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ATPL Meteorology (050) study materials
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ATPL Meteorology (050) practice questions

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Question 1The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

In the ICAO Standard Atmosphere, what are the sea-level pressure and temperature values used as the reference datum?

  1. 1013.25 hPa and 15 °C Correct answer.
  2. 1000 hPa and 15 °C
  3. 1013.25 hPa and 0 °C
  4. 1000 hPa and 0 °C

Explanation

The ICAO Standard Atmosphere fixes mean sea level at 1013.25 hPa and 15 °C, with a standard lapse rate of 1.98 °C per 1000 ft in the lower layer. These values define the pressure altitude and ISA deviation conventions used throughout aviation.

Question 2The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

Approximately what proportion of the atmosphere's total mass lies within the troposphere?

  1. About one half
  2. About three quarters Correct answer.
  3. About one quarter
  4. About one tenth

Explanation

Because density decreases rapidly with height, roughly 75 % of atmospheric mass is contained in the troposphere, the layer below the tropopause. The remaining quarter is spread through the much thinner stratosphere and above.

Question 3The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

Which gas is the most abundant constituent of dry air by volume?

  1. Nitrogen Correct answer.
  2. Carbon dioxide
  3. Oxygen
  4. Argon

Explanation

Dry air is about 78 % nitrogen and 21 % oxygen by volume, with argon near 0.93 % and carbon dioxide around 0.04 %. Nitrogen therefore dominates the composition, although oxygen is the gas most relevant to combustion and physiology.

Question 4The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

At approximately what height does the tropopause lie in the ISA at mid-latitudes?

  1. 5 km
  2. 20 km
  3. 50 km
  4. 11 km Correct answer.

Explanation

In the ICAO Standard Atmosphere the tropopause is placed at 11 km (about 36 000 ft), where the temperature reaches −56.5 °C. Above this level the model assumes an isothermal stratosphere up to 20 km.

Question 5The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

Which statement describes the vertical variation of atmospheric pressure correctly?

  1. Pressure falls by a constant amount per unit height at all levels
  2. Pressure rises with height in the troposphere and falls in the stratosphere
  3. Pressure is constant within the troposphere and changes only above the tropopause
  4. Pressure falls most rapidly near the surface and more slowly aloft Correct answer.

Explanation

Pressure decreases approximately exponentially with height, so the change per unit height is greatest at low levels where air density is highest. Near the surface roughly 1 hPa is lost per 27 ft, while at 40 000 ft about 1 hPa corresponds to 100 ft.

Question 6The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

An aircraft's altimeter, set to 1013 hPa, indicates 5000 ft. If the true mean sea-level pressure is 1013 hPa, what does this indication represent?

  1. Radio altitude above the terrain
  2. True altitude above mean sea level
  3. Pressure altitude Correct answer.
  4. Density altitude

Explanation

With the subscale set to 1013.25 hPa, the altimeter displays pressure altitude, the height above the standard pressure datum. It equals true altitude only when the actual pressure and temperature profile matches the standard atmosphere.

Question 7The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

What is the standard atmosphere temperature lapse rate in the troposphere?

  1. 3 °C per 1000 ft
  2. 2 °C per 1000 ft
  3. 1.98 °C per 1000 ft Correct answer.
  4. 0.65 °C per 100 m

Explanation

The ISA tropospheric lapse rate is 1.98 °C per 1000 ft, often rounded to 2 °C per 1000 ft, giving 6.5 °C per km. This rate applies only up to the tropopause, above which the model is isothermal.

Question 8The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

Which atmospheric layer contains the ozone layer that absorbs most solar ultraviolet radiation?

  1. Thermosphere
  2. Mesosphere
  3. Stratosphere Correct answer.
  4. Troposphere

Explanation

The ozone layer is concentrated in the stratosphere, mainly between about 15 and 35 km, where ozone absorbs ultraviolet radiation. This absorption warms the stratosphere and produces the temperature inversion that stabilises the layer.

Question 9The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

What does the term QNE refer to in altimetry?

  1. The pressure at the transition level
  2. The altimeter reading when the subscale is set to 1013.25 hPa Correct answer.
  3. The regional pressure setting used to give true altitude at the aerodrome
  4. The pressure setting that gives height above the aerodrome

Explanation

QNE is the indication on the altimeter when the pressure subscale is set to the standard 1013.25 hPa, producing pressure altitude. It is used above the transition altitude so that all aircraft share a common datum.

Question 10The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

An aircraft flies at a constant indicated altitude from a region of high pressure into a region of low pressure without changing the subscale setting. What happens to its true altitude?

  1. It increases
  2. It remains unchanged
  3. It increases only above the tropopause
  4. It decreases Correct answer.

Explanation

Moving toward lower pressure, the aircraft is at a level where the true pressure is lower than the subscale setting assumes, so the true altitude is lower than indicated. This is the basis of the rule 'high to low, look out below'.

Question 11The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

What is the primary reason temperature decreases with height in the troposphere?

  1. Expansion and cooling of air rising from the heated surface Correct answer.
  2. Cooling caused by decreasing gravitational acceleration with height
  3. Loss of heat by radiation from the tropopause
  4. Absorption of ultraviolet radiation by ozone

Explanation

The troposphere is heated mainly from below by the Earth's surface, so rising air expands into lower pressure and cools adiabatically. This, together with radiative and convective processes, produces the observed lapse rate.

Question 12The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

Which statement correctly describes the tropopause in the ISA?

  1. It is the level of maximum ozone concentration
  2. It is defined by a fixed pressure of 500 hPa
  3. It is a level where temperature begins to increase sharply with height
  4. It marks the base of the stratosphere, above which temperature is constant in the ISA Correct answer.

Explanation

The tropopause is the boundary between troposphere and stratosphere; in the ISA the temperature stops decreasing there and remains constant up to 20 km. In the real atmosphere the tropopause is identified by a marked change in lapse rate, often an inversion.

Question 13The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

In the ISA, what is the temperature at 20 000 ft pressure altitude?

  1. About −45 °C
  2. About −35 °C
  3. About −25 °C Correct answer.
  4. About −57 °C

Explanation

Starting from 15 °C at sea level and applying about 2 °C per 1000 ft gives a reduction of roughly 40 °C at 20 000 ft, so the ISA temperature is about −25 °C. This value is used to compute ISA deviation for performance calculations.

Question 14The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

An aircraft at 10 000 ft pressure altitude reports an outside air temperature of −10 °C. What is the ISA deviation?

  1. +5 °C Correct answer.
  2. 0 °C
  3. −5 °C
  4. −10 °C

Explanation

The ISA temperature at 10 000 ft is 15 °C minus 20 °C, i.e. −5 °C. With an actual temperature of −10 °C the deviation is −10 − (−5) = −5 °C, so the air is 5 °C colder than standard.

Question 15The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

Which statement about atmospheric composition and its vertical variation is correct?

  1. Water vapour concentration increases steadily up to the tropopause
  2. Ozone concentration is highest near the surface and falls with height
  3. Water vapour is concentrated in the lower troposphere and decreases rapidly with height Correct answer.
  4. The proportion of nitrogen is greatest in the stratosphere

Explanation

Water vapour enters the atmosphere mainly by evaporation from the surface, so its concentration is highest in the lower troposphere and falls sharply with height. This is why humidity is negligible in the stratosphere and why most weather occurs near the surface.

Question 16The Atmosphere: composition, vertical structure, standard atmosphere, ICAO pressure/altitude relationships

What is the significance of the 500 hPa surface in aviation meteorology?

  1. It is the pressure at the tropopause
  2. It is the standard pressure level used to analyse upper-air flow and is near 18 000 ft Correct answer.
  3. It is the level at which altimeters are set to 1013 hPa
  4. It marks the top of the mesosphere

Explanation

The 500 hPa surface lies at roughly 18 000 ft in the standard atmosphere and is a standard chart level for upper winds and temperatures. Analysing flow at this level helps identify troughs and ridges that steer surface weather.

Question 17Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

In the standard atmosphere, the mean lapse rate of temperature in the troposphere is approximately:

  1. 10.0 °C per 1000 m
  2. 6.5 °C per 1000 m Correct answer.
  3. 0.65 °C per 1000 m
  4. 2.0 °C per 1000 m

Explanation

The ICAO standard atmosphere assumes a mean tropospheric lapse rate of about 6.5 °C per 1000 m of height, equivalent to roughly 2 °C per 1000 ft. This is the figure used for standard atmosphere computations and altimetry.

Question 18Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

A rising unsaturated air parcel cools at the dry adiabatic lapse rate, which is approximately:

  1. 6 °C per 1000 ft
  2. 0.5 °C per 1000 ft
  3. 3 °C per 1000 ft Correct answer.
  4. 1.5 °C per 1000 ft

Explanation

The dry adiabatic lapse rate is about 9.8 °C per 1000 m, which converts to roughly 3 °C per 1000 ft. It applies to unsaturated parcels and is independent of the surrounding air temperature.

Question 19Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

A temperature inversion in the lower troposphere is best described as a layer in which:

  1. temperature increases with increasing height Correct answer.
  2. the dewpoint increases with increasing height
  3. temperature remains constant with height
  4. temperature decreases more rapidly than the standard rate

Explanation

An inversion is defined by a positive lapse rate of temperature, meaning temperature rises as height increases. This stable layer suppresses vertical motion and can trap moisture and pollutants beneath it.

Question 20Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

On a clear, calm night, the ground surface loses heat mainly by:

  1. advection of warm air from aloft
  2. latent heat release from condensation
  3. long-wave (infrared) radiation to space Correct answer.
  4. absorption of incoming solar radiation

Explanation

With little cloud and no wind, the ground radiates infrared energy to the atmosphere and space faster than it receives energy, so it cools. This nocturnal radiative cooling is the basis for radiation fog and ground inversions.

Question 21Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

Which surface condition produces the greatest diurnal temperature range?

  1. Open ocean under scattered cloud
  2. Dry sand in a desert under clear skies Correct answer.
  3. Moist vegetated soil under broken cloud
  4. Snow-covered ground under overcast skies

Explanation

Dry surfaces have little moisture to absorb heat as latent energy, and clear skies allow strong daytime solar heating and strong nighttime radiative loss. Together these give the largest day-to-night temperature swing.

Question 22Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

A valley inversion formed by cold air draining downslope at night is most likely to be dispersed by:

  1. a further fall in surface temperature after sunrise
  2. strong daytime surface heating causing convective mixing Correct answer.
  3. continued clear calm conditions through the following night
  4. increasing surface pressure with light winds

Explanation

Insolation after sunrise heats the valley floor, destabilises the layer and generates convection that mixes the cold pool with warmer air above. This is why valley inversions typically break down during the morning.

Question 23Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

An unsaturated parcel of air at 20 °C at the surface is lifted 2000 ft. Using the dry adiabatic lapse rate, its temperature becomes approximately:

  1. 14 °C Correct answer.
  2. 17 °C
  3. 8 °C
  4. 20 °C

Explanation

The dry adiabatic rate is about 3 °C per 1000 ft, so 2000 ft of ascent cools the parcel by roughly 6 °C. From 20 °C this gives about 14 °C, provided the parcel remains unsaturated.

Question 24Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

The saturated adiabatic lapse rate is smaller than the dry adiabatic lapse rate because:

  1. latent heat released by condensation partly offsets adiabatic cooling Correct answer.
  2. water vapour makes saturated air heavier and slows expansion
  3. the saturated rate applies only above the tropopause
  4. saturated air conducts heat more efficiently to its surroundings

Explanation

As a saturated parcel rises and cools, water vapour condenses and releases latent heat into the parcel. This partly cancels the adiabatic cooling, so the parcel cools more slowly than a dry parcel would.

Question 25Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

During the night, a shallow layer of air over land cools while the air a few hundred metres above remains warmer. This situation indicates:

  1. a stable surface inversion with limited vertical mixing Correct answer.
  2. a conditionally unstable layer with high convective cloud
  3. a neutrally stratified boundary layer
  4. an unstable layer favouring strong thermals

Explanation

Temperature increasing with height is a stable inversion, which suppresses vertical motion and traps moisture and haze near the surface. This is typical of clear calm nights over land.

Question 26Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

The Earth's global radiation balance is maintained because, averaged over the year:

  1. the atmosphere absorbs all incoming solar radiation
  2. incoming short-wave solar radiation equals outgoing long-wave radiation Correct answer.
  3. incoming short-wave radiation exceeds outgoing long-wave radiation
  4. outgoing long-wave radiation exceeds incoming short-wave radiation

Explanation

On a planetary scale and over a year, absorbed solar short-wave radiation is balanced by emitted terrestrial long-wave radiation, keeping the mean temperature roughly constant. Local imbalances drive winds and ocean currents.

Question 27Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

Cloud cover reduces the diurnal temperature range mainly because clouds:

  1. lower the surface pressure and reduce heating
  2. increase the dry adiabatic lapse rate
  3. prevent any convection within the boundary layer
  4. reflect solar radiation by day and reduce long-wave loss at night Correct answer.

Explanation

Clouds reflect incoming short-wave radiation, reducing daytime heating, and absorb and re-emit long-wave radiation, reducing nighttime cooling. The combined effect is a smaller day-to-night temperature swing.

Question 28Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

The environmental lapse rate between two levels is measured as 9 °C per 1000 m. For a saturated air parcel rising through this layer, the layer is:

  1. conditionally unstable
  2. absolutely unstable Correct answer.
  3. neutrally stable
  4. absolutely stable

Explanation

The saturated adiabatic lapse rate is roughly 5 to 6 °C per 1000 m in typical conditions. An environmental lapse rate of 9 °C per 1000 m exceeds it, so even a saturated parcel stays warmer than its surroundings and the layer is absolutely unstable.

Question 29Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

A surface-based radiation inversion is most likely to form when the wind at night is:

  1. strong and the sky is clear
  2. light and the sky is clear Correct answer.
  3. light and the sky is overcast
  4. strong and the sky is overcast

Explanation

Clear skies allow strong radiative loss from the ground, and light winds prevent turbulent mixing that would spread the cooling through a deeper layer. The result is a shallow, intense surface inversion.

Question 30Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

The warmest part of a typical clear day over land usually occurs:

  1. shortly after sunset
  2. in the early to mid afternoon Correct answer.
  3. just before sunrise
  4. at local noon

Explanation

Peak solar elevation occurs at noon, but the surface continues to gain more heat than it loses for some hours afterwards. The maximum temperature is therefore reached in the early to mid afternoon, when incoming and outgoing energy balance.

Question 31Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

Two air masses have the same temperature but one is much drier. Which statement about the dry air mass is correct?

  1. It cools more slowly when lifted unsaturated
  2. It cools more rapidly with height when lifted unsaturated Correct answer.
  3. It has a smaller dry adiabatic lapse rate
  4. It cannot form an inversion

Explanation

The dry adiabatic lapse rate is essentially the same for all unsaturated air, but dry air reaches its condensation level at a higher altitude, so it continues to cool at the dry rate over a deeper layer. Moist air switches to the slower saturated rate sooner.

Question 32Temperature: heating/cooling, lapse rates, inversions, diurnal variation, radiation balance

Advection fog forms when:

  1. the ground cools by radiation on a clear calm night
  2. warm moist air moves over a colder surface and is cooled to its dewpoint Correct answer.
  3. air is lifted and cools adiabatically to saturation
  4. cold air moves over a warm surface and is heated

Explanation

Advection fog requires horizontal movement of relatively warm moist air over a colder surface, which cools the air from below to its dewpoint. It is common over cold sea areas and can persist with moderate wind.

Question 33Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

An aircraft is flying at a constant indicated altitude from a region of high pressure to a region of low pressure, with the subscale left unchanged. What happens to the true altitude of the aircraft?

  1. It decreases, so the aircraft is lower than the altimeter indicates. Correct answer.
  2. It remains constant because indicated altitude is unaffected by pressure changes.
  3. It initially increases, then returns to the original value.
  4. It increases, so the aircraft is higher than the altimeter indicates.

Explanation

The altimeter measures pressure, not height. Flying toward lower pressure at constant indicated altitude means the aircraft descends to a level where the pressure matches the subscale setting, so true altitude falls below the indicated value. The mnemonic is 'high to low, look out below'.

Question 34Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

What does the QFE setting represent when set on an altimeter subscale?

  1. The pressure at mean sea level, reduced to sea level.
  2. The pressure at the tropopause for the standard atmosphere.
  3. The pressure at the standard datum of 1013.25 hPa.
  4. The pressure at the aerodrome reference point, so the altimeter reads height above that point. Correct answer.

Explanation

QFE is the actual atmospheric pressure at the aerodrome reference point. With QFE set, the altimeter reads zero on the ground at that point and indicates height above the aerodrome rather than altitude above mean sea level.

Question 35Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

An altimeter subscale is set to QNH. When the aircraft is on the ground at the aerodrome, what does the altimeter indicate?

  1. The aerodrome elevation above mean sea level. Correct answer.
  2. Zero.
  3. The flight level corresponding to the local pressure.
  4. The height above the aerodrome reference point.

Explanation

QNH is the mean sea level pressure derived from the aerodrome pressure. With QNH set, the altimeter reads aerodrome elevation when the aircraft is on the ground, giving altitude above mean sea level.

Question 36Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

Which pressure setting must be set on the altimeter subscale when the aircraft is flying at a flight level?

  1. QFE of the departure aerodrome.
  2. QNE of the destination aerodrome.
  3. QNH of the nearest aerodrome.
  4. 1013.25 hPa. Correct answer.

Explanation

Flight levels are defined with reference to the standard pressure datum of 1013.25 hPa. Above the transition altitude the subscale is set to this value so that all aircraft share a common datum and vertical separation is assured.

Question 37Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

What is meant by the term QNE?

  1. The pressure at the transition level.
  2. The sea level pressure at the destination aerodrome.
  3. The pressure at the aerodrome reference point.
  4. The altimeter reading at touchdown when the subscale is set to 1013.25 hPa. Correct answer.

Explanation

QNE is a term used for the indicated altitude shown at touchdown with the standard pressure setting 1013.25 hPa selected. It is not a pressure value and is not used as a subscale setting.

Question 38Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

On a surface pressure chart, how are isobars drawn?

  1. At fixed intervals of height, joining points of equal temperature.
  2. At fixed intervals of pressure, joining points of equal mean sea level pressure. Correct answer.
  3. Joining points of equal wind speed.
  4. At irregular intervals chosen by the analyst.

Explanation

Isobars are lines joining places of equal mean sea level pressure, drawn at fixed intervals such as 4 hPa. Their spacing indicates the pressure gradient and hence the strength of the geostrophic wind.

Question 39Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

An aircraft flies at a constant indicated altitude from a warm air mass into a cold air mass. Assuming the subscale setting is unchanged, how does the true altitude change?

  1. It decreases because the cold air column contracts. Correct answer.
  2. It remains constant because pressure is unchanged.
  3. It first increases, then decreases to the original value.
  4. It increases because cold air is denser.

Explanation

In cold air the pressure surfaces are compressed toward the surface, so a given pressure level lies at a lower true altitude. Maintaining a constant indicated altitude therefore places the aircraft lower than the altimeter suggests, which is the cold-air trap.

Question 40Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

An aircraft is at a true altitude of 5000 ft in air that is 10 degrees C colder than the ISA value for that level. Approximately what does the altimeter indicate with QNH set?

  1. About 5400 ft.
  2. About 5000 ft.
  3. About 5800 ft.
  4. About 4600 ft. Correct answer.

Explanation

Cold air makes the altimeter over-read, so indicated altitude is higher than true altitude. A rough rule is about 4 percent error per 10 degrees C of ISA deviation, and 4 percent of 5000 ft is about 200 ft, so the indicated value is roughly 5200 ft. Because the air is cold, the true altitude is lower than indicated, so with a true altitude of 5000 ft the indicated value is about 5200 ft, meaning the aircraft is actually lower than shown.

Question 41Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

An aircraft is cruising at FL 100 in an area where the pressure at mean sea level is 1030 hPa. The subscale is set to 1013.25 hPa. What is the approximate effect on the true altitude?

  1. The aircraft is lower than FL 100 indicates.
  2. The aircraft is higher than FL 100 indicates. Correct answer.
  3. The true altitude cannot be determined from pressure alone.
  4. The aircraft is exactly at 10 000 ft.

Explanation

With a sea level pressure above standard, the pressure level corresponding to 1013.25 hPa at FL 100 is found at a greater height. The aircraft is therefore higher than the flight level suggests, consistent with the rule that high pressure means true altitude exceeds indicated altitude.

Question 42Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

Which statement correctly describes how an altimeter with QNH set behaves when the aircraft flies from a region of low pressure into a region of high pressure?

  1. The altimeter under-reads, and the aircraft is higher than indicated. Correct answer.
  2. The altimeter under-reads, and the aircraft is lower than indicated.
  3. The altimeter reads correctly because QNH is a sea level pressure.
  4. The altimeter over-reads, and the aircraft is lower than indicated.

Explanation

Flying from low to high pressure at constant indicated altitude, the aircraft climbs to reach the pressure shown on the subscale, so its true altitude is greater than indicated. The altimeter therefore under-reads relative to true altitude.

Question 43Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

Why is the transition altitude defined in terms of a fixed value rather than the transition level?

  1. Because the transition level is the same at all aerodromes.
  2. Because the transition altitude is a constant height above mean sea level, while the transition level varies with pressure. Correct answer.
  3. Because the transition altitude is used only for approach procedures.
  4. Because the transition altitude changes with QNH while the transition level is fixed.

Explanation

The transition altitude is a fixed altitude above mean sea level, published for the area. The transition level is a flight level and varies with the local QNH, so it is determined by the pressure of the day.

Question 44Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

An aerodrome has an elevation of 1000 ft and a QNH of 1000 hPa. If the pressure at the aerodrome reference point is required, which statement is correct?

  1. QFE cannot be related to QNH without temperature data.
  2. QFE is higher than QNH because pressure increases with height.
  3. QFE equals QNH because the aerodrome is at sea level.
  4. QFE is lower than QNH because pressure decreases with height. Correct answer.

Explanation

Pressure decreases with height in the atmosphere, so the pressure at an aerodrome 1000 ft above sea level is lower than the sea level pressure QNH. QFE is therefore lower than QNH, with the difference roughly 1 hPa per 30 ft.

Question 45Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

An aircraft on final approach has the QFE set at an aerodrome with elevation 2000 ft. The altimeter indicates 500 ft. What is the approximate height above the aerodrome reference point?

  1. 500 ft. Correct answer.
  2. 2500 ft.
  3. 2000 ft.
  4. 1500 ft.

Explanation

With QFE set, the altimeter reads height above the aerodrome reference point directly. An indication of 500 ft therefore corresponds to about 500 ft above that point, independent of the aerodrome elevation.

Question 46Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

What is the main reason an altimeter requires a temperature correction when operating in very cold air?

  1. Cold air causes the static port to become blocked.
  2. Cold air reduces the speed of sound, which affects the pressure sensed by the static port.
  3. The altimeter assumes a standard temperature lapse rate, and cold air compresses the pressure levels toward the surface. Correct answer.
  4. Cold air increases the density of the atmosphere, which changes the calibration of the instrument.

Explanation

Altimeters are calibrated to the ISA temperature profile. When the actual air is colder than ISA, the pressure levels are closer to the ground, so the altimeter over-reads and the aircraft is lower than indicated. This is why cold temperature corrections are applied to procedure minima.

Question 47Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

An aircraft is flying at FL 150 with the standard pressure setting. The actual QNH at the aircraft's position is 990 hPa. Which statement about the aircraft's true altitude is correct?

  1. The aircraft is lower than FL 150 suggests. Correct answer.
  2. The aircraft's true altitude is unaffected by the QNH.
  3. The aircraft is at exactly 15 000 ft.
  4. The aircraft is higher than FL 150 suggests.

Explanation

With a QNH below standard, the pressure at a given flight level is reached at a lower true altitude. The aircraft is therefore lower than the flight level indicates, which is the 'low to high' inversion of the usual rule when the sea level pressure is low.

Question 48Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

Which of the following best explains why isobars on a chart are usually drawn at intervals such as 4 hPa?

  1. To provide a consistent scale for comparing pressure gradients between charts. Correct answer.
  2. To ensure the chart shows only high-pressure systems.
  3. To allow the chart to be used as a flight level chart.
  4. To match the resolution of the altimeter subscale.

Explanation

Fixed intervals such as 4 hPa give a consistent scale so that the spacing of isobars can be compared between charts and regions. Closely spaced isobars indicate a steep pressure gradient and stronger wind.

Question 49Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

An aircraft is descending through the transition layer. Which statement about the altimeter subscale is correct?

  1. It is changed from QFE to QNH at the transition altitude.
  2. It is changed from QNH to QFE at the transition level.
  3. It is changed from the local QNH to 1013.25 hPa when climbing through the transition altitude.
  4. It is changed from 1013.25 hPa to the local QNH when passing the transition level. Correct answer.

Explanation

When descending through the transition level, the subscale is changed from the standard setting 1013.25 hPa to the local QNH. This provides terrain clearance referenced to mean sea level for the approach.

Question 50Atmospheric pressure and altimetry: pressure systems, isobars, QNH/QFE/QNE, altimeter errors, cold- and warm-air effects on true altitude

An aircraft is on the ground at an aerodrome with QNH set and the altimeter indicates 1500 ft. The aerodrome elevation is 1500 ft. What does this confirm?

  1. The altimeter is set to the standard pressure setting.
  2. The altimeter is correctly indicating altitude above mean sea level. Correct answer.
  3. The altimeter is correctly indicating height above the aerodrome.
  4. The altimeter has a temperature error.

Explanation

With QNH set, the altimeter on the ground should read the aerodrome elevation, which is its altitude above mean sea level. A reading of 1500 ft matching the elevation of 1500 ft confirms correct operation and setting.