conditions lie ahead with sufficient lead time to avoid
3.3.2 Human factors
them (Erickson 1997). According to Coleman (1996)
Development of icing-avoidance avionics is a
of the Regional Airline Association, the answer to main-
human-centered development process because the intent
is to display information to pilots. Thus, information
taining safety in icing conditions is to locate severe icing
needs must be assessed, and perceptual issues vs.
accurately and then avoid it. Because icing forecasts
display design must be considered (Hansman 1997,
cannot provide the needed accuracy at the present time,
Vigeant-Langlois and Hansman 1999). A useful
remote detection or standoff (prediction detection) sys-
approach to designing a human/machine interface for
tems may (Green et al. 1996).
icing avoidance is to review issues addressed in other
Standoff guidance of icing conditions ahead of air-
weather-avoidance areas. Recent developments of
craft could be provided in at least three ways, all using
onboard wind-shear alert systems and other weather-
a form of remote-sensing system. One method under
avoidance systems, especially since cockpit resource
development utilizes satellite remote-sensing to map
management has been recognized as a consideration in
icing potential and uplink information to aircraft (Lee
single- and multiple-pilot cockpits, may serve as reason-
and Clark 1995, Vivekanandan et al. 1996, Lee 1997,
able analogs. One important finding of cockpit resource-
Thompson et al. 1997, Curry and Liu 1992). Satellite-
management research has been that automation can
derived information can be used to delimit areas with
cause human error as well as reduce it (Helmreich
liquid water, subfreezing temperatures, and cloud cover.
1997). Because icing-avoidance systems are likely to
Analyses could be accomplished in near real-time and
be in greatest demand during the approach and depar-
would provide a useful predictive detection capability.
ture phases of flight, balancing the distraction against
Another method, also under development, utilizes
the aid provided by an advisory system is critical to
ground-based sensors at airports to map icing condi-
its usefulness. A poorly designed interface may actu-
tions in approach and departure areas (Gary 1983, Deck-
ally produce a hazard to flight, so proper human/
er et al. 1986, Stankov et al. 1992). Remote sensors to
machine interface design is nearly as crucial to final
detect temperature profiles, cloud boundaries, liquid-
success as is the ability to sense cloud microphysics
water content, drop-size spectra, and cloud phase from
accurately.
the ground are nearly available. Walter and Moynihan
Icing is probably a more complex problem than wind
(1997) even propose a mobile system for military use.
shear and convective turbulence because it is less com-
An airport-based system would serve all aircraft, util-
pact geographically, it is a hazard in all modes of flight,
ize largely existing technologies or technologies that
and there is significant variation in the ability of differ-
are nearing maturity, and serve the phases of flight most
ent aircraft to cope with the hazard. However, there may
likely to experience icing. It would be a cost-effective
be similarities. Wanke and Hansman (1991) evaluated
approach, considering cost per aircraft served (Owen
graphical displays of microburst alerts from both
1997).
ground-based and airborne detection systems. The
A third system would be an in-flight, aircraft-mounted
issues ranged from display clarity to pilot response to
remote detection system (Sand and Kropfli 1991; Fourn-
alerts. Questions addressed involved the visual clutter
ier 1993; Siquig 1993; EWA 1996; Ryerson 1996, 1997,
of adding alerts to existing navigational displays, val-
1998). An airborne system would require elements simi-
ue of single- vs. multiple-level intensity display, value
lar to a ground-based system, with the ability to detect
of indicating the alert source (ground or airborne), and
temperature, liquid-water content, and drop spectra.
effect of alert source on pilot procedural response.
However, the technologies may be quite different
Active airline pilots were tested in a realistic transport-
because of their use on a small moving platform, scan-
aircraft flight simulator. The results showed that multi-
ning primarily horizontally, and operating within
level intensity displays are desirable, the source of infor-
restricted power and weight limits.
mation was not important because confidence was
Pilots need better information than is now available,
placed in the alert whatever the source, and correlation
and they require information that is easily understood
with other information was not important. The study
and provides options (Vigeant-Langlois and Hansman
also suggested needed training areas, because pilots
1999). An ability to see through an icing weather sys-
often responded to alerts with evasive action that was
tem and map the extent of a threat area would be opti-
inappropriate or not necessary.
mal, but any more information than is now available
The amount of information displayed in the Wanke
would be welcome (Clark 1997). A warning time of 1
and Hansman (1991) study did not appear to be an issue.
to 5 minutes, preferably integrated into an existing dis-
That is not always the situation, however, and it may
play system, of areas that are of risk to aircraft would
be related to single- vs. multiple-pilot cockpit environ-
be most useful, and even no warning time may be accept-
able (Erickson 1997).
ments. For example, Svensson et al. (1997) evaluated
7
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