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among these factors must also be considered, as must the possibility that "exogenous"
factors might impact more than one of the primary safety-related factors.
SEPARATION SAFETY MODELING
A-4
An Annotated Outline Of Factors Potentially Affecting Separation Safety
A. Relative aircraft positions and velocities (encounter geometry)
1. "Blind-flying" risk [factors that affect risk¾no intervention]
a. Horizontal and vertical positions and closing angles
b. Aircraft velocities and accelerations
c. Climb/descent rates and accelerations
d. Vertical path separation at crossing point
2. Pilot intervention - factors that affect timely pilot detection and correction
a. Closure rate
b. Relative bearings and aspect angles in relation to cockpit field of view
restrictions, the horizon.
[Aircraft design dictates available field of view; small windshields and
side windows, interior fitments (HUD mount, sunshades) that intrude
into the field and external aircraft structure (wing, nose, propeller
etc.) all limit the pilot’s ability visually to acquire targets. The
prudent pilot takes pains to clear the area into which the aircraft is
being flown; this is particularly true when a radical change is being
made in the velocity vector. The relative bearing of the target from
the pilot’s eye must be within the field of view if visual detection is to
be achieved. Windshield dirt can adversely affect the field of view;
since squashed bugs are the primary source of windshield
disfigurement, time of year may be a factor.]
c. Rate of change of the above angles (zero for linear collision courses)
[Rate of change of relative bearing: aircraft in rectilinear flight on a
collision course maintain a fixed bearing relative to each other thus
reducing probability of early detection. If either subject aircraft or
target is maneuvering, then judgment of collision risk becomes more
complex.]
d. Aircraft attitudes and bank angles
[The attitude of the target aircraft can be a cue to relative motion
between subject aircraft and target in close proximity, and maneuver
also reduces the value of these data. Even in steady state flight,
interpretation of target attitude can be difficult.]
e. Meteorological conditions and background conditions, including
location of the sun (affecting ability to perceive other aircraft and their
relative distance, velocity, and trajectory)
[The background, or whatever lies beyond the target within the field of
view, affects the pilot’s ability to acquire the target. Military aircraft
are camouflaged for a reason and they are very difficult to detect
against like-colored surface features. Above the horizon, at least by
day, all aircraft appear black when they are distant, increasing the
chance of acquisition. Visual ranges of 30 miles are not uncommon.
As the target closes, its skin color may have an effect and this variable
APPENDIX A
FACTORS POTENTIALLY AFFECTING SEPARATION SAFETY
A-5
should be considered for collision intervention, especially for large
targets.
Discharge tube anti-collision lights are very effective enhancers of
visual acquisition, whatever the background, even in daylight. Since
any beacon can be intermittently masked from the viewer by target
aircraft structure and since flash duration is very short, some
manufacturers offer “synchronized” flashers which seek to ensure that
lights do not all flash at the same time.
At night, a bright star field or a field of lights on the ground can
effectively prevent visual detection of targets in all phases of flight.
Fighter aircraft attack out of the sun for a reason; looking in the
direction of the sun will almost always deny the pilot visual acquisition
of targets and can materially affect vision for some time afterward.
Meteorological effects can severely hamper visual acquisition;
clearly, the pilot cannot be expected visually to detect a target at a
range greater than the prevailing visibility. However, especially at
high altitude, it is often difficult for the pilot to know the value of the
visibility because of the lack of visual reference. What may appear to
be almost zero visibility can actually be 3 or 4 miles. In these
circumstances, the pilot’s lookout may be less vigilant than it would be
in clear air since it may be assumed that nothing can be detected in
the conditions.]
f. Natural lighting conditions (e.g., day, night, dawn, dusk)
g. Threat aircraft size, skin color, and lighting
h. Condensation trails
[Can significantly enhance visual acquisition. Equally, the apparent
disappearance of a target as it passes out of the Mintra band can
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a concept paper for separation safety modeling(58)
