3.3 Pilot needs and human factors
both remote-sensing and in-situ sensors aboard aircraft,
will improve temporal and spatial accuracy beyond what
Pilots have three concerns about the icing environ-
is now possible with pilot reports. Accurate downlinked
ment (Vigeant-Langlois and Hansman 1999):
cloud liquid-water content, drop sizes, and temperature
How to recognize that they are approaching or are
will improve icing forecasts and provide more accurate
in icing conditions hazardous to their aircraft
icing warnings for other aircraft. Up- and downlinking
How to avoid icing
of weather information to and from the cockpit are areas
How to escape icing.
of research being addressed by the Advanced General
In-flight icing is a frequent topic in pilot safety briefs
Aviation Technology Experiment (AGATE) program
and popular literature (Buck 1988, Collins 1989,
and by NASA Langley Research Center in the Aviation
Schuyler 1989, Taylor 1991, Bertorelli 1992, Horne
Weather Information (AvWIN) program.
1994, and others). Over the years, rules of thumb, advice,
Efficient, cost-effective methods for testing remote-
and regulatory requirements have created ad hoc proto-
sensing technology, testing display and information-
cols for icing avoidance and escape. As a result, most
management techniques, and developing avoid-and-exit
pilots manage to avoid forecasted icing by not flying,
protocol and training are necessary for development and
or by making route deviations to avoid the conditions,
certification. Sensors may be tested from ground-based
or they encounter ice and escape safely through good
test beds and airborne platforms. Ground-based test beds
fortune. Tales of icing mishaps and escape are com-
include wind tunnels, spray rigs, and mountain-top test
mon fare in winter aviation literature (Creley 1990,
sites. The advantages of ground-based test beds include
McClean 1992). Many pilots do not survive icing
cost, accessibility, and control of test conditions. Moun-
encounters because they did not recognize that they
tain-top test sites allow less control over conditions,
were in ice until too late, and they did not have the
but they do provide the variability of natural icing. Wind
ability or capability to escape once immersed.
tunnels and spray rigs cannot provide the spatial con-
One of the larger causes of this avoidance and escape
ditions necessary for testing remote sensors, but they
problem is the quality of icing forecasts. Most pilots
can be used to test in-situ sensors and the environmen-
who want to avoid icing cannot, because icing fore-
tal effects of icing conditions on sensors and airfoils.
casts do not have sufficient accuracy as to spatial, tem-
Airborne platforms provide the best environment for
poral, and intensity criteria (Erickson et al. 1996, Green
testing aircraft-based remote sensors. Overall, a combin-
et al. 1996, Stack 1996, Clark 1997). Forecasts are often
ation of ground and airborne test beds will be necessary
made conservatively, on the side of safety, to minimize
to test both ground-based and airborne remote-sensing
accidents and compensate for inadequacies in forecast
systems.
procedure. However, this causes aircraft to not fly or to
3.2 Introduction
divert when it may not be necessary because large areas
Operations establish the functional requirements of
forecasted for icing may not have ice or even clouds.
a remote-sensing system designed to detect icing. The
As a result, the aviation system is less efficient, though
goal of system development is to improve the safety
safer.
and efficiency of aircraft operations. However, opera-
tions is a complex, multifaceted problem. A compre-
3.3.1 Pilot needs
Pilots need information for making risk-management
hensive review of general operational needs in icing
decisions about in-flight icing. They want to be able to
environments is presented by Brayton and Hakala
determine whether they are in or about to enter icing,
(1996).
because icing clues are often not visible from the cock-
One element, and ultimately the most important ele-
pit windows (Erickson 1997). Pilots also need to know
ment, of operations has to do with pilots and their needs
the location of icing and how intense the icing might
(Vigeant-Langlois and Hansman 1999). Although pilots
be without dipping their wings into it, as is now neces-
are on the leading edge of the icing problem because
sary (Green et al. 1996). Onboard, in-situ ice detectors
they are actually within the icing environment, they deal
(reactive detection systems) are a solution to the prob-
with more than icing. Systems from which pilots seek
lem of determining exposure to icing for many fixed-
icing guidance must be designed in a manner that best
wing aircraft and a few helicopters (Bracken et al. 1996),
suits the operational requirements of the cockpit envi-
but even these systems require that the aircraft enter
ronment and that effectively and efficiently helps pilots
icing conditions before determining that they are in
make management decisions. This includes the design
hazardous conditions.
of the display and information delivery system and train-
Pilots need clear, unambiguous guidelines as to when
ing in its use.
severe conditions are entered or warning that severe
6
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