Aviation Safety and Pilot Control Understanding and Preventing Unfavorable Pilot-Vehicle Interactions (1997) / Chapter Skim
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Pages 14-29
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From page 14... ...
1Aircraft-Pilot Coupling Problems: Definitions, Descriptions, and History INTRODUCTION ''Aircraft-pilot coupling (APC) events" are inadvertent, unwanted aircraft attitude and flight path motions that originate in anomalous interactions between the aircraft and the pilot.
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the aircraft are contributing factors to the adverse motions. APC events are collaborations between the pilot and the aircraft in that they occur only when the pilot attempts to control what the aircraft does.
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that the systems are operating at their limits, may call for a greater response from the control surface than is allowed by the system's rate or position limits* for that effector.
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example is given here to capture the reader's attention and to show that such events, although extremely unusual, can be very serious. Although severe APC events are rare, they continue to occur, and, what is of more concern, they seem to be increasing in variety and complexity as aircraft systems advance.
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provide cues for the higher-frequency PVS loops are of practical consequence. This simplifies the analysis considerably and emphasizes as key cues the aircraft attitudes and accelerations and the pilot-perceived control forces and displacements (proprioceptive variables)
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NECESSARY CONDITIONS FOR OSCILLATORY AIRCRAFTPILOT COUPLING EVENTS The pilot, controlled element, task, and goal elements shown in Figure 1-2 are the principal constituents that can interact to cause a PIO when the PVS is a tightly-coupled closed-loop. Figure 1-3 shows the sufficient conditions for a continuous oscillation of the pilot-controlled-element system.
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Fi gu re 1 -2 T he p ilo t c on tro lle del em en t s ys te m .
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which can be caused by wind gusts, turbulence, or other unexpected events (e.g., runway incursions) in the external environment.
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HISTORICAL ANTECEDENTS Aircraft with Conventional Flight Control Systems The committee assessed the historical record of aircraft accidénts and incidents from publicly available records and detailed discussions with a representative set of aircraft manufacturers, airlines, and accident investigation authorities in the United States and Europe. This assessment revealed a remarkably diverse set of severe PIOs and other APC events.
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TABLE 1-1a Single Axis PIOs Associated with Extended Rigid Body Effective Aircraft Dynamics Aircraft Date Description XS-1 Oct. 24, 1947 PIO during gliding flight approach and landing XF-89A Early 1949 PIO during dive recovery Mirage 1950s Several severe pitch PIOs on early aircraft with FCSs not equipped with a pitch-damping system KC-135A late 1950s Mild lateral-directional PIO associated with lateraldirectional coupling effects X-15 June 8, 1859 PIO during gliding flight approach and landing X-15 1961 Lateral PIOs during research study of lateraldirectional coupling Parasev 1962 Lateral rocking PIO of paraglider research vehicle during ground tow B-58 Sept.
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TABLE 1-1c Single-Axis, Higher-Frequency PIOs Aircraft Date Description YF-12 Several incidents in late 1960s and early 1970s PIO involving high-frequency flexible modes of the airframe structure CH-53E 1978–1985 PIOs involving flexible modes during precision hover with heavy sling loads, which resulted in heavy landings and dropped loads F-111 unknown Several PIO incidents caused by coupling of the pilot with heavy underwing stores, which resulted in sustained lateral oscillations Voyager 1986 PIOs caused by coupling of the pilot with symmetric bending of the wing Source: Adapted from McRuer.42 TABLE 1-1d Combined Three-Dimensional, Multi-Axis PIOs Aircraft Date Description X-5 Mar. 31, 1952 Three-axis PIO leading to crash AD-1 Several incidents in early 1980s Three-axis PIOs associated with inherent couplings of oblique wing aircraft F-14 Jan.
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and control challenges; these PIOs have helped to define the limits of piloted control and have underscored the need for sophisticated FCSs to redress imbalances in certain configurations. For those aircraft that were already operational or that became operational, the specific problems leading to PIOs were identified, and the aircraft were modified to reduce PIO tendencies.
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TABLE 1-2 Noteworthy APC Events Involving FBW Aircraft Aircraft Date Description YF-16 1974 Unplanned first flight during a high-speed taxi test Tornado Jan. 26, 1976 Landing accident during flight test of prototype #5 Shuttle Oct.
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auspices of the Aeronautics and Space Engineering Board, focuses attention on key steps that could be taken to minimize the kind of problems seen recently and that could counter new types of APC events. Statement of Task and Committee Membership To fulfill this assignment the Aeronautics and Space Engineering Board assembled the Committee on the Effects of Aircraft-Pilot Coupling on Flight Safety.
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The committee was also challenged with finding understandable and straightforward language (in fields replete with jargon) to communicate with a community that has diverse interests, needs, and time horizons.
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better identify APC possibilities in operational situations. Chapter 4 lists lessons learned and recommends management and design policies, procedures, and processes to avoid adverse APC events.
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