曝光台 注意防骗
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change to the AFMs, “wing anti-ice is
required to be ‘ON’ for all takeoff operations
when the outside air temperature
is less than or equal to 5 degrees C, and
visible moisture is present below 400
ft above ground level, or the runway
is wet or contaminated, or there is any
precipitation.” The new procedure and
a new definition of ground icing conditions
supersede a former 1-mi (1.6-km)
visibility criterion that was found to be
ineffective in ensuring that wing antiice
was used appropriately.
High-altitude ice crystals have
recently been connected to engine
power loss and aircraft damage. Since
1991, more than 100 such events have
been recorded. Jeanne Mason, senior
specialist engineer in engine icing
and inclement weather with Boeing
Commercial Airplanes, described an
incident in which high-altitude ice
crystals resulted in multiple engine
flameouts in a 747 on descent into
Manila, Philippines.
“‘Icing conditions’ has always
referred to conditions where supercooled
liquid drops cling to airframe
surfaces, typically below 22,000 ft,” she
said. “But high-altitude water is likely
to be frozen ice particles — crystals —
rather than super-cooled liquid drops.”
Crystals can form ice even on surfaces
warmer than freezing temperature,
such as compressor surfaces aft of the
engine fan, she said. Ice shed from
compressor surfaces can cause surges,
flameouts or engine damage.
Convective, cumulonimbus clouds
have a high concentration of ice
crystals, Mason said. “Strong updrafts
and heavy rain are conducive to water
and lots of potential ice crystals,” she
said. “The key to identifying clouds
that contain ice crystals is heavy rain
below the freezing levels.” Crystals
accumulate in the “anvil” part of a
cumulonimbus cloud and have poor
reflectivity for aircraft weather radar.
“Use the tilt feature of the radar to
identify heavy rain below, a good indicator
that ice crystals may exist above
the rain,” she said.
Bryon Mask, a retired Air Canada
captain and ACPA director of flight
safety, discussed the use of flight data
analysis (FDA) in winter operations
in a program “designed to enhance
safety through the controlled, automated
recording and analysis of flight
data generated during routine line
AeroSafety World: Why did you
organize this conference?
Wiszniowski: For one thing, because
the Air Canada Pilots Association
was respected but not well known. We
have 3,000 professional pilots with experience
and expertise operating in the
Canadian winter environment. This is
one of our specialties, and we wanted
to share it with the industry, including
foreign carriers coming into Canada
— because for many of them, operating
in icing conditions is anything but
a normal procedure, and some have
never seen a major snow or ice event
before. For us, winter operations are
normal operating procedures.
ASW: Quite a few Canadian pilots are
here as well. They must have felt they
had something to learn, too.
Wiszniowski: It’s like what one of
your Americans, [former Secretary of
Defense] Donald Rumsfeld, said: There
are the known knowns, the known unknowns
and the unknown unknowns.
There are things we don’t even know
that we don’t know.
ASW: What are some of the things
that even pilots experienced in winter
ops might not understand, or not
fully understand?
Wiszniowski: [Deicing] fluid failures,
deicing techniques, some of the
technological advances that will make
operations safer and things that we
should avoid — the traps in deicing. So
through the education process we had
today, with the airport authorities, fluid
and deicing equipment manufacturers,
and so on, we can eliminate the known
unknowns.
ASW: What if anything is still uncertain?
Wiszniowski: We don’t know the
characteristics of a fluid failure. As one
of the presentations demonstrated,
we don’t know the effect of one wing
being contaminated and what level
of contamination is going to lead you
into a serious event. From the airport
side, we don’t know the effect of an
unstable approach or noncompliance
with SOPs that is going to put you in
harm’s way.
ASW: What kind of noncompliance is
especially risky in winter operations?
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