A Vertical Situation Display for Automated Aircraft - Design and
Evaluation in Full Mission Simulation

Thomas Prevot and Barry Crane

San Jose State University\
NASA Ames Research Center\
Moffett Field, CA

# Introduction

This paper presents the design and evaluation of a flight deck display
for "glass-cockpit" aircraft that provides feedback for managing the
vertical flight path. 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.
Current aircraft displays provide excellent feedback for managing the
automation in the lateral domain, but are lacking similar feedback for
the vertical domain. Therefore, during climbs and descents automation
surprises occur and may result in incidents or accidents. Additionally,
flight crews may not be able to follow given vertical and speed profiles
as efficiently and precisely as necessary to cope with the requirements
of the increasing air traffic anticipated in the coming years.

# Design of the Vertical Situation Display (VSD)

Analyzing current and future tasks related to vertical path management
and evaluating available feedback resources drove the development of the
Vertical Situation Display VSD. The example of the very successful
Navigation Display and results from previous vertical navigation display
studies contributed to the design as well as inputs from the potential
users of the display. A more thorough description of the theoretical
background can be found in Prevot (1998).

The VSD is integrated into the cockpit infrastructure to complement
existing displays. The constraints on modern flight decks including
available display size, color coding and data accessibility have been
taken into account as far as possible and feasible. From this standpoint
the VSD could be part of next generation flight decks as well as
retrofitted into current generation "glass" aircraft.

![](media/image1.wmf)The VSD shares the display space with the
Navigation Display and can be accessed from the Navigation Display
Control Panel in two different views. The first view is a co-planar view
of the bird's eye MAP depiction and the along track picture of the VSD.
The VSD occupies the bottom 40% of the Navigation Display, which is
re-scaled to fit into the top 60% of the display area. In the second
view the VSD occupies 80% of the Navigation Display Space and leaves the
readouts for winds and waypoints as well as the Heading/Track indication
unchanged. Figure 1 shows the co-planar view of MAP and VSD.

Figure 1: Vertical Situation Display in "shared mode"

# Full mission simulation study

In fall 1998 a full mission simulation was conducted at NASA Ames'
Advanced Concepts Flight Simulator (ACFS) to investigate flight crew
factors for Flight Management System (FMS) usage in the extended
terminal airspace. The ACFS is a full-mission simulator with a "generic"
glass cockpit layout based on current generation Boeing-type displays.
The simulation model represents a Boeing 757. Twelve airline flight
crews participated in the study and flew seven descents from cruise
altitude to touchdown in the Dallas Fort Worth airspace. The crews were
subject to different interface conditions. They were required to fly at
different levels of automation, ranging from current day procedures,
requiring step-by-step entry of target values for altitude, speed and
heading into the autopilot to fully automated modes, coupled to the FMS
until final approach. The main purpose of the study was to investigate
crew interfaces that enhance the compatibility between ground automation
and flight deck automation.

The VSD was an independent variable in this study made available to half
of the crews. Crews provided with the VSD were free to select the
co-planar or the full mode at any time. They were asked to turn it off
in the final phase of flight, because the VSD was not designed for
controlling aircraft during approach.

A comprehensive data analysis is still ongoing, evaluating aspects of
crew performance, workload, acceptance and subjective assessment of
several interface modifications. The following paragraphs present an
overview on some general results and discuss the particular results on
the subjective assessment of the VSD by the flight crews and how they
were using it. For details on other aspects see Crane et al. (1999).

# General results

The flight crews considered the scenarios flown realistic for moderate
traffic situations, but not very challenging. Overall flight crew
performance was at a very high level for all interface conditions and
runs. The VSD did not affect this overall high crew performance. The
workload assessment using the NASA TLX methodology showed no significant
differences between the crews having the VSD available and those, who
did not.

We believe that in order to expect differences in workload or crew
performance caused by the VSD more challenging scenarios are required
including higher traffic density and worse weather environments.

# Subjective assessment by the flight crews

The six flight crews that had the VSD available were asked to state
their opinion and experience with the VSD in a questionnaire at the end
of the experiment. 11 Results from 6 first officers and 5 captains were
received. Table 1 summarizes the main questions. The subjects were also
asked which display features they found most helpful. The following
features were named most frequently:

1\. Magenta vertical flight path depiction: 9\
2. Altitude/speed crossing restrictions: 8\
3. 1 minute green flight path angle predictor line: 7\
4. Altitude display, speed display, speed bug value, color coding\
for managed and unmanaged crossing restrictions: 4-5

Comments on the flight path depiction stated that it's "easy to
interpret", a "planview of descent" and "same as magenta LNAV path, it's
where we want to be". The crossing restrictions were said to be a "good
memory aid", "allowed advanced planning to stay ahead", "Not too
useful", "Very useful", "easy to read" and "too small".

+-------------------------+--------+--------+---+---+---+--------+-------+
| **Question**            | **Ans  |        |   |   |   |        |       |
|                         | wer-op |        |   |   |   |        |       |
|                         | tion** |        |   |   |   |        |       |
+-------------------------+--------+--------+---+---+---+--------+-------+
| Did you feel more       | *Much  | *So    | * |   |   | *So    | *Much |
| "ahead" or less "ahead" | less\  | mewhat | B |   |   | mewhat | m     |
| of the airplane with    | \      | less*\ | o |   |   | more*\ | ore*\ |
| the VSD?                | *0     | **1**  | r |   |   | **5**  | **5** |
|                         |        |        | d |   |   |        |       |
|                         |        |        | e |   |   |        |       |
|                         |        |        | r |   |   |        |       |
|                         |        |        | \ |   |   |        |       |
|                         |        |        | l |   |   |        |       |
|                         |        |        | i |   |   |        |       |
|                         |        |        | n |   |   |        |       |
|                         |        |        | e |   |   |        |       |
|                         |        |        | \ |   |   |        |       |
|                         |        |        | * |   |   |        |       |
|                         |        |        | 0 |   |   |        |       |
+-------------------------+--------+--------+---+---+---+--------+-------+
| Did use of the VSD      | *Yes*  |        |   | * |   |        |       |
| distract you from       |        |        |   | N |   |        |       |
| performing other        | 0      |        |   | o |   |        |       |
| cockpit tasks?          |        |        |   | * |   |        |       |
|                         |        |        |   |   |   |        |       |
|                         |        |        |   | 1 |   |        |       |
|                         |        |        |   | 1 |   |        |       |
+-------------------------+--------+--------+---+---+---+--------+-------+
| Did use of the VSD      | *Yes*  |        |   | * |   |        |       |
| distract you from       |        |        |   | N |   |        |       |
| monitoring other        | 0      |        |   | o |   |        |       |
| cockpit displays?       |        |        |   | * |   |        |       |
|                         |        |        |   |   |   |        |       |
|                         |        |        |   | 1 |   |        |       |
|                         |        |        |   | 1 |   |        |       |
+-------------------------+--------+--------+---+---+---+--------+-------+
| In general, how helpful | *Very\ | *So    | * |   |   | *Som   | *Very |
| or unhelpful was the    | unhe   | mewhat | B |   |   | ewhat\ | hel   |
| VSD in aiding your      | lpful* | unhe   | o |   |   | he     | pful* |
| management of the       |        | lpful* | r |   |   | lpful* |       |
| descent?                | 0      |        | d |   |   |        | 7     |
|                         |        | 0      | e |   |   | 4      |       |
|                         |        |        | r |   |   |        |       |
|                         |        |        | \ |   |   |        |       |
|                         |        |        | l |   |   |        |       |
|                         |        |        | i |   |   |        |       |
|                         |        |        | n |   |   |        |       |
|                         |        |        | e |   |   |        |       |
|                         |        |        | * |   |   |        |       |
|                         |        |        |   |   |   |        |       |
|                         |        |        | 0 |   |   |        |       |
+-------------------------+--------+--------+---+---+---+--------+-------+
| Did having the VSD      | *G     | *So    | * |   |   | *So    | *Gr   |
| increase or decrease    | reatly | mewhat | U |   |   | mewhat | eatly |
| your monitoring         | decr   | decr   | n |   |   | incr   | incre |
| demands?                | eased\ | eased\ | a |   |   | eased\ | ased\ |
|                         | *0     | ***2** | f |   |   | ***6** | *     |
|                         |        |        | - |   |   |        | **1** |
|                         |        |        | f |   |   |        |       |
|                         |        |        | e |   |   |        |       |
|                         |        |        | c |   |   |        |       |
|                         |        |        | t |   |   |        |       |
|                         |        |        | e |   |   |        |       |
|                         |        |        | d |   |   |        |       |
|                         |        |        | \ |   |   |        |       |
|                         |        |        | * |   |   |        |       |
|                         |        |        | * |   |   |        |       |
|                         |        |        | * |   |   |        |       |
|                         |        |        | 3 |   |   |        |       |
|                         |        |        | * |   |   |        |       |
|                         |        |        | * |   |   |        |       |
+-------------------------+--------+--------+---+---+---+--------+-------+
| Did having the VSD      | *G     | *So    | * |   |   | *So    | *Gr   |
| increase or decrease    | reatly | mewhat | U |   |   | mewhat | eatly |
| your overall workload?  | decr   | decr   | n |   |   | incr   | incre |
|                         | eased\ | eased\ | a |   |   | eased\ | ased\ |
|                         | *1     | ***5** | f |   |   | ***2** | *     |
|                         |        |        | - |   |   |        | **0** |
|                         |        |        | f |   |   |        |       |
|                         |        |        | e |   |   |        |       |
|                         |        |        | c |   |   |        |       |
|                         |        |        | t |   |   |        |       |
|                         |        |        | e |   |   |        |       |
|                         |        |        | d |   |   |        |       |
|                         |        |        | \ |   |   |        |       |
|                         |        |        | * |   |   |        |       |
|                         |        |        | * |   |   |        |       |
|                         |        |        | * |   |   |        |       |
|                         |        |        | 3 |   |   |        |       |
|                         |        |        | * |   |   |        |       |
|                         |        |        | * |   |   |        |       |
+-------------------------+--------+--------+---+---+---+--------+-------+
| Did the VSD help you to | ####   |        |   |   | * |        |       |
| understand how the FMS  | Yes ** |        |   |   | N |        |       |
| manages the flight      | 7** {# |        |   |   | o |        |       |
| path?                   | yes-7  |        |   |   | \ |        |       |
|                         | .unnum |        |   |   | * |        |       |
|                         | bered} |        |   |   | * |        |       |
|                         |        |        |   |   | * |        |       |
|                         |        |        |   |   | 4 |        |       |
|                         |        |        |   |   | * |        |       |
|                         |        |        |   |   | * |        |       |
+-------------------------+--------+--------+---+---+---+--------+-------+

Table 1: Summary of questionnaire

# Usage of the Vertical Situation Display

The crews were trained on how to interpret the VSD in a 15 minute
briefing using display snapshots, in which the symbology was explained.
They were briefed on how to select and deselect the two available modes
co-planar and full VSD, and told to deselect the VSD during final
approach. Figure 2 shows the time the VSD was used in relation to the
flight time from cruise altitude to 5000 feet for 40 runs performed by 6
different flight crews.

![](media/image4.wmf)Usage of the VSD was very inconsistent throughout
the subjects, as the big standard deviations indicate. One captain
hardly ever used it, whereas many subjects used the VSD during the
entire descent. In average either the Pilot Flying (PF) or the Pilot Not
Flying (PNF) had the VSD selected during 75% of the flight time. Both
crewmembers used the VSD simultaneously for 30%. The shared co-planar
mode was clearly preferred and used almost all the time (\>98 %) the VSD
was selected. The full mode was rarely used and only for a few seconds.
VSD usage between the PF and the PNF was similar.

# Discussion

The very positive crew feedback and frequent usage of the VSD
demonstrate that design and integration of the VSD are appropriate for
current glass cockpits. Subjectively the crews indicate to be more ahead
of the airplane, not distracted by the VSD and get a better
understanding of the aircraft automation. This possible enhancement in
situation awareness did not result in a significant difference in crew
performance or workload in this full mission simulation. However, this
study did not present very challenging tasks or abnormal situations,
whereas situation awareness usually becomes a key factor in cognitively
demanding situations.

# References

Prevot, T. (1998) A Display for Managing the Vertical Flight Path -- an
Appropriate Task with Inappropriate Feedback *-* *Proc. HCI Aero '98*,
Montreal, Canada, May 1998.

Crane, B., Prevot, T. and Palmer, E. (1999) Flight Crew Factors for
CTAS/FMS Integration in the Terminal Airspace*. Proc. 8^th^ Int
Conference on Human-Computer Interaction*, Munich, Germany, August
22-27.