ATC Basics: Hazardous Weather - Part 1

What are the 3 factors that can influence aviation weather safety?

1. Pilot

2. Aircraft

3. Equipment

What is the cause of the most weather-related accidents?

Adverse wind

What are the 2 actions that ATC can take when adverse wind is reported in the terminal area?

1. Change runway configuration

2. Reduce arrival rates

What is the term for a wind that is not parallel to the runway or path of an aircraft?

Crosswind

What 2 things can happen if an aircraft does not correctly compensate for crosswind?

1. The aircraft may drift off the side of the runway

2. Side load on landing gear can occur, possibly leading to gear collapse

What aircraft has a maximum crosswind component at which they can operate?

All aircraft

What is a second, brief increase in the speed of the wind?

Gusts

Why can a gust cause an aircraft’s nose to briefly rise?

It increases airspeed, which may increase lift

When the gust ends, why is that dangerous for the aircraft?

A sudden decrease of airspeed occurs, which may decrease lift & cause aircraft to sink, leading the aircraft to potentially bounce on the runway

What is a wind with a component of motion from behind the aircraft?

Tailwind

When a tailwind is happening, what is happening to takeoff and landing?

1. Longer takeoff & landing roll

2. Less time for decisions due to increased ground speed

What is wind that changes direction frequently?

Variable wind

During the 2 minute evaluation period, what 2 conditions must wind complete to be considered variable?

1. Fluctuate by 60 degrees or more

2. Speed more than 6 knots (Doesn’t matter as much)

What is a VERY fast change in wind direction?

Wind shift

What 2 conditions must wind complete to be considered a wind shift?

1. Change in direction of 45 degrees or more

2. Speed of 10 knots or more

How long does wind have to complete the conditions to be considered a wind shift?

15 minutes

Who is affected more by tailwinds & crosswinds and why?

Smaller aircraft; they have slower takeoff & approach speeds

How do most aircraft accidents happen?

Pilots who are not instrument qualified operating in IFR conditions

What is the lowest layer aloft reported as broken or overcast, or the vertical visibility into an indefinite ceiling?

Ceiling

What are the two types of ceiling?

1. Layer aloft

2. Indefinite

When a pilot descends below a ceiling, they can see both the ground below & the runway ahead despite the cloud cover is caused by which type of ceiling?

Layer aloft

What cloud layers are included in layer aloft ceiling?

1. Overcast (OVC)

2. Broken (BKN)

When a layer aloft is unbroken or completely overcast, what occurs?

Equal ceiling

What is the ceiling classification that occurs when the reported ceiling value represents the vertical visibility (VV) upward into a surface-based obscuration?

Indefinite ceiling

What type of ceiling classification restricts the pilot’s slant-range (air-to-ground) visibility?

Indefinite ceiling

What is a visible aggregate of minute water droplets based at the Earth’s surface that reduces horizontal visibility to less than 5/8 statute mile?

Fog

Does fog fall to the ground?

No

How much visibility is there for weather to be considered fog?

5/8 statute mile

How does fog differ from clouds?

Its base must be at the Earth’s surface

How does fog form?

The dew point & temperature are identical

What is the most common & persistent weather hazards in aviation?

Fog

What is the term for any of the forms of weather particles, whether liquid or solid, that fall from the atmosphere and reach the ground?

Precipitation

What is snow lifted from the surface of the Earth by the wind to a height of 6 feet or more above the ground & blown about in such quantities that the reported horizontal visibility is reduced to less than 7 statute miles?

Blowing snow

What are the height of the snow being blown to & the horizontal visibility conditions to be considered blowing snow?

1. Height of 6 feet

2. Visibility less than 7sm

What is the phenomena where light, powdery snow is blown by the wind and reduces the visibility to almost zero?

Whiteout

What are fine particles of rock powder that originate from a volcano and that may remain suspended in the atmosphere for long periods?

Volcanic ash

What are conditions over significant portions of mountainous geographical areas?

Mountain obscuration

What is the irregular motion of an aircraft in flight, especially when characterized by rapid up/down motion caused by a rapid variation of atmospheric wind velocities?

Aircraft turbulence

What are 3 causes of aircraft turbulence?

1. Convective turbulence

2. Mechanical turbulence

3. Wind shear

What is the result of convective storms, particularly thunderstorms, that are felt by the aircraft?

Convective turbulence

How is turbulence caused by convective storms?

Strong updrafts & downdrafts

When are convective currents most active?

Warm summer afternoons & when winds are light

Why will turbulence strength vary within short distances?

Uneven surface heating

What type of clouds indicate convective turbulence?

Billowy cumuliform

What is turbulence produced by shear flow caused by obstructions like trees, buildings, and mountains?

Mechanical turbulence

In mechanical turbulence, what 2 factors do turbulence intensity directly relate to?

1. Wind speed

2. Shape/roughness of obstructions

What is an atmospheric gravity wave formed when stable air flow passes over a mountain/mountain barrier?

Mountain wave

How far could mountain winds extend to downwind of the mountain range?

100 miles or more

What section of the atmosphere can mountain waves extend into?

Stratosphere

What is a change in wind speed and/or wind direction in a short distance resulting in a tearing or sheering effect (can be vertical or horizontal)?

Wind shear

What 3 conditions of wind shear are of special interest?

1. Temperature inversion

2. Frontal zone

3. Clean air turbulence (CAT)

What is a layer within which temperature increases with altitude, which can cause wind shear?

Temperature inversion

What is the interface or transition zone between two air masses of different density?

Frontal zone

Are clouds required for wind shear to be caused by frontal zone?

No

What is a higher altitude (~20,000-50,000ft) turbulence phenomenon occurring in the cloud-free regions associated with wind shear, partially between the core of a jet stream and the surrounding air?

CAT (clear air turbulence)

How can jet stream CAT be best avoided?

Changing altitude by a few thousand feet

What are the 4 turbulence intensity classifications?

1. Light (LGT)

2. Moderate (MOD)

3. Severe (SEV)

4. Extreme (EXTRM)

Which classification causes slight, erratic changes in altitude and/or attitude?

LGT

What turbulence classification may cause passengers to feel a slight strain against their seat belts, slightly displace unsecured objects, & still allow food service to be conducted with little to no difficulty?

LGT

What turbulence classification causes changes in altitude/attitude while the aircraft remains in positive control at all times (usually causes variations in indicated airspeed)?

MOD

Which turbulence classification causes passengers to feel definite strains against their seat belts, dislodges unsecured objects, and makes food service difficult?

MOD

What turbulence classification causes large, abrupt changes in altitude and/or attitude, usually causing large variations in indicated airspeed and momentarily putting the aircraft out of control?

SEV

What turbulence classification causes passengers to be forced violently against their seat belts, tosses out unsecured objects, and makes food service impossible?

SEV

Which turbulence classification violently tosses and practically makes it impossible to control aircraft while potentially causing structural damage?

EXTRM

What is a category of turbulence that causes rapid and somewhat rhythmic bumpiness without appreciable changes in altitude or attitude?

Chop

What turbulence category is chop considered to be?

LGT or MOD

What are the 5 categories that makes an aircraft vary in reaction to turbulence?

1. Windspeed difference in different categories

2. Aircraft size

3. Wing loading

4. Airspeed

5. Aircraft altitude

At what radius are controllers required to advise pilots of hazardous weather?

150nm