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))

Output
Interface
Input
User
System
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Multifunctional Control Display Unit
MCDU used to preprogram flight from take-off
through en-route to landing
Line Select Keys (LSK)
Video display terminal

• Flight path planning
• identifying flight plan waypoints
• waypoint data entry
• headings
• altitude
• airspeed

Mode keys
Alpha keypad
Numeric keypad
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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 1
• 2. Enter first waypoint using keypads
• 3. Verify waypoint is correct and insert into
  flight plan
• 4. Repeat Steps 2 and 3 for 2nd and 3rd
  waypoint
• 5. Go to LR Page using LSK keys
• 6. 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 Steps

• 9. Enter information on altitude, speed, etc.
  using keypads
• 10. Go to AFP Page 1 using LSK keys
• 11. Go to AFP Page 2 using mode keys
• 12. Go to VR Page 2 using LSK keys
• 13. Enter information on altitude, wind speed,
  etc. using keypad
• 14. Return to AFP Page 2 using LSK keys
• 15. 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 1
AFP 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
Vertical Revision P2
Active Flight Plan P2
BAQ BIVOS OTU
Vertical Revision P1
Vertical Revision p2
BAQ BIVOS OUT
BAQ N10 53.6 BIVOS N09 17.4 OUT
N07
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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