the effects of information complexity on fighter pilot
alert system is the warning time provided for pilot reac-
performance in the Swedish air force. They found that
tion. The warning time needed may be a function of
even moderately complex information, measured by the
airspace class, aircraft type, mission, and mode of flight.
amount of information provided, interfered with flight
Though any warning time, no matter how short, may
tasks. The critical flight measure was an ability to main-
be helpful (Erickson 1997), there may be minimum
tain altitude above undulating terrain. When informa-
warning times that are more acceptable than others.
tion load increased to more than 8 to 10 items, pilots
Anderson and Carbaugh (1993) address this problem
could no longer integrate information and still fly the
for wind-shear-alert systems and consider it a critical
airplane. The authors indicate, through numerous exam-
factor in how pilots judge the value of an alert system.
ples, that humans have severe limitations in what they
Vigeant-Langlois and Hansman (1999) address warning
can receive, process, and remember, and the 8 to 10
distances for icing, with commuter pilots reporting as
information load items found in this study is consistent
little as 20 nautical miles as sufficient. All other classes
with the generally 7 information load items found in
of pilots wanted longer warning distances, and thus
many other studies. They conclude that modern technol-
greater warning times.
ogy can provide large quantities of information that
According to Hansman (1997), aircraft certified for
often make the pilot feel more confident, but perfor-
flight in icing have only to avoid severe icing, whereas
mance is governed by human, not technological, limi-
aircraft not certified for flight in icing require more deci-
tations. Information overload can be a serious issue
sion support for strategic and tactical planning, go/no-go
because pilots will either fixate on one, perhaps trivial,
decisions, and escape guidance. A simple pilot deci-
problem or lose the ability to ably accomplish any tasks.
sion structure has two options if icing is forecast, either
Though flying in icing may not be as stressful as ter-
to not go--the risk-adverse path, or to go--the risk-
rain-following flight in a high-performance aircraft,
tolerant path. There are three outcomes for the risk-
icing often is most threatening in the busy, critical depar-
tolerant path:
ture and approach phases of flight.
Encountering no ice
Another issue for icing displays is the type of graphic
Encountering ice but having options for avoiding
image provided to the pilot. Displays may be aircraft-
its effects
referenced or ground-referenced, and each may have
A catastrophic outcome.
plan, profile, or perspective views. Though perspective
views look realistic, plan and profile views are better
In the decision-making process, the risk of making
for decision making (Hansman 1997). Early MIT stud-
a flight is weighed against the flight's value. For high-
ies of terrain-avoidance displays indicated that the type
risk flights, the incentive to make the flight must be
of display affects behavior and thus the avoidance strat-
high for it to occur, or options must be available to
egy used by pilots, for example by avoiding terrain by
reduce the risk. The decision to fly into potential icing
climbing vs. turning. Aircraft performance characteris-
involves having options for avoidance and escape, such
tics, vertical and horizontal range, resolution, accuracy,
as seeking dry or warm air or turning back or landing
scan rate, and sensor limitations also affect the displayed
at alternates, to ensure a successful outcome. Other
information.
possible outcomes are to reach the destination without
Pilots need information, not data, so the display must
encountering ice or to have an ice-induced accident. A
be a rendition of the icing environment that allows the
remote-sensing ice-avoidance system may provide
pilot to obtain the needed information unambiguously
information for exercising options and reducing risk.
and in a form that promotes appropriate response. One
Escape options are either vertical--finding warm or dry
of the issues is 2-D vs. 3-D displays and the way pilots
air, or lateral--finding dry air (Vigeant-Langlois and
relate to each for different tasks. Cloutier (1997) pre-
Hansman 1999). Research must be conducted on each
sented two potential 2-D displays showing plan and
of the risk paths described above into how operators
profile views of icing potential for helicopter pilots.
and pilots may use in-flight ice detection to make flight
Boyer (1994) indicated that little research had been done
decisions. Vigeant-Langlois and Hansman (1999) also
evaluating the effectiveness of 3-D weather displays,
indicate that pilots want escape guidance to be displayed
and he addressed the benefits and costs of 3-D vs. 2-D
in the cockpit.
displays and conducted an evaluation using student
3.4 Manufacturers and operators
pilots for navigating around weather systems. He con-
cluded that 2-D displays offer advantages for navigating
Aircraft operators and manufacturers are concerned
around weather, with few benefits attributable to the
with the cost, weight, space, power, maintenance, and
3-D display.
training requirements of placing additional avionics
A measure of effectiveness of a look-ahead weather
packages on aircraft. They are also concerned about
8
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