Aviation Meteorology Exam 3 (chapter 12, 13, 14)

Where and at what temperatures are droplets for rime ice usually found?

-10C to -20C

What is mixed ice and how does it occur?

A combination of rime and clear ice, and it occurs about 20% of the time that icing is present.

On what factors is the image on a weather radar dependent?

A function of the size and number of precipitation particles.

Describe the appearance and formation process of rime ice.

A milky, opaque, rough kind of ice, is formed when small drops strike the aircraft surface and freeze rapidly.

What factors must be present in order for a thunderstorm to form?

A source of lift, unstable air and high moisture content.

Define "haze;" where is it most commonly found?

A suspension of dry particles, other than smoke or dust. Most often found below 15,000 feet.

Define "advection fog;" "sea fog."

Advection fog: forms whenever moist air moves over colder ground or water. Sea fog: an advection fog formed at sea.

What are the cloud and visibility requirements for special VFR?

All special VFR flights must remain clear of clouds and maintain at least one statute mile flight visibility for operations within Class B, C, D, and E surface area.

What is the "minimum safe altitude for all operations"?

An altitude of 500 feet above the surface, except over open water or sparsely populated areas

Carburetor heat is primarily a(n) (anti-icer, deicer).

Anti-icer.

Define "squall line."

Any line or narrow band of active thunderstorms (with or without squalls). A squall line is often found 100 to 300 miles ahead of a cold front.

How should you conduct changes in altitude relative to possible icing?

Ascend or descend at as large an angle as practical, but not at an excessive airspeed since accretion rates are greater with increasing speed.

What does "basic VFR" mean?

Basic VFR = 1,000 Feet Vertical and/or 3 SM Prevailing (LVFR)

Distinguish between a cloud ceiling and an obscuration ceiling.

Beneath the 500 ft cloud ceiling, you may have unrestricted visibility. But while you may have 500 ft of vertical visibility and can see the ground beneath you, it is likely that you cannot identify the end of the runway until you are at a lower altitude. Thus the obscuration ceiling reduces your slant range visibility.

State the two basic ways that fog forms.

By cooling the air to near its dewpoint and by adding moisture.

What is the effect on an aircraft's lifting power of an accumulation of half an inch (1.25 cm) of structural ice, and what does this imply about operating an aircraft?

Can reduce the lifting power of some aircraft by as much as 50%. Avoid too low an airspeed, for the extra weight and change in the shape of the wing will cause an increase in stall speed.

Describe the effects of blowing dust and sand.

Can restrict visibility, dust can be lifted to heights of 15,000 feet.

What is the main means for preventing carburetor ice.

Carburetor heat.

Name and describe the types of controlled airspace?

Class A: airspace from 18,000 ft MSL up to and including FL 600. Class B: from the surface to 10,000 ft. MSL Class C: surface to 4,000 ft above airport elevation. Class D: surface to 2,500 ft above the airport elevation surround airports that have an operational control tower. Class E: airspace, such as a surface area for an airport.

State the three kinds of structural ice.

Clear, rime and mixed.

Define "clear;" "few;" "scattered;" "broken;" and "overcast."

Clear: 0 or 0 below 12,000 Few: >0 but 2/8 Scattered: 3/8-4/8 Broken: 5/8-7/8 Overcast: 8/8

State the types of air mass thunderstorms.

Convective, orographic and nocturnal.

State factors on which the ice accretion rate depends.

Depends primarily on droplet size, aircraft speed and airfoil shape.

Why is icing at temperatures below -20C usually less of a problem?

Due to less moisture because of the reduced capacity for moisture at colder temperatures and because most of the moisture is in the form of ice crystals that do not adhere to aircraft.

Under what conditions is frost most likely to occur at cruise altitudes?

Forms when descending into warm, moist air. Generally, not a problem at cruise altitude and airspeed.

Define "upslope fog."

Forms when moist, stable air is cooled adiabatically when forced above higher terrain.

What causes most icing in a frontal area?

Freezing rain.

Why is frost a special concern on takeoffs and landings?

Frost is more of a problem on takeoffs and landings when the aircraft is at low speeds. While frost does not substantially change the shape of the wing, the roughness of its surface causes a surprisingly large disruption in the smooth flow of air over the wing, resulting in enough loss of lift so that when combined with a heavily loaded aircraft and high density altitude, it can prevent the aircraft from becoming airborne.

Define "funnel cloud;" "tornado;" "waterspout."

Funnel cloud: a tornado cloud or vortex cloud extending downward from the parent cloud but not reaching the ground. Tornado: a violently rotating column of air, pendant from a cumulonimbus cloud and nearly always observable as "funnel-shaped." Waterspout: an intense columnar vortex that occurs over a body of water.

Compare fog, haze, and smoke in terms of how they are dispersed.

Haze: dispersed by strong winds or destabilizing the atmosphere. Smoke: dispersed by breaking the inversion or strong winds.

State the three types of induction icing. Describe the formation of each.

Impact, throttle and carburetor ice. Impact ice forms at the air intake and requires freezing temperatures and some form of water particles, liquid or solid in order to pose a problem. Throttle ice most often forms when the throttle is in the closed position. Carburetor ice is the vaporization of fuel, like the evaporation of water, will remove heat from the surrounding air in the carburetor, add to this a carburetor venture effect and this process can result in a temperature drop as much as 60F.

Define "plow wind." What are its typical horizontal and vertical limits?

Initial downdraft or first gust or gust front.

Where are the droplets necessary for clear ice formation usually found? What is the usual temperature range for clear ice formation?

Most often found in cumuliform clouds and freezing rain. Between 0 C and -15C, but can occur at temperatures much colder in cumulonimbus clouds.

State the effect of an iced over static port on the altimeter, rate of climb indicator, and indicated airspeed.

Not function correctly, needles move in incorrect direction and rate. If the drain hole remained open with the air input blocked, then the indicated airspeed would generally drop to zero.

Under what conditions does radiation fog form? Describe the formation process.

On a clear night with a light wind when there is sufficient moisture. Forms under an inversion.

What is one good means of preventing throttle icing? Where and why is such icing especially critical?

One should open the throttle occasionally with the cockpit throttle control in order to reduce the likelihood of such icing. Especially likely when taxiing or when making an approach for a landing.

Why are thunderstorm downdrafts particularly hazardous in mountainous terrain?

Peaks can be hidden by clouds and downdrafts can push your aircraft into the mountains.

What is the cause of about one out of every four general aviation accidents?

Pilots trying to continue VFR into adverse weather

List and define four kinds of visibility.

Prevailing: surface visibility and is the greatest distance objects can be seen and identified through at least half the horizon circle. Flight: sometimes call air-to-air visibility, that is, how far one can see horizontally from a flight altitude. Slant: the visibility that a pilot can expect to have on final approach to a runway, for his/her vision is slanted from his/her altitude to the surface. Vertical: it is the ceiling value when the sky and/or clouds are totally hidden by a surface-based obscuration, such as fog.

Compare warm and cold front thunderstorms with regard to bases and severity.

The base of cold front thunderstorms are generally lower and more severe than those with a warm front.

Define "ceiling."

The height (AGL) of the lowest broken or overcast layer aloft, or the vertical visibility into an obscuration.

Describe the appearance of clear ice and state the reasons for that appearance.

The relatively slow freezing allows the drops to spread out before freezing, giving this ice its clear, glassy appearance.

Why is evaporative icing less a problem in fuel injected engines?

There is less danger of such icing in the fuel injected engine because vaporization takes place in or near the cylinders.

What is one of the chief dangers of warm front thunderstorms?

They are often embedded within a large air mass.

How long do air mass thunderstorms usually last? How far across are they?

They usually last anywhere from 20 minutes to an hour and a half. From less than 5 to more than 30 miles.

What is usually consider to be the number one hazard associated with thunderstorms?

Turbulence.

When landing and encountering the plow wind, in which direction should you turn? Why?

Turn toward the plow wind. Plow wind acts like a front so the wind will shift clockwise.

Which is typically larger and stronger, updrafts or downdrafts?

Updrafts are generally larger and stronger, both horizontally and vertically.

How is VFR determined?

VFR is defined by cloud visibility requirements for various combinations of altitude and airspace.

State the relationship between icing and aircraft control surfaces, landing gear and braking.

Very little ice is required to freeze the various control surfaces of small aircraft. For maximum effectiveness of the brakes, use them on and off for brief periods of time. Do not lock the brakes. After taking off and raising the gear in order to break or shake off some of the slush or mud.

Pressure changes near a thunderstorm may cause how much error in the altimeter? Describe the sequence of pressure changes as a thunderstorm approaches, arrives, and moves out.

1,000 ft of error. An approaching developing thunderstorm is an intense small-scale low, surface pressure often lowers initially, then rises with the onset of the plow wind, then gradually returns to normal as the storm moves out.

State the primary stages in thunderstorm development.

1. The cumulus or growth stage 2. The mature or fully developed stage 3. The dissipating or degenerating stage

What percent of thunderstorms should you assume contain hail?

100%.

Which two fogs are considered to be the most significant to the pilot? Compare them.

Radiation and advection fog. Advection fog is primarily along coastal areas during winter, advection fog occurs with stronger winds, can occur when skies are cloudy, usually cover a greater geographical area, last longer and can occur at any time. Radiation fog forms on a clear night with a light wind when there is sufficient moisture, primarily in flat, inland regions.

What is the sign that a thunderstorm has reached the mature stage?

Rain at the earth's surface.

Name the two basic kinds of airspace.

Regulatory and non-regulatory

Compare clear and rime ice with regard to weight and ease of removal.

Rime ice is not as heavy as clear ice, rime ice occurs about 70% of the time that icing is present, while clear ice is only 10% of the time. Clear ice is hardest to remove while there is less opportunity for rime icing as the ice crystals don't stick.

What kind of icing is the most hazardous with thunderstorms? Where (at what temperature) does the most severe icing occur?

SLD icing and clear ice. -25C.

State the effects of carburetor ice on aircraft with a constant speed propeller.

Same sequence of events as evaporative ice on RPM will apply, except that it will be manifold pressure that is involved rather than RPM.

What are the two main types of aircraft icing?

Structural and induction icing.

What is necessary for structural icing to form? List some of the consequences of such icing. State the effects on the flying ability of an aircraft, fuel consumption, and stall speed.

Visible liquid moisture or high humidity and below freezing temperatures. Consequences: incorrect readings on aircraft instruments, restricted vision, loss of flying ability of the airplane, loss of radio communication, and loss of proper usage of brakes/landing gear, and control surfaces. Loss of flying ability occurs due to a loss of lift and thrust and increases in weight and drag; fuel consumption is also greater. Due to a change in the shape of the wing, the critical angle of attack will be lower, resulting in an even higher stall speed.

What do wet snow and ice pellets suggest about temperatures aloft?

Wet snow will collect on the aircraft and it is evidence of above freezing temperatures at your altitude. Ice pellets are evidence of warmer temperatures aloft, as snow melts in a warm layer to form rain which, when passing through a layer of below freezing temperature, freezes as ice pellets.

How does clear ice form?

When large drops strike the aircraft surface and freeze slowly.

State the effects of ice on the propeller. What is one means of reducing the amount of ice on the propeller and how would you know that such a means is effective.

Will reduce its efficiency. Varying the speed of the propeller can help sling off some of the ice.

Relative to fronts, where do squall lines develop?

Within the interior of an air mass under certain conditions.