METEOROLOGY
1. What is a microburst and what do you do about it?
A Microburst is a small, localised downburst within a total horizontal
distance of 4 Km. The complete life-cycle is around 6 minutes.
Be cautious of a high dewpoint/temperature spread. This means that
the air near the ground has a high potential for water evaporation. Rain
falling into the dry air will evaporate, either partially in the case of a
visible storm or completely in the case of a dry microburst. This will
further cool the air and accelerate its descent.
If windshear is encountered apply power to NTOP and maintain best
gradient airspeed to maintain the flightpath.
If preventative action proves unsuccessful and flight path control
becomes marginal due to windshear during take-off or approach,
conduct the Terrain Avoidance Procedure as follows;
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Disengage the autopilot.
Power to MTOP.
Pitch attitude 15 degrees or stick shaker, whichever comes first.
Maintain the configuration.
(If the descent cannot be arrested, the power levers should be
positioned aggressively fully forward and the pitch attitude increased
up to stick shaker activation.)
2. Explain windshear in a microburst.
As the descending air from the microburst strikes the ground, it
spreads out in all directions and forms a gust front. An aircraft that
enters this gust front may first experience an increasing airspeed that
is then followed by a rapidly decreasing airspeed with the associated
control problems.
3. What is ISA (ICAO standard atmosphere)
15 degrees C and 1013.2 Hpa at sea level. Decrease in temperature of
2 degrees C / thousand feet until the tropo-pause at 36000 feet is
reached at –57 degrees C.
4. What is CAT?
CAT is Clear Air Turbulence. It is often associated with jetstreams
and is usually strongest on the lower, poleward side of the jetstream.
5. What is Windshear and what do you do about it?
See question 1.
6. What happens to wind direction as you climb?
The wind backs and increases in speed. A “backing wind” means that
the wind direction in degrees is decreasing (below approx’ 3000 feet).
7. How many feet are there in a hectopascal?
At sea level, 30.
8. How is windshear detected? Where do you find windshear?
LLWAS. The Low Level Windshear Alert System uses a centrefield
wind sensor and several surrounding wind sensors to detect
windshear.
Aircraft can also be fitted with systems that use information from
angle of attack, airspeed and acceleration sensors to compare an
aircraft’s actual performance with what it should be under the existing
circumstances. This system can then provide flight director commands
for a successful escape.
9. Where do you find microbursts?
In the area of thunderstorms.
10. If you are at 33,000 feet, OAT is –45, What is ISA deviation?
ISA plus 6 degrees.
11. What is a Typhoon?
A cyclonic system with a windspeed greater than gale force (34 kts).
12. How does a tropical cyclone form?
Tropical cyclones usually move westward and slightly polewards after
they first form.
In the Northern Hemisphere the cyclone season runs from June to
November with the peak in August to October.
The mean sea temperature usually exceeds 28 degrees C over a wide
area.
Tropical cyclones are rare within 5 degrees of the equator.
A deep low pressure area creates a strong pressure gradient that is
balanced by the Coriolis force at the appropriate latitude. This results
in Cyclonic flow with a very high windspeed.
Tropical cyclones last for an average of six days before they traverse
land or enter sub-tropical latitudes. Some last only two days; others
two weeks. Four stages of the complete life cycle can be described,
but the development may be terminated during any of the stages if
conditions are not favourable.
(a). Formative stage. Tropical cyclones form only in pre-existing
disturbances. Deepening to a pressure below 1000 Hpa may take days
or only a few hours. Winds reach gale force (34 knots), usually only in
one quadrant, and the eye forms.
(b). Immature stage. This is reached when the central pressure falls
below about 1000 Hpa. Winds reach hurricane force and spiral bands
are formed. The area affected is small and the hurricane force winds
(64 kts) may only blow within a 20 to 30 nm radius. The surface
pressure at the centre continues to fall. The cyclone may die within 24
hrs of this stage.
(c). Mature stage. The surface pressure no longer falls but the area of
the storm expands, with hurricane winds extending to as far as 100
nautical miles from the centre. The bad weather is further to the left
than to the right of the direction of motion, and is likely to be worst in
the left forward quadrant in the Southern hemisphere.
(d). Decaying stage. Here the surface pressure rises and the area
affected contracts. In many cases it slowly dissipates over land,
possibly as a rain depression, or more commonly passes to the higher
latitudes, and becomes an extra-tropical cyclone, frequently of
considerable intensity.
13. Why don’t tropical cyclones form near the equator?
Tropical cyclones develop in most tropical oceans at latitudes usually
greater than 5 to 15 degrees North or South of the equator. They don’t
form near the equator because of the lack of coriolis force. i.e. air
flows directly between high and low pressure areas.
14. Which way do tropical cyclones rotate?
Clockwise in the Southern hemisphere and Anti-clockwise in the
Northern hemisphere.
15. Why do tropical cyclones require large amounts of water?
A tropical cyclone derives its energy from the heat stored in the
tropical waters, and the latent heat released during the condensation of
water vapour in the moist tropical atmosphere. Because of the
convergence associated with the low pressure area, rising air
condenses and releases heat. This causes the air to rise faster and
therefore lowers the air pressure further.
There is a large amount of heat stored in tropical water and this latent
heat is released during condensation and cloud formation. As the
tropical cyclone moves over land, the source of moisture is removed
and the ground friction slows the windspeed. This leads to a steadily
decreasing intensity.
16. How do Thunderstorms form?
For a thunderstorm to form, there must be a considerable depth of
unstable air, abundant moisture (dew point greater than 12 degrees C)
and a lifting mechanism.
There are three types of thunderstorm, air-mass, steady state and
severe.
Air mass storms form within a moist, unstable air mass by the action
of heat and convergence, orographic effects or cold stream effects.
Steady state storms are more violent and develop when there is a large
change in wind direction with height. These steady state storms can
become severe if there is sufficient moisture and instability present.
17. What is the meaning of Tempo in an ICAO forecast?
Tempo is used to indicate change in prevailing conditions expected to
last for a period of less than one hour in each instance.
18. If the TAT is –30 C and the adiabatic temperature rise is 10 C,
what would be the SAT?
-40.
19. What does the sequence R28 11V16 in a METAR decode as?
The RVR on runway 28 is variable between 1100 and 1600 meters.
20. In an ICAO TAF forecast, what does the term RAPID mean?
A change in conditions taking place in less than 30 minutes.
21. In an ICAO forecast, what does PROB 10 mean
10 percent probability of the event occurring.
22. Where are lightning strikes most likely to occur?
There are two environments where the risk of lightning strike is the
greatest. The first is at high altitude, in and around thunderstorms
(including the anvil), with an ambient temperature of –40 degrees C or
colder, and with a fairly low level of lightning activity in the storm.
The second environment is near the freezing level (+ or – 5 degrees
C), in clouds with some precipitation and with little or no turbulence.