Microburst Encounter Research Articles

Three-dimensional model predictive controller design for approach to landing with microburst encounter

Microburst is considered an extreme powerful hazard for aircrafts, especially during takeoff, approach and landing phases of flight. Current airborne piloting practices involve taking alternative routes, if early detection of microburst wind shear (MBW) for its effective avoidance is possible. In this respect, design and analysis of precision automatic flight path control systems for microburst penetration are of outmost importance whose success can significantly reduce crash risks and thus enhance the flight safety. The current study is focused on the design and analysis of a three-dimensional model predictive controller for a wide body transport type aircraft encountering MBW in approach to landing phase of flight. This task is performed utilizing the full nonlinear six degrees of freedom aircraft equations of motion and the most complete 3D model of the MBW and its gradients. The results are promising for online applications as the proposed model predictive controller-based controller has effectively guided and kept the aircraft on the approach glide path with negligible deviations against aircraft initial lateral displacements, sharp edge gust disturbance as well as the MBW.

Modified guidance laws to escape microbursts with turbulence

This paper introduces Modified Altitude‐ and Dive‐Guidance laws for escaping a microburst with turbulence. The goal is to develop a procedure to estimate the highest altitude at which an aircraft can fly through a microburst without running into stall. First, a new metric is constructed that quantifies the aircraft upward force capability in a microburst encounter. In the absence of turbulence, the metric is shown to be a decreasing function of altitude. This suggests that descending to a low altitude may improve safety in the sense that the aircraft will have more upward force capability to maintain its altitude. In the presence of stochastic turbulence, the metric is treated as a random variable and its probability distribution function is analytically approximated as a function of altitude. This approximation allows us to determine the highest safe altitude at which the aircraft may descend, hence avoiding to descend too low. This highest safe altitude is used as the commanded altitude in Modified Altitude‐ and Dive‐Guidance. Monte Carlo simulations show that these Modified Altitude‐ and Dive‐Guidance strategies can decrease the probability of minimum altitude being lower than a given value without significantly increasing the probability of crash.

Escaping Microburst with Turbulence: Altitude, Dive, and Pitch Guidance Strategies

Three escape strategies are compared for microburst encounters during e nal landing approach: altitude guidance, dive guidance, and pitch guidance. The main difference between pitch guidance and the other two strategies is that pitch guidance immediately attempts to increase altitude at the expense of airspeed, whereas dive and altitude guidances initially trade altitude for airspeed. We use a full, six-degree-of-freedom, nonlinear, rigid-body aircraft model, including the effects of windshear and wind vorticity, and a model of microburst with turbulence. We also model the effect of stall prevention on the escape path. Two different approaches are used for comparison: 1) In a sample analysis approach, typical samples of the time histories of various variables are analyzed. 2 ) In a statistical approach, the probability distribution of the minimum altitude is estimated by the Monte Carlo method when the statistical properties of the microburst parameters are known. In the sample analysis and statistical approaches, the simulations take into account turbulence in addition to windshear. Both approaches suggest that, within the modeling assumptions presented, and in the absence of human factors, altitude and dive guidance with low commanded altitude may provide better safety than pitch guidance.

Windshear recovery using thrust vectoring

This study presents a preliminary evaluation of the application of Thrust Vectoring (TV) technology for improving windshear recovery of civil aircraft in microburst windshear encounters. A numerical trajectory optimization technique based on the method of multiple shooting is applied to achieve a microburst escape with minimal loss of altitude for a Boeing 727 type aircraft. Although the application of TV does result in a slight improvement in recovery altitude, there is also a price to be paid in the sense that TV utilization significantly hampers the ability to gain specific energy during recovery. Maintaining an energy buffer during a microburst encounter is highly desirable to achieve robustness with respect to uncertainness in windshear size and strength. TV aided windshear recovery has also been compared with an alternative approach to improve the windshear survivability capability, namely, the application of lateral maneuvering. The comparison shows that lateral maneuvering is not only a far more effective means to improve the recovery altitude, it also vastly improves energy preservation. In a view of the results established in this study, we feel that TV does not hold out great promise as a useful means to truly improve windshear recovery.

Windshear Recovery Using Fuzzy Logic Guidance and Control

Many aircraft accidents are related to hazardous windshear phenomena, in particular to the microburst. The energy loss which is associated with a microburst encounter can be very dangerous for the aircraft at low altitude. In this paper, a recovery concept is introduced, making a distinction between control, guidance, and flight envelope protection. For control, a fuzzy logic controller is developed based on energy principles, since the windshear is basically an energy problem. Additional energy is automatically supplied during the microburst by increasing the thrust. The available energy is distributed between altitude and airspeed by pitch angle according to a priority assignment, activated at the encounter of the windshear. This priority is determined with respect to a minimum airspeed and altitude, the flight envelope protection mechanism. Both controller and protection are integrated in one fuzzy logic system. Once the flight bounds are guaranteed, the controller tracks the flight path indicated by a predetermined guidance strategy. The application of the concept is demonstrated by a realistic simulation example.

Minimax Optimal Control Analysis of Lateral Escape Maneuvers for Microburst Encounters

This study examines the optimization of lateral escape trajectories in a microburst wind e owe eld for an aircraft one nalapproach.Theperformanceindexbeingminimizedisthemaximumvalueofaltitudedropatanypointalong the trajectory. In contrast to earlier work, the Chebyshev minimax performance index has not been approximated by a Bolza integral performance index. Rather, true Chebyshev solutions have been established by transforming the minimax problem into an equivalent optimal control problem with state variable inequality constraints. In comparison with Bolza solutions, Chebyshev solutions demonstrate a marked improvement in reducing the peak value of altitude drop. Moreover, the general trajectory behavior turns out to be radically different. In Chebyshev solutions, altitude typically is traded for airspeed in the initial phase of the encounter, such as to position the aircraft in a region of relatively low downdraft. The overall benee ts of lateral escape vis-a -vis nonturning escape were recone rmed in this study. OW-LEVEL windshear phenomena, and most notably microbursts, have long been recognized as potential hazards to aircraft in takeoff or approach-to-landing. A microburst is a shaft of cold air that descends rapidly, striking the ground and producing winds that diverge radially from the impact point.Flight crews need to be warned in time to avoid the hazard region or to escape in the event that avoidance is not possible. Most modern jet airliners are currently e tted with areactivewindshear sensorsystemthatpermits in situ detection of such potentially hazardous situations. Now in development are forward-look windshear detection systems to look ahead of the aircraft, thus offering improved alert times. Extensive researcheffortsalsohavebeendevotedtothedevelopmentofescape techniques that can be applied to prevent a possible crash resulting from a microburst encounter. Optimal trajectory studies have contributed signie cantly to insight about how to best e y an aircraft in a

Optimal lateral-escape maneuvers for microburst encounters during final approach

This paper is concerned with the optimization of lateral-escape trajectories in a microburst wind field for an aircraft on final approach. The objective is to minimize the peak value of altitude drop. An extensive numerical effort has been undertaken to investigate the characteristics of open-loop extremal solutions for various locations of the microburst. When a sufficiently large aerodynamic roll-angle limit is specified and the center of the microburst is not too far offset from the centerline extension of the approach runway, typically three trajectories can be found that satisfy the first-order necessary conditions of optimality for a given set of boundary conditions, namely, a trajectory that passes the microburst center to the left, a trajectory passing the center to the right, and a trajectory passing right through the center. The results bear out that a lateral-escape maneuver, in which an aircraft is turned away from the microburst center, may significantly improve an aircraft's surv ivability, in comparison to an escape maneuver that is restricted to a vertical plane. One of the most striking observations in this study is that, in contrast to nonturning escape maneuvers, lateral-escape maneuvers often exhibit a climb, rather than a descent, in the initial phase. The insight obtained from the present study may help the development of near-optimal lateral-escape guidance strategies for onboard application.

Target pitch angle for the microburst escape maneuver

Recovery performance of a commuter-type aircraft in a microburst encounter is studied using a constant-pitch-attitude strategy and flight path optimization. Results obtained indicate that the pitch attitude which maximized climb rate in a wind shear condition is strongly dependent on whether the aircraft is subjected to a horizontal shear or a downdraft. The pitch attitude which maximizes ground clearance depends on the altitude of the encounter, the strength of the microburst, and the initial position of the aircraft with respect to the downburst core. Best results are obtained at relatively low target pitch angles, in severe wind shear encounters at very low altitudes. A technique for maximizing ground clearance involves maintaining a low pitch attitude early in the encounter, followed by a gradual pitch-up that ceases when the wind shear has been excited.

Escape strategies for turboprop aircraft in microburst windshear

The dynamic reponse of a P-3 aircraft and a light twin-engine turboprop to a low-level microburst encounter is modeled. The response to the microburst is depicted for various escape maneuvers. Plots of altitude, velocity, and specific energy are shown for all cases. Takeoff escape strategies are discussed. The optimal escape procedure is found to be flying a constant value of pitch angle. Constant angle of attack maneuvers sometimes result in superior performance.

Forward-look wind-shear detection for microburst recovery

An effort is in progress by NASA, the Federal Aviation Administration, and the industry to reduce the threat of convective microburst wind-shear phenomena to aircraft. This paper describes an effort to quantify the benefits of forward-look sensing and to develop and test a candidate set of strategies for recovery from inadvertent microburst encounters during the landing approach. Initial development of recovery strategies was performed in batch simulation prior to piloted simulation evaluation using a full dynamic airplane model. The results of this effort indicate that the factor that most strongly effects a microburst recovery is the time at which the recovery is initiated. Improving the alert time by 5 s generally provided a greater recovery performance increase than could be achieved by changing the recovery strategy. Forward-look alerts given 10 s prior to microburst entry permitted recoveries to be made with negligible altitude loss. Nomenclature F = wind-shear hazard index g = gravitational acceleration //ref = reference altitude for recovery strategies V = airplane airspeed Wh = vertical wind component, updraft positive Wx = horizontal wind component, along the airplane ground track

Optimal aircraft performance during microburst encounter

The effects of microburst characteristics on the optimal penetration performance of jet transport and general aviation aircraft are presented. The purpose is to determine the best possible performance that can be achieved in a broad range of microbursts. A secondary goal is to illustrate good strategies for dealing with a range of microbursts during takeoff and landing. Over 1100 optimal trajectories were computed for two aircraft types flying through idealized microbursts using a Successive Quadratic Programs trajectory optimization algorithm. Contours of safety metrics are plotted as functions of the length scales, magnitudes, and locations of horizontal wind shears and vertical downdrafts. These performance contours show three length-scale regimes for optimal microburst penetration. At short length scales, hazards usually associated with gustiness predominate (e.g., high normal load factor, rotational upset). At intermediate length scales, a degraded ability to maintain flight path and/or vertical velocity poses the most serious threat. At very long microburst length scales, excessive touchdown velocities may result. The ability to transit a microburst successfully also varies strongly with microburst location. The results show that both aircraft types could penetrate some very severe microbursts if optimal control histories were followed. Nevertheless, these control strategies assume perfect prior knowledge of the wind, and practical limits to successful encounter with real-time control capabilities would be lower. The optimally controlled jet transport can successfully penetrate higher intensity microbursts than can the general aviation aircraft.

Analysis of aircraft control strategies for microburst encounter

Analyses have indicated that improved control strategies could reduce the threat posed by the presence of microburst-type wind shear during aircraft takeoffs and landings. The attenuation of flight path response to microburst inputs by feedback control to elevators and throttle was studied for the cases of a jet transport and a general aviation aircraft, using longitudinal equations of motion, root locus analysis, Bode plots of altitude response to wind inputs, and nonlinear numerical simulation. Energy management relative to the airmass, a pitch-up response to the decreasing airspeed, increased phugoid mode damping, and decreased phugoid natural frequency, are found to improve microburst penetration aircraft behavior. Aircraft stall, and throttle saturation, are limiting factors in an aircraft's ability to maintain a given flight path during a microburst encounter.