Exam 3 Will Be a Multiple Choice Exam Consisting of 35 Questions
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 appliesto all icing that affects the powerplant 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 de-icing/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) – associatedwith heavy icing and especially with runback icing problems
Collision/coalescence – small water droplets can grow into large supercooled 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.