Exam 3 – Review
**Exam 3 will be a multiple choice exam consisting of 35 questions
**Focus on definitions - (blue highlighted concepts in text)
**Focus on blue boxes - (important information given in these boxes)
Ch 11 – Wind Shear
Section A: Wind Shear Defined
Wind shear – a gradient in wind velocity. It is interpreted in the same sense as a
pressure gradient or temperature gradient; that is, it is a change of wind velocity over a
given distance.
Horizontal wind shear – it is convenient to visualize wind shear as being
composed of two parts: a horizontal wind shear (a change in wind over a horizontal
distance) being one part.
Vertical wind shear - a change in wind over a vertical distance
***Wind shear is best described as a change in wind direction and / or speed within
a very short distance
***During departure under conditions of suspected low-level wind shear, a sudden
decrease in headwind will cause a loss in airspeed equal to the decrease in wind
velocity
Section B: Causes of Wind Shear
***An important characteristic of wind shear is that it may be associated with a
thunderstorm, a low-level temperature inversion, a jet stream, or a frontal zone
Downburst – Professor T. Fujita, an atmospheric scientist from the University of
Chicago, coined the term downburst for a concentrated, severe downdraft that induces an
outward burst of damaging winds at the ground
Micro bursts
Microburst - Professor T. Fujita, an atmospheric scientist from the University of
Chicago, introduced the term microburst for a downburst with horizontal dimensions of
2.2 n.m. (4km) or less.
Vortex ring – The microburst is characterized by a strong core of cool, dense air
descending from the base of a convective cloud. As it reaches the ground, it spreads out
laterally as a vortex ring which rolls upward as a vortex ring which rolls upward along its
outer boundary.
***An aircraft that encounters a headwind of 45 knots with a microburst may expect a
total shear across the microburst of 90 knots
***The duration of an individual microburst is seldom longer than 15 minutes from
the time the burst strikes the ground until dissipation
***When a shear from a headwind to a tailwind is encountered while making an
approach on a prescribed glide slope, the pilot should expect airspeed and pitch attitude
decrease with a tendency to go below glide slope
***If there is thunderstorm activity in the vicinity of an airport at which you plan to
land, you should expect wind shear and turbulence on approach
Low-level wind shear systems (LLWAS) – These alert systems have been
installed at many large airports around the U.S. where thunderstorms are frequent.
Terminal Doppler Weather Radar (TDWR) – These systems are being
installed across the U.S. at many vulnerable airports to provide more comprehensive
wind shear monitoring.
Fronts and Shallow Lows
Frontal wind shear – a front is a zone between two different air masses and
frontal wind shear is concentrated in that zone
***With a warm front, the most critical period for LLWS is before the front passes
Air mass Wind Shear
Air mass wind shear – occurs at night under fair weather conditions in the
absence of strong fronts and/or strong surface pressure gradients. It develops when the
ground becomes cooler than the overlying air mass as a result of radiational cooling. If
the cooling is strong enough, a ground-based or surface inversion will result. In this case,
the temperature increases with altitude from the surface to an altitude of a few hundred
feet.
Nocturnal inversion – low-level soundings taken throughout the day and night
during fair weather conditions have revealed stable layers developing at night due to
radiational cooling of the ground. By sunrise the stability has increased to a maximum as
indicated by the nocturnal inversion.
***A pilot can expect a wind shear zone in a surface-based temperature inversion
whenever the wind speed at 2,000 to 4,000 feet above the surface is at least 25 knots.
Elevated Stable Layers
Elevated stable layers – In addition to fronts and surface-based nocturnal
inversions, wind shears may be found in the free atmosphere, in elevated stable layers.
These layers are frequently found over shallow, relatively cool air masses. Convection
from the ground concentrates wind shear at the base of the stable layer.
***When a climb or descent through a stable layer is being performed, the pilot should
be alert for a sudden change in airspeed
Jet Streams – Certain patterns of upper level, short wave troughs and ridges
produce significant wind shear. The strongest shears are usually associated with sharply
curved contours on constant pressure surfaces and / or strong winds. Stable layers near
jet streams and within a few thousand feet of the tropopause have the highest
probabilities of strong shears. Occasionally, the shear is strong enough to cause large
airspeed fluctuations, especially during climb or descent.
Ch 12 – Turbulence
Section A: Turbulence Defined
Aviation turbulence – Based on descriptions from pilots, crew, and passengers,
aviation turbulence is best defined simply as “bumpiness in flight.” This definition is
based on the response of the aircraft rather than the state of the atmosphere.
Aircraft and Pilot Response
Turbulent gusts – Atmospheric motions produced by turbulent eddies are often
referred to as turbulent gusts
Maneuvering – If the pilot (or autopilot) overreacts, control inputs may actually
add to the intensity of bumpiness.
Turbulence Measures
Turbulence reporting criteria – Turbulence intensity varies from light,
moderate, severe to extreme and is related to aircraft and crew reaction and to movement
of unsecured objects about the cabin.
G-load – Also known as gust load, this force arises because of the influence of
gravity.
Section B: Turbulence Causes and Types
Low-Level Turbulence – Defined as that turbulence which occurs primarily
within the atmospheric boundary layer. The boundary layer is the lowest few thousand
feet of the atmosphere; that is, where surface heating and friction influences are
significant.
Mechanical Turbulence – Over flat ground, significant LLT occurs when
surface winds are strong.
***The type of approach and landing recommended during gusty wind conditions is a
power-on approach and a power-on landing
Turbulent wake – Typically, a trail of turbulent eddies is produced downwind of
an obstacle with a sheared layer between the ground-based turbulent region and smooth
flow aloft.
Funneling effect – Similar to the increase in the speed of the current of a river
where it narrows, strong local winds with substantial LLT and wind shear are created
when a broad air stream is forced to flow through a narrow mountain pass. Strong winds
due to this funneling effect may extend well downstream of the pass.
Thermal Turbulence
Thermal turbulence – Thermal turbulence is LLT produced by dry convection in
the boundary layer. It is typically a daytime phenomenon that occurs over land under fair
weather conditions.
***The characteristics of an unstable cold air mass moving over a warm surface are
cumuliform clouds, turbulence, and good visibility. A stable air mass is most likely to
have smooth air.
Capping stable layer – This layer is caused by a very slowly sinking motion
aloft; typically associated with a macro scale high pressure region.
Turbulence in Fronts
Wake turbulence – The term wake turbulence is applied to the vortices that form
behind an aircraft that is generating lift.
***The greatest vortex strength occurs when the generating aircraft is heavy, clean
and slow. Wake turbulence is near maximum behind a jet transport just after takeoff
because of the high angle of attack and high gross weight.
***The wind condition that prolongs the hazards of wake turbulence on a landing
runway for the longest period of time is a light quartering tailwind
Turbulence in and near Thunderstorms
Turbulence in and near Thunderstorms (TNT) – Turbulence which occurs
within developing convective clouds and thunderstorms, in the vicinity of the
thunderstorm tops and wakes, in downbursts, and in gust fronts.
***When landing behind a large aircraft, the pilot should avoid wake turbulence by
staying above the large aircraft’s final approach path and landing beyond the large
aircraft’s touchdown point. When departing behind a heavy aircraft, the pilot should
avoid wake turbulence by maneuvering the aircraft above and upwind from the heavy
aircraft.
Turbulence within Thunderstorms
Overshooting tops – Although updrafts weaken above the equilibrium level, in
intense thunderstorms, they may penetrate several thousand feet into the stratosphere
before they are overcome by the stability. The strongest updrafts can often be identified
by cumuliform bulges that extend above the other-wise smooth anvil top of the
thunderstorm. These are called overshooting tops and they are evidence of very strong
thunderstorms and turbulence.
Turbulence below thunderstorms
Turbulence below thunderstorms – The downdrafts, downbursts and micro
bursts define the primary turbulent areas below the thunderstorm. These phenomena
produce intense turbulence as well as wind shear. Strong winds in the outflow from the
downdraft generate mechanical turbulence, which is especially strong along the edge of
any microburst and/or gust front.
Turbulence around thunderstorms
Overhang – A turbulent wake occurs under the anvil cloud downwind of the
thunderstorm. This is one of the most hazardous regions outside of the thunderstorm and
above its base. Sometimes identified as the region under the overhang (anvil), it is an
area well known to experienced pilots and is a location of severe turbulence and possibly
hail.
Clear Air Turbulence
Clear Air Turbulence – Turbulence which occurs in the free atmosphere away
from any visible convective activity.
Billow clouds – In the clouds that show evidence of shearing-gravity wave
activity, the “herring bone” pattern of billow clouds is a common feature in high cloud
layers subjected to vertical shear.
***When a pilot enters an area where significant CAT has been reported, an
appropriate action when the first ripple is encountered is to adjust airspeed to that
recommended for rough air
Shearing gravity waves – Short atmospheric gravity wave disturbances that
develop on the edges of stable layers in the presence of vertical shears.
Jet stream front – In the vicinity of the jet stream, there are two specific regions
where CAT occurs most frequently. One is in the sloping stable layer below the jet core.
This is a high-level frontal zone, also called a jet stream front.
***A sharply curving jet stream is associated with greater turbulence than a straight
jet stream
Mountain Wave Turbulence (MWT)
Mountain Wave Turbulence (MWT) – Turbulence produced in connection with
mountain lee waves. It is responsible for some of the most violent turbulence that is
encountered away from thunderstorms.
Lee Wave Region
Lee Wave Region – Lee waves are more often smooth than turbulent, but if
turbulence does occur in the lee wave region, it is most likely to occur within 5,000 feet
of the tropopause.
Lower Turbulent Zone
***One of the most dangerous features of mountain waves is the turbulent area in and
below rotor clouds
Ch 13 – Icing
Section A: Aircraft Icing Hazards
Icing – refers to any deposit or coating of ice on an aircraft. Two types of icing
are critical in the operation of aircraft: induction icing and structural icing.
Induction Icing
Induction icing – a general term which applies to all icing that affects the power
plant operation. The main effect of induction icing is power loss due to ice blocking the
air before it enters the engine, thereby interfering with the fuel/air mixture. Induction
icing includes carburetor icing and icing on air intakes such as screens and air scoops.
Carburetor icing – occurs when moist air drawn into the carburetor is cooled to a
temperature less than 0 degrees Celsius by adiabatic expansion and fuel vaporization.
Structural icing
Structural icing – Airframe or structural icing refers to the accumulation of ice
on the exterior of the aircraft during flight through clouds or liquid precipitation when the
skin temperature of the aircraft is equal to, or less than 0 degrees Celsius. The primary
concern over even the slightest amount of structural icing is the loss of aerodynamic
efficiency via an increase in drag and a decrease in lift.
Ground icing – Another important form of structural icing to be
considered is that which may occur prior to take off. An aircraft that is ice-free is as
critical for takeoff as it is in other phases of flight, if not more so. Causes of ground icing
include freezing rain, freezing drizzle and wet snow. Also, frost can be a significant
hazard.
***Test data indicate that ice, snow, or frost having a thickness and roughness similar
to medium or coarse sandpaper on the leading edge and upper surface of a wing can
reduce lift by as much as 30 percent and increase drag by 40 percent
***A hard frost can increase the stalling speed by as much as 5 or 10 percent. An
aircraft carrying a coating of frost is particularly vulnerable at low levels if it also
experiences turbulence or wind shear, especially at slow speeds and in turns. Frost
may prevent an airplane from becoming airborne at normal takeoff speed
Section B: Observing and Reporting Structural Icing
Observations of Icing Type and Severity
Rime ice – Structural icing occurs when super cooled cloud or precipitation
droplets freeze on contact with an aircraft. The freezing process produces three different
icing types: clear, rime, and mixed ice. Rime ice is the most common icing type. It
forms when water droplets freeze on impact, trapping air bubbles in the ice. This type of
ice usually forms at temperatures below -15 degrees Celsius. Rime ice appears opaque
and milky white with a rough, porous texture. Although rime icing has serious effects
on the aerodynamics of the aircraft wing, it is regarded as the least serious type of icing
because it is lighter, easier to remove, and tends to form on the part of the aircraft
where, if available, anti-icing and/or deicing equipment is located.
Clear ice – forms when droplets impacting an airplane freeze slowly, spreading
over the aircraft components. Air temperatures are usually between 0 degrees Celsius
and – 5 degrees Celsius. These conditions create a smooth, glossy surface of streaks and
bumps of hard ice. Clear ice is less opaque than rime ice. It may actually be clear but
often is simply translucent (clear ice is also called “glaze”). Clear ice is the most
dangerous form of structural icing because it is heavy and hard; it adheres strongly to
the aircraft surface; it greatly disrupts the airflow over the wing and it can spread
beyond the location of de-icing or anti-icing equipment.
Runback icing – when ice spreads beyond the ice protection equipment.
Mixed ice – a combination of rime and clear ice; forms at intermediate
temperatures (about -5 degrees Celsius to -15 degrees Celsius) and has characteristics of
both types. The variation in liquid water content in this temperature range causes an
aircraft that is flying in these conditions to collect layers of both less opaque (clear) and
more opaque (rime) ice.
Icing intensity – The severity of icing is determined by its operational effect on
the aircraft. Icing intensity is classified as trace, light, moderate and severe and is related
to the rate of accumulation of ice on the aircraft; the effectiveness of available deicing/anti-icing equipment; and the actions you must take to combat the accumulation of
ice.
Icing PIREPs
Icing PIREPs – Pilot reports of structural icing are often the only direct
observations of that hazard and, as such, are of extreme importance to all pilots and
aviation forecasters. The critical information that an icing PIREP should contain includes
location, time, flight level, aircraft type, temperature, icing intensity, and icing type.
Excellent aids to pilots in the diagnosis of icing conditions are graphical presentations of
recent icing PIREPs from the Aviation Digital Data Service (ADDS).
Section C: Micro scale Icing Processes – icing occurrence, type, and severity depend on
three basic parameters: temperature, liquid water content and droplet size
Temperature – icing types and critical outside air temperatures include clear (0
to -5 degrees Celsius, clear or mixed (-5 to -10 degrees Celsius), mixed or rime (-10 to 15 degrees Celsius) and rime (-15 to -20 degrees Celsius)
Liquid Water Content (LWC) – simply a measure of the liquid water due to all
the super cooled droplets in that portion of the cloud where your aircraft happens to be
Droplet Size
Super-cooled large droplets (SLD) – associated with heavy icing and especially
with runback icing problems
Collision/coalescence – small water droplets can grow into large super cooled
droplets; through this process, water droplets are super cooled and they initially formed in
subfreezing surroundings
Warm layer process - small water droplets can grow into large super cooled
droplets; through this process, when snow falls into a warm layer (temperature greater
than 0 degrees Celsius) where ice crystals melt, and then fall into a cold layer
(temperature less than 0 degrees Celsius) where the rain droplets become super cooled.
***The presence of ice pellets (PL) at the surface is evidence that there is freezing rain
at a higher altitude
Section D: Icing and Macro scale Weather Patterns
Cyclones and Fronts – extra tropical cyclones provide a variety of mechanisms
to produce widespread, upward motions. These include convergence of surface winds,
frontal lifting and convection.
Influence of Mountains – mountainous terrain should always be considered a
source of icing hazards when subfreezing clouds are present.
Icing Climatology – refers to the average distribution of icing for a given area
Section E: Minimizing Icing Encounters – know capabilities of your aircraft, decision
tree
Freezing level – analyzed on the freezing level chart and appears on some
aviation forecast charts
Freezing level chart – solid lines on this chart indicate the position of particular
freezing levels. The dashed lines indicate where the freezing level intersects the ground.
The open circles indicate the location of sounding stations where freezing levels are
reported in hundreds of feet MSL.
Ch 14 – Instrument Meteorological Conditions
Section A: Background
Visual meteorological conditions (VMC) – The counterpart to IMC; these two
terms are a rather broad classification used to describe the state of the ceiling and/or
visibility with regard to aviation operations. Key terminology used in the evaluation of
IMC conditions includes ceiling, cloud amount, cloud height, cloud layer, obscuration,
prevailing visibility, radar summary chart, relative humidity, runway visibility (RVV),
runway visual range (RVR), sector visibility, temperature-dew point spread, tower
visibility, vertical visibility and weather depiction chart.
Slant range visibility – another important consideration is slant visibility on final
approach. This is the oblique distance at which you can see landing aids, such as runway
lights and markings.
Section B: Causes of IMC – visibility is decreased by particles that absorb, scatter, and
reflect light. We can separate atmospheric particles into two groups: those composed of
water, such as water droplets and ice crystals; and dry particles, such as those from
combustion, wind-borne soil, and volcanoes.
Fog and Low Stratus Clouds
Radiation fog/Advection fog – fog forms in stable air; that is, it is cooled to
saturation by contact with the cold ground
Upslope fog – fog caused by adiabatic cooling of stable air
Steam fog – fog that forms in unstable air (at least in the lowest layers); water
evaporates and saturates a thin layer of colder air, which causes the fog.
Ice fog – forms in cold climates; a radiation-type fog which is composed of ice
crystals; forms at low temperatures (-20 degrees F or less) and may be quite persistent,
especially in cities or industrial areas where many combustion particles are present to act
as cloud nuclei. At colder temperatures (-30 F or colder), the sudden addition of moisture
and particulates can cause ice fog to rapidly form
Precipitation
Fractocumulus or fractostratus clouds – sometimes called scud; form below the
original cloud base, causing the ceiling to lower over time.
Precipitation fog – may develop when rain saturates the layer near the ground
Blowing snow (BLSN) – reported when the wind raises snow particles more than
6 feet above the surface and reduces visibility to 6 s.m. or less.
Blizzard – exists when low temperatures combine with winds that exceed 30
knots and great amounts of snow, either falling or blowing.
Weather Systems – fog and low stratus clouds develop under identifiable larger
scale weather conditions; IMC conditions may also occur when warm, moist air over runs
cold air trapped in valleys; radiation fog favors clear skies, cold ground and light winds;
radiation fog typically dissipates after the sun rises; advection fog is common whenever
warm, moist air is carried over a cold surface
Smoke and Haze
Smoke – is the suspension of combustion particles in the air
Haze (HZ) – is a suspension of extremely small, dry particles
Air pollution – as with smoke, some of the worst haze problems occur in large
industrial areas and cities where many air pollution sources add gases and more
particulates to any naturally occurring haze particles.
Dust
Dust (DU) – refers to fine particles of soil suspended in the air
Blowing dust (BLDU) – dust raised by the wind to 6 feet (2 m) or more,
restricting visibility to 6 statute miles (10 km) or less
Dust storm – visibility less than 5/8 sm (1km)
Severe dust storm – visibility less than 5/16 sm (500 m)
Weather depiction chart – one of the most useful charts for evaluating current
ceiling and visibility conditions at a glance
Section C: Climatology- knowledge of the favored areas of IMC is useful background
for flight planning, especially in unfamiliar geographical regions.
Ch 15 – Additional Weather Hazards
Section A: Atmospheric Electricity
Lightning – defined as any or all of the various forms of visible electric discharge
produced by thunderstorms
Lightning Effects – lightning strikes on aircraft result in a variety of adverse
effects. Although most of them are minor, in some cases, the damage can be severe
enough to result in an accident or incident. A lightning flash can be extremely bright;
temporary blindness is not an unusual occurrence
Static Electricity – refers to the spark or point discharges that occur when the
electric charge difference between the aircraft and its surroundings become large enough
St. Elmo’s fire – a corona discharge that appears as a bushy halo around some
prominent edges or points on the aircraft structure and around windscreens
Section B: Stratospheric Ozone
Ozone (O3) – A prominent feature in the lower stratosphere; has both good and
bad qualities; good qualities include its absorption of damaging UV radiation from the
sun; bad qualities include it not being good in an environment where animals, people and
plants are present because it is toxic; large quantities have an acrid smell which irritates
the eyes and can cause respiratory difficulties
Section C: Volcanic Ash – consists of gases, dust and ash from a volcanic eruption and
can spread around the world and remain in the stratosphere for months or longer
Volcanic Ash Hazards – when an aircraft approaches an ash cloud some distance
from a volcano, the cloud is not always easy to distinguish from ordinary water or ice
clouds
Ash Cloud Behavior – volcanic ash clouds are most dangerous close to the
volcano when an eruption has just occurred because the ash particles are large
Reports and Warnings
Volcanic Ash Advisory Centers (VAAC) – These 9 centers have the
responsibility for the preparation and worldwide dissemination of a Volcanic Ash
Advisory Statement in a timely manner so that appropriate Meteorological Watch Offices
(MWO) may issue SIGMETs; VAAC in the U.S. also prepare Volcanic Ash Forecast
Transport and Dispersion (VAFTAD) charts
Volcanic Ash Advisory Statement – gives the volcano location; describes the
ash cloud; and provides a forecast of the plume; issued within 6 hours of an eruption and
at a 6 hour interval as long as conditions warrant.
Volcanic Ash Forecast Transport and Dispersion (VAFTAD) charts – show
computer forecasts of the future locations and relative concentrations of ash clouds for a
number of atmospheric layers up to FL550. If there has been an actual volcanic eruption,
the charts will be labeled “ALERT.” If the chart is issued for a potential eruption, it will
be labeled “WATCH.”
Section D: Condensation Trails
Condensation trail or contrail – defined as a cloud-like streamer that frequently
forms behind an aircraft; develop in the upper troposphere; they can occur at any altitude
depending on a variety of things such as temperature, humidity, and type of aircraft.
Aside from obvious military concerns (aircraft detection), the hazard presented by
contrails is the development of a cloud deck with reduced visibility at a flight level
where, previously, no cloud existed.
Aerodynamic contrails – formed when the pressure is lowered by air flowing
over propellers, wings, and other parts of the aircraft; adiabatic cooling brings the air to
saturation; typically thin and short-lived
Exhaust contrails – form when hot, moist exhaust gases mix with cold air; a
critical condition for this type of contrail is low temperature, depending on the altitude
(less than -24 C near sea level and less than -45 C at FL5000 for the formation of exhaust
contrails
Dissipation contrail or distrail – a streak of clearing that occurs behind an
aircraft as it flies near the top of, or just within a thin cloud layer; the heat added by the
aircraft exhaust and/or mixing of the dry air into the cloud layer by the aircraft downwash
causes the dissipation of the cloud along the aircraft track; distrails are less common than
contrails.
Section E: Miscellaneous Hazards
Whiteout – situation where all depth perception is lost because of a low sun angle
and the presence of a cloud layer over a snow surface
Runway Conditions
Hydroplaning – with water or wet snow, braking effectiveness may be greatly
reduced by hydroplaning which occurs when a thin layer of water separates the tire from
the runway surface; heavy rain and/or slow drainage of the runway surface cause these
conditions. It’s always important to be aware of the potential for hydroplaning on wet
runways. The popular convention for calculating hydroplaning speeds for your aircraft
for either landing or takeoff is really quite easy. Aside from the hydroplaning formula,
the only piece of information you need to have is your aircraft main tire pressure. The
hydroplaning formula is simply calculated as:
V (HP) = 9Tire Pressure