Usability Inspection of the MD-11 Aircraft Multifunctional Control Display Unit Kheng-wooi Tan and Jennifer M. Riley Mississippi State University

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

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

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

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

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

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

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 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

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

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

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

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

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 LRVR 1AFP 2DUP VR 2

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 p2 BAQ BIVOS OTU Vertical Revision P2 Vertical Revision P1 BAQ N BIVOS N OUT N07 BAQ BIVOS OUT

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

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