V. Answer the questions using the underlined words in your answers.

1. Why is weather forecasting of crucial importance for flight?

2. What weather conditions are marginal and adverse?

3. Why is jet stream of great advantage for the flight?

4. What can deteriorate visibility?

5. What can impair flying characteristics of the aircraft?

6. Does decision as for clearing the landing in thick fog rest with an ATC?

7. What precipitation poses risk for take off?

8. Which type of the plane’s skin can resist hail strike?

9. Where can turbulence be encountered?

10. What can lead to skidding off the RW or sliding of the RW?

11. Due to what reasons can airport come into standstill?

12. What does crew take into account if they see bolt of lightning ahead of them?

 

VI. Answer the following questions.

1. How significant is the weather for flight?

2. What types of weather forecasts exist? What do they involve?

3. What can cause airport coming to the standstill?

4. How does wind affect the aircraft?

5. What is wind shear? Why and when can it be hazardous?

6. What actions should be carried out by the crew if they encountered wind shear?

7. How can controller assist the crew in this situation?

8. What is jet stream? How can it be of advantage for the air companies?

9. What kind of danger can CB activity cause?

10. What can lightning strike to the plane lead to?

11. What is turbulence? Why does it appear? What threat can it pose?

12. What is CAT? Can it be forecasted?

13. What phenomenon do we call icing?

14. In what way can it negatively affect the aircraft?

15. How is it possible to prevent icing in the air and on the ground?

16. What can decrease visibility?

17. What should the pilots take into account while landing in poor visibility?

18. What hazards can volcano eruption pose to the aircraft?

 

VII. Read the text and discuss it.

WEATHER

Weather is of paramount importance for aviation. It influences every flight greatly because there is direct connection between weather and safety of flight. Marginal weather may cause postponing or canceling the flight, diversion to another airport, circumnavigation of areas with bad weather conditions, losing orientation in unfamiliar airport. Rough weather may also lead to communication problems because of noise static and poor readability. That’s why before each flight the pilots receive meteorological information for the airport of departure, for the airport of destination and on the route.

For example, wind greatly affects the flight. A headwind will obviously suspend the arrival of flights and is to be avoided on the route if it is possible but it is of an advantage while landing and take off as it increases lift and reduces landing distance. A tailwind on the other hand, can be of great advantage on the route as it increases the ground speed and results in a reduction of fuel consumption. Severe cross wind can pose great risk while landing as the plane may slide off or skid of the RW. That’s why wind direction and strength are taken into account before planning the flight.

The most hazardous weather phenomena are:

· CB clouds

· Lightning

· Hail

· Wind shear

· Severe turbulence

· Icing

· Fog

· Shower rain

· Snow rain

· Squall

· Blizzard

· Drizzle

· Volcanic ash

 

  CB clouds create the greatest threat for the safety of the flight due to ascending and descending air flows, as a result severe turbulence. Their tops can reach 10 000-12 000 meters. These areas can pose another risk - lightning and hail and another severe precipitation. 

Lightning strike can cause

- electrical system failure on the aircraft

- communication failure

- ignition and malfunction of any another system that in its turn can result in loss of control

- may blind the pilot

Hail can also damage the fuselage skin or windshield that can lead to depressurization or any other unforeseen consequences. But the most significant influence on the plane have air currents within CB clouds area, they can easily disable the aircraft by throwing it up and down. Lost the speed and been unable to be supported in the air the plane will sure to plunge down.

That’s why it is strictly prohibited to enter CB clouds areas. It is allowed to circumnavigate them under the cloud base if the aircraft can maintain altitude not less than 200 meters above the ground and not less than 600 meters above mountainous area while vertical separation between the plane and the cloud base has to be also 200meters. The distance between clouds top and the aircraft has to be not less than 500 meters. Thunderstorms cells have to be avoided with the distance of 15 kilometers.

 

Wind shear is a rapid change of wind speed or direction over a short distance horizontally or vertically. It can occur at any height, but is far more dangerous when encountered close to the ground as it can result in loss of controllability of the aircraft because during approach phase the plane reduces its speed and becomes more vulnerable to the influence of outside factors. Encountered in the air it can lead to stall, overshooting or touching down before landing zone.

Wind shears are usually common due to thunderstorms (they appear under thunderstorms cells because of downdrafts and updrafts) or jet streams.

As wind shear is a rapid change of wind so it is rather complicated to foresee it for meteorologists. In the majority of cases the ATCs and meteor centers obtain report about wind shear from the previous plane. Sophisticated aircraft are equipped with wind shear alerting system which warns the crew about the danger with a woman’s voice.

 

  Microburst is a localized hazardous wind shear condition. It is a narrow downdraft of very high speed wind. When the downdraft approaches the surface of the ground, the wind flows outward from the core in all directions. Encountering microburst the aircraft will pitch up and climb and then rapidly pitch down and descend. These conditions can exceed the performance capability of some aircraft. For this reason it is imperative to avoid microburst.

 

Turbulence is a situation when the smooth flow of air is disturbed by something in its path on the ground or by rising or descending air. It affects the plane so the abrupt jolts and bumps of the fuselage are felt. Turbulence can occur in mountainous area, while entering the clouds, in the zone of atmospheric fronts, in the zones of jet streams or due to air friction close to the ground because of differences in surface and air temperatures.

Turbulence can be light, moderate and severe. In severe turbulence an aircraft is tossed greatly: it can lose or gain altitude and attitude, experience structural damages and sometimes become out of control.

It’s recommended for the pilots to avoid the turbulence by changing the altitudes and it is forbidden to land under severe turbulence.

 

Clear Air Turbulence (CAT) is the turbulent movement of air masses in the absence of any visual cues such as clouds. It is impossible to note CAT with a naked eye because it is invisible and it is very complicated to identify it with conventional radar. The most susceptible altitudes for CAT are between 7000 and 12000 meters, in the regions where jet streams pass. At lower altitudes it may also occur near mountain ranges. Thin cirrus cloud can also indicate high probability of CAT.

 

  Jet stream is a fast flowing air current moving from west to east in the upper portion of the troposphere. The main jet streams are located near the tropopause, the transition between the troposphere (where temperature decreases with altitude) and the stratosphere (where temperature increases with altitude).

Jet streams may be of great advantage for aviation. Commercial use of the jet stream started in 1952, when Pan Am flew from Tokyo to Honolulu. It cut the trip time by over one-third, from 18 to 11.5 hours. It also saved the fuel.

 

 Icing is build up of ice on the surfaces of aircraft which increases the weight of the plane, makes it difficult to climb and maintain altitudes and can lead to dangerous and even fatal results:

 -increased weight of the plane can cause worsening of aerodynamic characteristics of the plane

- frozen contaminants cause critical control surfaces to be rough and greatly degrading the ability of the wing to generate lift and increasing drag

- movable controls may be jammed

- engines propellers may be crippled and cause unbalanced vibration (due to injection of ice)

- engine stoppage (due to icing up of carburetor, cowling and intakes)

- flame outs may take place

- appearing of ice on internal or external windscreen can impair visibility

- sometimes landing gear extending may be affected

- antennas can vibrate so severely that can easily break

- different sensors can be covered with ice and transfer incorrect data to the cockpit

- excessive fuel consumption

 The combination of all these factors can lead to stall and even crash of the aircraft.

 In order to prevent icing de-icing procedure takes place on the ground. De-icing is a procedure that can be accomplished by mechanical methods (scraping, pushing); with the application of heat; by spraying the plane with liquid chemicals designed to lower the freezing point of water; or by a combination of these different techniques.

Anti-icing system is used in the flight. Leading edges of the wing, windscreen, engine clawing are heated to prevent built up of ice while flying in extremely low temperatures.

  Fog is a phenomenon caused by water droplets suspended in the air that decreases visibility. Fog is dangerous when the aircraft approaches to landing as it reduces visibility and aircraft flying in VFR will experience hazardous situations when there is no visual contact with the ground.

Reduced visibility because of fog may result in:

- restrictions on movements in an airport, reduced capacity (because of procedural increased separation between aircraft take-offs and landings in order to maintain safety)

- RW incursion

- disorientation (especially in unfamiliar airport) that in its turn can cause near collision

Thick fog creates obvious hazards for landing. Nowadays the responsibility rests with the pilots- they decide themselves to perform landing or not, taking into account airport category, aircraft minima, and crew minima.

There are three airport categories:

1. ILS CATEGORY I - An ILS approach procedure which allows to perform landing with decision height not lower than 60m and a visibility not less than 800m or a runway visual range not less than 550m.

2. ILS CATEGORY II (Special authorization required) - An ILS approach procedure which provides for an approach to a decision height lower than 60m but not lower than 30m and a runway visual range not less than 350m.

3. ILS CATEGORY III (Special authorization required) -

a. IIIA - an ILS approach procedure which provides for approach with either a decision height lower than 30m or with no decision height and with a runway visual range of not less than 200m.

b. IIIB - an ILS approach procedure which provides for approach with either a decision height lower than 15m or with no decision height and with a runway visual range of less than 200m but not less than 50m.

c. IIIC - An ILS approach procedure which provides for approach with no decision height and no runway visual range limitations.

   Landing is the most complicated phase of flight, that’s why a great attention is paid to RW condition. It may be: dry, wet and dump, with water patches, flooded, slippery, covered with slush, covered with rime or frost/ ice, covered with compacted snow, covered with ruts and ridges

 

Volcano eruption

Erupted volcanic ash reaches high altitudes and easily is spread by winds. It can cause significant threat for aircraft over a large territory of the planet.

Volcanic pieces (rock particles) get into the engine, melt as there is temperature more than 1000 C, stick to the blades and compressor and result in engine flame out or cutting off or fooling of the engines temperature sensors. Volcanic ash is charged so it will negatively affect communication. Air speed indicators will be clogged and will fail to operate. Safety of the aircraft flying through volcanic ash cloud is endangered as volcanic parts floating in the air reduce visibility, can cause damage of the fuselage, lights and movable surfaces.