A Display for Managing the Vertical Flight Path

\- an Appropriate Task with Inappropriate Feedback -

Thomas Prevot

San Jose State University

NASA Ames Research Center

Moffett Field, CA 94035-1000, USA\
+1 650 604 2441 tprevot@mail.arc.nasa.gov

# ABSTRACT

This paper focuses on feedback for managing the vertical flight path in
automated glass cockpits. Current aircraft displays provide feedback for
lateral path management and vertical path control. When pilots use a
higher level of automation for navigating in the vertical domain,
automation surprises may result in serious incidents or accidents. The
paper presents a Vertical Situation Display (VSD) that is being
developed and evaluated at NASA Ames Research Center. The VSD shall
provide valuable feedback for glass-cockpit pilots managing automated
vertical navigation devices. Capacity and economic constraints may
require aircraft to use high levels of automation to follow
predetermined 3D/4D flight paths precisely from takeoff to touchdown in
the near future.

## Keywords

Automation, Flight Management, Display, Task Analysis, Feedback, Man
Machine Interaction, Vertical Navigation, Situation Awareness

# INTRODUCTION

Navigating modern aircraft in the vertical domain is usually full of
automation surprises and altitude busts occur frequently. CFIT accidents
due to a loss of vertical situation awareness are the most serious
consequences of unsuccessful vertical flight path management. Research
by Wiener \[26\], Sarter and Woods \[19\]\[28\], Palmer et al. \[14\],
Funk et al. \[9\], Degani \[3\], Feary et al. \[7\] and others
demonstrate that automation surprises are common events in all automated
aircraft types. Furthermore they are mostly evident in the vertical
domain \[1\]\[22\]. This problem is so serious that certain air carriers
have disabled the possibility to engage the 'vertical navigation'
function of their flight management system or do not train their flight
crews on using it \[11\].

In the long term, such drastic means may result in less cost-effective
flights and incompatibilities with future air traffic requirements.
Programs aimed at increasing airspace capacity are focused on using
ground-based and airborne automation. Tools like the NASA/FAA Center
TRACON Automation System \[5\] are most effective, if the aircraft
flight paths are highly predictable from take off to touchdown. A
contributing factor to increase flight path accuracy and efficiency is
the usage of FMS departure, arrival and approach routes. Such routes
allow aircraft to fly at the highest level of automation close to the
ground, while having to meet a set of charted constraints concerning
particular altitudes and speeds at several waypoints along the route.

Clearly vertical navigation is shifting towards strategic vertical
flight path management. Nevertheless, there will always be situations,
when pilots have to revert from highly automated to less automated or
manual modes. In order to cope with these requirements, current and
future cockpit systems should be carefully reviewed with regard to
providing the necessary feedback for the different tasks. In the course
of this paper a Vertical Situation Display (VSD) will be proposed, well
aware of the fact that this is an old idea and that other VSDs exist in
operation (Gulfstream) and research \[6\]\[11\]\[22\]\[23\].
Nevertheless, such a display is increasingly important to cope with
current and future air traffic requirements. In the first part of the
paper it is explained, for which kinds of tasks feedback should be
provided and where the feedback is already there and more appropriately
situated on other displays. In the second part a VSD designed to this
task specification is introduced.

# TASK DECOMPOSITION AND ALLOCATION 

For the subsequent discussion the relevant elements of the overall task
to perform a commercial air transport mission are decomposed into the
tasks management, navigation, flight planning, guidance and control.
More comprehensive but slightly different descriptions of the task
decomposition can be found by others \[2\] \[21\].

The (flight) management task entails programming and/or selecting those
aircraft systems that are appropriate in a given situation to comply
with all given constraints necessary to complete the mission. Parts of
the management task can currently be carried out by the flight
management system, others like flight planning remain with the flight
crew. It includes navigation, flight planning, guidance and control (and
more).

The navigation task consists of deriving the current aircraft state in
terms of position, velocities and accelerations from a number of
redundant information sources. This task is generally considered to be
completely performed by automated systems. However, it should be noted
that the absolute position information derived from these functions is
only valuable for cockpit crews, if it is referenced to known meaningful
locations, like airports, waypoints, elevations or meaningful flight
plan values. Thus, the automated navigation task is most useful to the
pilot if he or she can derive the relative position information
necessary to perform or understand the flight planning and the guidance
tasks.

The goal of the flight planning task is to determine the
four-dimensional path to be flown by the aircraft, typically referred to
as the flight plan. This task can be performed by the cockpit crew or
ground based semi-automatic systems used by the air carrier or air
traffic control and communicated into the aircraft. In experimental
cockpit systems like the Cockpit Assistant System (CASSY), the flight
planning task has also been automated and flight tested with promising
results \[16\]\[17\]. The European Advanced Flight Management (AFMS)
System utilizes some of these functions and is currently in experimental
use as part of European air traffic management projects\[27\].

While full operational use of airborne flight planning functions is
still a few years ahead, the guidance task can already be delegated to
the flight management system, if a flight plan has been stored and
activated. The guidance task compares the actual position of the
aircraft with the flight plan and issues respective commands to the
control task. Based on this the control task generates the commands that
manipulate the aircraft's control surfaces and thrust to achieve these
targets. The control task is usually performed by the automation in
modern aircraft except for the flight portions on or close to the
ground.

The following section reviews how feedback is provided in most of the
current glass cockpit aircraft concerning these tasks.

# FEEDBACK IN CURRENT AIRCRAFT COCKPITS

Current aircraft displays provide feedback for lateral path management
and vertical flight path control. Lateral flight path management has
been enabled through the integration of an electronic map display into
modern glass-cockpits. With few exceptions (like some Gulfstream
aircraft) there is nothing equivalent for the vertical domain \[1\].

One of the most important accomplishments of the map display in
glass-cockpits is to enable flight crews to assess their lateral
position as determined by the navigation task. This enables flight crews
to derive the relative position information necessary to perform and
understand lateral flight planning and guidance tasks. This information,
depicted on the map display with its MAP mode for local areas and its
PLAN mode for extended areas, allows pilots to program flight plans into
the flight management system and graphically evaluate the resulting
lateral flight path. When the lateral guidance of the aircraft is
delegated to the FMS, flight crews can monitor the state of the aircraft
relative to the lateral flight path and anticipate the future behavior
as far out as the display range they have selected. The control task can
be monitored using the Flight Mode Annunciation (FMA), the heading
indicator and the Attitude Direction Indicator (ADI), where the bank
angle represents the direct feedback of the roll steering commands the
control function generates. Thus, all management tasks Ðnavigation,
flight planning, guidance and controlÐ regarding the horizontal domain
can be monitored by the cockpit crew. This kind of appropriate feedback
has resulted in very good performance in terms of lateral flight path
management in modern glass-cockpit aircraft.

In the vertical domain the displays only depict information supporting
the control task \[12\]\[21\]. The FMA annunciates the speed and pitch
control modes. The altitude, vertical speeds and pitch can be derived
from the ADI. Feary et al. \[7\] developed a guidance FMA, that
annunciates the operational procedures used to develop the guidance
behavior of the MD 11 aircraft. This FMA was evaluated during training
sessions in order to determine, whether it helps pilots understanding of
the vertical navigation of the aircraft. Although it revealed positive
results, the guidance FMA does not completely resolve the problem.

It helps pilots within the limitations of current cockpits with the
guidance task, but does not provide additional feedback for the
navigation (and flight planning) task. The relative position of the
aircraft in the vertical domain still has to be inferred from a variety
of sources. The absolute position is given at the altitude tape while
the reference positions of the flight path are depicted in an
alphanumeric format on the CDU LEGS page or on the map display attached
to the flight plan waypoints, when selected by the pilot. Since easing
position assessment for flight crews was one of the main accomplishments
in the lateral domain, this can also be the key for appropriate feedback
for vertical flight path management. This holds true also for other
outcomes of the navigation task, like the airspeed and the vertical
speed.

One reason for the feedback discrepancy between lateral and vertical
flight path management is that the displays have not kept up with FMS
evolution. Older and less sophisticated flight management systems
provide only automation for lateral path management and require that the
pilots perform most of the tasks in the vertical domain in less
automated modes. Additionally, vertical flight path management is only
important in climb and descend phases of flight (and the transitions
between different flight phases). In today's ATC systems, these phases
are mainly subject to tactical flight level changes instructed by air
traffic controllers. There are several developments that will require
increasing use of vertical flight path (including speed) management in
the near future. Some of them are briefly covered in the next section.

# THE NEED FOR VERTICAL FLIGHT PATH MANAGEMENT

Many of the aircraft incidents reported to the Aviation Safety Reporting
System can be attributed to problems in the vertical domain \[22\]. This
section is focused the discussion on one major safety concern
--Controlled Flight Into Terrain (CFIT)­-- and two upcoming economic and
capacity issues --FMS routes in terminal areas and new air traffic
control tools-- All three underline the increasing importance of
vertical flight path management in the current and future air traffic
environment.

## CFIT 

CFIT (Controlled Flight Into Terrain) is one of the main categories of
aircraft accidents. Clearly flight crews controlling their aircraft into
terrain have not been able to manage their vertical flight path
appropriately. Although they may have been aware of their absolute
altitude, the relative altitude to the ground elevation has not been
inferred correctly and early enough to initiate corrective actions.
Enhanced Ground Proximity Warning Systems (EGPWS) shall use a terrain
data base to predict possible ground impacts and warn pilots early
enough to avoid this kind of accident. Although this will certainly
prevent several CFIT accidents, ultimately the feedback problem in the
vertical domain is not resolved. If the aircraft state information was
presented appropriately in relation to the terrain elevation, flight
crews would have a better opportunity to assess the situation themselves
and make reasonable adjustments without having to rely on yet another
automated warning system in the cockpit. EGPWS should be the last guard
not the first.

## FMS routes in terminal areas

The Federal Aviation Administration (FAA), several Civil Aviation
Authorities (CAAs) and air carriers are currently advocating the
establishment of FMS routes in terminal areas. The goal is to be able to
use the aircraft flight management system for vertical and lateral path
management during almost all phases of flight. This requires that
continuous flight paths be defined and depicted on arrival and
transition charts. These routes including altitude and speed constraints
can be loaded into the FMS. Without having the necessary feedback,
pilots will have to trust their flight management automation to meet all
given constraints. Additionally, if pilots have to cancel this highest
level of automation because of traffic or other constraints, they have
to have the complete situation awareness in order to switch to a lower
level of automation.

## New air traffic control tools

The constraints imposed on the aircraft by FMS routes are generally
static once the route has been identified. If a flight management system
cannot comply with these constraints flight crews have to select a lower
level of automation. New decision support tools for air traffic
controllers add a dynamic dimension to the constraints for generating
vertical flight paths. In Frankfurt (am Main) the COMPAS system aids air
traffic controllers in sequencing and assigning runways \[24\]. FMS
routes are put into place that allow for adjustments of the final
approach length in the flight plan \[20\]. In the United States the
NASA/FAA Center TRACON Automation System (CTAS) provides decision
support tools for center and TRACON controllers in order to increase the
capacity of major US airports. Arriving aircraft will be able to
communicate their preferred routing to certain CTAS tools. CTAS then
computes constraints on the flight path that may be necessary to avoid
conflicts and to manage the traffic arriving at certain metering fixes
or runways \[9\]\[18\]. Understanding and compliance with these
dynamically generated constraints is a major flight management task in
the cockpit and crucial for beneficial air traffic management.

# DISPLAY DESIGN

The previous discussion leads to the conclusion that there is a strong
need to provide feedback for the vertical flight management tasks of
navigation, flight planning and guidance for certain flight phases.
Regarding the fact that flight path management is at least a three
dimensional task the question of the display dimensionally has to be
raised. A variety of research has addressed this. One common result is
that the appropriate format is task dependent.

## Display dimensionally

It was decided to use a co-planar view consisting of MAP display and VSD
based on the following thoughts:

-   First, feedback for the flight path management task shall provide
    global situation awareness, while aircraft control feedback (e.g.
    pitch and thrust modes) shall still be provided through the
    information on the ADI and the FMA. Information for global situation
    awareness is better represented in a co-planar view, control
    feedback in a perspective view.

-   Secondly, one of the main goals of the VSD is to display the
    vertical position information unambiguously (navigation task). 3D
    scenes are always ambiguous as to the true position of any point in
    space.

-   Thirdly, the flight management system manages the lateral and the
    vertical flight path mainly independently. A co-planar view provides
    the same kind of feedback.

-   Finally, as noted earlier vertical flight path management is only
    important in certain phases of flight. During other long portions
    (like the cruise flight) the profile view may not be necessary and
    can be turned off. The available region for the map display can
    increase, without changing the main internal display geometry. Thus,
    the pilot does not have to accommodate a new display in his
    representation.

By choosing the co-planar view one should be aware of the mental
geometry necessary for pilots to integrate the information on the VSD
and the ND. But as neither map display nor VSD are intended to provide
the essential feedback for the control task, this shortcoming is
considered less problematic but can be addressed during the evaluation.

## Color-coding

The color-coding used for the VSD shall reflect the color-schemes used
in the particular aircraft. Therefore, for an operational implementation
the color schemes have to be adapted to be as analogous as possible to
the MAP display. The currently implemented prototype uses the following
underlying scheme:

[magenta]{.underline}: active targets (active FMS flight plan, active
waypoint, commanded speed, commanded MCP altitude, if the vertical
flight path is not managed by the FMS)

[white:]{.underline} preselected values (modified FMS flightplan,
altitude and speed constraints, if the FMS is managing the vertical
flight path)

[white (on gray background)]{.underline}: aircraft state information for
current altitude and speed,

[green:]{.underline} extrapolation of the current flight path
(projection of the green arc on the Map display)

[amber:]{.underline} altitude and speed constraints, if the vertical
flight path is not managed by the FMS in order to draw the pilot's
attention to upcoming constraints.

# INTEGRATING THE VSD WITH THE MAP DISPLAY

Before describing the particular feedback elements in relation to the
identified tasks, the VSD integration with the MAP display is addressed
subsequently. Since the VSD may not be needed during all phases of
flight, it should be selectable. It could be argued whether an automatic
selection or a pilot selection is preferable. However to avoid a
complicated logic and be consistent with the current display selection
philosophy it was integrated to be brought up upon pilot request. The
VSD can be selected at the navigation display control panel in addition
to the MAP display in two co-planar combinations. The display has been
implemented in the part-task and the full mission version of NASA Ames
Advanced Concepts Flight Simulator. Figures 1 and 2 represent two
possible pilot selections:

The waypoint and wind information in the upper left and right corners of
the display remain unchanged. The range of the VSD is slaved to the
range of the map display and similar color conventions are used.

![](media/image1.emf){width="2.6152777777777776in"
height="2.620833333333333in"}\
Figure 1: 80% MAP / 20% VSD

In cases, where pilots want to focus only on the lateral domain, the VSD
can be turned off and the graphical map display remains unchanged. In
figure 1 the map display has been rescaled to 80% of its original size
and translated above the VSD. Pilots may select this view if they
consider the lateral domain more important than the vertical domain, but
want to maintain vertical situation awareness.

![](media/image1.emf){width="2.686111111111111in"
height="2.691666666666667in"}\
Figure 2: 60% Map/ 40% VSD

Figure two represents a view, where the MAP uses 60 % and the VSD
utilizes 40% of the display space. The map display has been rescaled and
translated accordingly. In this case, the VSD provides a more
comprehensive view of the future flight situation. Additionally a speed
indicator (current vs. commanded) is depicted, which is now possible
because of the increased display space. This more detailed view could be
useful in situations, where vertical path management is more important
and complicated. Feedback for the lateral domain is always given.

# CHARACTERISTICS OF THE VSD

The particular VSD characteristics will be described using the flight
situations depicted in figure 2 and figure 3. In this example the
display is scaled to a range of 40 nautical miles. The altitude range is
scaled such that most of the future flight path is visible. Up to a
selected display range of 80 NM the range/altitude ratio remains
constant to allow pilots to create a mental picture of a steep vs. a
shallow path. The altitude range in feet is determined as the selected
display range (NM) times 500. (E.g. a selected display range of 40 NM
leads to an altitude range of 20.000 feet). The aircraft symbol (white
triangle) is at a constant position at the lower half during climb and
at the upper half during descent, like in this case. When the aircraft
approaches the ground (or the cruise altitude), the aircraft symbol
moves down (or up) and the altitude scale remains constant. Thus, the
closure to the ground (cruise altitude) becomes visible.

The display supports vertical navigation, flight planning and guidance
tasks as follows:

## Navigation 

To support the flight crews understanding of the navigation task, the
display indicates the aircraft position and velocity in the vertical
domain in relation to meaningful and important objects. The aircraft
symbol is indicated as a triangle, rotating according to the current
pitch angle around the reference point depicted as a green dot. The
green line starting from this dot represents the current flight path
angle. The aircraft altitude is displayed on the left side. The example
above shows that the aircraft (white triangle) is high on the descent
path in 18890 feet. The current altitude target is 11000 feet, which is
indicated by the number (110) in the box on the right side and a line
across the display. The line is solid, if the MCP altitude constraints
the descent and dashed, if not. The airspeed is indicated in relation to
the commanded (magenta) or preselected (white) speed underneath the
aircraft symbol. When both differ significantly the gap between current
and target speed becomes visible. The shaded area between them indicates
the current speed envelope limitations

## Flight planning

The display supports vertical flight planning tasks by depicting the
current state of the active flight plan and any modification to it as it
will be used for managing the aircraft in an along track picture.
Therefore, all points along the flight plan, at which new commands will
be issued to the guidance system are displayed. Furthermore, it
indicates constraints along the flight path and enables flight crews to
determine, whether the generated flight plan will meet the constraints.
Altitude constraints are indicated as triangles, speed constraints in
alphanumeric format below. A modified flight plan is indicated as a
white line overlaying the magenta line of the active flight plan

## Guidance

The display shows the current target values for altitude and speed and
clearly indicates, whether the FMS manages the vertical flight path or
the flight crew must guide the aircraft along the path. This is achieved
by using a solid flight path line if the FMS manages the vertical flight
path, and a dashed flight path line, if not. The green line extrapolates
the aircraft velocity vector for one minute. The relation of the green
predictor line to the magenta flight path allows pilots to assess,
whether the aircraft is trying to get back to the path. The relation of
the current airspeed to the commanded airspeed indicates, whether the
speed is held. This combination shall allow flight crews to anticipate
the future behavior of the aircraft as far out as necessary to issue
commands to the control task that will lead to compliance with
constraints in the vertical domain.

# Relation TO OTHER VSD designs

Unlike other co-planar displays \[11\]\[13\]\[22\] this VSD is not
intended to provide direct control mode information. Hutchins'
Integrated Mode Management Interface (IMMI) \[11\] combines a lateral
and a vertical mode manager (including a VSD) as an integrated interface
to the autoflight control system for FMS equipped aircraft and
represents a new approach to mode management. The VSD proposed in this
paper is less comprehensive and radical. It complements current aircraft
displays rather than replacing them.

The main characteristics of this display are similar to the display
elements and geometry described in \[6\] although less alphanumeric
information is presented to keep the VSD as simple and uncluttered as
possible and to integrate it with the MAP display instead of replacing
it. Other vertical situation displays that appear similar to the one
introduced in this paper also include and focus on control mode
information in their design.

The MIT developed Electronic VSD \[22\] includes alphanumeric control
mode information for current and future states. The vertical situation
display used for the Georgia Tech developed VNAV tutor \[13\] is aimed
at training pilots and also depicts the current control mode in an
alphanumeric format. However, as discussed above the tasks that are
mainly lacking feedback in the operational use are navigation, flight
planning and guidance. In terms of mode management, specific emphasis is
put only into visualizing otherwise salient but critical transitions
from an FMS-managed mode to a pilot-managed mode through color changes
and broken vs. solid
lines.![](media/image1.emf){width="5.508333333333334in"
height="2.0527777777777776in"}

# A SOURCE OF AUTOMATION PROBLEMS?

Since the benefits of almost all additional automation in the cockpit so
far have been accompanied by new kinds of problems with the automation
it is a valid and important issue to raise with regard to the VSD. In
the author's opinion the automation (VNAV) is already there and causing
the problem, because the appropriate feedback (the VSD) is missing.
However, the introduction of the VSD may cause pilots to lose even more
basic piloting skills and manual control may be less possible than ever.
This is traded off against a better understanding of how the automation
is working and improved capabilities for managing the aircraft. However
the main effects of new kinds of automation unfortunately become
apparent and observable only after the automation is being used in day
to day operation for a significant amount of time. A thorough
context-bound evaluation can only contribute in avoiding a disastrous
misconception, but can hardly detect and resolve the long-term effects.

## PLANNED EVALUATION

The VSD is currently implemented in a mid-fidelity part task simulator
at NASA Ames. Comments on the VSD of pilots using this simulator were
extremely positive.

The VSD is being evaluated using a variety of methods. The first two
evaluations use low cost methods to detect flaws and problems in early
design stages. One evaluation uses a set of meaningful MAP/VSD snapshots
and a questionnaire to each snapshot. The goal is to identify, whether
pilots can gain an understanding of the flight situation by looking at
the map/VSD combination, and where problematic areas in the display
design are. Additionally, Polson et al. at the University of Colorado
use a modeling approach to investigate whether the display provides the
necessary information to support the task. A comparison to other
displays for the vertical domain will also be made.

The current part task implementation provides additional input for
another refinement step in preparation of a simulator based evaluation.
The display will be one variable in a full mission experiment focusing
on CTAS/FMS integration in NASA Ames Advanced Cockpit Flight Simulator.

# CONCLUDING REMARKS

Vertical flight path management is currently one of the most problematic
areas in glass cockpit aircraft. The need for this kind of strategic
flight management will increase in the near future. Additional feedback
is required to enable pilots carry out the navigation, flight planning
and guidance task in the vertical domain. A vertical situation display
addressing these tasks has been introduced and is being evaluated at
several fidelity levels.

# REFERENCES

1.  AW&ST (1995) Aviation Week and Space Technology (1995) *Automated
    Cockpits Special Report I& II*. Mcgraw Hill Publication, January 30,
    1995, February 6 1995.

2.  Billings, C.E. (1996) *Human-centered aviation automation:
    principles and guidelines.* NASA TM 110381, Moffett Field, CA

3.  Degani, A. (1996) *Modeling Human-Machine Systems: On Modes, Error
    and Patterns of Interaction*. Dissertation. Georgia Tech

4.  Ellis, S. R., Kaiser, M. K. and Grunwald, A. C. (Eds.)(1991*)
    Pictorial Communication in Virtual and Real Environments*. Taylor &
    Francis, London

5.  Erzberger, H. (1994) *Concerning the Center-TRACON Automation System
    (CTAS)* Presented to the FAA R & D Advisory Committee, July 12,
    1994, Washington, DC

6.  Fadden, D. M., Braune, R. and Wiedemann, J. (1993) *Spatial displays
    as a means to increase pilot situational awareness* in \[4\]

7.  Feary, M., McCrobie, D., Alkin, M., Sherry, L., Polson, P.,
    Palmer, E. and McQuinn, N *Aiding Vertical Navigation
    Understanding*, Final Report NASA Ames Research Center.

8.  Funk, k., Lyall, B. and Riley, V. (1995) *A comprehensive analysis
    of flightdecks with varying levels of automation* (Phase 1 Final
    Report-Perceived human factors problems of flightdeck automation).
    Eugene OR: Oregon State University

9.  Green, S. M., Goka, T. and Williams, D. H. (1997) *Enabling User
    Preferences Through Data Exchange.* AIAA

10. Green, S. M., Vivona, R. A. and Sanford, B. (1995) *Descent Advisor
    Preliminary Field Test*. AIAA Guidance, Navigation, and Control
    Conference, Baltimore, MD

11. Hutchins, E. (1996*) The Integrated Mode Management Interface Final
    Report*. NASA Ames Research Center, Moffett Field, CA

12. Mangold, S.J., and Eldridge, D. (1995) *Flight management systems
    information requirements.* Eighth Int. Aviation Psychology
    Symposium, Ohio State University, Columbus, OH.

13. Mitchell , C. M. (1998) *Horizons in Pilot Training: Desktop
    Tutoring Systems* in Sarter, N. & Amalberti, R., (Eds.) Cognitive
    engineering in the aviation domain, Erlbaum, New Jersey: Mahwah

14. Palmer, E. A., Hutchins, E., Ritter, R. and van Cleemput, I.
    (1993*). Altitude Deviations: Breakdowns of an Error Tolerant
    System* (NASA TM 108788). Moffett Field, CA

15. Palmer, E. A. (1995*). "Oops, it didn't arm." A case study of two
    automation surprises*. Proceedings of the Eighth International
    Aviation Psychology Symposium, Ohio State University, Columbus, OH.

16. Prevot, T. & Onken, R. (1996) *In-Flight Evaluation of CASSY: A
    System Providing Intelligent On-Board Pilot Assistance*. ATC
    Quarterly, 3(3), 183 - 204

17. Prevot, T. (1996*) Maschineller Flugplaner fuer Verkehrsflugzeuge
    als autonomes und kooperatives System*. Dissertation. VDI -Verlag,
    Duesseldorf Reihe 12, Nr. 262

18. Prevot, T., Palmer, E. A. and Crane, B. (1997*) Flight Crew Support
    for Automated Negotiation of Descent and Arrival Clearances*.
    Proceedings of the Ninth International Aviation Psychology
    Symposium, Ohio State University, Columbus, OH.

19. Sarter, N. B. and Woods, D. D. (1993*) Cognitive Engineering in
    Aerospace Application: Pilot Interaction with Cockpit Automation*.
    NASA Contractor Report 17761

20. Scheidt, J. and Rockel, B. (1997) *Optimization of Arrival and
    Departure Procedures using airborne "Flight Management System FMS",
    for Example Frankfurt (NeSS)* ATA-Adv. FMS Task Force Presentation

21. Sherry, L. and Polson, P. A New Direction for Automation Research:
    *Shared Models of the Avionics*.

22. Vakil, S. S., Midkiff, A. H. and Hansmann, R. J. (1996) *Development
    and Evaluation of an Electronic Vertical Situation Display.* NASA
    GRANT NAG1-1581

23. van Grent, R. N. H. W. (1997) *Free Flight with Airborne Separation
    Assurance*. Proceedings of the 10th European Conference, Free
    Flight, Amsterdam

24. Voelckers, U. (1991) *Application of Planning Aids for Air Traffic
    Control: Design, Principles, Solutions, Results*. in "Automation and
    System Issues in Air Traffic Control". J.A. Wise, V. D. Hopkin &
    M.L. Smith (Eds.). Springer Verlag, Berlin, Heidelberg

25. Wickens, C. D. (1993) *Three-dimensional Displays for Aviation: A
    Review of Research at Illinois*. APA Division 21 Meeting

26. Wiener, E.L (1989). *Human factors of advanced technology
    ("glass-cockpit") transport aircraft*. NASA Contractor Report
    No. 177528. NASA Ames Research Center, Moffett Field, CA

27. Wittig, T. & Dudek, H.-L. (1996) *The Flight Management System
    within World-Wide Communication/Navigation/Surveillance and Air
    Traffic Management*, ICAS 96-3.9.2., Sorrento, Italy.

28. Woods, D. D. and Sarter, N. B. (1998) *Learning from Automation
    Surprises and "Going Sour" Accidents: Progress on Human-Centered
    Automation*. NASA Contractor Report (NCC 2-592) NASA Ames Research
    Center, Moffett Field, CA