Draft submitted to International Journal of Aviation Psychology, 5/13/97

# Simulator Platform Motion---The Need Revisited

Judith Bürki-Cohen

Volpe National Transportation Systems Center

Cambridge, Massachusetts

Nancy N. Soja

Consultant

Brookline, Massachusetts

Thomas Longridge

Federal Aviation Administration

Washington D.C.

## Abstract

The need to provide increased access to flight simulator training for
U.S. regional airlines, which historically have been limited by cost
considerations in the use of such equipment for pilot recurrent
training, is discussed. In light of that need, the issue of whether more
affordable fixed-base simulators, identical to full flight simulators in
all respects except for absence of platform motion, might provide an
equivalent level of safety when employed for recurrent training, is
examined. Pertinent literature from the past two decades is reviewed.
The paper observes that no definitive conclusion can be drawn that would
warrant modification of current qualification requirements for platform
motion in full flight simulators. The article concludes that this
situation will remain unchanged unless new research is undertaken, which
takes into account the lessons learned from past research, and the
opportunities engendered by new technology. Broad guidelines for an
appropriate research design are discussed.

## Platform Motion---A Need To Re-Examine The Requirement

The use of full flight simulators for pilot training and evaluation is
universal among major air carriers in the United States, all of whom
have, within their own corporate resources, access to full flight
simulators equal to both the maneuver and scenario oriented requirements
of Federal Aviation Administration (FAA) approved training programs.
Flight simulators not only enable savings in training costs, they also
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. One might well conclude that this type of training is
essential to safety, and should therefore be required of all air
carriers under CFR 14, Part 121 and Part 135 operations (National
Transportation Safety Board, 1993). The use of flight simulators remains
optional, however, in the United States. U.S. airlines electing to
conduct training and checking in the aircraft are free to do so, subject
to FAA approval of their respective programs, including acceptable
provisions for windshear training. Indeed, under current regulations
U.S. airlines not conducting initial or transition training under CFR
14, Part 121, Appendix H (Advanced Simulation Plan, 1980), or under SFAR
58 (Advanced Qualification Program, 1990), **must** complete certain
checking requirements in the aircraft. Many U.S. regional airlines
conduct their pilot training programs on that basis.

Compared to U.S. major airlines, regional airlines, most of which do not
own their own training equipment, have historically not had equal access
to full flight simulators. Regional airlines electing to use flight
simulators for training must establish contractual arrangements with
training centers, or with other air carriers, who have the appropriate
simulation equipment. As it turns out, the cost of such contractual
arrangements, when coupled with the travel expenses for cockpit crew,
can exceed the per hour cost of conducting training in some regional
aircraft. Moreover, for some regional aircraft operated in the U.S., the
worldwide availability of qualified flight simulators may be extremely
limited. As a result, though most U.S. regional airlines would clearly
prefer to conduct all their training in flight simulators, many such
carriers have found it necessary to either conduct all training in the
aircraft, or to limit the use of simulators to initial and transition
training. The cost and limited availability of flight simulator access
for recurrent pilot training has simply been prohibitive for small
airlines. For many of these U.S. regional carriers, recurrent
proficiency checks, and recurrent flight operations training, if any,
are conducted in the aircraft. However, the need for flight simulation
training for regional airline pilots is at least equal to that for
pilots in major airlines, when considered in light of the fact that (a)
the experience levels of regional pilots tend to be lower, (b) pilot
turnover tends to be higher, (c) certain regional airport environments
are less well equipped with navigation aids, (d) U.S. regional aircraft
certification standards entail certain reduced system redundancy
requirements, and (e) the procedures for powerplant malfunction or
engine failure in turboprop aircraft can be more demanding than for jet
aircraft. Clearly it is in the interest of safety to consider what
measures can be taken to increase the accessibility of simulation
equipment for regional air carriers.

In recent years the cost of full flight simulators has fallen
significantly, and the availability of even less costly flight training
devices (FTDs) has grown. At the upper end of the FAA defined continuum
of approved FTDs (AC-120-45A, FAA 1992), the equipment fully duplicates
a flight simulator, except for visual and platform-motion cueing
requirements, which are optional. Since the cost of high fidelity
simulator visual image generation and display equipment has also become
more affordable, U.S. regional airlines are increasingly interested in
the question of whether an FTD equipped with such a visual system (i.e.,
a fixed-base simulator) could be employed to fully accomplish the FAA
requirements for recurrent training and checking, which constitutes a
major cost consideration for such airlines. Allowing complete credit for
the use of such devices in recurrent training could reduce the cost of
access, or permit the direct acquisition of such equipment by regional
airlines to accomplish their own training. It 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 overall safety of regional
airlines could thereby be enhanced.

The FAA is therefore undertaking to revisit 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 field-of-view (FOV)
visual system produce a result equivalent to that which would be
obtained in a like system having platform-motion cueing? Specifically,
with regard to the sudden onset of asymmetrical thrust, does recurrent
training accomplished in the absence of motion-platform cueing have any
measurable effect on the pilot's capacity to respond in a timely and
appropriate manner in the aircraft during maneuvers entailing powerplant
failure? And finally, from a regulatory perspective, do recurrent
proficiency checks conducted in a visually equipped fixed-base simulator
provide an equivalent opportunity to verify the line-operational
readiness of air-carrier pilots?

In the interest of obtaining information pertinent to the issue of
simulator-motion fidelity requirements for recurrent training, the FAA
has convened two workshops comprised of recognized experts in
aeromodeling, and in platform-motion cueing, respectively (Transcripts,
1996; Longridge, Ray, Boothe, & Bürki-Cohen, 1996). It was generally
concluded from these meetings that while certain economies in existing
simulator qualification standards could be achieved without
significantly degrading the cueing effectiveness of such equipment, an
absence of platform-motion cueing is likely to have a detrimental effect
on pilot control performance in fixed-base devices, particularly in
maneuvers entailing sudden motion-onset cueing, such as loss of engine
during initial segment climb, where visual references are limited. It
was also noted, however, that there is no evidence that training
conducted in such an equipment configuration would lead to degraded
control performance in the aircraft. It was observed that pilots readily
adapt their control strategies to the equipment at hand, whether in the
direction of simulator to aircraft, or vice versa.

The FAA has also sponsored a comprehensive review of the past two
decades of research literature pertinent to the contribution of
simulator platform motion to training effectiveness, selections from
which are summarized below.

## The FAA Perspective

A flight simulator is intended to imitate or simulate, from the point of
view of the pilot, both the physical characteristics and the behavior of
an airplane and its environment, on the ground and in the air. A
simulator that "successfully imitates" the airplane will, on the one
hand, effectively train a pilot for flying the airplane and, on the
other hand, accurately reflect a pilot's proficiency in the airplane.
Substituting the simulator for the airplane in training and
qualification of airline pilots avoids training accidents, enables
controlled flight scenarios including emergencies, helps identify and
satisfy individual training needs, and, dependent on the nature of the
air carrier's operations, can reduce costs.

It is important to note that the use of flight simulators in air-carrier
training and checking activities goes beyond the standard
transfer-of-training paradigm. When used as a substitute for the
aircraft, the evaluation of pilot performance in the device constitutes
a determination of the readiness of the pilot to perform immediately in
line operations involving the flying public. That is, unlike many
classical transfer-of-training situations, the simulator-trained
air-carrier pilot is expected to perform within satisfactory standards
of proficiency in the aircraft from day one. Consequently, the simulator
must be capable of supporting 100 percent transfer of performance to the
aircraft. **Anything less would compromise safety**. The existing
standards for full flight simulator qualification, all of which entail a
requirement for platform-motion cueing, have a twenty year record of
meeting the requisite criterion for transfer of performance. In the
absence of compelling evidence to the contrary, it is therefore prudent
to maintain these standards in the interest of public safety. Regulatory
authorities will therefore continue to require platform motion for
flight-operations training and checking conducted in higher-end devices,
even under the more flexible requirements of SFAR 58, as long as there
is any reasonable indication that simulator platform motion is
beneficial, and, concomitantly, the FAA will continue to limit the
credit permitted for use of non-motion equipped Flight Training Devices
(FAA-S-8081-5B).

## An Alternative Viewpoint

While it is certainly the case that there is no compelling evidence that
platform-motion cueing can safely be eliminated from present flight
simulator qualification requirements, it can also be observed that the
evidence in favor of the requirement is itself less than compelling, and
therefore warrants reexamination. As Bussolari, Young, & Lee comment in
1989, "\[t\]he requirement for platform motion is ostensibly based on
the assumption that physical fidelity is highly correlated with training
effectiveness. Since airplanes are capable of motion in all six axes
(three translational, three angular), it is believed that the absence of
motion in the simulator would significantly reduce its training
effectiveness." Since there are hardly any objective criteria available,
however, on what type of motion is required (given the fact that a
simulator can never duplicate the range of motion cueing experienced in
an aircraft), the existing regulations in FAR Part 121 Appendix H and
the guidance given in the Advisory Circular on Airplane Simulator
Qualification AC-120-40B (FAA, 1991; and its draft revision AC-120-40C)
are largely based on subject matter expert opinion. While the Advisory
Circular recommends extensive subjective evaluation by trained FAA
flight inspectors, the reliability and validity of this subjective
evaluation strategy has never been subject to systematic quantification.
The principle argument in favor of present qualification standards for
simulator motion---that they have stood the test of time---is weak. To
the extent that continued adherence to these standards may actually
preclude a significant segment of the air-carrier industry from the
safety benefits of flight simulator training, it is reasonable to
suggest that, unless objective criteria for motion requirements can be
obtained, the requirement has no justifiable basis in fact.

## Objective Vs Perceptual Fidelity

Since Edwin Link conceived his "Blue Box" in the late twenties,
simulator engineers and engineering psychologists have been grappling
with the question of what makes a simulation successful. The North
Atlantic Treaty Organization's Advisory Group for Aerospace Research &
Development distinguishes between objective (i.e., physical) and
perceptual fidelity of a flight simulator (Advisory Group for Aerospace
Research and Development, 1980). **Objective fidelity** of a flight
simulator is relatively easy to determine. Using precise instruments
that are free from the limitations and distortions of the human
perceptual system, 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 the more elusive **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 or behavior in the simulator and the airplane. Its
determination requires carefully controlled experiments.

The discussion of objective versus perceptual fidelity is especially
pertinent in the context of simulator motion, which is inherently
limited in its objective fidelity despite substantial technological
advances. Even as late as 1989, Brown, Cardullo, & Sinacori (p. 78)
state that "\[b\]arring an unforeseen revolution in the technology of
force and motion cueing, it is evident that it is hopeless to attempt to
provide realistic force and motion stimuli in the sense that the
acceleration forces produced by the aircraft can be replicated in the
simulator." In particular, it is impossible to simulate sustained
acceleration without sustained displacement, and any direct application
of whole body acceleration forces will require inappropriate counter
forces. The only way out of this dilemma is to focus not on the reality
of the force and motion stimuli, but on the perceptions associated with
force and motion, i.e., perceptual fidelity. The question that needs to
be answered is how can pilots best be stimulated to perceive airplane
motion in the simulator.

Motion occurs in space and over time. The most important sensor of
motion occurring in the world around us is our visual system, perceiving
motion from changes in position; and velocity and acceleration by
additionally taking time into account (Sedgwick, 1986). Vision is also
important for the perception of our own motion and posture, especially
in the case of sustained, constant motion as often occurs when riding
within a vehicle. Psychophysical evidence points to the ambient or
peripheral visual system as especially important for processing dynamic
and orientation information (see, e.g., McCauley, 1984; Dichgans &
Brandt, 1978). However, we also rely on our tactile and somatic
(perceiving pressure changes on skin and organs), our kinesthetic
(perceiving joint position and muscle forces), and, more importantly, on
our vestibular system (registering angular velocity and linear
acceleration) for the perception of self-motion (Hall, 1989). All four
of these perceptual systems have been called upon, either together or in
isolation, to stimulate pilots to perceive motion in airplane
simulators, and the degree of their success has been the subject of
extensive research and controversy. Although there have been some
promising results from tactile and somatic stimulation via dynamic seat
pans (see, e.g., Martin, 1985), such devices have not gained much
popularity beyond the armed forces. We will therefore restrict this
discussion to a comparison of airplane simulations using either
whole-body motion or visual displays or both to stimulate pilots to
perceive motion.

## Acceptability Of Simulator

As we will see, there are few points of general agreement in the
discussion of whether whole-body motion is a required stimulus for
successful training and qualification in the simulator. One area of
consensus, however, is that pilots prefer vestibular motion cues to be
present in the simulator. This has been confirmed both in informal
discussions with pilots and in controlled experiments (but see Lee &
Bussolari, 1989, discussed below).

### Acceptability Of Several Motion Algorithms With Limited Visual Stimulation

In 1988, e.g., Reid & Nahon compared nine motion conditions (three
different motion algorithms, each with three different parameter sets)
with no motion using a B-747 simulator with a state-of-the-art six
degrees-of-freedom (DOF) synergistic motion base incorporating
hydrostatic bearings. Although the presence or absence of motion did not
appear to affect pilots' performance and control behavior, it definitely
affected their opinion regarding the simulation environment, both in
their comments and ratings. Pilots were asked to "judge the quality of
the motion cues and not any other aspects of the simulation," on two
different rating scales. The University of Toronto Institute for
Aerospace Studies (UTIAS) scale was used to assess the quality of motion
associated with control inputs on the column, wheel, rudder pedals and
throttle, as well as with turbulence and ground contact. The
Massachusetts Institute of Technology (MIT) scale rated smoothness,
sense, amplitude, phase lag, discomfort, disorientation and overall
impression. The summary of average UTIAS rankings by the seven pilots
shows that the no-motion condition was consistently in the last place
for all items but for turbulence, where it was in the second to last
place. In the MIT ratings, the no-motion condition fared somewhat
better, although it still was in the last position for overall
impression. Disorientation was experienced second to worst without
motion; and sense, discomfort, and phase lag occupied middle rankings.
With regard to discomfort, for all three algorithms the parameter set
resulting in the largest travel was rated worse than the no-motion
condition. Smoothness of the simulator, of course, was rated best
without motion, as amplitude was worst. Taking into account both ratings
and comments from pilots, the authors conclude that "\[t\]he pilots
preferred physical motion to be present in the simulator. They felt that
it added to the realism of the simulation and was helpful in the
piloting task."

### Acceptability Of Motion Vs No Motion With A Wide Field Of View

One explanation for the preference for motion in the Reid & Nahon study
might be that the visual stimulus was very sparse, thus requiring
platform motion to provide the necessary cues to achieve the best
percept of motion. They used a collimated out-the-window CRT with a
narrow FOV (40 degrees horizontally and 30 degrees vertically) on which
they displayed a yellow line drawing indicating depth and path on a
black background. Hall (1978), however, extended the FOV to 200 degrees
horizontally using a skyscape shadowgraph projector and found that even
with this wide FOV (and less-than-perfect motion cues), the pilots still
preferred the motion to the no-motion conditions for controlling a
vehicle with an unstable Dutch roll. Specifically, he used a simulated
Harrier GR Mk 3 with a three DOF motion system (roll, pitch, and heave)
that was "suffering from backlash, low gain and hence reduced perception
thresholds." The pilots rated lateral control in transition from
hovering to jet-borne forward flight on a Cooper-Harper scale, where 10
is the worst score and means that the vehicle is uncontrollable.
Unfortunately, Hall reports no queries regarding pilot comfort. There
were eight different conditions resulting from all possible combinations
of the presence or absence of motion, TV monitor, and skyscape (which
provided the additional peripheral view). All conditions also included
an instruments display (both head-down and head-up). Pilot C's results
were provided as an example of the overall results. Each of the motion
conditions was preferred to the corresponding no-motion condition,
including the case in which the best vision was available. That is, the
condition with motion, TV monitor, and skyscape (6, unsatisfactory) was
preferred to the condition with no-motion, TV monitor, and skyscape (7,
unacceptable). Interestingly, however, motion appeared to be most
important when there was no visual information available besides
instruments. Here, removing motion worsened the rating from 7
(unacceptable) to 9 (unacceptable and just controllable). Thus, Hall's
study confirms Reid & Nahon's finding that pilot acceptance of a
simulator depends on the presence of motion, extending it to simulators
including a wide FOV visual system.

### Acceptability Of Full Motion Vs Special-Effects Vibration With A Wide Field Of View And "Naïve" Pilots

Lee & Bussolari (1989, also reported in Bussolari, Young, & Lee, 1987)
also looked at the effect of motion on pilot acceptance. They used a
Boeing 727 Phase II (now Level C) simulator with a wide FOV (75 degrees
horizontal and 30 degrees vertical per pilot seat) (FAR Part 121,
Appendix H). There were two significant differences, however, between
their study and Hall's (1978). First, the pilots in the Lee & Bussolari
study did not know when the motion was on and off. Second, Lee &
Bussolari used a "special-effects" condition instead of an actual
no-motion condition. In this condition, the motion platform heaved at an
extremely small amplitude (0.25 inches). This slight movement was
intended to provide cues for the touchdown bump; runway roughness;
buffets associated with flap, gear, and spoiler extension; and Mach and
stall buffets. This condition was compared to full six DOF motion and to
two DOF motion (heave and sway). In contrast to the other studies, Lee &
Bussolari found that there were no differences in pilots' ratings of
workload, control responsiveness, utility for training and checking, and
overall realism, between any of the three conditions (or in performance
and control behavior either). No information on simulator sickness is
given. Young, however, in response to a question after his presentation
at the Aerospace Medical Panel Symposium on Motion Cues in Flight
Simulation and Simulator Induced Sickness in Brussels (Bussolari et al.,
1987), reported that informal queries revealed no simulator sickness.
These results indicate that the preference for motion found in the other
experiments might be due to pilots' **expectation** that motion would be
better, not to actual preference (see, e.g., Ebbinghaus, 1964). Another
possible explanation is that some vibration as feedback for certain
events is important for pilot acceptance, but that large displacements
are not required.

Clearly, motion improves pilot acceptance of the simulator in some
cases. Whether that improvement is due to a real preference or just a
positive bias towards motion, and whether a full motion platform is
required, are less clear.

## Performance/Control Behavior Assessment In Simulator

The studies discussed in this section examined whether the preference
pilots expressed for simulators including a motion platform over
fixed-base simulators manifests itself also in improved performance and
control behavior in the presence of vestibular motion cues compared to
visual cues alone.

### Motion Vs Visual Cues For Control Of An Unstable Vehicle

The Hall (1978) study previously described examined the impact of motion
on pilots' control of Dutch roll oscillations in addition to pilot
acceptance. Recall that Hall compared the effect of a less-than-perfect
three DOF motion system with the effect of a central visual display (TV
monitor) and the effect of a peripheral visual display (skyscape) on
lateral control of a Harrier GR Mk 3 without autostabilizers. He
measured aileron deflection or stick activity, roll rate, bank angle,
and sideslip while transitioning from hovering to jet-borne forward
flight. As with the Cooper-Harper ratings, the motion condition fared
better than the corresponding no-motion condition regardless of whether
there were both, only one, or no visual displays added to the
instruments. This is seen in consistently higher-amplitude residual
oscillations without motion in all measurements for pilot C (sideslip
was not given for any of the conditions with skyscape). As with the
pilot ratings, the difference appeared most pronounced for the
instruments-only condition.

Hall concludes that even a "practical" motion system is "as good or
better (in terms of performance) than nominally perfect peripheral
vision for controlling a vehicle with an unstable Dutch roll." He
continues to explain that this was due to the inability to generate
sufficient lead to reduce the amplitude of the oscillations to an
acceptable level in the absence of motion cues. It appears, though, that
this explanation results from a comparison of the instruments-only
conditions with and without motion, rather than from a comparison of the
conditions including visual cues.

### Motion Vs Visual Cues For Disturbance and Target Following (Tracking) Tasks

Hosman & van der Vaart (1981) also compared the effect of central and
peripheral visual cues with motion cues on pilot performance and control
behavior. In addition, they compared two different types of control
tasks, a disturbance task and a target following task. In a
**disturbance** task a random signal perturbs the controlled system and
requires correction. This can be compared to a pilot stabilizing an
airplane in turbulence. The signal affects all information displays the
same, including the motion system. In a target-following or
**compensatory tracking** task, a displayed random signal needs to be
tracked. This task corresponds to a pilot following another airplane in
formation flight. The lateral control task in the Hall (1978) study
would also qualify as a compensatory tracking task, where pilots "track"
a straight and level flight path. In fact, all flying tasks that do not
involve any weather or mechanical failures can be looked upon as
compensatory tracking of a flight path. Here, the signal goes only to
the central display (or instruments), and **not** to the peripheral
display or the motion system. The **maneuver** motion experienced during
a compensatory tracking task contributes to the pilots' perception of
the handling qualities of the simulator (or airplane) and of the effect
of their control actions.

Hosman & van der Vaart (1981) included both kinds of tasks because
motion is assumed to serve different functions in each case. Gundry
(1976, for example) asserts that disturbance motion, but not maneuver
motion, is generally assumed to serve an alerting function. Maneuver
motion, on the other hand, provides feedback on pilot control behavior,
but even so may be necessary only when controlling unstable vehicles,
especially under high gain (cf. Hall, 1978; 1989).

Peripheral visual cues were provided by two CRTs displaying a moveable
checkerboard pattern against the side windows of the simulator.
Vestibular motion cues were provided using a three DOF (pitch, roll, and
heave) system with hydrostatic bearings and "low noise motion
characteristics." Three qualified jet transport pilots were tested. For
both kinds of maneuvers, subjects had to correct for a quasi-random
signal with a standard deviation of 1.875 degrees affecting roll
attitude. In the disturbance task, the signal affected all available
cueing systems, i.e., motion and peripheral and central visual displays,
the CRT providing the central visual cues displaying the roll angle as
the difference between airplane attitude and artificial horizon. In the
tracking task, the signal affected only the central display, which
showed the difference between the quasi-random signal and the roll angle
of the simulator, i.e., the roll angle error. For both tasks, pilots
were to minimize the difference displayed on the central CRT, using a
spring-centered side stick controller.

Hosman & van der Vaart (1981) examined both the performance and control
behavior of the pilots. Performance was reported as the standard
deviation of roll angle for the disturbance task and the standard
deviation of roll angle error for the tracking task. The results show
that in both kinds of tasks, the addition of vestibular motion cues had
a more significant impact on performance than the addition of peripheral
visual cues. This was especially pronounced for the disturbance task.

For the control behavior assessment, pilots' frequency responses
describing the relation between roll angle or roll angle error and
pilots' side stick deflections were calculated for all conditions. For
the purpose of the present discussion, we will report only the results
for crossover frequency and phase margin, which were "markedly"
different for the two tasks. A high **crossover frequency** reflects
high controller **gain** over a wide bandwidth, and will thus result in
good performance for both tasks. The **phase margin** reflects the
remaining margin of **stability** of the human-machine system and is
therefore also important for good performance. Generally, a trade-off
relationship exists between phase margin and crossover frequency. Hosman
(1996) reports that for the **disturbance task**, "the crossover
frequency increased only slightly as a result of the peripheral
displays, but strongly as a result of cockpit motion" in comparison with
central visual cues alone. Phase margin was affected by neither the
addition of peripheral visual or vestibular motion cues. That is, in the
disturbance task, vestibular motion provided the primary cueing enabling
pilots to increase gain without losing stability. In contrast, for the
**tracking task**, crossover frequency decreased when motion cues alone,
or motion and peripheral cues together, were combined with central
visual cues. This was offset, however, by a large increase in phase
margin when motion cues were present (or only a slight increase when
peripheral vision was combined with central vision). That is, in the
tracking task, vestibular motion also provided the primary cueing, but
in this case it resulted in an increase in stability with a concomitant
loss of gain. This, combined with Gundry's (1976) report that maneuver
motion is only useful in controlling unstable vehicles, suggests that
the primary role of motion during tracking tasks is increasing
stability.

Thus, the Hall (1978) and the Hosman & van der Vaart (1981) papers
concur in finding that the presence of motion improves pilot performance
and behavior in the simulator, and that this improvement cannot be
duplicated by the presence of peripheral vision in the absence of
motion. In addition, Hosman & van der Vaart 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 Assessment in Simulator (Quasi-Transfer)

None of the studies considered thus far have examined the impact of
motion on the **training** of pilots. That is, at best they have shown
that motion is important for the flying **of** **simulators**. But,
pilots are not trained to fly simulators---they are trained to fly
airplanes. To discern whether simulator motion is valuable in the
training of pilots, it is necessary to examine whether the presence of
motion **in** **a** **simulator** improves pilot performance and
behavior **in** **the** **airplane** above a baseline effect of
simulator training without motion.

However, for the same reasons that it is difficult to use airplanes for
the full training of pilots, it is also difficult to use airplanes in
experiments. That is, it is impossible to control the weather, it is
extremely difficult to do multiple repetitions of individual maneuvers,
the degree of danger is too high for certain maneuvers such as
responding to system failures, and airplane time is very costly.
Consequently, some scientists have chosen to test the validity of
simulator training by training pilots in a simulator and then testing
the acquired skills in a different simulator or in the same simulator
running under a different configuration. The assumption is that the new
simulator (or simulator configuration) is more like an airplane than the
trained-on simulator. This paradigm is called "Quasi-Transfer" because
it tests for transfer of training, but not to an actual airplane.

### Quasi-Transfer Of Training Of A Simple Tracking Task Under Different Motion Conditions

Levison (1981) used a quasi-transfer paradigm to study the effects on
training of simulator motion and of the time lags between simulator
vestibular motion and visual cues. He used the Multi-Axis Tracking
Simulator at the Air Force's Aerospace Medical Research Laboratory,
which was simulating a single seat cockpit. Presumably, only the
roll-axis motion capability was used in this experiment, and visual
information was presented on a television monitor (Levison & Junker,
1977). Subjects were to keep the simulator in straight and level flight
during gust-like disturbances and were described as "naïve to the task"
(no other information on subjects is given). Each subject was trained
under one of five conditions, vision-only, synchronous vision and
motion, and three lag conditions. In the lag conditions, motion lagged
vision by 80, 200, or 300 ms. During training, large reductions of
mean-squared tracking error (roll angle) were observed in all
conditions, but especially in the 80 ms lag and synchronous motion
conditions.

The subjects in all lag and in the vision-only conditions were then
tested in the synchronous motion condition as a stand-in for the real
airplane (the group trained with synchronous motion had reached
asymptotic performance very early in the training and was thus not
tested again). All groups showed immediate improvement with synchronous
motion, but only the group trained with the very short motion lag (i.e.,
80 ms) appeared to transfer their training to the new condition,
achieving the equivalent of the asymptotic performance of the
synchronous motion group on the first post-transition trial. The
vision-only group achieved the same performance after three more trials.
With large lags, however, the positive impact of motion on training was
gone or reversed. Specifically, after transition to the synchronous
condition, the subjects trained with a 200 ms motion lag performed
barely better than the vision-only group; and the subjects trained with
a 300 ms motion lag actually performed worse, still trailing behind all
other groups after seven post-transition trials. This shows that badly
synchronized motion is in fact worse than no motion at all. One
interesting note is that the advantage of near-synchronized motion was
much smaller after transfer to the synchronized condition than it had
been prior to transfer. Most likely, this is due to a floor-effect. That
is, because the 80 ms delay group could not have improved any further
(having immediately reached the best possible performance as defined by
the synchronous group), differences between the 80 ms delay group and
the other groups may appear smaller than they really are. Alternatively,
it is possible that the attenuation of group differences is not an
artifact, but indeed indicates that if there is a motion advantage in
the simulator, only a small portion will be transferred to a
higher-level device (and, presumably, the airplane). In either case, it
is clear that the presence of motion, if closely aligned with vision,
had a positive impact on the training of subjects, not just on their
performance within the original simulator configuration.

Pilot behavior was assessed by obtaining frequency response measures
from selected subjects. For our purposes, we will only report the
comparison between the control behavior of the vision-only and the 80 ms
motion lag groups during the early post-transition trials. The parameter
of interest is observation noise, which is an Optimal Control Model
parameter reflecting subjects' information-processing limitations. The
observation noise/signal ratios were lower for subjects trained with
motion than for subjects trained with only visual cues. This indicates
that the presence of delayed motion during training, if the delay is
short (i.e., 80 ms), improves the subjects' efficiency in processing
synchronized visual and motion cues when transferred to a higher level
device, compared to having had no motion at all 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."

### Quasi-Transfer Of Engine-Failure (Disturbance) Training Under Different Motion Conditions

A few years earlier, DeBerg, McFarland, & Showalter (1976) had used a
quasi-transfer design to study the effect of motion and visual cueing on
take-off engine-failure training. Recovery from a take-off engine
failure is exactly the high-gain, asymmetric, closed-loop disturbance
task where vestibular motion cues may serve as an early alert.
Thirty-six KC-135A aircraft commanders who were matched for initial
proficiency were trained in one of four simulator configurations,
resulting in nine pilots per condition. The National Aeronautics and
Space Administration\'s Flight Simulator for Advanced Aircraft (FSAA) at
Ames Research Center was used because of its "unique ability to generate
the types of aircraft motion cues which an outboard engine failure would
generate," namely "yaw, roll, and lateral motion." The four training
phase configurations ranged from maximum cueing with visual and motion
cues to minimal cueing with neither motion nor visual cues, via
motion-only and vision-only configurations. For the training
configurations, the FSAA motion was restricted to "an envelope roughly
analogous to that of a six-post synergistic motion system." The visual
system was described as a "six-degree of freedom system in which a color
television camera is mounted on a gantry and moves relative to a
fixed-model board. The scene is presented to the pilot, through
collimation optics, on a cathode-ray tube situated in the forward
cockpit window." After training, transfer was assessed in the
unrestricted motion configuration with the full visual system.

The authors maintain that their experiment shows an increase in training
effectiveness both with the addition of a visual or a motion system, and
a synergistic improvement in training when both are used together.
Neither subjective pilot opinion nor the analysis of the performance
variables measured during the evaluation phase fully warrant this claim.
Pilots rated both the "sufficiency of cues to negotiate engine failures"
and the "cueing system as a training device" twice, once after the
training and once after the assessment phase. When rating, on a scale
from one to five, the **sufficiency** **of** **cues** to negotiate
engine failure after the training phase, pilots indeed rated the
configuration with both motion and vision most positively (4.89). After
they had experienced also the assessment phase with the full simulator
capabilities, however, they gave the configuration with neither motion
nor visual cues the highest rating! The motion-only condition was rated
lowest after either phase (3.89 and 4.33, respectively). As a
**training** **device**, the no-motion/no-vision configuration was rated
least favorable after both phases (3.22 and 3.33, respectively), in each
case followed by the motion-only configuration. After training, pilots
rated vision-only highest (5); and after assessment, they rated vision
with motion highest (5). It appears, then, that the only claim
consistent with all results would be that, in most cases, pilots favor
simulator configurations including a visual system.

To assess performance, the authors claim to have measured 34 variables
during the evaluation phase. But most of their conclusions are based on
mean total roll and total yaw, which "best discriminated between the
four cueing systems employed," as determined by "multivariate
statistical analyses" (a somewhat obscure analysis of variance is also
presented). For ground engine failures (at 140 knots), De Berg et al.
correctly state that performance deteriorated with vision or motion
alone compared to the configuration with neither vision or motion.
Vision and motion combined, however, was no better than the
no-vision/no-motion condition, at least for roll (for yaw there was
indeed a slight improvement). For flight engine failures (at 47 feet
altitude), visual and motion together were indeed best, followed by
motion alone, neither motion nor vision, with vision in the last
position. Thus, with regard to performance, motion may be beneficial,
but only for flight engine and not at all for ground engine failures.
With the *caveat* that pertinent data may have been lost in the analysis
procedures, all we can conclude from the uneven results of this study is
that nine pilots in each condition may not be quite enough to allow true
differences between groups to emerge from the variability of pilots
within groups.

In sum, the Levison (1981) study confirms the previous results (Hall,
1978; Hosman & van der Vaart, 1981; Reid & Nahon, 1988) that demonstrate
a benefit of motion in simulator training, yet extends those findings in
a significant way. Levison (1981) showed that the advantage of motion in
the simulator transfers to a higher level device, suggesting that it may
transfer to the airplane as well. DeBerg, McFarland, & Showalter's
(1976) results, however, which were obtained using more realistic
equipment, real transport aircraft pilots, and a highly diagnostic task
with the quasi-transfer paradigm, do not fully confirm Levison's
conclusions.

## Training Assessment in Airplane (Transfer)

Despite the inherent constraints on transfer-to-airplane studies,
several people have attempted them. In contrast to the Levison (1981)
quasi-transfer study, in all cases the motion benefit found in the
simulator was completely lost in the airplane. However, each of the
studies has some form of methodological shortcoming; some out of the
control of the scientists such as the state of technology at the time of
the experiment and the inherent problems of airplane experimentation.
Below is a brief description of several such studies.

### Transfer Of Training---Tracking Maneuvers

Jacobs (1976) trained 27 subjects in a non-visual Singer-Link GAT-2
trainer with three DOF (presumably roll, pitch, and heave). He then
tested them, as well as a group of control subjects who received no
training, in a Piper Cherokee Arrow airplane. The subjects who received
training were evenly divided into three groups. One group was trained in
the simulator without motion, another with normal washout motion in bank
with sustained pitch angles, and the third with directionally-random
motion (i.e., "washout banking motion in which the direction of motion
relative to that of the simulated airplane was randomly reversed 50% of
the time as the cab passed through a wings-level attitude"). Subjects in
each of the three experimental groups were trained on 11 tasks, all
tracking maneuvers (straight and level flight, straight and level power
changes and airspeed transitions, climbs and descents, constant bank
angle and standard rate turns, airspeed transitions during turns,
climbing and descending turns, instrument navigation patterns). Training
performance was evaluated through experimenter observation of number of
"errors," i.e., violation of FAA private-pilot flight check standards.
Transfer was evaluated through time and trials to FAA performance
criteria and number of errors. Jacobs found that during simulator
training the group with washout motion had fewer errors than the other
groups, demonstrating again that in the simulator good motion is
advantageous---even with tracking maneuvers. However, after the subjects
transferred to the airplane, although all three groups performed better
than the control group with no simulator training on all of the three
dependent variables, there were no significant differences between the
three experimental groups. That is, simulator training improved
performance in the airplane, but motion in the simulator (whether no
motion, "bad" motion, or "good" motion) had no additional effect on
performance in the airplane.

Although the results from this study appear to be straightforward, their
credibility is undermined by at least two factors. First, the motion
platform on a Singer-Link GAT-2 trainer is much less advanced than the
motion platforms available now. Even if that type of simulator motion
did not affect airplane performance, current motion might be able to.
That is, it may be that skills learned under the more realistic motion
cues available today would transfer better to real flight than skills
learned under any of Jacobs' motion conditions. Second, Jacobs used
tracking maneuvers. Although this choice is understandable considering
the safety and logistical problems of performing disturbance maneuvers
in real flight, it undermined his goal of evaluating the usefulness of
motion. An additional factor that may have obscured a potential training
advantage of motion is that student subjects used in the study received
fixed amounts of training in the simulator instead of being trained to
asymptotic performance.

### Transfer Of Training---Disturbance Maneuvers

Ryan, Scott, & Browning (1978), on the other hand, used a more
diagnostic set of maneuvers to investigate the effect of simulator
motion on performance in the airplane, consisting of instrument
maneuvers and take-offs and landings with and without engine failures.
The asymmetric engine failures create a sudden disturbance that the
pilots must recognize and correct in the shortest possible time (Hall,
1989). The subjects were first-tour naval aviators that had recently
completed multi-engine undergraduate training and possessed "Standard
Instrument Cards." They were trained in a P-3 "Operational Flight
Trainer" with a narrow-angle television for (modelboard) visual cues and
a six DOF motion system that was disabled for the no-motion group. All
39 no-motion students and four of the motion students transferred to a
S-2, a small twin reciprocating-engine airplane. Six motion students
transferred to the T-44 twin turboprop airplane. Questionnaires revealed
that student and instructors "strongly favor\[ed\] having motion cues
available," but did not indicate any motion sickness associated with
either condition. Performance was rated by instructors. These results
show that even with these maneuvers, the results were again the same as
in the Jacobs study. That is, the presence of simulator motion improved
performance in the simulator, but had no bearing on performance in the
airplane. A footnote is that the presence of a sudden disturbance did,
indeed, increase the diagnosticity of maneuvers---the engine abort on
take-off[^1] was the **only** maneuver that demonstrated the motion
advantage **in** **the** **simulator**.

### Prediction Of Performance In The Airplane From Performance In The Simulator

Koonce (1974) had used the same non-visual simulator as Jacobs (1976)
(i.e., GAT-2, but with just pitch and roll) for a study examining
transfer of training to a Piper Aztec-D. In this study, he trained three
groups of thirty pilots with multi-engine and instrument ratings on five
maneuvers representative of those usually performed under instrument
flight rules (IFR) (cruise on a VOR airway, holding at a VOR station,
ADF approach, ILS approach, missed approach) and five maneuvers usually
performed under visual flight rules (VFR) (take-off and climbout; 360
degrees steep turn; chandelle; lazy eight; landing). In addition to the
no-motion and washout-motion conditions, he used a sustained motion
condition where the simulator moved in the appropriate direction and
then stayed there until pilot control activity indicated a change.
Koonce found the exact same results as Jacobs (1976). That is,
"simulator motion tends to increase the subject's acceptance of the
device, lower performance error scores, and reduce workload on the
subjects and the observers through the aiding effects of the motion
onset cues. But the differential effects of motion on the simulator
performance does not transfer to the performance in the aircraft."
Additionally, however, Koonce examined under which condition performance
in the airplane best predicted performance in the simulator*.* He found
that the sustained motion condition had the most predictive power. In
sum, although all three conditions trained the pilots equally well for
flying the airplane, the pilots' performance in the airplane could be
best predicted from their performance in a simulator with sustained
motion. He argued that this is due to greater stability of performance
in this simulator condition. Unfortunately, this study suffers from the
same flaws as the Jacobs study, outdated motion platform and
non-diagnostic maneuvers.

### Air Force Human Resources Laboratory Transfer Studies

The only other widely-known studies using transfer-of-training to real
airplanes were conducted by the Operations Training Division of the Air
Force Human Resources Laboratory. Martin (1981; Waag, 1981) reviewed six
of these studies. Each used a simulator with six DOF, five studies used
the Advanced Simulator for Pilot Training (ASPT) located at Williams Air
Force Base (AFB) and one used the Simulator for Air-to-Air Combat (SAAC)
located at Luke AFB. Most of the studies varied only the presence or
absence of motion during training, one varied also the FOV (without
finding an effect). A variety of different maneuvers were used, such as
basic contact maneuvers (including stalls), aerobatics, basic fighter
maneuvering, and air-to-surface weapon delivery. As with all other
transfer-to-airplane studies, there was no benefit of simulator motion
in the airplane despite a benefit of motion in the simulator for some of
the studies. Bussolari, Young, & Lee (1989) conclude that "while it is
arguable that the motion systems in these studies were of the highest
quality, the absence of motion effects across such diverse training
environments and simulator equipment considerably weakens the case for
requiring elaborate motion platform systems in flight simulators used
for training pilots in fixed wing aircraft operations."

### Summary of Transfer-Of-Training Studies

In sum, several investigators have examined transfer of training from
the simulator to the airplane. 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. However, the
indication from the Levison (1981) study that this advantage would
transfer to real airplanes was not borne out in any of these studies.
The only benefit of simulator found was an increase in the
predictability of airplane performance from simulator performance
(Koonce, 1974). This result, however, will need to be confirmed with
state-of-the-art motion and visual systems.

The failure of these studies to find an impact of simulator motion on
airplane flying might be due to aspects of the experiments, as opposed
to a real lack of benefit of simulator motion. This is of particular
concern due to the fact that all of these studies suffer from the same
set of problems. First, all used outdated equipment, in particular with
respect to the motion and visual systems. Also, most of the equipment
suffered from large transport delays, bad synchronization of the visual
and motion systems, and lack of calibration of the motion system.
Second, in most cases they used non-diagnostic maneuvers. Disturbances
are difficult or impossible to initiate and to terminate in the real
world and dangerous to maneuver. However, disturbance maneuvers are
required for testing the value of simulator 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 determine a specific
effect size. 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 or non-pilots (Young,
1967). Fourth, pilots and instructors were not naïve regarding the
motion condition, which may have allowed bias to affect performance or
performance evaluation, respectively (Ebbinghaus, 1964). Fifth, all of
the studies measured only performance. Control behavior and subjective
responses, however, may be more sensitive to the effects of motion. In
fact, these problems are not limited to the transfer-to-airplane
studies; many of them affect the simulator-only studies and
quasi-transfer of training studies, as well.

## Why Revisit Motion Fidelity Requirements Now?

The question of whether to require vestibular motion cueing in
simulators used for flight training has been researched for at least
four decades. A marked decline in research activity in the nineties may
be attributed to the failure of this extensive research to resolve the
issue. Our endeavor to readdress this question is spurred both by the
failure of previous work to adequately address the motion fidelity
requirements issue for current air-carrier pilots and equipment as well
as changes in the research environment and opportunities.

Major technological advances have occurred in the wake of the recent
"virtual reality"---or rather simulated reality---frenzy in the
entertainment industry. Due to its marketing value, efforts mainly
focused on the visual system. The most advanced image generators and
display systems are at a point where they can almost perfectly reproduce
the visual stimulation resulting from real airplane motion. In
particular, the widening of the FOV resulted in increased stimulation of
the peripheral visual system, resulting in "a more compelling visual
display of motion" (McCauley, 1984). As we have seen even in the
research showing an advantage of motion, at least in the simulator, this
advantage was often reduced with improved visual stimulation. In
contrast, the last major advances with regard to motion cueing date back
to at least the early eighties. They include the practice of providing
critical onset cues followed by subliminal washout, and to use "gravity
align" platform attitudes (Brown et al., 1989). These techniques do
indeed help to achieve some perception of sustained acceleration, but
still do not overcome the inherent limitations in simulating vestibular
motion cues. It is possible, then, that today's visual systems provide
such high quality motion cues as to render the inherently imperfect
vestibular motion cues superfluous, at least for recurrent pilot
training.

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). Experienced pilots'
increased reliance on vestibular cues may make them more sensitive to
sensory conflicts and thus simulator sickness. Potentially, then, even
if a sophisticated visual system alone were to provide sufficient motion
cues for recurrent pilot training in the simulator, forgoing motion may
still be unacceptable due to the effects of the ensuing sensory conflict
on pilots.

The final reason for returning to the question of how best to simulate
airplane motion is the ever increasing use of flight simulators in
air-carrier training. Not only does this increase the urgency of this
reexamination, but it also has greatly improved research opportunities.
One result of the increased experience with and improved quality of
flight simulators in air-carrier training is the practice of total
training and checking in a Level D, and, with appropriate pilot
experience prerequisites, a Level C simulator, sometimes referred to as
"zero-flight-time training." Total recurrent training can be
accomplished in either of these levels of simulators. This practice was
established in the Advanced Simulation Plan put forth by the FAA in 1980
(FAR Part 121, Appendix H). While the difficulty of doing
transfer-of-training experiments remains, the experience with
zero-flight-time training represents a *de facto* validation of
high-level full-platform-motion simulators as a stand-in for the
airplane in quasi-transfer studies.

## The Need for Further Research

It is clear from a review of the pertinent literature that no definitive
conclusion can be drawn that would warrant modification of current
qualification requirements for platform motion in full flight
simulators. The FAA believes that this situation will remain unchanged
unless new research is undertaken, which takes into account the lessons
learned from past research, and the opportunities engendered by new
technology.

The research literature suggests certain potentially fruitful strategies
to be considered in developing a practical research design. To assess
training effectiveness, the research might employ a quasi-transfer
paradigm, testing transfer of training to an FAA-certified stand-in for
the airplane for recurrent "zero-flight-time" training. To assess
evaluation, the study design could employ a modified backward or
reverse-transfer paradigm, that is, it could measure how well pilots'
control performance and behavior in the simulator reflect their
proficiency in the airplane (Cross, 1991). Such a research design would
allow a determination of the extent to which there are control strategy
differences now between qualified full flight simulators and their
target aircraft, since this represents an existing baseline which
constitutes an accepted standard of safety. Combining these two
approaches, quasi-transfer and reverse transfer, could strengthen the
validity of results, provided that they are in agreement.

In setting up the experiments, the study design should build on the
lessons from previous work: It should use a state-of-the-art, FAA
qualified Level C simulator with a wide-angle collimated cross-cockpit
visual system and a modern six DOF freedom synergistic motion system
that is carefully calibrated before each experimental session. It should
use a homogeneous pilot sample from the population of interest, that is,
regional airline pilots qualified on the simulated airplane. It should
seek to prevent pilot or instructor bias by concealing both the purpose
of the experiment, and the specific simulator motion/no-motion condition
to be applied (through automated programming of motion conditions, with
an identical motion platform initialization sequence). Pilots should be
asked to fly highly diagnostic disturbance (closed-loop) maneuvers that
are characterized by high-gain, high-workload and unpredictability. As a
worst case, 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). The study should examine both control performance and
control behavior by collecting objective data at a high sampling rate,
as well as pilot and instructor subjective data on the most pertinent
variables, including pilot queries regarding simulator sickness. The
study should compare the extremes of the continuum from full six DOF
platform motion to no motion at all. If no effect of simulator motion on
transfer is found, a follow-on study should be conducted to validate the
results. Should it be determined 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.

In conclusion, the findings to date do not solve the FAA's questions
regarding the role of platform-motion cueing in regional airline
recurrent pilot training and checking. Previous investigations have been
extremely useful, however, in defining the type of experimental design
that would best address these questions. Moreover, technological
advances and improved research conditions provide the ideal opportunity
for pursuing this research. It is hoped that by readdressing these
questions, simulator availability and affordability will be improved,
resulting in better training with a concomitant increase in overall
safety.

## Acknowledgments

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 his insightful comments
on an earlier draft (and all else he teaches them about simulation); and
Ms. Mary Townsend for conducting the literature search and providing
superb overall 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.

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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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[^1]: It is unclear whether the take-off was rejected or continued.

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