AOPA Pilot Magazine - January 2014 - 86

P&E

WX WATCH

INTERMITTENT MAXIMUM (CUMULIFORM
CLOUDS) ATMOSPHERIC ICING CONDITIONS

SO YOU'RE PICKING UP ICE

(LIQUID WATER CONTENT VS MEAN EFFECTIVE
DROP DIAMETER)

R
AT TU
E R RA ER
MP PE MP
TE EM
T

2.5 AIR

LIQUID WATER CONTENT GRAMS PER CU. METER

3.0

2.0 AIR
TE

1. Pressure altitude
range, 4,000-22,000 ft.
2. Horizontal extent,
standard distance of
2.6 Nautical Miles.

Note: darker color
indicates Possible
extent of limits

RE
+
E 32°
AT +
F
14
AIR
UR °
TE
1.0
E F
MP
-4
ER
°F
AT
URE
0.5
-22°
F
AIR TEMP
ERATURE -40°F
0.0
15 20 25 30 35 40
1.5

MEAN EFFECTIVE DROP DIAMETER - MICRONS

efficient as ice collectors than wings with
smaller radiuses (think Mooneys)-but
lift erosion still takes place, just at different rates.
True, flight tests for FIKI certification
are conducted to ensure that ice-protection systems do their jobs within test
parameters-but those don't include all
icing possibilities. They do include tests
of ice accretions and their effects on
wings and other sections of an airplane
in an icing wind tunnel; flights with ice
shapes attached to leading edges; and,
finally, flights in actual icing conditions. If
the airplane passes, then FIKI is granted.
The tests in actual icing are a process that
can take a long time, by the way, which
explains why icing certification often is
the last test program in a new airplane's
certification process. Delays happen when
there are difficulties finding the correct,
FAA-prescribed icing conditions.

Let's say everything has gone wrong and now you're icing up. This is no
time to blame a bad forecast or a lousy go/no-go decision. It's time to
take action. Right now.
* Maintain control of the aircraft.
* If it isn't on already, turn on all ice-protection equipment. There is
an exception to this rule for turbine aircraft: turning on engine inlet
heat once ice has formed can cause ice to shed and be ingested by the
engine. Check your pilot operating handbook or Aeronautical Flight
Manual for specific guidance. Some advise turning on one engine's inlet
heat to ascertain if shed ice is a problem-if it isn't, then turn on both
inlet heat valves. But a good rule is to turn on ice protection before
entering icing conditions, using items such as windshield heat, pitot and
static port heat, propeller, and engine inlet heat as anti-ice protection.
Deice equipment such as inflatable deice boots are used at the first sign
of ice accretion. The old adage about letting a small amount of ice form
before activating the boots is just that; research has shown that immediate activation is most effective in removing ice.
* Inflate deice boots as soon as icing is detected. Don't wait for ice to
build to a 1/4 or 3/8-inch extent. The latest knowledge indicates that
ice-bridging (a condition where ice can form beyond a boot's inflation
limits) does not exist.
* Inform ATC. Ask for vectors to the nearest suitable airport-one having the longest and widest runways. If you're noninstrument-rated, you'll
need ATC guidance for the descent and landing if low cloud bases and/
or terrain are factors.
* Disengage the autopilot, if you are using one. It can mask adverse
handling, or signs of an incipient stall.
* Climb or descend to ice-free conditions. A descent is often a bad
choice, as it could lead to more dangerous scud-running. Climbing in
icing conditions can be a viable choice. Much research has shown that
the vertical extent of icing conditions seldom exceeds 3,000 feet.
Hopefully you will have planned your flight so as to have above-freezing
temperatures and low terrain below your initial cruising altitude. Another option is a 180-degree turn, assuming that you came from ice-free
conditions.
* Keep your power up, and flaps and gear retracted.
* Gently exercise the flight controls to prevent them freezing up.
In carbureted airplanes, turn on carburetor heat. This will both bypass
what may soon be an ice-blocked induction air filter and prevent ice
from forming in the carburetor venturi. In fuel-injected airplanes, open
the alternate air door. This also will bypass the normal induction-air
pathway.
* Cycle the propeller. This can help shed propeller ice, but know that
there's a risk that not all blades will shed ice at the same time.
* Use extra airspeed for the landing, and keep the power up if airspeed
decays or an excessive sink rate develops. Land in a flat attitude-save
full-stall landings for a nicer day. Keep flaps retracted. Extending the
flaps and using extra power can contribute to tailplane stalls, especially
in stabilator-equipped airplanes. Recovery from tailplane stalls is counterintuitive: Apply aft stick pressure, reduce power, and retract flaps.

THE ENVELOPES, PLEASE

FAR Part 25, Appendix C sets down the
certification parameters for flight tests in
actual icing conditions. The parameters
include temperature, water droplet diameter, and liquid water content (the amount
of liquid water in a cloud mass, expressed
in grams per cubic meter). There are two
86 | AOPA PILOT January 2014

envelopes, one for what's called continuous maximum icing conditions (this
corresponds to the conditions that are
typically prevalent in stratus clouds), and
another for intermittent maximum conditions (corresponding to typical icing
associated with cumulus clouds).

For the stratus cloud tests, liquid
water contents are lower, as well as droplet diameters-just what you might expect
in rime-ice-producing stratiform clouds.
For the cumulus-cloud envelope, droplet diameters and liquid water contents
are larger. But here's something more

AOPA Pilot Magazine - January 2014

Table of Contents for the Digital Edition of AOPA Pilot Magazine - January 2014