Usability Inspection of the MD-11 Aircraft Multifunctional Control Display Unit
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Usability Inspection of the MD-11 Aircraft Multifunctional Control Display Unit
Kheng-wooi Tan and Jennifer M. RileyMississippi State University
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Human-Centered Design of Automation• Human factors issues associated with design and
implementation of automation of interest:– Scerbo, 1996– Hilburn et al., 1997
– Endsley, 1996– Parasuraman et al., 1998
• Research driven by need for human-centered design of automated systems:– need to consider human cognition and behavioral effects
associated with use of automation (static or flexible)• Lack of focus, however, in automated system design
on human-computer interaction (HCI) :– communication (input / output) between human user and
computer - direct or indirect - influenced by style of interface (Dix et al., 1998)
– usefulness and usability important to effective HCI in interactive systems
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HCI in the Aircraft Cockpit• HCI important in cockpit automation:
– pilot uses Multifunctional Control Display Unit (MCDU), flight deck computer, to interact with automated flight management system
– good pilot-MCDU interaction critical to aircraft safety:• aviation accidents attributed to problems with pilot-MCDU
interaction (e.g., the American Airlines flight 965 CALI incident (1995))
Input
Output
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Multifunctional Control Display Unit
Video display terminal
Numeric keypad
Alpha keypad
Line Select Keys
(LSK)
Mode keys
MCDU used to preprogram flight from take-off through
en-route to landing
• Flight path planning:– identifying flight plan
waypoints– waypoint data entry
• headings• altitude• airspeed
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Study Objectives• Assess usability of MCDU based on general usability
principles (Dix et al., 1998)• Identify usability violations of MCDU design and
functionality:– three major principles of interest, including supporting
heuristics Learnability
•Predictability
•Synthesizability
•Familiarity
•Generalizability
•Consistency
Flexibility
•Dialog Initiative
•Multi-threading
•Task Migratability
•Substitutivity
•Customizability
Robustness
•Observability
•Recoverability
•Responsiveness
•Task Conformance
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Procedure• Conducted usability inspection with high-fidelity,
simulated MCDU using typical flight planning task:– usability inspection methods:
• non empirical techniques relying on judges to predict user problems with interfaces
• demonstrated to be cost-effective and reliable for evaluating interactive systems, like MCDU (Virzi, 1997)
– group expert review on MCDU:• human factors specialists acted as
surrogate users of MCDU • six (6) experts critique design and
functionality– experts had background in industrial
engineering and specialization in ergonomics
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Flight Path Planning Task• Programming 3-waypoint flight plan using MCDU:
– required experts to:• navigate through “pages” of MCDU: Active Flight Plan (AFP)
Pages 1 and 2, Duplicate Waypoint (DUP) Page, Lateral Revision (LR) Page, Vertical Revision (VR) Pages 1 and 2
• use numeric and alpha keypads, LSK and mode keys
– task steps:1. Start at AFP Page 12. Enter first waypoint using keypads3. Verify waypoint is correct and insert into flight plan4. Repeat Steps 2 and 3 for 2nd and 3rd waypoint5. Go to LR Page using LSK keys6. Enter information on airway and STAR using keypads 7. Return AFP Page 1 using LSK keys 8. Go to VR Page 1 using LSK keys
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More Task Steps9. Enter information on altitude, speed, etc. using keypads10. Go to AFP Page 1 using LSK keys11. Go to AFP Page 2 using mode keys12. Go to VR Page 2 using LSK keys13. Enter information on altitude, wind speed, etc. using keypad 14. Return to AFP Page 2 using LSK keys15. Repeat Steps 5 - 14 for 2nd and 3rd waypoints
• Usability violations identified by experts for each principle:– learnability - ease with which new user can
begin effective interaction with system– flexibility - multiplicity of ways user and
system exchange information– robustness - level of support provided to user
in assessing and achieving goals
Definitions
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Violations of System Learnability• High level of system complexity:
– several different methods to accomplish same task – many buttons have multiple functions (e.g., LSK keys used
to navigate between pages and execute commands)• Design fails to facilitate guessability• Poor synthesizability/feedback on pilot actions at
interface:– feedback to pilot not displayed on MCDU – pilot must view other cockpit displays (e.g. navigational
display) to determine outcome of action• MCDU design fails to provide global assessment of
flight parameters and aircraft status:– requires extensive pilot interpretation and mental
transformation and aggregation of data
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Violations of System Flexibility• System does not allow for multi-threading:
– pilot may not interact with more than one task/page at same time
– pilot must enter data for one waypoint on several pages at different times
• Lack of modifiability:– system only allows for text entry (no direct-
manipulation interface)– cannot customize interactions on basis of pilot
preference/skill level• System pre-emptive design:
– pilot not free to initiate actions – system initiates dialog and user responds to requests for
information
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Violations of System Robustness• MCDU design fails to provide default mode/state to
assist pilot with passive recall of information and appropriate actions at interface
• Poor reachability, navigability, and observability:– difficult to navigate through pages in sequence– pilot may not go directly from VR Page 1 to VR Page 2
• System design suffers from lack of recoverability:– Only allows for backward recovery– difficult to apply changes to flight plan or correct mistakes
• Poor system transparency:– lack of instantaneous response/feedback through MCDU
display terminal
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Potential Design Improvements• Provide graphical user interface (GUI) to
incorporate direct manipulation (DM) in HCI:– provide GUI with icons and
menus (like Window- based systems):
• decrease complexity associated with command-line interface text entry
• increase familiarity and learnability of MCDU
– provide graphical representation of flight pages and flight paths:
• increase observability and ability to globally assess entire flight path
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Potential Design Improvements (Continued)• Provide hierarchical representation of flight pages
for selection as needed:– facilitate user pre-emptive interaction– improve overall pilot-MCDU communication– improve system browsability
AFP 1
LR VR 1AFP 2 DUP
VR 2
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Potential Design Improvements (Continued)• Provide capability for interleaved multi-threading of
activities:– permit temporary overlap between separate pages of
MCDU for waypoint data entry:• decrease pilot working memory load associated with remembering
what data has/has not been entered for particular waypoint on particular page
• facilitate user pre-emptive interaction• improve overall pilot-MCDU communication
Active Flight Plan P1
Active Flight Plan P2
Vertical Revision p2BAQBIVOS OTU
Vertical Revision P2
Vertical Revision P1
BAQ N10 53.6BIVOS N09 17.4OUT N07
BAQ BIVOS OUT
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Potential Design Improvements (Continued)
• Minimize number of functions associated with each LSK key - increase consistency of pilot interaction with MCDU
• Provide mode indicators - increase system transparency and pilot awareness of current functions of buttons and controls
• Change physical layout of control buttons on MCDU:– use QWERTY layout for alpha keypad – relate design of 12 mode keys to 12 function keys on
conventional keyboard • increase familiarity of system • decrease time for text data entry
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Operational Benefits• Performance improvements associated with lower
working memory load• Enhanced SA associated with increased system
transparency• Decreased time to achieve effective interaction
with MCDU for novice pilots