L12 Flight Over Mountainous Areas and Other Weather Hazards

Flashcards about flight over mountainous areas and weather hazards.

How do mountainous areas influence weather?

Localized conditions and altered weather patterns.

What is the effect of rising ground on air?

Rising ground forces air to rise, potentially leading to precipitation.

What is 'controlled flight into terrain' (CFIT)?

Pilots flying into the ground due to reduced visibility and icing.

How do mountains and valleys influence airflow?

Deflecting airflow and funnelling the wind.

Name two well-known winds influenced by valleys in Europe.

Mistral (Rhone valley) and Tramontane (Spanish/French Mediterranean coast).

What is the difference between katabatic and anabatic winds?

Katabatic winds flow down, anabatic winds flow up valley slopes.

What can katabatic winds cause in valleys?

Temperature inversion and radiation fog.

What effect do temperature inversions have on aircraft performance?

Decrease in air density and reduction in aircraft performance.

What are the disturbances created by wind blowing over a mountain range called?

Mountain waves, standing waves, or lee waves.

How do gliders use mountain waves?

Gliders use the upward movement to reach great heights.

What is a potential hazard when mountain waves turn downward?

Aircraft being forced to descend, even at full power.

What wind conditions are favorable for mountain wave formation?

Wind of 15 kts or more blowing at right angles to a ridge.

What air stability conditions favor mountain wave formation?

A layer of stable air just above the ridge, bounded by less stable air.

What effect can downdraughts on the lee side of high ground have?

They can defeat the best rate-of-climb of a light aircraft.

What might conflict an aircraft's rate of climb or descent with the power setting and attitude?

A mountain wave.

What type of cloud is often associated with mountain waves?

Lenticular.

Describe the appearance of lenticular clouds.

Smooth and elongated, almond-shaped.

How does a lenticular cloud remain stationary at the crest of a mountain wave?

The cloud forms at the leading edge and dissipates at the trailing edge.

Name two people associated with air flowing over high ground.

Daniel Bernoulli and Giovanni Venturi.

What does Bernoulli's principle state about air flow?

Increase in speed and decrease in pressure occur simultaneously.

What is a venturi?

A small tube through which air is forced, increasing speed and reducing pressure.

What is the altimeter error that can occur when flying across high ground?

Topographical Altimetry Error.

What is another effect associated with flying over high ground?

Increase in wind speed as air rushes through a narrower gap.

What will be found in the 'rotor' downwind of high ground?

Severe turbulence.

What is a 'roll' cloud?

A ragged cumulus that forms in the rotor zone.

What indicates the violent turbulence in a roll cloud?

It is rolling around its horizontal axis.

How strong is the turbulence in the first rotor downwind of a ridge?

Strong enough to destroy a powered aircraft.

What is the rule of thumb for safe terrain clearance altitude?

Double the elevation of the high ground.

What flight path can leave an aircraft in wave conditions for a longer time?

Flight across high ground at an angle or parallel to a ridge.

What happens when a thunderstorm occurs over high ground?

A particularly dangerous combination.

What type of icing is caused by orographic lifting?

More severe icing.

What is another way of writing Foehn with 2 dots above the vowel 'o'?

Föhn or Fohn.

What are the effects of the Föhn effect?

Higher cloud base, higher temperatures, and less precipitation on the downwind side.

What conditions usually develop with Föhn effect?

Stability and widespread air blown against a mountain ridge.

What rates are demonstrated in the Föhn effect?

Saturated and dry adiabatic lapse rates (SALR & DALR).

What is the dry adiabatic lapse rate (DALR)?

3°C per 1000 ft.

What is the saturated adiabatic lapse rate (SALR)?

1.5°C per 1000 ft.

What type of clouds does a Föhn system produce?

Cumulus cloud and rain on the windward side, Nimbostratus cloud and rotor clouds on the leeward side.

What are widespread strong winds associated with?

Steep pressure gradient.

What is the advice to pilots regarding strong winds?

Not to taxy, take-off, or land if the surface wind speed is more than 50% of the aircraft's stalling speed.

What surface winds demand extreme caution for most light aircraft?

Surface winds in excess of about 25 kts.

What crosswind limits do most light aircraft have?

Lower 'demonstrated' cross wind limits.

What type of 'lows' are the strongest gales usually associated with?

Deepening rapidly.

At what rate does the pressure at the center of a low deepen and cause strong winds?

More than one mb/hPa per hour for more than twelve hours.

Where do extreme lows usually reach their maximum intensity as far as Europe is concerned?

Over the ocean.

What atmospheric conditions can produce mountain waves?

Stable atmospheric conditions.

What can mountain waves cause?

Structural damage or a stall

What intensifies mountain side updrafts on the windward side?

Vertical thermal currents.

What is turbulence?

Any disturbance of the air flow causing eddies and variations.

When does turbulence become a problem?

When it affects the handling of the aircraft and/or causes discomfort.

What are the two principal causes of low-level turbulence?

Convective (thermal) and frictional (mechanical).

When is convective turbulence at its worst?

Light winds when surface heating is strongest.

What type of rising convection currents may be topped by cumulus clouds?

Thermals.

When is mechanical turbulence most marked?

Strong wind conditions involving irregular terrain.

What is a good way to reach smoother air?

Increasing altitude

What will the aircraft's POH/FM state if turbulence warrants it?

Recommended turbulence or 'rough air' speed (Va).

What should be maintained during slight and temporary fluctuations in airspeed?

Correct attitude and power setting.

How much should you increase approach speed in turbulent conditions?

5-10 kts

What are aircraft subject to the low-level effects of around during the final approach to land or just after take-off.

Buildings, trees, or local terrain.

What is windshear?

Change of wind velocity over a distance.

When does windshear become a significant hazard to aircraft?

When the change in wind velocity is very marked within a small height band.

What happens to an aircraft transitions fro a 20 kts headwind to a 10 kts tailwind over a 100 ft height band?

30 kts loss of airspeed and a loss of lift.

When is an aircraft more vulnerable to windshear?

The heavier the aircraft and the greater its momentum.

What is the golden rule where windshear is suspected or known to exist?

Avoidance.

What factor will give some element of protection from windshear?

Approaching at a slightly higher than normal airspeed.

What decision must you be prepared to make as a result of windshear symptoms?

Early decision to go-around.

When can strong windshear sometimes develop?

Marked temperature inversion near the surface.

What is the result of temperature inversion?

To separate the friction layer from the general airflow.

How low can a low-level windshear zone be?

A few hundred feet above the surface.

What is aircraft performance affected by?

Reduced by a temperature inversion

What triggers Thunderstorms triggered across high ground?

Orographic Lift.

What makes a hazardous combination when coupled with mountains?

High Winds.

What is the 'Föhn' effect causing?

The drier and warmer condition on the leeward side of a range of hills.

What occurs in the 'rotor' that can form downwind of the high ground beneath the crest of the waves?

Severe Turbulence.

What weather occurrence should be associated with Steep Pressure Gradient?

Widespread Strong Winds

What significant weather issues can be expected at their local airfield when the wind blows from a certain direction?

Turbulence and Windshear.

What geographic feature influences the general airflow by deflecting it's direction.

Mountains and Valleys.

What cloud has a hard center, and is a risk of Controlled Flight Into Terrain?

Cumulus Granitus.

What angle does a wind need to be blowing to a ridge to form mountain waves?

At Right Angles.

What effect is caused by air rushing through a narrower vertical gap above a mountain?

Venturi Effect.

What is a disturbance of the air flow causing eddies and variations?

Turbulence.

What is the change of wind velocity over a distance?

Windshear.

What is the causation of Mountains and Air Flow relationship?

Mountains cause the air flow to undulate, like waves in the ocean

What common weather condition leads to strong Windhsyear?

A Marked Temperature Inversion.

What are alternate spelling of the technical word for wind, Foehn?

The word Foehn is sometimes written as Fohn with 2 dots above the vowel 'o', an umlaut, Föhn.

Is better to maintain the correct attitude and power setting than to chase airspeed when dealing with what weather condition?

Turbulence

Airspeed my fluctuate, and attempts to 'chase' the speed may make matters worse in which type of weather condition?

Turbulence

Approaching at a slightly higher than normal airspeed will give some element of protection during which weather condition?

Low-level windshear

Similar to mountains and strong winds making a hazardous combination, what other factor increases danger?

Mountains and low cloud are dangerous

Convective turbulence is at its worst in light winds when surface heating is strongest, and over which geographical locations?

areas such as cities, towns, or factories generating a lot of heat

Besides extreme examples, such as that encountered in and around thunderstorms and rotors, what other condition is a principal cause of low-level issue?

Turbulence

For practical purposes, this weather condition only becomes a problem when it affects the handling of the aircraft and/or causes discomfort to the aircraft's occupants

Turbulence

The real danger of what weather condition is the dramatic and rapid effect it can have on an aircraft's airspeed?

Windshear

Windshear in association with thunderstorms and what other factor has already been discussed in the lecture notes?

strong winds

Pilots may expect what weather condition and windshear at their local airfield when the wind blows from a certain direction?

turbulence

n turbulence the airspeed may fluctuate, and attempts to 'chase' the speed may make matters worse, what weather condition?

Turbulence

A slight (5-10 kts) increase in approach speed is a worthwhile precaution if approaching to land in what type of conditions?

turbulent conditions

Strong windshear can sometimes also develop when there is a marked temperature where near the surface?

Inversion Layer

What is the strongest factor in wind?

Widespread strong winds are associated with a steep pressure gradient

What effect does TRAMONTANE have on Spain?

Airflow being 'funnelled' through a valley