2.6 Organization of this report
icing is most frequently encountered. Because wind-
Broadly, research and development for remotely
shear alert systems have evolved since the development
detecting icing conditions can be placed in three cate-
of cockpit resource-management concepts, they may
gories: operations, meteorology, and technology. Op-
serve as useful analogs for designing an effective pilot
erations includes the human/machine interface,
interface for icing avoid-and-exit advisory systems.
regulatory issues, avoid/escape strategies, aircraft inte-
Research is needed in this area. In addition, unlike wind
gration, training, and terminology. Meteorology involves
shear, which is a directly sensed threat to aircraft, icing
atmospheric environment and characteristics that must
does not occur until aircraft enter icing conditions, pro-
be sensed. Technology refers to the remote-sensing
cess cloud microphysical conditions, and create ice on
systems that may be able to sense icing potential. Sub-
the airframe (Fig. 1). Thus, icing potential is a virtual
areas of research and development needed are identi-
phenomenon, and the most appropriate methods for
fied within each primary category. This report gives an
quantifying, analyzing, and displaying the virtual threat
overview of the state of the art, describes barriers and
must be determined. The types of display, terminology,
opportunities to development, and recommend devel-
methods of indicating potential icing intensity, sensor
opment directions.
range, resolution, accuracy, and refresh rate and warning
time needed are a function of airspace class, aircraft
type and configuration, and mode of flight. This mix of
3.0 OPERATIONAL REQUIREMENTS
conditions needs to be considered in developing opti-
3.1 Summary
mal pilot information systems, training protocol, and
Pilots are risk managers. When it is a question of
sensing systems.
flight safety, they want clear, unambiguous informa-
Cost, weight, space, power, and maintenance are
tion about the location and intensity of weather threats
some of the concerns of aircraft manufacturers and
before they enter them. A top-level requirement with
operators. The aircraft most needing protection--com-
regard to icing is to provide pilots with a decision-support
muters, helicopters, and light aircraft--offer the fewest
system specific to the remote sensing of icing potential
of these resources, so for airborne sensing systems, the
ahead of aircraft. Standoff guidance about icing poten-
need is to provide the greatest benefit for the least
tial could be provided from satellite and ground-based
impact. The spatial and temporal threat of icing is gener-
sensors uplinking information to the cockpit or from
ally small when viewed annually, so it is probable that
aircraft-mounted remote-sensing systems. However,
icing remote-sensing systems will not be installed in
satellites still do not have the capability of providing
lieu of competing avionics or weapons systems. They
high spatial- and temporal-resolution icing information.
will probably be used only if mandated or required
Ground-based sensing systems at airports would be
because of market or extreme safety pressures.
most cost-effective per aircraft served, protect the most
Remote sensors may provide pilots with the location
critical phases of flight, and are systems for which
and intensity of icing potential ahead of their aircraft.
sensing technologies are most mature. Aircraft-based
However, pilots must also be able to determine how
systems would be most costly per aircraft and the tech-
this icing potential will affect safety, because a deci-
nologies are least mature, but aircraft would be pro-
sion to enter or avoid the sensed conditions is a func-
tected in all phases of flight, especially when arriving
tion of the aircraft's ability to operate in icing. Aircraft
or departing from small, remote airports that do not have
are certified for flight in icing conditions according to
remote-sensing systems.
atmospheric criteria specified in FAA FAR 25, Appen-
Ground-based systems should be developed first,
dix C, but pilots need to know how aircraft respond to
because of their near-term technological maturity and
conditions outside of Appendix C. They also need to
cost effectiveness as an operational test bed, and to pro-
know how much additional icing an iced aircraft can
tect congested airport approach and departure areas.
tolerate. That is, they need to know how much ice is
Satellite-based sensors need continued development to
necessary to produce unsafe operating conditions. Air-
supplement local sensing systems and to provide pro-
craft may have to be tested outside of Appendix C con-
tection during cruise flight where spatial and temporal
ditions to determine their operational limits. In addi-
detail may not be as critical. Aircraft-based systems need
tion, the development of smart aircraft-monitoring sys-
the greatest development, but they offer the greatest
tems may also be needed to guide the pilot's decision
potential for providing the information pilots need.
to enter or avoid icing.
Pilots need information, not data. Thus, remote-
An important side benefit of onboard icing remote-
sensing systems must provide clear, simple displays that
sensing systems is the potential for downlinking weather
reduce and do not add to flight-management demands
information to other aircraft, air traffic controllers, and
in critical approach and departure flight regimes where
meteorologists. Downlinked weather information, from
5
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