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Instrument Flying Handbook
Emergency Operations
Unforecasted Adverse Weather

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Instrument Flying
Handbook

Preface

Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Flying
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Flying
Using an Electronic Flight
Display

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight
Display

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency
Operations

Unforecasted Adverse Weather

Inadvertent Thunderstorm Encounter
A pilot should avoid flying through a thunderstorm of any
intensity. However, certain conditions may be present that
could lead to an inadvertent thunderstorm encounter. For
example, flying in areas where thunderstorms are embedded
in large cloud masses may make thunderstorm avoidance
difficult, even when the aircraft is equipped with thunderstorm
detection equipment. Therefore, pilots must be prepared to
deal with an inadvertent thunderstorm penetration. At the
very least, a thunderstorm encounter subjects the aircraft to
turbulence that could be severe. The pilot and passengers
should tighten sent belts and shoulder harnesses and secure
any loose items in the cabin.

As with any emergency, the first order of business during
an inadvertent thunderstorm encounter must be to fly the
aircraft. The pilot workload is heavy; therefore, increased
concentration is necessary to maintain an instrument scan.
If a pilot inadvertently enters a thunderstorm, it is better to
maintain a course straight through the thunderstorm rather
than turning around. A straight course minimizes the amount
of time in the thunderstorm and turning maneuvers only
increase structural stress on the aircraft.

Reduce power to a setting that maintains a speed at the
recommended turbulence penetration speed as described in the
Pilot's Operating Handbook/Airplane Flight Manual (POH/
AFM), and try to minimize additional power adjustments.
Concentrate on maintaining a level attitude while allowing
airspeed and altitude to fluctuate. Similarly, if using the
autopilot, disengage the altitude hold and speed hold modes,
as they only increase the aircraft's maneuvering - thereby
increasing structural stress.

During a thunderstorm encounter, the potential for icing
also exists. As soon as possible, turn on anti-icing/deicing
equipment and carburetor heat, if equipped, Icing can be
rapid at any altitude and may lead to power failure and/or
loss of airspeed indication.

Lightning is also present in a thunderstorm and can
temporarily blind a pilot. To reduce this risk, turn up flight
deck lights to the highest intensity, concentrate on the flight
instruments, and resist the urge to look outside.

Inadvertent Icing Encounter
Because icing is unpredictable in nature, pilots may find
themselves in icing conditions even though they have done
everything practicable to avoid it. In order to stay alert to this
possibility while operating in visible moisture, pilots should
monitor the outside air temperature (OAT).

The effects of ice on aircraft are cumulative, thrust is
reduced, drag increases, lift lessens, and weight increases.
The results are an increase in stall speed and a deterioration
of aircraft performance. In extreme cases, two to three inches
of ice can form on the leading edge of the airfoil in less than
5 minutes. It takes only 1/2 inch of ice to reduce the lifting
power of some aircraft by 50 percent and increases the
frictional drag by an equal percentage.

A pilot can expect icing when flying in visible precipitation,
such as rain or cloud droplets, and the temperature is
between +02 and -l0° Celsius. When icing is detected, a
pilot should do one of two things, particularly if the aircraft
is not equipped with deicing equipment: leave the area of
precipitation or go to an altitude where the temperature is
above freezing. This "warmer" altitude may not always be
a lower altitude. Proper preflight action includes obtaining
information on the freezing level and the above-freezing
levels in precipitation areas.

If neither option is available, consider an immediate landing
at the nearest suitable airport. Even if the aircraft is equipped
with anti-icing/deicing equipment, it is not designed to allow
aircraft to operate indefinitely in icing conditions. Anti-
icing/deicing equipment gives a pilot more time to get out of
the icing conditions. Report icing to ATC and request new
routing or altitude. Be sure to report the type of aircraft, and
use the following terms when reporting icing to ATC:

1. Trace. Ice becomes perceptible. Rate of accumulation
is slightly greater than sublimation. Deicing/anti-icing
equipment is not utilized unless encountered for an
extended period of time (over 1 hour).

2. Light. The rate of accumulation may create a problem
if flight is prolonged in this environment (over 1
hour). Occasional use of deicing/anti-icing equipment
removes/prevents accumulation. It does not present a
problem if deicing/anti-icing equipment is used.

3. Moderate. The rate of accumulation is such that even
short encounters become potentially hazardous and
use of deicing/anti-icing equipment or flight diversion
is necessary.

4, Severe. The rate of accumulation is such that deicing/
anti-icing equipment fails to reduce or control the
hazard. Immediate flight diversion is necessary.

Early ice detection is critical and is particularly difficult during
night flight. Use a flashlight to check for ice accumulation on
the wings. At the first indication of ice accumulation, take
action to get out of the icing conditions. Refer to the POH/
AFM for the proper use of anti-icing/deicing equipment.

 
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