CSLB General Building (B) — All Questions

A METAR reads: KRDU 141753Z 21014G24KT 10SM FEW040 26/17 A3002. How should you interpret the wind group?

• a.From 140 degrees true at 21 knots, with gusts to 24 knots
• b.From 210 degrees true at 14 knots, with gusts to 24 knots✓
• c.From 210 degrees magnetic at 24 knots, with lulls to 14 knots
• d.From 240 degrees true at 21 knots, with gusts to 14 knots

In a METAR wind group the first three digits are the direction the wind is blowing from, the next two are the sustained speed, and the digits after the G are the peak gust, so 21014G24KT is 210 degrees at 14 knots gusting 24 knots. METAR and TAF wind directions are referenced to true north, not magnetic north, which rules out the magnetic option. The other choices scramble the direction and speed digits or reverse the gust value, which is always higher than the sustained speed.

A METAR reads: KBOI 091853Z 30008KT 5SM HZ SCT007 BKN013 OVC025 19/12 A2988. What is the reported ceiling?

• a.700 ft AGL, because SCT007 is the lowest reported layer
• b.2,500 ft AGL, because OVC025 is the only solid overcast layer
• c.1,300 ft AGL, because BKN013 is the lowest broken or overcast layer✓
• d.1,900 ft AGL, the average height of the three reported layers

Ceiling is defined as the height above ground of the lowest layer reported as broken or overcast, so BKN013 gives a 1,300 ft AGL ceiling. Cloud heights in a METAR are given in hundreds of feet above the reporting station, so 013 means 1,300 ft. Scattered layers such as SCT007 are not ceilings, the overcast at 2,500 ft is above the broken layer, and averaging the layers is not a recognized method.

A METAR reads: KMEM 231553Z 09006KT 2SM BR OVC004 08/08 A3010. What do the elements 2SM BR tell you?

• a.Visibility of 2 statute miles restricted by mist✓
• b.Visibility of 2 statute miles restricted by blowing rain
• c.A 2,000 ft ceiling with a broken layer above it
• d.Visibility of 2 nautical miles restricted by drizzle

Surface visibility in a US METAR is always given in statute miles, and BR is the code for mist, so 2SM BR means 2 SM visibility in mist. The temperature and dew point of 08/08 show a zero-degree spread, which is exactly why the air is saturated and mist plus a 400 ft overcast are present. BR is not blowing rain, visibility is never reported in nautical miles, and cloud amounts are reported separately in the OVC004 group.

A TAF reads: KOKC 121120Z 1212/1318 14008KT P6SM SCT030 FM121800 18015G25KT 4SM -RA BKN015. What does the FM121800 group forecast?

• a.Conditions expected only briefly, for less than one hour after 1800Z
• b.The end of the valid forecast period at 1800Z on the 12th
• c.That 14008KT and more than 6 SM visibility will persist all day
• d.A rapid change at 1800Z to 18015G25KT, 4SM in light rain, BKN015✓

FM means "from" and marks a rapid, sustained change that begins at the stated day and time, so from 1800Z on the 12th the forecast is wind 180 degrees at 15 knots gusting 25, 4 SM visibility in light rain, and a broken layer at 1,500 ft. Brief, temporary fluctuations would be coded TEMPO, and a gradual transition would be BECMG. The validity period 1212/1318 runs from 1200Z on the 12th to 1800Z on the 13th, so 1800Z on the 12th is not the end of the forecast, and the earlier conditions do not persist.

The airport nearest your job site reports OVC012. What is the highest altitude you may operate your small UAS under Part 107?

• a.700 ft AGL, since staying 500 ft below the 1,200 ft ceiling is the only limit
• b.1,200 ft AGL, since you may operate right up to the reported cloud base
• c.400 ft AGL, since 500 ft below the clouds allows 700 ft but 400 ft still applies✓
• d.200 ft AGL, since you must remain 1,000 ft below any overcast layer

OVC012 is an overcast base at 1,200 ft AGL, and the required 500 ft of clearance below clouds would permit 700 ft AGL, but Part 107 separately caps routine operations at 400 ft AGL, so 400 ft is the controlling limit. When two rules apply, the more restrictive one governs. Flying at 700 ft would bust the altitude limit, flying at the cloud base violates cloud clearance, and there is no 1,000 ft below-cloud requirement for Part 107.14 CFR §107.51

What is the minimum flight visibility, as observed from the control station, required for small UAS operations under Part 107?

• a.3 statute miles✓
• b.1 statute mile
• c.5 statute miles
• d.3 nautical miles

Part 107 requires a minimum flight visibility of 3 statute miles measured from the location of the control station, which is what lets the remote pilot see and avoid other aircraft and obstacles. One statute mile is the special VFR figure used by manned aircraft, not the Part 107 minimum. Five statute miles applies to certain manned operations in Class E above 10,000 ft, and Part 107 visibility is stated in statute miles rather than nautical miles.14 CFR §107.51

You are flying at 300 ft AGL with 4 SM flight visibility, and a cloud bank sits about 1,200 ft horizontally from your aircraft. Is this operation legal?

• a.Yes, because 4 SM already exceeds the 3 SM visibility minimum
• b.Yes, because 300 ft AGL keeps the aircraft below the 400 ft limit
• c.No, because flight visibility must be at least 5 SM when near clouds
• d.No, because you must remain at least 2,000 ft horizontally from clouds✓

Part 107 requires the small UAS to stay at least 500 ft below and 2,000 ft horizontally away from clouds, so a cloud only 1,200 ft laterally makes the flight illegal even though visibility and altitude are fine. Meeting one requirement does not excuse violating another, so the two "yes" answers fail. The visibility minimum is 3 SM, not 5 SM, so the 4 SM reported here is legal and is not the reason the operation must stop.14 CFR §107.51

Which combination of conditions produces the highest density altitude at a given airport?

• a.Low field elevation, low temperature, and low humidity
• b.High field elevation, high temperature, and high humidity✓
• c.High field elevation, low temperature, and low humidity
• d.Low field elevation, high temperature, and high pressure

Density altitude rises whenever the air becomes less dense, and heat, moisture, high elevation, and low pressure all thin the air, so a hot, humid day at a high-elevation site gives the highest density altitude. Water vapor is lighter than dry air, so high humidity lowers density rather than raising it. Cold air and high pressure both increase density, which lowers density altitude, so the remaining combinations all produce better performance.

You launch a multirotor from a 6,500 ft mountain site on a 95 °F afternoon. What performance change should you expect?

• a.Propeller efficiency improves because thin air offers less resistance
• b.Battery voltage rises in thin air, giving noticeably longer endurance
• c.Lift increases because the warm air rising around the aircraft helps it climb
• d.Propellers produce less thrust, reducing climb rate and shortening flight time✓

High elevation plus high temperature means high density altitude, so the propellers move fewer air molecules per revolution and generate less thrust, which slows the climb, lengthens the takeoff run for fixed-wing UAS, and drains the battery faster for a shorter flight. Thin air does reduce drag slightly, but the loss of thrust dominates, so efficiency drops rather than improves. Density altitude has no effect on battery voltage, and localized warm air does not reliably add lift to a small UAS.

What are the standard atmospheric conditions used as the reference for aircraft performance at sea level?

• a.15 °C (59 °F) and 29.92 inHg✓
• b.0 °C (32 °F) and 30.00 inHg
• c.20 °C (68 °F) and 29.92 inHg
• d.15 °C (59 °F) and 28.92 inHg

The standard atmosphere at sea level is defined as 15 °C, which equals 59 °F, with a pressure of 29.92 inHg, and performance charts are built around that baseline. Density altitude is simply pressure altitude corrected for how far the actual temperature differs from this standard. The other options misstate either the standard temperature or the standard pressure, and a setting of 28.92 inHg would represent a very deep low-pressure system.

Your sUAS has a maximum airspeed of 30 knots. You fly straight out directly into a steady 12-knot wind, then return on the reciprocal course. What are your groundspeeds?

• a.30 knots outbound and 30 knots inbound, since wind does not change groundspeed
• b.42 knots outbound and 18 knots inbound
• c.18 knots outbound and 42 knots inbound✓
• d.12 knots outbound and 30 knots inbound

Groundspeed is airspeed adjusted for wind, so flying into a 12-knot headwind gives 30 minus 12, or 18 knots, and returning with that wind as a tailwind gives 30 plus 12, or 42 knots. This is why the outbound leg eats far more battery per mile and why you should turn back well before the halfway point of your endurance. Wind clearly does affect groundspeed, and the reversed option applies the headwind on the wrong leg.

The surface wind is 18 knots and you must launch from a ramp immediately downwind of a large metal hangar. What should you expect there?

• a.Smooth, steady air because the hangar blocks the wind completely
• b.Mechanical turbulence and rolling eddies on the lee side of the hangar✓
• c.A dependable updraft off the roof that improves your climb performance
• d.A wind gradient that reverses the wind direction above the roofline

Wind flowing over and around a building breaks into rolling eddies and downdrafts on the downwind, or lee, side, and this mechanical turbulence can flip or slam a light sUAS during launch and landing. The stronger the wind and the larger the obstruction, the more violent and further downwind the turbulence extends. An obstruction does not create a wind shadow of truly calm air, and there is no reliable updraft or reversal you could count on for performance.

Which set of conditions is most characteristic of a stable air mass?

• a.Cumuliform clouds, showery precipitation, and excellent visibility
• b.Clear skies, strong vertical currents, and unrestricted visibility
• c.Towering cumulus, gusty surface winds, and rapid temperature drops
• d.Stratiform clouds, steady precipitation, haze, and smooth flying air✓

Stable air resists vertical motion, so moisture and pollutants stay trapped near the surface, producing flat stratiform layers, steady drizzle or rain, haze that cuts visibility, and generally smooth flight conditions. That poor visibility is the main hazard for a remote pilot, since it can quickly drop below the 3 SM minimum. Cumuliform clouds, showers, gusts, and turbulence are all signatures of unstable air, not stable air.

During a morning survey you notice building cumulus clouds, gusty winds, and unusually crisp visibility. What does this suggest?

• a.Unstable air, so expect turbulence and possible afternoon showers✓
• b.Stable air, so expect drizzle, smooth flight, and hazy conditions
• c.A surface temperature inversion that will keep the air calm all day
• d.A stationary front that will hold conditions unchanged for many hours

Cumuliform cloud growth, gusty surface winds, and sharp visibility are the classic signature of unstable air, where rising currents mix out the haze but also create turbulence and can build into showers or thunderstorms later in the day. A remote pilot should plan for rough handling and a shrinking weather window. Drizzle, smooth air, and haze belong to stable conditions, and an inversion actually caps vertical motion and traps haze near the ground.

The surface temperature is 20 °C. Using the standard lapse rate, what temperature would you expect at 3,000 ft AGL?

• a.17 °C
• b.14 °C✓
• c.11 °C
• d.20 °C

The standard lapse rate is a decrease of about 2 °C for every 1,000 ft of altitude gain, so 3,000 ft produces roughly a 6 °C drop and 20 minus 6 leaves about 14 °C. Answering 17 °C applies only 1 °C per 1,000 ft, and 11 °C applies 3 °C per 1,000 ft. Temperature does not stay constant with height unless an inversion is present, which is an exception rather than the standard model.

An evening METAR reports the temperature and dew point as 14/12. What does this small spread tell the remote pilot?

• a.The air is very dry, so visibility should improve through the night
• b.A strong temperature inversion has formed just above the airport
• c.Humidity is high and fog or low clouds are likely as cooling continues✓
• d.The altimeter setting will fall rapidly over the next several hours

A 2 °C spread between temperature and dew point means the air is nearly saturated, and as the surface keeps cooling overnight the temperature can reach the dew point and produce fog or a low cloud deck. That directly threatens the 3 SM visibility and cloud clearance requirements for a dawn flight. A narrow spread indicates moist rather than dry air, and it says nothing by itself about inversions or the trend in the altimeter setting.

After a clear, calm night over damp farmland, a shallow layer of fog appears around sunrise. What type of fog is this?

• a.Advection fog, formed when warm moist air moves over a colder surface
• b.Radiation fog, formed when the ground cools under a clear, calm night sky✓
• c.Upslope fog, formed when moist air is pushed up gradually rising terrain
• d.Steam fog, formed when cold air moves across much warmer open water

Radiation fog forms on clear, nearly calm nights when the ground radiates its heat away, chills the moist air just above it to the dew point, and leaves a shallow ground fog that is usually thickest near sunrise. It typically burns off within a few hours after the sun warms the surface. Advection fog requires horizontal movement of warm moist air over a cold surface, upslope fog requires terrain and wind, and steam fog requires a warm water surface under cold air.

Which thunderstorm stage is the most hazardous, and what defines it?

• a.The mature stage, with strong updrafts and downdrafts and heavy precipitation✓
• b.The cumulus stage, with continuous downdrafts and a well-developed gust front
• c.The dissipating stage, with the strongest hail, lightning, and wind shear
• d.The cumulus stage, with heavy rain already reaching the surface

A thunderstorm is most dangerous in the mature stage, which begins when precipitation reaches the ground and updrafts and downdrafts coexist inside the cell, producing severe turbulence, wind shear, hail, lightning, and a gust front that can race far ahead of the storm. The cumulus stage is dominated by updrafts only, with no rain yet at the surface, and the dissipating stage is dominated by weakening downdrafts. Remote pilots should stay at least 20 NM away from any thunderstorm.

What best describes a microburst?

• a.A slow, wide column of rising air that can lift an sUAS above 400 ft AGL
• b.A gradual change of wind direction with altitude over several thousand feet
• c.An intense localized downdraft causing severe wind shear for about 15 minutes✓
• d.A steady sea breeze front that pushes inland during the warmest afternoon hours

A microburst is a small but extremely strong downdraft that slams into the ground and spreads outward, generating severe wind shear with horizontal winds that can exceed 100 knots, and an individual microburst typically lasts only about 15 minutes. That short life and small size make it hard to see coming, which is exactly why remote pilots avoid the area near any convective cell. It is a downdraft rather than an updraft, and it is far more violent and abrupt than a normal wind gradient or a sea breeze.

On a cold morning you find a thin coat of frost on your aircraft's arms and propeller blades. What is the correct action?

• a.Polish the frost smooth so that airflow stays attached to the blades
• b.Launch as planned, since frost is harmless at the low speeds a UAS flies
• c.Hover briefly at low power and let the rotor wash blow the frost away
• d.Remove all frost before flight, since it disrupts airflow and adds weight✓

Frost roughens the surfaces that generate lift, disrupting smooth airflow over the propeller blades and airframe while also adding weight, which reduces thrust and can prevent a normal takeoff. The only acceptable action is to remove all of it before flight. Polishing frost smooth is specifically not acceptable, low airspeed does not make contamination harmless, and attempting to hover it off means the aircraft is already flying in a degraded condition.