Celeste M. Belcastro

Closed-loop HIRF experiments performed on a fault tolerant flight control computer

During the third quarter of 1996, the Closed-Loop Systems Laboratory was established at the NASA Langley Research Center (LaRC) to study the effects of High Intensity Radiated Fields on complex avionic systems and control system components. This new facility provided a link and expanded upon the existing capabilities of the High Intensity Radiated Fields Laboratory at LaRC that were constructed and certified during 1995-96. The scope of the Closed-Loop Systems Laboratory is to place highly integrated avionics instrumentation into a high intensity radiated field environment, interface the avionics to a real-time flight simulation that incorporates aircraft dynamics, engines, sensors, actuators and atmospheric turbulence, and collect, analyze, and model aircraft performance. This paper describes the layout and functionality of the Closed-Loop Systems Laboratory, and the open-loop calibration experiments that led up to the commencement of closed-loop real-time flight experiments.Closed-loop HIRF experiments were performed on a fault tolerant flight control computer (FCC) at the NASA Langley Research Center. The FCC used in the experiments was a quad-redundant flight control computer executing B737 Autoland control laws. The FCC was placed in one of the mode-stirred reverberation chambers in the HIRF Laboratory and interfaced to a computer simulation of the B737 flight dynamics, engines, sensors, actuators, and atmosphere in the Closed-Loop Systems Laboratory. Disturbances to the aircraft associated with wind gusts and turbulence were simulated during tests. Electrical isolation between the FCC under test and the simulation computer was achieved via a fiber optic interface for the analog and discrete signals. Closed-loop operation of the FCC enabled flight dynamics and atmospheric disturbances affecting the aircraft to be represented during tests. Upset was induced in the FCC as a result of exposure to HIRF, and the effect of upset on the simulated flight of the aircraft was observed and recorded. This paper presents a description of these closed-loop HIRF experiments, upset data obtained from the FCC during these experiments, and closed-loop effects on the simulated flight of the aircraft.

Fault detection in dynamic systems via decision fusion

Due to the growing demands for system reliability and availability of large amounts of data, efficient fault detection techniques for dynamic systems are desired. In this paper, we consider fault detection in dynamic systems monitored by multiple sensors. Normal and faulty behaviors can be modeled as two hypotheses. Due to communication constraints, it is assumed that sensors can only send binary data to the fusion center. Under the assumption of independent and identically distributed (1ID) observations, we propose a distributed fault detection algorithm, including local detector design and decision fusion rule design, based on state estimation via particle filtering. Illustrative examples are presented to demonstrate the effectiveness of our approach.

Distributed Fault Detection with Correlated Decision Fusion

Quick and accurate fault detection is critical to the operation of modern dynamic systems. In this paper, the fault detection problem when using multiple sensors is investigated. At each time step, local sensors transmit binary data to the fusion center, where decision fusion is performed to detect the potential occurrence of a fault. Since the sensors observe a common dynamic process, their measurements, and thus the local decisions, are correlated. Under a likelihood-ratio-based local decision rule constraint, we propose efficient suboptimal system designs involving local sensor rules and fusion rule that include the correlation consideration. Two correlation models are proposed to approximate the complicated correlation between sensor measurements for general systems. Experimental results show that the designs with correlation consideration outperform the design under the independence assumption significantly when the correlation between sensor measurements is strong.

Distributed fault detection via particle filtering and decision fusion

Due to the growing demands for system reliability and availability of large amounts of data, efficient fault detection techniques are desired. In this paper, we consider nonlinear, non-Gaussian systems monitored by multiple sensors. Normal and faulty behaviors can be modeled as two hypotheses. Due to the communication constraints, it is assumed that sensors can only send binary data to the fusion center. Under the assumption of independent, identically distributed observations, we propose a distributed fault detection algorithm, including local detector design and decision fusion rule design, based on the state estimation by particle filtering. Experimental results show the efficiency of our proposed algorithm and its superiority over the conventional Kalman filter-based methods.

Ensuring control integrity of critical systems subjected to electromagnetic disturbances: problem overview

An assessment process for verifying the control integrity of critical flight systems in adverse, as well as nominal, operating environments is currently under development at the NASA Langley Research Center. The assessment process involves a combination of analysis, simulation and tests, and it addresses: 1) closed-loop operation of the controller under test, 2) real-time dynamic detection of controller malfunctions, and 3) the resulting effects on the aircraft relative to the stage of flight, flight conditions, and required operational performance. Closed-loop high-intensity radiated fields (HIRF) effects experiments were performed on a fault tolerant flight control computer. This paper presents an overview of the problem of ensuring the integrity of critical control systems operating in harsh electromagnetic environments, and an approach for the assessment of these systems. A description of the closed-loop HIRF experiments and closed-loop effects on the simulated flight of the aircraft are also presented.

Monitoring Functional Integrity in Fault Tolerant Aircraft Control Computers for Critical Applications

Abstract Verifying integrity of control computers in adverse operating environments is a key issue in the development, certification, and operation of critical control systems. For example, future commercial aircraft will necessitate flight-critical systems with high reliability requirements for stability augmentation, flutter suppression, and guidance and control. This paper considers the problem of applying distributed detection techniques and decision fusion to monitoring the integrity of fault tolerant redundant control computers. A monitoring strategy is presented and demonstrated from glideslope engaged until flare using a detailed simulation of a quad-redundant longitudinal control system for the B737 Autoland. The performance of the distributed monitoring system is assessed.

A low-cost comprehensive process for assessing electromagnetic environment (EME) effects on flight-critical control computers

A process is presented for assessing the effects of electromagnetic environments on flight-critical aircraft control computers. The assessment process is a combination of analysis, simulation, and tests and is currently under development for demonstration at the NASA Langley Research Center in the High Intensity Radiated Fields (HIRF) Laboratory and Closed-Loop Test (CLT) Laboratory. The assessment process is comprehensive in that it addresses (i) closed-loop operation of the controller under test, (ii) real-time dynamic detection of controller malfunctions that occur due to the effects of electromagnetic disturbances caused by lightning, HIRF, and electromagnetic interference and incompatibilities, and (iii) the resulting effects on the aircraft relative to the stage of flight, flight conditions, and required operational performance. In addition, this method uses electromagnetic field modeling codes to determine internal electromagnetic environments to which onboard electronic equipment will be subjected. Lower cost demonstrations of certification compliance should be realizable using this method due to the reduction or elimination of costly full-aircraft tests.

Detecting controller malfunctions in electromagnetic environments. II. Design and analysis of the detector

For part I see ibid. Verifying the integrity of control computers in adverse operating environments is a key issue in the development, validation, certification, and operation of critical control systems. Future commercial aircraft will necessitate flight-critical systems with high reliability requirements for stability augmentation, flutter suppression, and guidance and control. Operational integrity of such systems in adverse environments must be validated. The paper considers the problem of dynamic detection techniques to monitoring the integrity of fault tolerant control computers in critical applications. Specifically, the paper considers the detection of malfunctions in an aircraft flight control computer (FCC) that is subjected to electromagnetic environment (EME) disturbances during laboratory testing. A dynamic monitoring strategy is presented and demonstrated for the FCC from glideslope engaged until flare under clear air turbulence conditions using a detailed simulation of the B737 Autoland. The performance of the monitoring system is analyzed.

Fusion Techniques Using Distributed Kalman Filtering for Detecting Changes in Systems

The objective of this paper is to compare the performance of two detecion strategies that are based on different data fusion techniques. The application of the detection strategies is to detect changes in a linear system. One detection strategy involves combining the estimates and eror covariance matrices of distributed Kalman filters, generating a residual from the fused estimates, comparing this residual to a threshold, and making a decision. The other detection strategy involves a distributed decision process in which estimates from distributed Kalman filters are used to generate distributed residuals which are compared locally to a threshold Local decisions are made and these decisions are then fused into a global decision. The relative performance of each of these detection schemes is compared and it is concluded that better performance is achieved when local decisions are made and then fused into a global decision.