The document discusses various weather hazards for aviation. It begins by explaining how weather affects aircraft operation in terms of lift, drag, thrust and weight. It then discusses important observed weather elements for aviation like wind, visibility, clouds and pressure readings. Several dangerous weather systems are also covered such as thunderstorms, turbulence and icing. Specific thunderstorm hazards like severe turbulence, hail and lightning are explained. The document concludes by discussing techniques for flying in thunderstorm conditions and details different types of turbulence hazards.

1. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
ENV 111: Introduction to Meteorology
Lecture 9
Introduction to Aviation Meteorology
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Presentation outline
1 Introduction
Weather and aircraft operation
2 Observed weather elements for aviation
3 Dangerous weather systems to air transport
Thunderstorm weather hazards
Flight techniques in thunderstorm
Weather hazards of turbulence
Weather hazards of Aircraft icing
4 Volcanic Ash Clouds
ndettoel@2016 ENV 111: Introduction to Meteorology

2. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
2/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Weather and aircraft operation
Modern aircrafts exhibit excellent
performance
Still weather affects their operation;
Meteorological observations at
aerodrome are very important in
ensuring that landings and take-offs
are made safely
Wind dictate the runway to be used,
and the maximum take-off and
landing weights
Temperature is also important and
affects engine performance
Figure 2 : Weather and aircraft
operation
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
3/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Weather and aircraft ...
Thrust Weight
Lift Drag
Figure 3 : The forces that affect an aircraft
Weight acts on a single
point (gravity)
Lift
⇒ Aerodynamic force due
to aircraft motion
⇒ Depends on shape, size
and velocity of aircraft
⇒ The wings generates
most of it
⇒ Acts on a single point
(centre of pressure)
ndettoel@2016 ENV 111: Introduction to Meteorology

3. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
4/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Weather and aircraft ...
Drag
⇒ Aerodynamic force opposing aircraft motion
⇒ Depends on the shape of aircraft, stiffness of the air, and velocity of the
aircraft
⇒ It also acts through the aircraft’s centre of pressure
Thrust
⇒ Generated by aircraft’s propulsion system to overcome drag
⇒ Direction of thrust depends on how the engines are attached to the aircraft
⇒ Magnitude depends on the type and number of engines, and throttle setting
So, is the condition of the atmosphere affects the forces
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
5/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Observed weather elements for aviation
Surface wind
⇒ Measurements of airflow and low-level
wind shear in the vicinity of the
landing and take-off areas are of
primary interest
⇒ Air traffic control towers, and
approach control offices are normally
equipped with wind-speed and
wind-direction indicators
⇒ So air traffic controllers supply
arriving and departing aircraft with
wind readings
Figure 4 : A windsock at the
aerodrome
ndettoel@2016 ENV 111: Introduction to Meteorology

4. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
6/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Observed weather ...
Visibility
⇒ First defined for meteorological purposes as a
quantity to be estimated by a human observer
⇒ Meteorological visibility is defined by day or at
night
It is the greatest distance at which a black
object of suitable dimensions (on the ground)
can be seen and recognized when observed
against the horizon sky during daylight or could
be seen and recognized during the night if the
general illumination were raised to the normal
daylight level (WMO, 1992a; 2003)
Figure 5 : Visibility
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
7/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Observed weather ...
Runway visual range (RVR)
⇒ A range over which the pilot of an
aircraft on the centre line of a runway
can see the runway surface markings
or the lights delineating the runway
or identifying its centre line
⇒ Measurements need to be taken
during periods when horizontal
visibility is less than 1500 m
⇒ A height of approximately 5 m is
regarded as corresponding to the
average eye-level of a pilot in an
aircraft on the centre line of a runway
Figure 6 : An aircraft landing
ndettoel@2016 ENV 111: Introduction to Meteorology

5. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
8/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Observed weather ...
Present weather
⇒ Observe and report the onset, cessation,
intensity and location of phenomena of
significance to the safe operation of aircraft
⇒ Example: thunderstorms, freezing rain and
elements that restrict flight visibility
Clouds
⇒ Require: amount, base height, type
⇒ Representative of the aerodrome and its
immediate vicinity
⇒ Required for landing, of the approach area
Figure 7 : Fog inhibiting visibility
on runway
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
9/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Observed weather ...
Air temperature
⇒ it is necessary to know the air temperature over the runway
Dew point temperature
⇒ Atmospheric moisture at aeronautical stations is usually expressed in terms
of the dew-point temperature
Atmospheric pressure for setting aircraft altimeters:
⇒ Pressure value at an elevation corresponding to the official elevation of the
aerodrome, i.e. field elevation pressure (QFE)
⇒ Pressure value at which an aircraft altimeter is set so that it will indicate the
official elevation of the aerodrome when the aircraft is on the ground at that
location, i.e. atmospheric pressure at nautical height (QNH)
ndettoel@2016 ENV 111: Introduction to Meteorology

6. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
10/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Observed weather ...
Any other available information on meteorological conditions in the
approach and climbout areas relating to:
⇒ cumulonimbus or thunderstorms,
⇒ moderate or severe turbulence,
⇒ horizontal and/or vertical wind shear and significant variations in the wind
along the flight path,
⇒ hail, severe line squalls, moderate or severe icing, freezing precipitation,
⇒ marked mountain waves, sandstorms, dust storms, blowing snow or funnel
clouds
Other information may be air pollution e.g. during volcanic eruptions
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
11/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Dangerous weather systems for aviation
Delay hours in the National Airspace System for January 2001 to July 2002
ndettoel@2016 ENV 111: Introduction to Meteorology

7. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
12/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Dangerous weather ...
In US alone, weather is the cause of approximately 70 percent of the
delays in air transport
Weather also plays a significant role in a number of aviation accidents
and incidents
While human error could be the direct accident cause, weather is a
primary contributing factor in many aviation accidents
The total weather impact costs $ billion for accident damage and
injuries, delays, and unexpected operating costs
Read about the aviation accident report at Mwanza airport
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
13/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Thunderstorm weather hazards
Thunderstorms contain many of the most severe weather hazards:
⇒ extreme turbulence,
⇒ lightning,
⇒ microbursts
⇒ severe icing,
⇒ hail and tornadoes
Turbulence is the worst hazard and hail is the second worst
Thunderstorms occur frequently, an encounter is expected
ndettoel@2016 ENV 111: Introduction to Meteorology

8. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
14/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Thunderstorm weather hazards ...
Thunderstorms hazards occur during its mature and dissipating stages
An attempt to takeoff or land with an approaching thunderstorm
nearby could have disastrous results
Figure 8 : Severe turbulence along the gust front
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
15/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Thunderstorm weather hazards ...
Severe turbulence
⇒ Turbulence occurs in all thunderstorms due to updrafts and downdrafts
⇒ Can extend over 5000 feet above the cloud tops and down to the ground
beneath the cloud base
⇒ Can damage an airframe and cause serious injury to passengers and crew
Hail
⇒ As a rule the larger the storm, the more likely it is to produce hail
⇒ Aircrews should anticipate possible hail with any thunderstorm, especially
beneath the anvil of a large thunderstorm
⇒ Hailstones larger than 1/2 to 3/4 of an inch can cause significant aircraft
damage in a few seconds
ndettoel@2016 ENV 111: Introduction to Meteorology

9. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
16/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Thunderstorm weather hazards ...
Lightning and Electrostatic Discharge
⇒ Occurs in all levels of thunderstorms
⇒ Most lightning bolts occur between clouds or within the same cloud
⇒ Lightning strikes can also occur in the anvil of a well-developed or dissipated
thunderstorm
⇒ An electrostatic discharge (ESD) is similar to a lightning strike, but caused
by the aircraft itself
⇒ The larger and faster the aircraft, the more particles it impacts, generating a
greater static electricity charge on the airframe
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
17/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Thunderstorm weather hazards ...
Most lightning strikes occur when
aircraft is in such conditions:
⇒ Within 8 ◦
C of the freezing level
⇒ Within approximately 5000 feet of the
freezing level
⇒ In precipitation, including snow
⇒ In clouds
⇒ In some turbulence
Lightning strikes have varied effects on
aircraft and aircrews
Figure 9 : Lightning Hazards
ndettoel@2016 ENV 111: Introduction to Meteorology

10. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
18/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Flight techniques in the vicinity of thunderstorm
Avoid thunderstorms if at all
possible
⇒ Fly around (circumnavigate) the
storm
⇒ Fly over the top of the storm.
⇒ Fly under the storm
⇒ If it is not possible to avoid the
storm(s), fly through the lower
1/3 of the storm
Urgency or fuel state dictates
whether penetration is required Figure 10 : Flight techniques
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
19/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Flight techniques ...
The lower in the storm the
penetration is made, the less the
chance of encountering severe
hazards
However, with the strong
updrafts and downdrafts,
adequate terrain clearance
should be considered
Once inside the storm during
penetration, attempt not to turn
back
Figure 11 : Penetrating the storm
ndettoel@2016 ENV 111: Introduction to Meteorology

11. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
20/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Weather hazards of turbulence
Turbulence is any irregular or disturbed flow in the atmosphere
producing gusts and/or eddies
Types of turbulence can be divided according to their causative
factors:
⇒ thermal,
⇒ mechanical,
⇒ frontal,
⇒ large-scale wind shear
Any of the four types of turbulence may occur without the visual
warning associated with clouds
Turbulence in the absence of or outside of clouds is referred to as clear
air turbulence (CAT)
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
21/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Weather hazards of turbulence ...
Clear Air Turbulence
⇒ Normally occurs outside of clouds in jet streams due to strong wind shears
Thermal Turbulence
⇒ Localized vertical convective currents resulting from surface heating or cold
air moving over warmer ground
Figure 12 : Varying strength of thermal currents due to surface
ndettoel@2016 ENV 111: Introduction to Meteorology

12. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
22/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Weather hazards of turbulence ...
Mountain Wave Turbulence
⇒ Due to strong winds blowing
approximately perpendicular to a
mountain range
⇒ Dangerous in the vicinity of the rotor
clouds and to the leeward side
⇒ Avoid the turbulence, if possible; fly
at a level at least 50 % higher than
the height of the mountain range
⇒ Avoid the rotor, lenticular, and the
cap clouds
Figure 13 : Mountain wave turbulence
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
23/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Weather hazards of turbulence ...
Frontal Turbulence
⇒ Due to lifting of warm air, a frontal
surface leading to instability
⇒ Or due to abrupt wind shift between
the warm and cold air masses
⇒ Most severe cases are associated with
fast-moving cold fronts
Wind Shear Turbulence
⇒ Eddy currents produced by a
relatively steep gradient in wind
speed or direction
⇒ Most in the vicinity of jet streams Figure 14 : Mountain wave turbulence
ndettoel@2016 ENV 111: Introduction to Meteorology

13. .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
24/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Weather hazards of Aircraft icing
Two types of aircraft icing:
⇒ Structural icing: ice forming on the
external structure of an aircraft
⇒ Engine icing: ice forms on the
induction or compressor sections of
an engine, reducing its performance
Most hazardous aspect of structural
icing is its aerodynamic effects
To avoid icing hazard:
⇒ climb to the colder temperatures
where the precipitation will be frozen
⇒ descend to an altitude where the air
temperatures are well above freezing
Figure 15 : Cumulative effects of icing
ndettoel@2016 ENV 111: Introduction to Meteorology
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
25/ 25
Introduction Observed weather Dangerous weather Volcanic Ash Clouds
Volcanic Ash Clouds
Volcanic eruptions are rare, but the ash clouds have severe effect on
an aircraft
Aircraft flying through volcanic ash clouds have experienced a
significant loss of engine thrust and/or multiple engine flameouts
along with wing leading edges and wind-shields being sandblasted
Avoid flight into an area of known volcanic activity may occur
without the visual warning associated with clouds
Volcanic ash clouds are not displayed on airborne or Air Traffic
Control (ATC) radar, as the radar reflectivity of volcanic ash is
roughly a million times less than that of a cumuliform cloud
ndettoel@2016 ENV 111: Introduction to Meteorology