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A different method of performing Failure Modes and Effects Analyses (FMEAs) is described that is beneficial in improving product quality and in avoidance of product problems in-house and in the field. The method is usefully applied to mechanical products since there is a dearth of mechanical failure rate data and is suitable for new product introductions during the concept or early design phase to help answer many of the quality, producibility, safety and reliability questions that arise concerning new product designs. The method is different from the traditional methods of performing FMEAs since it is accomplished without historical part failure rate data, an area that frequently creates significant problems to the analyst of new product introductions. The method of performing FMEAs allows for continuing update during a product design program since the analysis can be automated.

Space Shuttle missions are currently limited to 11 days*, primarily due to depletion of the power reactants (hydrogen and oxygen). A power system Mission Extension Kit (MEK) is described which could provide the capability to stay on orbit 10 additional days**. These extra days would benefit Space Station construction and missions such as materials processing, Earth and celestial observation, and life science studies (Spacelab). Other constraints to longer missions which may dictate minor Orbiter modifications will be discussed. The power system MEK is particularly desirable because of its existing flight qualified hardware which can be delivered within 3 to 4 years.

Significant improvements in engine readiness with reductions in maintenance costs and turnaround times can be achieved with an engine condition monitoring systems (CMS). The CMS provides health status of critical engine components, without disassembly, through monitoring with advanced sensors. Engine failure reports over 35 years were categorized into 20 different modes of failure. Rotor bearings and turbine blades were determined to be the most critical in limiting turbopump life. Measurement technologies were matched to each of the failure modes identified. Three were selected to monitor the rotor bearings and turbine blades: the isotope wear detector and fiberoptic deflectometer (bearings), and the fiberoptic pyrometer (blades). Signal processing algorithms were evaluated for their ability to provide useful health data to maintenance personnel. Design modifications to the Space Shuttle Main Engine (SSME) high pressure turbopumps were developed to incorporate the sensors.

A study is being conducted for NASA on potential diagnostic system improvements to the Space Shuttle Main Engine (SSME). This paper reports midterm progress including: (1) the results of a failure mode review identifying key diagnostic needs; (2) the results of a survey of diagnostic techniques that might be applied to the SSME; and (3) application to the SSME of a Battelle developed tool (the Failure Information Propagation Model, or FIPM) for analysis of diagnostic needs. It is concluded that opportunities for significantly improved diagnostics exist in a number of areas. Future plans are described that are directed toward development of a diagnostics strategy and design recommendations for an improved diagnostic system for the SSME.

NASA's confidence in the flight readiness of aerospace hardware and software is achieved by a thorough integration of safety activities into every program facet, from concept through the mission. This involves technical and administrative personnel, organizations that specify requirements, design, manufacturing, test and the operators. Reviews by inhouse and external specialists form an integral part of the assurance process. Examples of safety issues and their resolution for some power and propulsion functions are given (lithium cells, autoignition/fretting in high pressure oxygen environments, ignition sources from auxiliary power unit, and low thrust rocket engines). Finally, some comments on NASA's integrated safety activities and the Aerospace Safety Advisory Panel's role in the NASA review and assessment process all of which provides added confidence in achieving a high level of mission safety and success.

Pilot incapacitation can occur among all age groups. It can be obvious or subtle; temporary or permanent; and partial or complete. Its origin can be physiological or psychological or both. Its inherent risk to aviation safety can be virtually eliminated in a multi-crew operation. Control of the operational consequences of pilot incapacitation is both a traditional aeromedical problem and a training problem. Despite very considerable progress, the importance of its training aspects are not always recognized. Controlling “cognitive” incapacitation is the newest challenge.

The decision to fly and the capacity to carry a. flight to a successful termination involves a wide spectrum of background determinants. These range from considerations of the pilot as a physical being with specific potentials and limitations of body structure, mental ability and emotional capacities to the adequacy of learning related to a specific performance and the character and condition of the aircraft, Specific factors relevant to each of these categories is discussed including the psycho-social, physiological and pathological. Crucial to success is the pilot's self-critical judgement. There is a necessary tension between the ongoing activity of carrying out a positive decision to fly and the requirements for continual assessment of the situation.

Three studies compared different computer generated voices for helicopter voice warnings. Study 1 compared three LPC-encoded voices (human female, human male, and phoneme synthesized) while pilots flew simulated nap-of-the earth missions. Flight performance and pilots' ratings via semantic differential scales were measured. Study 2 produced pilot preferences for direct synthesized speech compared to LPC-encoded human female speech and compared to LPC-encoded synthesized speech. Study 3 used phonetically balanced (PB) words heard in simulated helicopter noise to compare intelligibility of direct synthesized and LPC-encoded phoneme synthesized speech. There were no flight performance differences due to voice type (Study 1), but pilots preferred direct synthesized speech over both LPC-encoded human female speech and LPC-encoded synthesized speech (Study 2).

The theme for this conference is “Automation Workload Technology: Friend or Foe?” It was this question that has led to the development of a research simulator for the investigation of advanced helicopter cockpit concepts at the U. S. Army Human Engineering Laboratory, Aberdeen Proving Ground, Maryland. This research simulator is scheduled to be operational in February, 1985. This paper describes the development of this simulator as a research tool through which advanced controls and displays can be evaluated in terms of their impact on human performance.

Practical guidelines for transient response calculation and peak response estimation for linear structural dynamic systems are described and illustrated. The response spectrum of the dynamic excitation environment is utilized to clearly define the low frequency dynamic response range and the high frequency quasi-static response range. Low frequency dynamic behavior is described by superposition of modal transient responses in that range while high frequency quasi-static behavior is approximated by residual vector response. For the task of peak response estimation, a sensible “vectored” approach to modal response spectrum superposition is introduced. This technique is shown to provide a more reliable estimate than currently popular summation approaches.

The publication in the Spring of 1979 of NAVMAT P–9492 “Navy Manufacturing Screening Program” engendered a very significant increase in the use of Environmental Stress Screens of Electronic Hardware (ESSEH), particularly in the area of vibration screens. Such screens are employed to remove manufacturing defects and eliminate infant mortality failures prior to delivery. This paper will review the principles which govern the selection of suitable vibration screens; those areas where reasonable understanding has been achieved; and those areas where significant advances are still required. The presentation will include an update based on the output from the Third ESSEH Conference and Workshop, September 10-13, 1984, sponsored by IES.

Nonlinear finite element analysis techniques were applied in the optimization of energy absorbers in weapon systems. Powerful analytical tools for establishing trends due to various designs were developed without involving extensive and time consuming testings. A case study was performed to evaluate the benefits and efficiencies gained through the use of Computer Aided Engineering and Finite Element Applications to Ordnance Systems.

A formal procedure for generating a stochastic model for flexible structures is presented herein. The “best” available analytical model is taken and modeling errors and other random uncertainties are incorporated in the given model to generate a stochastic model. The optimal stochastic control for the system is derived and its performance is compared both with the deterministic model using a deterministic controller and with the stochastic model using the deterministic controller. A specific example is simulated whereby the results are plotted for different cases. Comments regarding applicability of the procedures are included.

This paper discusses the effects of omitting constraint modes corresponding to applied loads in systems modeled with component mode synthesis. A method of correcting for the omitted constraint modes is also developed. The free component mode synthesis method is applied to the continuous model of a axial rod-spring system, and the effect of omitted constraint modes on the static, steady state harmonic, and transient response is studied. The effect of omitted constraint modes on the transient response of an asymmetric beam is studied using the free and fixed component mode synthesis implemented in MSC/NASTRAN. A simple pinned truss finite element model is also studied.

Several modal test techniques were employed in the recently completed modal test of a meteorological spacecraft. The primary technique, which was required by the customer, was the classical multiple-shaker sine-dwell method. Although this method is quite time-proven, it takes considerable time to perform the test. Very good results were obtained from this method. The results are used as a basis for comparison with the results of state-of-the-art, less proven but more time efficient test methods. The paper presents the results of the multiple-shaker sine-dwell test, and comparison is made with the results of both single-point random and multiple-point random tests. The paper concludes with a short discussion of the relative merits of each technique.

Accelerometer data from Space Shuttle flights are used to identify the modal components of decaying response. This is done using a modified version of the Ibrahim time domain (ITD) method. Identified modal response coherences and the data from which they are extracted are maximized by manipulating sample sizes and start times and by filtering. This leads to a more consistent set of damping rates and thus provides greater confidence in projected flutter margins. Applying this procedure to response data that are less noisy than flight test data should produce satisfactory results with less filtering.

The recent advances in multiple-input techniques for experimental modal analysis have given the test engineer alternatives for performing aircraft ground vibration tests (GVT). Multiple-input random excitation and polyreference analysis are two of the methods that are being used instead of the traditional sine dwell approach. The efficiency and advantages of these new methods are examined and examples of this application to recent aircraft GVT's are described.

Since World War II, the use of simulators for training has increased, due primarily to cost, maintenance, availability and safety. Orlansky and String (1977 Orlansky and String (1979) have summarized simulator training effectiveness and cost effectiveness. Technologically advanced simulators, such as those for training air combat maneuvering, air cushion vehicles, and Skylab crews, are now commonplace. Unfortunately, there has been a recent increase in reports of discomfort and distress associated with the use of flight simulators. The data from a Navy sponsored survey of simulator sickness are described and a theoretical model is proposed.

At times, a reliability analyst is faced with life data where failures are found only by inspection. Test items must be inspected at the end of a test period, and then classed as failure or non-failure. Individual failure times are not known. When each item is inspected at a common age, the binomial distribution is routinely applied in practice and in the literature. This paper uses combinatorial mathematics to apply the binomial distribution to the more complicated case where each item is inspected at an arbitrary age. Conditional probabilities are used to extend the analysis when items undergo intermediate inspections.

As the United States Air Force looks to the twenty-first century, changes in its undergraduate pilot training system will lead to a modernization of the training aircraft fleet, and a more specialized training program which will be specifically tailored to the pilot trainee's follow-on aircraft assignment. These modifications, in aircraft and training philosophy, will enable the Air Force to provide our nation a more efficient and effective pilot training system which will continue to produce the best trained pilots in the world.