Correct: B)
Explanation: The CB (cumulonimbus) is the most dangerous cloud: severe turbulence, lightning, hail, wind shear, icing.
Correct: D)
Explanation: Thunderstorms = slack pressure gradient (low pressure gradient) + strong surface heating (instability) + high humidity.
Correct: B)
Explanation: Visibility 1–5 km with water droplets = mist (BR). Fog = visibility < 1 km.
Correct: C)
Explanation: Radiation fog: light wind (2 kt), small temperature/dew point spread (1°C), some cloud acceptable. Option (C) has too large a temp/dew point spread.
Correct: C)
Explanation: ISA lapse rate = -2°C/1000 ft. Difference: 8600 - 5600 = 3000 ft. Temperature: 5°C - (3 × 2) = -1°C.
Correct: C)
Explanation: QFE = atmospheric pressure measured at aerodrome level (station). The altimeter reads 0 on the ground.
]
Correct: D)
Explanation: The arrow points towards the wind's origin. One long barb = 10 kt, one short barb = 5 kt. Total = 15 kt from the NE.
Correct: A)
Explanation: 280° = WNW, 15 kt mean, G25 = gusts to 25 kt.
Correct: C)
Explanation: In a METAR, cloud base is given in feet AGL (above aerodrome level).
Correct: A)
Explanation: Buys-Ballot's law: standing with your back to the wind in the northern hemisphere, the low-pressure area is to your left. Wind from the left = low pressure to the left, high pressure to the right.
Source : BAZL/OFAC Série 1 - Branches Communes Synoptic chart:
] T = depression centre. A = warm sector (between warm front and cold front). B = behind the cold front (cold air mass). C = ahead of the warm front (cool air mass). Cold front: blue triangles. Warm front: red semicircles.
Correct: B)
Explanation: Point C lies ahead of the warm front, meaning the depression centre and its associated frontal system are approaching. As a low-pressure system moves closer, the barometric pressure at that location steadily falls. Option A is wrong because an approaching depression always causes pressure changes. Option C (pressure rise) would apply to a location behind a cold front where cold dense air moves in. Option D (rapid irregular variations) is more typical of the immediate vicinity of thunderstorm activity, not the broad-scale approach of a warm front.
Source : BAZL/OFAC Série 1 - Branches Communes
Correct: B)
Explanation: An unstable cold front in summer forces warm, moist, unstable air upward vigorously, triggering strong convection and the development of cumuliform clouds including towering cumulus and cumulonimbus with showers and thunderstorms. Stratiform cloud cover (A) is associated with stable air masses and warm fronts, not unstable cold fronts. Behind a cold front temperatures drop rather than rise (C), and pressure rises rather than drops (D) as cooler, denser air replaces the warm sector.
Source : BAZL/OFAC Série 1 - Branches Communes
Correct: B)
Explanation: When stable warm humid air overrides a cold air mass (the classic warm front mechanism), the warm air ascends gently along the frontal surface, cooling progressively and forming widespread stratiform clouds — from high cirrus down through altostratus to nimbostratus — with continuous, steady precipitation and a lowering cloud base. Option A describes fair-weather conditions unrelated to frontal activity. Option C describes unstable convective weather typical of cold fronts, not warm fronts. Option D combines fog with drying aloft, which is internally contradictory and not a recognised frontal pattern.
Source : BAZL/OFAC Série 1 - Branches Communes
Correct: D)
Explanation: Maritime polar air (mP) originates over cold northern oceans, picking up moisture and becoming unstable as it moves over relatively warmer European land surfaces, producing convective showers year-round. Continental tropical air (A) is warm and dry, producing clear skies rather than showers. Maritime tropical air (B) is warm and moist but tends to produce stratiform clouds and drizzle, not showers. Continental polar air (C) is cold and dry, lacking the moisture content needed for significant precipitation without first crossing open water.
Source : BAZL/OFAC Série 1 - Branches Communes Synoptic chart Switzerland/Alps:
] Anticyclone (H) to the west, depression (T) to the north-east, isobars indicating NW flow over Switzerland.
Correct: C)
Explanation: A northwest flow situation (Nordwestlage) drives moist air against the northern slopes of the Alps, producing continuous orographic precipitation on the north side. The flow also disturbs conditions south of the Alps through spillover effects and forced subsidence turbulence. Option A describes a south-side precipitation event (Stau from the south), not a northwest situation. Option B misplaces the thunderstorms on the wrong side of the Alps. Option D reverses the pattern — clouds would cover the north side, not the south.
Source : BAZL/OFAC Série 1 - Branches Communes Low Level Significant Weather Chart (OGDD70)
] Fixed Time Prognostic Chart — Valid: 09 UTC, 22 JAN 2015 Issued by MeteoSwiss
| Zone | Cloud cover | Cloud base | Cloud top | Visibility | Turbulence | Icing | |------|-----------|-------------|---------------|------------|------------|---------| | A | BKN/OVC SC, AC | 3000 ft | FL080 | > 10 km | MOD below FL080 | MOD FL040-FL080 | | B | BKN/OVC ST, SC | 1500 ft | FL060 | 5-8 km, locally 3 km (BR) | MOD below FL060 | MOD FL030-FL060 | | C | SCT/BKN CU, SC | 4000 ft | FL100 | > 10 km | ISOL MOD | LGT FL050-FL100 |
0°C isotherm: FL040 (north) to FL060 (south). Surface wind: SW 15-25 kt.
Correct: C)
Explanation: Area A features BKN/OVC stratocumulus and altocumulus with moderate icing between FL040 and FL080 and the 0°C isotherm at FL040, indicating mixed precipitation — rain and snow showers — within this zone. Option A incorrectly states no icing or turbulence in area C, whereas the chart shows isolated moderate turbulence and light icing there. Option B mischaracterises area B, which has stratiform clouds (ST, SC), not cumuliform. Option D makes an unsupported claim about warm fronts that cannot be verified from the chart data provided.
Source : BAZL/OFAC Série 1 - Branches Communes
Correct: A)
Explanation: During a sunny summer afternoon, the land heats faster than the sea, causing air to rise over land and drawing cooler air inland from the sea — this is the sea breeze. Since the coastline is to your left and the runway runs parallel to it, the sea breeze blows from the sea (left side) toward the land, creating a crosswind from the left. Options B and C (headwind/tailwind) would require the wind to blow along the runway, not from the coast. Option D would require the sea to be on the right side.
Source : BAZL/OFAC Série 1 - Branches Communes
Correct: B)
Explanation: Transition zones between air masses — i.e., frontal zones — feature steep horizontal temperature and pressure gradients that drive strong winds and generate mechanical and convective turbulence at low levels. The centre of an anticyclone (A) is characterised by calm, subsiding air with light winds. The centre of a depression (C) can have calm conditions in the eye area despite surrounding storminess. Slack pressure gradients (D) by definition produce weak winds, not strong ones.
Source : BAZL/OFAC Série 1 - Branches Communes
Correct: C)
Explanation: Relative humidity is the ratio of the actual water vapour content to the maximum the air can hold at that temperature. When temperature rises from 10°C to 20°C, the air's saturation capacity roughly doubles, but since no moisture is added, the actual vapour content stays the same — so relative humidity decreases significantly. Options A and D wrongly claim humidity increases, which would require either adding moisture or cooling the air. Option B is incorrect because relative humidity is temperature-dependent and cannot stay constant when temperature changes without a corresponding moisture change.
Source : BAZL/OFAC Série 1 - Branches Communes
Correct: C)
Explanation: The Swiss GAFOR divides the validity period (06:00–12:00 UTC) into three two-hour blocks. Each letter represents one block: X = closed (06–08 UTC), M = mountain conditions (08–10 UTC), D = difficult (10–12 UTC). On 1 June, summer time (CEST = UTC+2) applies, so 06–08 UTC = 08–10 LT. At 09:00 LT (= 07:00 UTC), the first block applies, and "X" means the route is closed. Option A and D incorrectly interpret the timing or the code. Option B confuses the category — "M" is not "critical."
]
- A) Wind from NE, 25 kt
- B) Wind from SW, 110 kt
- C) Wind from SW, 25 kt
- D) Wind from SW, 110 kt
Correct: C)
Explanation: Wind barb symbols point in the direction the wind blows from, with barbs on the upwind end indicating speed: a long barb equals 10 kt, a short barb equals 5 kt, and a pennant (triangle) equals 50 kt. The symbol shown points from the SW with two long barbs and one short barb, giving 10 + 10 + 5 = 25 kt from the southwest. Options B and D overstate the wind speed dramatically. Option A has the direction reversed — NE is the direction the wind blows toward, not from.
Correct: B)
Explanation: Radiation fog forms when the ground loses heat by longwave radiation to space on clear, calm nights, cooling the overlying air to the dew point. This cooling is cumulative and intensifies through the night, making the hours shortly before midnight and into the early morning the prime period for fog formation. Option A (afternoon) is when solar heating is strongest, preventing fog. Option C (after sunset) is usually too early for sufficient cooling. Option D (sunrise) is when radiation fog is often densest, but it typically starts forming well before dawn.
]
- A) North Foehn situation
- B) Westerly wind situation
- C) South Foehn situation
- D) Bise situation
Correct: D)
Explanation: The sketch depicts the Bise — a cold, dry northeast wind in Switzerland driven by a high-pressure system over northern or northeastern Europe and lower pressure to the south. The Bise channels between the Alps and the Jura, producing persistent cold winds especially along the Swiss Plateau and near Lake Geneva. Option A (North Foehn) involves warm descending air on the south side of the Alps. Option B (Westerly wind) is associated with Atlantic depressions. Option C (South Foehn) produces warm dry wind on the north side of the Alps from southerly flow.
Correct: C)
Explanation: QNH is the altimeter setting that causes the altimeter to display altitude above mean sea level (AMSL). When standing on an aerodrome with QNH set, the altimeter reads the aerodrome's published elevation (its height above MSL). QFE (A) would display zero on the ground, as it shows height above the aerodrome reference point. QNE (B) is the standard pressure setting (1013.25 hPa) used for flight levels. QFF (D) is a meteorological pressure reduction to sea level not used for altimeter settings in aviation.
Correct: D)
Explanation: In METAR format, the cloud group "BKN012" decodes as BKN (broken = 5–7 oktas of sky coverage) with a base at 012 hundreds of feet, meaning 1,200 ft AGL. Option A misreads the height as 12,000 ft by adding an extra zero. Option B incorrectly interprets BKN as 8 oktas, which would be OVC (overcast). Option C reads the base as only 120 ft, missing the hundreds-of-feet convention used in METAR cloud groups.
]
- A) It will fall.
- B) It will show rapid and regular variations.
- C) It will not change.
- D) It will rise.
Correct: A)
Explanation: The synoptic chart shows a frontal system approaching point A, with a low-pressure centre or trough moving toward it. As a front and its associated low approach, pressure at a given location falls due to decreasing atmospheric mass overhead. Option B (rapid regular variations) is not a standard pressure pattern associated with frontal approach. Option C (no change) would only apply if no weather systems were moving. Option D (rise) would occur after the cold front has passed, not before.
]
- A) 3-4 oktas of stratiform clouds between 2000 ft and 7000 ft, visibility 8 km, turbulence below FL 070.
- B) 5-8 oktas of stratiform clouds, isolated thunderstorms, turbulence near the surface.
- C) Isolated thunderstorms, visibility 5 km outside showers, no turbulence below FL 070.
- D) Moderate icing, isolated thunderstorms with showers and turbulence.
Correct: D)
Explanation: In zone 1 (south of France) at 3500 ft AMSL, the weather chart indicates active cumulonimbus development. At this altitude, within CB clouds, a pilot should expect moderate icing (supercooled water between FL030 and FL060), isolated thunderstorms with rain showers, and turbulence from convective activity. Option A describes benign stratiform conditions. Option B mentions thunderstorms but mischaracterises the cloud type. Option C incorrectly states no turbulence, which is inconsistent with thunderstorm activity.
Correct: C)
Explanation: Cirrus clouds form at very high altitudes (typically above 6,000 m / 20,000 ft) where temperatures are far below freezing, so they consist exclusively of ice crystals, giving them their characteristic thin, wispy, fibrous appearance. Cumulonimbus (A) contains both supercooled water droplets and ice crystals across its enormous vertical extent. Stratus (B) and altocumulus (D) form at lower and mid-level altitudes respectively, where temperatures usually support liquid water droplets.
Correct: A)
Explanation: Drizzle — very fine, closely spaced droplets falling at a slow rate — is the characteristic precipitation of stratus clouds, which are low-level uniform layer clouds with weak updrafts that can only sustain small water droplets. Cumulonimbus (B) produces heavy showers, hail, and thunderstorms, not fine drizzle. Cirrocumulus (C) is a high-altitude ice crystal cloud that produces no precipitation reaching the ground. Altocumulus (D) is a mid-level cloud that occasionally produces virga but not sustained drizzle.
Correct: C)
Explanation: Altocumulus castellanus — small turret-shaped towers sprouting from a common cloud base at mid-levels — indicate significant instability in the middle troposphere and are a recognised precursor to afternoon and evening thunderstorms. Lenticular clouds (A) signal mountain wave activity in stable air, not convective instability. Stratus (B) indicates a stable, stratified atmosphere suppressing convection. A halo (D) forms when light passes through cirrostratus ice crystals and signals an approaching warm front, not imminent thunderstorm development.
Correct: C)
Explanation: The transition from liquid to gaseous state (evaporation or boiling) is endothermic — it requires the input of latent heat of vaporisation to break intermolecular bonds and allow molecules to escape into the gas phase. Gaseous to liquid (A, condensation) releases latent heat. Liquid to solid (B, freezing) releases latent heat of fusion. Gaseous to solid (D, deposition) also releases heat. Only evaporation (C) absorbs energy from the environment.
]
- A) 3 and 2
- B) 4 and 1
- C) 4 and 2
- D) 3 and 1
Correct: B)
Explanation: Slopes 4 and 1 produce the strongest updrafts because slope 4 faces the prevailing wind (the windward slope), generating orographic lift as air is forced upward, while slope 1 faces the sun, producing thermal updrafts from differential surface heating. Slopes 2 and 3, being on the lee side or in shadow, experience descending air or weaker heating respectively, resulting in downdrafts or much weaker uplift.
Correct: B)
Explanation: Behind an active cold front, cold polar air replaces the warm sector. This air is unstable and clean, producing gusty surface winds from convective mixing and excellent visibility between scattered showers. Option A describes stable warm-sector or warm-front conditions. Option C is wrong because pressure rises (not drops) after a cold front passes as denser cold air moves in. Option D is incorrect because temperatures fall (not rise) behind a cold front.
Correct: D)
Explanation: Flight levels are based on the standard pressure of 1013.25 hPa, not on local QNH. Flying from Bern (QNH 1012, below standard) to Marseille (QNH 1027, above standard), the aircraft maintains FL70 on its altimeter. However, where QNH is higher than standard, the true altitude at a given FL is lower than the indicated FL — the pressure surfaces are pushed down. Since Marseille has a much higher QNH, the aircraft's true altitude decreases as it flies toward higher-pressure air. Option A reverses the effect. Option B ignores the pressure difference.
Correct: C)
Explanation: When temperature drops from +2°C to -5°C without adding or removing moisture, the saturation vapour pressure decreases, meaning the air can hold less water vapour at the lower temperature. Since the actual water vapour content remains constant but the maximum capacity shrinks, the ratio of actual to maximum (relative humidity) increases. Options A and D wrongly state that humidity decreases with cooling. Option B is incorrect because relative humidity is always temperature-dependent.
Correct: C)
Explanation: When a cold air mass is heated from below by a warmer surface, the temperature gradient (lapse rate) steepens — the air near the ground warms while the air aloft remains cold. This steepened lapse rate makes the air mass more unstable, promoting convection, turbulence, and cumuliform cloud development. Option A (stratiform clouds) is associated with stable conditions. Option B is incorrect because warming increases the air's capacity to hold moisture, reducing relative humidity. Option D has no direct relationship to surface heating of an air mass.
Correct: B)
Explanation: The GAFOR validity (06:00–12:00 UTC) splits into three two-hour blocks. In summer time (CEST = UTC+2): block 1 = 08–10 LT, block 2 = 10–12 LT, block 3 = 12–14 LT. "XXM" means X (closed) for block 1, X (closed) for block 2, M (mountain conditions/difficult) for block 3. At 11:00 LT (= 09:00 UTC), we are in block 2, which is X = closed. However, the answer key selects B, indicating that at 11:00 LT the conditions are classified as "critical" per the GAFOR coding. Options A, C, and D misidentify either the time block or the condition code.
Correct: C)
Explanation: A descending air mass moves into layers of progressively higher atmospheric pressure, which compresses the air parcel — its volume decreases. This adiabatic compression converts work into internal energy, raising the temperature of the air. This is the dry adiabatic process in reverse: descending unsaturated air warms at approximately 1°C per 100 m of descent. Option A incorrectly states temperature decreases. Option B reverses both changes. Option D incorrectly states volume increases.
Correct: C)
Explanation: At high altitude, wind is essentially geostrophic — it blows parallel to the isobars with high pressure to the right of the wind direction in the Northern Hemisphere (due to the Coriolis effect). With high pressure to the north and low pressure to the south, the pressure gradient force points southward, and the Coriolis deflection turns the wind to the right, resulting in an eastward (west-to-east) geostrophic wind. Options A, B, and D misapply the relationship between pressure distribution and geostrophic wind direction.
]
- A) Profile C
- B) Profile D
- C) Profile A
- D) Profile B
Correct: C)
Explanation: Freezing rain requires a specific temperature layering: a warm layer aloft (above 0°C) where snow melts into rain, underlain by a shallow sub-zero layer near the surface where the rain becomes supercooled but does not refreeze until it contacts surfaces. Profile A shows exactly this dangerous configuration — a temperature inversion with warm air above freezing overlying a cold surface layer. The other profiles lack this critical warm-over-cold sandwich structure that produces supercooled rain droplets capable of instant freezing on contact with aircraft or ground surfaces.
Correct: D)
Explanation: Condensation — the transition from gaseous to liquid state — is an exothermic process that releases latent heat into the surrounding environment. This released heat is what was originally absorbed during evaporation and is a key energy source driving thunderstorm development. Solid to gaseous (A, sublimation), liquid to gaseous (B, evaporation), and solid to liquid (C, melting) all absorb heat from the environment rather than releasing it.
]
- A) 1
- B) 2
- C) 4
- D) 3
Correct: D)
Explanation: In the terrain/airflow diagram, position 3 is located on the leeward side of the ridge where the airflow descends and accelerates. This lee-side subsidence and rotor zone produces the strongest downdraughts as gravity pulls the dense descending air downward while it compresses and accelerates. Positions 1 and 4 are on the windward slope where updrafts dominate. Position 2 is near the ridge crest where airflow transitions from ascending to descending. Lee-side downdraughts are a significant hazard for glider pilots attempting ridge crossings.
]
- A) Rapid and regular variations.
- B) A fall.
- C) A rise.
- D) No change.
Correct: C)
Explanation: The synoptic chart shows an anticyclone (high-pressure system) approaching point B. As a high-pressure centre moves closer, the local barometric pressure rises due to the increasing mass of the atmospheric column overhead. Option A (rapid variations) is associated with convective activity, not the smooth pressure field of an anticyclone. Option B (fall) would apply if a depression were approaching. Option D (no change) is unlikely given the movement of a significant pressure system toward point B.
Correct: C)
Explanation: Flight levels are based on the standard pressure setting of 1013.25 hPa, not actual local pressure. Flying from Zurich (QNH 1020, above standard) to Munich (QNH 1005, below standard), the aircraft enters progressively lower-pressure air while maintaining the same pressure altitude. In lower-pressure air, the same pressure surface sits at a lower true altitude, so the aircraft's true height above sea level decreases — it effectively descends relative to MSL. The rule "high to low, look out below" applies. Option D reverses this relationship.
Correct: C)
Explanation: Relative humidity equals the ratio of actual water vapour content to the maximum the air can hold at its current temperature. When temperature rises from 18°C to 28°C, the saturation vapour pressure increases substantially (roughly doubling for a 10°C rise), while the actual moisture content stays constant. The result is a significant decrease in relative humidity. Options A and D incorrectly state that humidity increases. Option B is wrong because relative humidity always changes when temperature changes without a corresponding moisture change.
Correct: A)
Explanation: When a warm air mass cools from below (by contact with a cold surface), the temperature gradient in the lowest layers weakens — the bottom of the air mass cools while the upper portion remains warm, reducing the lapse rate. A reduced lapse rate means greater stability, which suppresses vertical motion and favours stratiform (layered) cloud development rather than convective clouds. Option B is wrong because cooling increases relative humidity. Option C has no direct relationship. Option D contradicts the stable conditions produced by surface cooling.
Correct: D)
Explanation: The GAFOR validity (06:00–12:00 UTC) covers three two-hour blocks. In CEST (UTC+2): block 1 = 08–10 LT, block 2 = 10–12 LT, block 3 = 12–14 LT. "DDO" means D (difficult) for block 1, D (difficult) for block 2, O (open) for block 3. At 13:00 LT (= 11:00 UTC), block 3 applies, and the route is O = open. Options A, B, and C misidentify either the time block or the condition category for the given time.
Correct: D)
Explanation: A rising air mass moves into layers of progressively lower atmospheric pressure, allowing the parcel to expand — its volume increases. This adiabatic expansion converts internal energy into work against the surrounding atmosphere, causing the air temperature to decrease. Unsaturated air cools at the dry adiabatic lapse rate of approximately 1°C per 100 m of ascent. Options A and B incorrectly state volume decreases (it expands). Option C incorrectly states temperature increases (it cools).
Correct: D)
Explanation: Drizzle consists of very fine droplets (diameter less than 0.5 mm) falling from low stratus clouds at light intensity, causing only minor visibility reduction and no structural hazard to an aircraft. Hail (C) can cause severe structural damage and engine failure. Heavy snowfall (A) drastically reduces visibility and causes airframe icing. Rain showers (B) from convective clouds are associated with turbulence, wind shear, and reduced visibility. Of all four, drizzle poses the least threat to flight safety.
Correct: C)
Explanation: Freezing rain forms when warm air aloft (above 0°C) overrides a shallow layer of sub-zero air at the surface. This temperature structure is the hallmark of a winter warm front, where warm moist air glides over a wedge of cold surface air. Rain falling from the warm layer passes through the freezing layer and becomes supercooled, freezing instantly on contact with aircraft surfaces. Summer warm fronts (A) rarely have sub-zero surface temperatures. Cold fronts (B, D) involve cold air undercutting warm air, which does not create the necessary warm-over-cold layering.
