# Simulator Fidelity Requirements: The Case of Platform Motion[^1]

Judith Bürki-Cohen

Volpe National Transportation Systems Center

Cambridge, Massachusetts

Nancy N. Soja

Consultant

Brookline, Massachusetts

Thomas Longridge

Federal Aviation Administration

Washington D.C.

## Simulators Needed for All Airlines

Today, the use of airplane simulators in pilot training and evaluation
is universal. Simulators not only enable savings in training cost, but
they have also practically eliminated training accidents for major
airlines. They allow the training of emergency maneuvers which are
inherently unsafe in the aircraft; and they permit crews to gain
experience in operationally realistic scenarios that focus on both
technical and crew resource management skills. In fact, initiatives such
as the Federal Aviation Administration's (FAA) Advanced Qualification
Program (SFAR 58, 1990), which heavily relies on crew resource
management and need-based proficiency objectives, would be unthinkable
without ready access to a full flight simulator. Nevertheless, some
regional airlines elect to do at least their recurrent training in the
airplane. In part, this situation is due to a shortage of qualified
simulators, especially for certain turboprop airplanes where the flight
test data is not readily available. A second, and perhaps even more
important, reason can be found in the high rental and purchase costs for
full flight simulators, which, for small turboprops, may even exceed the
cost of the airplane.

## Simulator Qualification Standards Review

As a first step in addressing the availability and affordability
problems of airplane simulators, the FAA convened a group of experts
from industry, academia, and government to review the existing simulator
qualification standards contained in Advisory Circular AC 120-40B
(Federal Aviation Administration, 1991; Transcripts, 1996; Longridge,
Ray, Boothe, & Bürki-Cohen, 1996). The subject of this review was the
Level B simulator, which can be used for 100 percent recurrent training
and evaluation of qualified airline pilots. The mandate was to examine
the standards for ways to simplify the requirements such as to achieve a
reduced-cost simulation without loss in safety. A first symposium
focused on the aeromodel validation standards. The participants
envisioned a savings of up to 50 percent on the flight test data package
by simplifying the validation test and flight instrumentation and using
some predictive modeling for flight data estimation.

A second symposium focused on the motion requirements for the Level B
simulator. The international panel of experts felt that motion may have
an important alerting function in maneuvers entailing sudden
motion-onset cueing, such as loss of engine during initial segment
climb, where visual references are limited. Currently, the Advisory
Circular requires motion in three unspecified degrees of freedom (DOF).
The panel recommended that for motion to have a beneficial effect, it
should at least encompass four DOF, namely, pitch, roll, sway, and
heave. Also, the panel advised that the allowable motion transport delay
should be reduced from 300 to 150 ms. Both of these suggestions ran
somewhat counter to the FAA's goal of finding a safe way to make
simulators more affordable, and are indicative of the conflict apparent
throughout the symposium discussions between recommending the "best
available motion" and "motion good enough" for the intended purpose.

## Simulator Fidelity Requirements

In the past, technical constraints provided a natural limit to the
fidelity of a simulation. Today, however, technical capabilities have
expanded to a point where they may enable a degree of fidelity that may
exceed the one required for a particular purpose. This may lead to a
situation where the benefit resulting from increased fidelity no longer
justifies its cost. Our focus thus needs to shift from ever more
sophisticated virtual reality technology to the level of fidelity
required to train and evaluate to a specific safety standard.

When determining the required fidelity of a device for a particular
purpose, we have to distinguish between objective and perceptual
fidelity (Advisory Group for Aerospace Research and Development, 1980).
**Objective fidelity** of a flight simulator is relatively easy to
determine. Using carefully calibrated instruments, simultaneous
recordings of all pertinent variables of both the airplane simulator and
the simulated environment are compared with the corresponding
measurements from the pilot's seat in the actual airplane (Ashkenas,
1985). The closer the match, the more objectively faithful the simulator
is to the airplane. A more valid measure, however, may be **perceptual
fidelity**. It is defined as a match between not only pilots' subjective
perception of the simulator and the airplane, but also between pilots'
performance and control strategy in the simulator and the airplane. Its
determination requires carefully controlled experiments.

As a second step in its effort to increase the availability and
affordability of airplane simulators, the FAA is addressing the question
of what level of fidelity is required to simulate airplane motion in
pilot recurrent training and evaluation, and how it can best be
achieved.

## Can Vision Alone Evoke Faithful Perception of Motion?

Motion occurs in space and over time. The most important systems for the
perception of self-motion are the vestibular system and the visual
system. The vestibular system resides in our inner ear and perceives
angular velocity and linear acceleration (Hall, 1989). Our visual system
perceives motion from changes in position, and velocity and acceleration
by additionally taking time into account (Sedgwick, 1986). For the
perception of self-motion, the peripheral visual system is especially
important (see, e.g., McCauley, 1984; Dichgans & Brandt, 1978). Both the
vestibular and visual systems are being stimulated in airplane
simulations to induce the perception of self-motion. The tactile or
somatic systems also perceive self-motion and have been stimulated in
the past with dynamic seatpans, but these have been abandoned for the
time being (see, e.g., Martin, 1985).

The phenomenon of perceiving illusory self-motion from vision alone is
called vection. A familiar example of such an illusion may occur while
seated in a stationary car. When the neighboring car moves forward,
people in the stationary car perceive their car as moving backward. In
an experimental setting, a subject is put in a patterned drum moving
around her. At first, the subject correctly perceives the drum to
rotate, but very rapidly the illusion of self-rotation develops. It is
this illusion that may enable vision to replace physical motion in the
simulator. However, the delay in the onset of the illusion may undermine
the possibility of using vision alone because a primary role for
physical motion in simulators may be as an [early]{.underline} alerting
system (e.g., Gundry, 1976).

## The Need for Objective Empirical Evidence

Operational personnel, especially those who favor the view that motion
is not required, have said that when they have forgotten to turn
simulator motion on, nobody noticed. The problem with such anecdotal
evidence is that we are often not aware of how we are affected by our
environment. Background low-level noise, e.g., is often ignored when
focusing on the task at hand, but may still result in exhaustion at the
end of the day. In fact, most of human information processing is
subconscious, as the originators of the now outlawed subliminal
advertising techniques were well aware of. Just as we are able to
prevent unwanted information from distracting us, pilots may also be
very good at compensating for cues that are missing perhaps by simply
working harder, while remaining unaware of both the missing cues and the
extra effort.

For the FAA, whose primary concern is passenger safety, to even consider
a change in regulations that have been historically validated,
compelling evidence from controlled studies addressing the role of
motion in airplane simulations is needed. We will start with a look at
the existing evidence.

## Acceptability of Simulator

The consensus is that pilots prefer simulators with motion. For example,
Reid and Nahon (1988) and Hall (1978) used different simulators and
different acceptability ratings and yet both found that pilots prefer
that the simulator move. Interestingly, however, motion appeared to be
most important when there was no visual information available besides
instruments. Also, there is still some question as to the impact of
motion on acceptability ratings because in most studies the pilots were
informed of the simulator's motion state and that knowledge could have
influenced their ratings as much as the actual state of the simulators.
Indeed, when Lee and Bussolari (1989; Bussolari, Young, and Lee, 1987)
did not inform the pilots of the motion state of the simulator, these
pilots did not prefer the simulator with six DOF motion. However, this
study is not fully conclusive either because of an additional change
they made: Instead of turning the motion off completely, they let the
simulator vibrate at an amplitude of 1 cm in heave.

Thus, it is not clear whether the general preference among pilots for
motion is due to an actual preference or the presence of a preconceived
bias towards motion. Additionally, even if there is a real preference,
it may be possible to eliminate it by simply adding vibration to the
no-motion simulator.

## Performance/Control Behavior *in Simulator*

More important than subjective preference is which simulator
configuration results in best flying performance and behavior. The vast
majority of studies examining this question obtained data in the
simulator only.

When investigating the role of motion cues when controlling an airplane,
it is important to differentiate between two general kinds of tasks,
tracking tasks and disturbance tasks. In a **tracking task** the crew is
asked to track a random signal, such as a specific flight path or the
lead airplane in formation flight. In this sort of task the signal
affects only the central visual cues and not the peripheral or the
motion cues. Motion cues become relevant only after the pilots' response
to the signal, by giving feedback on the pilots' control actions.

In a **disturbance task** the crew needs to correct for a random
perturbation of the controlled system, such as stabilizing the airplane
in turbulence or compensating for a mechanical failure (e.g., an engine
failure). In this case the random signal affects the entire controlled
system (i.e., the motion system as well as the visual systems and
instruments). Thus, platform motion provides an early alerting cue to
the disturbance which could potentially enable a more rapid response
with motion than without motion.

Given these differences in the role of motion for the two kinds of
tasks, it is important to examine the role of platform motion
individually for each. For tracking tasks, Hall (1978) and Hosman & van
der Vaart (1981; Hosman, 1996) found only a small effect of motion on
performance. Pilots provided with motion cues showed slightly less roll
angle error than pilots without. Moreover, control behavior was affected
by motion cues only with unstable aircraft. In that case, there was an
increase in stability for pilots with motion, but there was a
concomitant loss in gain.

In contrast, there was a large effect of motion with disturbance tasks.
Hosman & van der Vaart (1981) found that pilots who received motion cues
performed much better, in terms of roll angle, than the pilots who
didn't. Furthermore, the presence of motion cues improved control
behavior for all aircraft, whether stable or unstable, by increasing
gain without impacting stability.

In addition, Hall (1978) and Hosman & van der Vaart (1981) each examined
the interaction between vision and motion cues. For both kinds of tasks
they found that the effect of motion was strongest when there was no
visual information available. That is, visual information could
compensate for the lack of motion to a certain extent. Even so, vision
alone, even with peripheral vision included, was not as good as vision
and motion together.

Thus, both Hall (1978) and Hosman & van der Vaart (1981) concur in
finding that the presence of motion improved pilot performance and
behavior in the simulator. Hosman & van der Vaart (1981) further
demonstrated that the effect of motion is mediated by the kind of
maneuver, both in terms of the strength of the effect and the type of
the effect. That is, the performance results indicate that the need for
motion is greater with disturbance maneuvers than with tracking
maneuvers; and the control behavior assessment indicates that the effect
on disturbance maneuvers is an increase in pilot gain, whereas the
effect on tracking maneuvers is an increase in stability (and a loss of
gain).

## Training Transfer *to Simulator* (Quasi Transfer)

So far, all we have learned is that platform motion may benefit
performance and behavior in the simulator. The real task, however, is
flying the airplane. For simulator motion to be useful in training, it
would have to increase the proficiency of the pilot after the training
session, in the airplane. Similarly, pilot evaluations conducted in the
simulator with motion would have to better reflect pilots' proficiency
in the airplane than evaluations conducted without platform motion.

Using simulators for experiments, however, shares some of the same
advantages as using simulators in training and evaluation, that is,
enabling controlled conditions in a safe and cost-effective setting.
Consequently, some scientists compared the training effectiveness of
competing simulator configurations by evaluating which elicits the best
transfer to a configuration that more faithfully represents the
airplane. This paradigm is called "Quasi-Transfer" because it does test
transfer, but not to an actual airplane.

Levison (1981; Levison and Junker, 1977) used a quasi-transfer paradigm
to study the effects on training of different types of simulator motion,
including vision-only, synchronous vision and motion, and three
conditions where motion lagged vision by 80, 200, and 300 ms,
respectively. Subjects were trained to control roll angle in gust-like
disturbances. During training, large roll angle reductions were observed
in all conditions, but especially in the 80 ms lag and synchronous
motion conditions. In fact, the synchronous motion group achieved
asymptotic performance so early that transfer testing was omitted for
this group.

When testing transfer of this training using the synchronous motion
condition as a stand-in for the airplane, all groups showed immediate
improvement, but only the 80 ms group appeared to transfer their
training to the new condition, catching up with the synchronous motion
group on the first post-transition trial. The vision-only group caught
up eventually, but for the two groups with larger lags, any motion
benefit during training was lost. The group trained with 300 ms motion
lag actually performed worse than in training, showing that badly
synchronized motion is worse than no motion at all. Thus, the
performance benefit of simulator motion experienced during training did
transfer to the higher-fidelity simulator, provided that motion and
vision were nearly synchronized.

The same was true also for control behavior. Subjects' efficiency in
processing synchronized visual and motion cues when transferred to a
higher level device was better if they had been exposed to no-lag or
short-lag motion cues during training. Presumably, "subjects trained
initially with the 80-msec delayed motion cues were exposed to a
perceptual situation more like the transfer task than were subjects
trained fixed base, and were therefore able to more quickly learn to
process faithful motion cues and adopt the appropriate control strategy
in the transfer condition."

In sum, the Levison (1981) study significantly extends the findings that
motion increases proficiency in the simulator. It showed that this
motion advantage transfers to a higher-fidelity device, suggesting that
it may transfer to the airplane as well.

## Training Transfer *to Airplane:* Tracking and Disturbance Tasks

Despite the inherent constraints on transfer-to-airplane studies,
several people have attempted them (e.g., Koonce, 1974; Jacobs, 1776;
Ryan et al., 1978; Martin, 1981). In nearly all cases, the advantage of
simulator motion during training within the simulator, seen in most
simulator-only and quasi-transfer studies, is confirmed. In addition,
the effectiveness of simulator training , regardless of motion state, on
proficiency in the airplane was also supported. In contrast, the
indication from the Levison (1981) study that the advantage of motion
would transfer to real airplanes was not borne out in any of these
studies. Each of the studies, however, has some form of methodological
shortcoming; some beyond the control of the scientists such as the state
of technology at the time of the experiment and the problems inherent in
using airplanes.

## Summary of Empirical Evidence

In sum, there were many benefits of platform motion within the
simulator. First, it improved the acceptability of the simulator, at
least when pilots were aware of the motion manipulation (but the amount
of motion required may be very small). Second, it improved pilot
performance and control behavior for disturbance tasks. Third, it
improved behavior during a tracking task with an unstable vehicle.
Finally, it was particularly useful when visual information was limited.
Some of the benefits of platform motion transferred to a higher fidelity
simulator. In contrast, motion did not help in the critical case, the
transfer of training to the airplane.

All of the transfer-to-airplane studies, however, share a number of
problems that may have diminished their diagnosticity. Many of these
problems also apply to the simulator-only and the quasi-transfer studies
as well. First, many studies used outdated motion and visual systems.
These studies did show that even a rudimentary visual system can
compensate somewhat for the lack of motion, leaving open the question of
whether a more sophisticated visual system could fully replace motion at
least for some purposes. Similarly, they showed that an outdated motion
system improved how the simulator was flown, raising the question of
whether with a newer system, this improvement would transfer to the
airplane.

Second, most of the experiments used tracking instead of disturbance
maneuvers, the latter being both difficult and dangerous to test in the
air. Only disturbance maneuvers, however, may be able to diagnose the
advantage of exposure during training to the early alerting cues
provided by motion.

Third, many of the experiments used non-representative subject samples,
both with respect to number of subjects sampled and their flying
experience. None of the studies cited so far analyzed the interpilot
variability within groups to determine the number of pilots required to
find a specific size of effect. Moreover, most of the studies used
student pilots. There is evidence, however, that well-trained pilots may
be more sensitive to the presence or absence of motion than beginner
pilots (Young, 1967).

Fourth, only some of the studies analyzed both pilot performance and
behavior. Pilots, if at all possible, will adapt to deficiencies in
equipment by changing their control strategy. So pilots, to achieve the
same performance in different equipment, may have to increase, e.g., the
frequency and/or amplitude of their control interventions. Such
differences may become critical in emergency situations.

Fifth, pilots and instructors were not naïve regarding the motion
condition, which may have allowed bias to affect their performance or
performance evaluation, respectively (Ebbinghaus, 1964).

## Why Revisit Motion Fidelity Requirements Now?

Given all of these problems, it is not surprising that four decades of
research do not provide conclusive evidence that vestibular motion
cueing in simulators used for recurrent pilot training and checking is
beneficial. Technological advances, industry interest, as well as the
lessons learned from previous research provide an excellent opportunity
to readdress this question.

In the wake of "virtual reality"---or rather simulated
reality---technology, progress was made especially with visual systems.
In particular, the widening of the field of view (FOV), and resultant
increase in stimulation of the peripheral visual system, has created "a
more compelling visual display of motion" (McCauley, 1984). As we have
seen, the advantage of motion observed in the simulator was often
reduced with improved visual stimulation. In contrast, the last major
advances with regard to motion cueing date back at least 15 years. They
include the introduction of critical onset cues followed by subliminal
washout, and of "gravity align" platform attitudes to simulate sustained
acceleration (Brown et al., 1989). But these innovations still don't
overcome the limitations resulting from the fact that simulators are
stationary. The question of interest is whether a state-of-the-art
visual system wouldn't simulate airplane motion at least as faithfully
on a perceptual level as the inherently limited physical simulator
motion does.

One *caveat* that needs to be raised here, however, is simulator
sickness. A widely accepted explanation of simulator sickness is the
sensory conflict resulting from discrepancies between visual and
vestibular cues (see, e.g., McCauley, 1984; Oman, 1991). As the quality
and, in particular, the FOV of the visual system increase
disproportionately compared to the motion system, so will the sensory
conflict between visual and vestibular motion cues. Guedry (1987)
suggests that this, coupled with an overall increase in simulator use,
is one of the main reasons for the increase in reports of simulator
sickness over the past decade. McCauley, Hettinger, Sharkey, & Sinacori
(1990) cite evidence found by McGuiness, Bouwman, & Forbes (1981),
indicating that more experienced pilots may be more susceptible to
simulator sickness than novice pilots, just as they may be more likely
to rely on vestibular motion cues (Young, 1967). Potentially, then, even
if a sophisticated visual system alone were to provide sufficient motion
cues for recurrent pilot training in the simulator, forgoing physical
motion may still be unacceptable due to the effects of the ensuing
sensory conflict on pilots.

Regional airlines in the U.S. are increasingly interested in the
question of whether a Level 6 flight training device (i.e., a fixed base
simulator) with an enhanced visual system could be employed to satisfy
FAA requirements for recurrent training and checking. This would permit
airlines now conducting such training in the aircraft to take full
advantage of the more comprehensive maneuver-oriented and scenario-based
training opportunities available in a simulator. The argument is that
this would enhance the overall safety of regional airlines, provided
that equivalent safety of training and evaluation with visual motion
cues alone can be empirically confirmed. A first step in such an
empirical investigation is a careful definition of the research scope.

## Research Question

The FAA is revisiting the issue of platform motion in the context of
regional airline recurrent pilot training and checking. Given a pilot
who is already qualified as a crew member in the aircraft and who has
been serving in line operations in that aircraft for at least six
months, the FAA is interested in obtaining data pertinent to the
following questions. Broadly, does the training conducted in a
fixed-base simulator with a wide FOV, cross-cockpit-view visual system
produce results equivalent to those produced in a like system having
platform-motion cueing? Specifically, with regard to disturbance tasks,
does recurrent training that is accomplished without motion cueing have
any measurable effect on the pilot's capacity to respond in a timely and
appropriate manner in the airplane? And finally, from a regulatory
perspective, do recurrent proficiency checks conducted in a visually
equipped fixed-base simulator verify the line-operational readiness of
airline pilots without compromising the safety of the flying public?

## Burden of Proof

It is much easier to prove the [existence]{.underline} of a requirement
than its [non-existence]{.underline}. A single positive finding would
[prove]{.underline} the need for a requirement. In contrast, any number
of negative findings would only [support]{.underline} that it is
unnecessary because the single positive finding could always be just
around the corner. Thus, it is imperative that every effort be made to
find any positive evidence that may exist. With this in mind, a research
strategy is described that is biased towards finding an effect of
motion. Not only is this good research design, but it is consistent with
the FAA's need to be biased towards keeping motion for the sake of
safety unless a watertight case for change can be made.

## Research Strategy

In planning the design, every effort should be made to find an effect of
motion. That is, every aspect of the study should be geared towards
maximum diagnosticity. Therefore, a simulator with the best available
motion platform (i.e., a modern six DOF freedom synergistic system)
should be used, comparing full motion with no motion. In addition, the
best available visual system (i.e., a wide-angle collimated
cross-cockpit system) must be used.

The maneuvers chosen should also be as diagnostic of the need for motion
as possible. The previous literature suggests that pilots should fly
disturbance (closed-loop) maneuvers that are asymmetric and high in
thrust, gain, workload, and unpredictability. Maneuvers involving engine
failures would be good candidates. The flight tasks should entail the
lowest level of outside-world visual cues (e.g., loss of engine during
initial segment climb) encountered in recurrent training and checking
(cf. Hall, 1978; 1989).

In addition, both subjective and objective data should be collected
during both training and testing. The subjective data should include a
grade provided by the instructor for each maneuver as well as opinions
from the crew and instructor on control precision, control strategy and
technique, gaining proficiency, physical and mental workload, comfort,
and acceptability. The objective data should be collected at a high
sampling rate and should be analyzed in both the time and frequency
domains. It should include variables measuring stimulation of the pilot
(e.g., motion, force feedback, instruments, and visual display), pilot
behavior (e.g., control inputs, throttle inputs, and brake pedal
inputs), and pilot performance (e.g., ground path control precision and
flight path control precision).

In order to evaluate these measurements once they are collected,
diagnostic performance standards must be developed. They need to include
each maneuver and measurement. Additionally, they need to include the
earliest period of the performance envelope in order to be diagnostic of
the potential alerting function of motion. They must define the smallest
operationally relevant differences so as to provide a way to evaluate
whether differences found between the two motion conditions are
meaningful. Finally, they must define the acceptable risk of reaching
the wrong conclusion. In this case the definition must take into account
that in the name of maintaining optimal safety, motion should be
required unless there is excellent evidence to the contrary.

Along with being as diagnostic as possible, the experiment should be
designed to minimize any possibility of mistaking spurious findings as
effects of motion. Thus, there should be no differences between the
motion condition and the no-motion condition, additional to the presence
or absence of motion. Accordingly, a homogeneous pilot sample from the
population of interest (e.g., regional airline pilots qualified on the
simulated airplane) should be used. They should be "fresh from the
airplane" to ensure no bias from recent simulator experience. The number
of subjects required should be determined on the basis of the smallest
operationally relevant effect size and the naturally occurring
variability between subjects. Following standard practice, any
uncontrollable variables that may affect performance, such as time of
testing, should at least be counterbalanced across the two conditions.
Finally, the equipment must be carefully calibrated at the beginning and
end of the experiment to demonstrate that simulator performance is the
same in both motion conditions and that the motion is as specified. To
catch any intermediate drift , there should also be an abbreviated daily
calibration (e.g., a visual comparison with the initial motion
calibration and a subjective inspection of the visual system).

## Experimental Design

With this strategy in mind, the experimental design can be constructed.
To assess the simulator as a training tool, a forward transfer paradigm
should be used. This will measure how well training in the simulator
transfers to the airplane. To assess the simulator as an evaluation
tool, a reverse transfer paradigm should be used (Cross, 1991). This
measures how well pilots' proficiency in the airplane is reflected in
their performance and behavior in the simulator.

As already mentioned, experiments in a real airplane are dangerous,
impossible to control, and costly. Given that the FAA has been allowing
total training and checking for qualified pilots in a high-fidelity
simulator (Level C/D) for almost twenty years (Advanced Simulation Plan,
1980), we feel that such a simulator has been validated as a stand-in
for the airplane. We thus recommend that both the forward transfer and
reverse transfer studies use a quasi structure. That is, in the
quasi-forward transfer study, pilots should be trained in the simulator,
with or without motion, and then tested in the simulator with motion.
The assumption is that the simulator training configuration that
produces the best results during testing provides the best training for
airplane flying as well. In the quasi-reverse transfer study because
pilots can't be originally evaluated in the airplane, a sample of
homogenous, experienced pilots should be used (on the assumption that
they would perform similarly and well in the airplane). They should be
evaluated in the simulator with and without motion. The assumption is
that the simulator configuration that produces the best performance and
behavior provides the most accurate reflection of pilot skills in the
airplane. Combining these two approaches, quasi forward transfer and
quasi reverse transfer, could strengthen the validity of results,
provided that they are in agreement

## Follow-Up Work

If no effect of simulator motion on transfer is found, a follow-on study
examining different maneuvers, simulators, and pilots should be
conducted to validate the results. In addition, some validation using
transfer to and from the airplane should be done. If it is found that
motion does affect transfer, the question should be further pursued by
examining whether anything less than a full six DOF motion platform
system could also impart the required cues. That is, the question of how
faithful platform motion needs to be would still be open. Possible
avenues of exploration are stroke length, DOF, and the special role of
vibration.

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Transcript[^2] of the Joint FAA/Industry Symposium on Level B Airplane
Simulator Aeromodel Validation Requirements, Washington Dulles Airport
Hilton, March 13 - 14, 1996

Transcript^2^ of the Joint FAA/Industry Symposium on Level B Airplane
Simulator Motion Requirements, Washington Dulles Airport Hilton, June
19 - 20, 1996

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1300-1303.

[^1]: An expanded version of this paper has been accepted for
    publication in the International Journal of Aviation Psychology
    under the title "Simulator Platform Motion---The Need Revisited."
    This work was funded by the Office of the Chief Scientist for Human
    Factors of the Federal Aviation Administration. The authors would
    like to thank FAA Program Manager Dr. Eleana Edens for her guidance
    throughout the project; Mr. Edward M. Boothe for contributing his
    flight simulation and training expertise; and Ms. Julie Guinn for
    her editorial support. The opinions expressed are those of the
    authors and not necessarily those of the Department of
    Transportation, the Federal Aviation Administration, or the U.S.
    Government.

[^2]: Available in electronic format from Thomas Longridge, Advanced
    Qualification Program Manager, AFS-230, Tel. (703) 661‑0275.