorded analysis data will provide the maintenance team with sufficient information to take corrective action without detailed fault-isolation procedures. This concept also would provide a more positive approach toward determining mission success capability and system reliability. The major advantage of this approach, however, is the dynamic analysis in the airborne environment. In most instances it is economically prohibitive to duplicate that environment—even approximately—in the ground test setting. If it is feasible from the economic point of view, the airborne environment just cannot be duplicated on the ground within other available resources.
The microminiaturization approach to airborne system design, in both the electronic and electromechanical areas, makes this concept of in-flight analysis and recording not only feasible but desirable and necessary. As the micro design techniques are more widely accepted, the function of fault detection and isolation to the lowest removable module will become exceedingly attractive. The cost of modules, through application to more systems, will be reduced to such a level that the remove/replace/discard concept for faulty items will become economical.
Although the emphasis here is on maintainability, a significant operator factor is associated with the plan for an on-board computerized fault detection, analysis, and recording system. The process of on-board fault isolation and recording must provide the operator an uncomplicated cockpit presentation of the results. A presentation of this type may very well afford him the opportunity to correct the problem in flight or take successful alternate courses of action. In addition to the operator presentation, it appears feasible to design into the system a maintenance presentation panel whereby a quick analysis of the problem may be effected and corrective action taken to insure minimum turnaround time in the combat environment.
Maintainability, although representative of quality control and first-class workmanship in production, is basically a product of design techniques and system reliability. The reduction of field-level adjustments, through consistently reliable operation designed into an airborne navigation system, is a must. As an example of the burden that is placed on the maintenance manager with the indiscriminate inclusion of field-level adjustments in a system, one radar set in one of the modern tactical weapon systems has approximately 100 field-level adjustments. Just imagine the complexity of the alignment task when components are replaced to correct a fault and a complete alignment of the system is necessary. The function of maintainability becomes obvious when viewed in this context.
With microminiaturization, more consideration should be given to accessible component location. In many instances several hours are now required literally to reach a component, remove it, replace it, and close the access area. Undoubtedly, the placement of components in readily accessible locations would eliminate a large part of the time expended in removal and replacement. The feasibility of combining various microtechniques and devices in the development of weapon system subsystems has been recognized. It is imperative that these design advantages be measured against the requirement for better packaging and placement of components within the weapon system to insure maintainability and the most effective utilization of the maintenance manager’s resources. If the functions of system performance and accuracy can be coupled with the factors of reliability and maintainability in the design and development of airborne navigation systems, we can look forward to vastly improved overall weapon system capabilities.
When one considers that 85 percent of the scientists who have ever lived are still living today, the advanced state of our scientific and technological progress is not so astounding. Commercial electronic products and their reliability attest to the industrial capability to provide the home with a host of labor-saving and entertaining devices. That capability also holds the potential to provide the combat crew a highly reliable airborne navigation system with the maximum of easily maintainable features. The state of the art, from a technological viewpoint, is capable of providing performance and accuracy with pinpoint precision without the surrender of reliability and maintainability as prime features.
It appears that design and development techniques are aligned to the parameters of accuracy required by the user and that the challenge to industry is unmistakably clear. The requirement for highly accurate, reliable, and maintainable airborne navigation systems in the tactical weapon system of the present and the future is clearly defined. This fact could not have been more emphatically underscored than it has been by the dilemma in Southeast Asia. If one may be permitted a pun, “X marks the spot,” and the tactical weapon systems of the present and the future require an airborne navigation system to reach that spot on an accurate and reliable basis.
Hq Tactical Air Command
Colonel Edward H. Curtis (M.A., San Francisco State College), an avionics officer most of his career, is Chief, Logistics Management Division, DCS/Materiel, Hq Tactical Air Command. Colonel Curtis has been an AFIT student, is a graduate of Squadron Officer School and Air Command and Staff College, and was a distinguished graduate, Air War College, 1968. A Korean War veteran, he was commander, 12th Avionics Maintenance Squadron, Cam Ranh Bay AB, Vietnam, prior to his present assignment.
Disclaimer
The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.
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