IEEE - Aerospace and Electronic Systems - April 2021 - 31

Ernst et al.
panel. Nevertheless, the pilots did not solely use the symbology but also-at times-looked to the obstacle on the
right. In contrast, the two variants with the head-coupled
VCI prompted the participants to make use of the VCI
being always in sight: They looked much more to the
right, where they could see both VCI and obstacle
[cf. Figure 2(b)].
Interestingly, with Mixed-HDD-Below, the subjects
hardly ever looked in directions between the two narrow
areas of interest, whereas for HeadFixed-Below the gap
between the peaks is less prominent and the right area of
interest is considerably wider. This can be explained by
the mode switching mechanism of the Mixed mode in the
first study. The VCI switched from its aircraft-fixed headdown position to its head-fixed position if the pilot looked
more than 23 to the side. This caused the VCI to jump
whenever the pilot's LOS crossed this limit. Thus, the subjects avoided this transition area. This behavior was
changed for the Mixed mode in the second study: The
position changes were not triggered by the pilot's LOS
anymore but coupled to the flight phase.
In the second study, the limited simulation environment prevented us from observing this head motion
behavior. The A350-like cockpit strongly restricted the
pilots' out-the-window view. Furthermore, the outside
vision projection system could not supply sufficient sideview. Therefore, the head-motion patterns were not as pronounced as during the VR study, which provided a much
more realistic simulation of the pilot's view from a real
helicopter cockpit.

DISCUSSION OF THE EVALUATION RESULTS
The subjective ratings clearly show that the pilots appreciate the advantages of a hover symbology in the form of a
VCI. The positive results of the first study were confirmed
by the more advanced second study with the JEDEYE
HMD. Both the head-fixed and the mixed VCI variant
appeared to be helpful and the evaluation did not reveal
major differences between the two VCI positioning modes.
It seems to depend on personal preferences, which one was
favored by the participant. Nevertheless, the idea to couple
the state of the VCI to the flight phase and the display content was perceived to be helpful. A possible conclusion
from this result is that one could provide a number of feasible VCI options, which can be selected depending on customer needs (defined in ConOps based on the task
requirements). As mentioned in the section " Virtual Cockpit Instruments, " this great flexibility is one of the major
benefits of such virtual instruments.
In good visual conditions (study I), we did not find
major differences in the achieved positional accuracy
between the three preselected VCI modes. The flight performance was already good with the conventional
APRIL 2021

AircraftFixed-HDD variant so that the head-fixed and
mixed options could not significantly improve the position holding accuracy. Nevertheless, the head motion
data reveal that both variants with head-coupled VCI
allowed the pilots to keep their heads up and eyes out
at the obstacles significantly more often. This is an
important safety gain in such maneuvers even though
this quantity is not directly measurable with our simulator study.
Due to the limited outside vision system of the GECO
simulator, the second study showed the advantages that
the VCI-OAWD creates if the out-the-window view is
restricted. As expected, the limited visual cues degraded
the overall hover performance considerably. Nevertheless,
the setup also revealed the differences between the VCI
variants and the baseline condition-where the OAWD
was only displayed on the PMD.
A proven method to enhance the hover performance in
DVE is to add acceleration cues to the display. However,
such elements may capture a lot of attention and require
excessive training before they can be used effectively. We
did not include such a symbol set as our symbology does
not target zero-visibility conditions. It is devised as an
addition to outside visual cues, not as a replacement. The
VCI-OAWD should enable the pilot to keep the eyes out
with the supplementary OAWD always in sight. It should
not fixate the pilot's attention on the symbology only. The
pilots should not be animated to practice instrument-flying
when they actually operate under visual flight rules.
Our research shows that the VCI appears to be a suitable alternative to a head-down OAWD. The pilots
reported that it did not clutter their view but provided
essential information in a user-friendly manner. A major
plus is that the VCI allows the pilot to conduct the hover
maneuver " head-up, eyes-out " while simultaneously monitoring the 360 obstacle awareness display. However-at
the current stage-we have not experimentally compared
this approach to spatial auditory or haptic cueing. Every
modality has individual strengths and weaknesses when
serving as an OAWD. For instance, a visual display with a
top-down view seems to be most powerful in providing
precise distance presentation and an overview of a complex environment, e.g., with several widespread obstacles.
A spatial audio warning, on the other hand, might be better
suited to indicate a high-priority obstacle. It can intuitively
and immediately guide the pilot's attention to an urgent
threat location, which might be outside of the pilot's current FOV. The human auditory distance perception is
rather inaccurate, which is why pulse-period cueing is
often used to synthesize distance (cf. parking assistants in
modern cars) [12]. Additionally, haptic feedback via
active inceptors/sticks can directly guide the pilot's control inputs. However, it does not provide the strategic
overall picture of the situation like a visual top-down
view. In our opinion, auditory and haptic cues can

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