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• recognizing / managing abnormal conditions
• predictability: when, how, why things happen
• mixing manual & automatic can defeat basic safety features
• design
• SISO control modes: can result in loss of control
• poor man-machine interfaces
• correct level of automation: keeping pilot “in the loop”
• adequacy of initial and recurrent training
Automation Safety Issues
Operational Complexity
• Who is in control? The pilot, FMS, autopilot, autothrottle?
• too many overlapping systems, modes , sub modes
• what is the system doing, what will it do next?
• crew confusion!
• inconsistent operations and performance:
• different modes, different results: automation surprises!
• complex mode logic, e.g. Flight Level Change, VNAV
• unsuitable man-machine interfaces,
• e.g. attention/ procedure intensive CDU keyboard
• inadequate mode annunciation /caution and warnings
• when should pilot intervene, or take over
• pilots putting too much trust in low integrity single
channel designs, not aware their limitations
Design Complexity
• historic systems evolution has led to
• new functions added-ons with each generation
• e.g. GLS on 737 NG: 11 LRUs involved!
• old problems “solved” by new modes / submodes
• e.g. Flight Level Change, VNAV, Thrust modes
• automation fragmentation into subsystems
• autopilot, autothrottle, FMS, SAS, FBW
• each subsystem handled by different organization
• design of each function approached as new problem
• SISO control : integration difficulties
• modes / sub modes cobbled together by intractable
mode logic
• mix of old and new technologies
• digital hardware with analog architectures!
• no overall design & integration strategy!
Design Requirements “Creep”
on a Recent AFCS Program
Successive Spec Revisions…..
B-777 Avionics Architecture
Flight Guidance and Control
Design Process
• 100 year evolution of systems & subsystems
• more capabilities with each generation
• most functions “Non-Flight Critical”
• only Autoland and manual control
considered “Flight Critical”
• new technologies/ old control strategies
• analog to digital / mechanical to FBW
• introduction of Augmented Manual Control
• Single Input / Single Output retained
• no certified Multi-Variable designs
• Major Issues:
• outdated Requirements and Design Approaches
Single-Axis SISO Control
• Single axis SISO automatic control modes have
been the standard since earliest days of automation
• It works…. most of the time, however….
• stability and performance cannot be guaranteed:
• loss of control possible, e.g. vert path modes
• full time pilot monitoring required!
•SISO control is root-cause of most automation complaints
• single controller input not only changes intended variable, but also
causes unintended responses of other variables:
• need other controller inputs to suppress unintended control
coupling errors
• poor damping, high control activity
• mode proliferation & complexities, operational inconsistencies and
pilot confusion
BASIC AIRPLANE CHARACTERISTICS:
THRUST AND DRAG AS FUNCTION OF SPEED
Trust,
Drag
Speed
Trim Drag
Speed
Power
Setting
Thrust
Point of
Neutral Stability
Front
Side
Back
Side
Stall
Speed
Stable T P
Unstable
Trim Point
• Generalized all-encompassing MIMO control strategy for
all automatic and augmented manual modes
• up-front integration of functions
• pitch/thrust control
• roll/yaw control (including rudder) - inherent
• yaw damping /turn coordination
• thrust asymmetry compensation
• improved failure detection, identification and isolation
• envelope protection
• airspeed, normal load factor, angle of attack, roll angle
FUTURE SYSTEMS REQUIREMENTS
• large cost reductions, achievable through
• reduced system complexity, less maintenance
• faster system development cycle
• design reusability- lower risk
• reduced customization
• standard off-the-shelf hardware
• less lab/flight testing
• reduction in pilot training need
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