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383 

Federal Aviation Administration, DOT 

Pt. 60, App. C 

T

ABLE

C2E—A

LTERNATIVE

D

ATA

S

OURCES

, P

ROCEDURES

AND

I

NSTRUMENTATION

—Continued 

[The standards in this table are required if the data gathering methods described in paragraph 9 of Appendix C are not used] 

QPS requirements 

Information 

Table of objective tests 

Level 

By 

only 

Alternative data sources, procedures, and instrumentation 

Notes 

Test entry number and title 

2.d.3.c. Handling Qualities. 

Dynamic Lateral and Di-
rectional Stability. Ad-
verse/Proverse Yaw.

Data may be acquired by using an inertial measurement system 

and a synchronized video of the calibrated helicopter instruments, 
the force/position measurements of flight deck controls.

lllllllllllllllllllllll

B

EGIN

I

NFORMATION

 

18. V

ISUAL

D

ISPLAY

S

YSTEMS

a. Basic principles of a FFS collimated dis-

play: 

(1) The essential feature of a collimated 

display is that light rays coming from a 
given point in a picture are parallel. There 
are two main implications of the parallel 
rays: 

(a) The viewer’s eyes focus at infinity and 

have zero convergence, providing a cue that 
the object is distant; and 

(b) The angle to any given point in the pic-

ture does not change when viewed from a dif-
ferent position so the object behaves geo-
metrically as though it were located at a sig-
nificant distance from the viewer. These 
cues are self-consistent, and are appropriate 
for any object that has been modeled as 
being at a significant distance from the 
viewer. 

(2) In an ideal situation the rays are per-

fectly parallel, but most implementations 
provide only an approximation to the ideal. 
Typically, an FFS display provides an image 
located not closer than about 20–33 ft (6–10 
m) from the viewer, with the distance vary-
ing over the field-of-view. A schematic rep-
resentation of a collimated display is pro-
vided in Figure C2A. 

(3) Collimated displays are well suited to 

many simulation applications as the area of 
interest is relatively distant from the ob-
server so the angles to objects should remain 
independent of viewing position. Consider 
the view of the runway seen by the flight 
crew lined up on an approach. In the real 
world, the runway is distant and the light 
rays from the runway to the eyes are par-
allel. The runway appears to be straight 
ahead to both crew members. This situation 
is well simulated by a collimated display and 
is presented in Figure C2B. Note that the dis-
tance to the runway has been shortened for 
clarity. If drawn to scale, the runway would 
be farther away and the rays from the two 
seats would be closer to being parallel. 

(4) While the horizontal field-of-view of a 

collimated display can be extended to ap-
proximately 210°–220°, the vertical field-of- 

view has been limited to about 40°–45°. These 
limitations result from tradeoffs in optical 
quality and interference between the display 
components and flight deck structures, but 
were sufficient to meet FFS regulatory ap-
proval for Helicopter FFSs. However, recent 
designs have been introduced with vertical 
fields of view of up to 60° for helicopter appli-
cations. 

b. Basic principles of a FFS dome (or non- 

collimated) display: 

(1) The situation in a dome display is 

shown in Figure C2C. As the angles can be 
correct for only one eye point at a time, the 
visual system in the figure has been aligned 
for the right seat eye point position. The 
runway appears to be straight ahead of the 
aircraft for this viewer. For the left seat 
viewer, however, the runway appears to be 
somewhat to the right of the aircraft. As the 
aircraft is still moving towards the runway, 
the perceived velocity vector will be directed 
towards the runway and this will be inter-
preted as the aircraft having some yaw off-
set. 

(2) The situation is substantially different 

for near field objects encountered in heli-
copter operations close to the ground. In 
those cases, objects that should be inter-
preted as being close to the viewer will be 
misinterpreted as being distant in a col-
limated display. The errors can actually be 
reduced in a dome display. 

(3) The field-of-view possible with a dome 

display can be larger than that of a col-
limated display. Depending on the configura-
tion, a field-of-view of 240°  by 90°  is possible 
and can be exceeded. 

c. Additional display considerations 

(1) While the situations described above 

are for discrete viewing positions, the same 
arguments can be extended to moving eye 
points produced by the viewer’s head move-
ment. In the real world, the parallax effects 
resulting from head movement provide dis-
tance cues. The effect is particularly strong 
for relative movement of flight deck struc-
ture in the near field and modeled objects in 
the distance. Collimated displays will pro-
vide accurate parallax cues for distant ob-
jects, but increasingly inaccurate cues for 

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