Weather Information

Question 1

What factor primarily determines the type and vertical extent of clouds? (AC 00-6)

Answer 1

The stability of the atmosphere.

Question 2

Explain the difference between a stable atmosphere and an unstable atmosphere. Why is the stability of the atmosphere important? (FAA-H-8083-25, AC 00-6)

Answer 2

The stability of the atmosphere depends on its ability to resist vertical motion. A stable atmosphere makes vertical movement difficult, and small vertical disturbances dampen out and disappear. In an unstable atmosphere, small vertical air movements tend to become larger, resulting in turbulent airflow and convective activity. Instability can lead to significant turbulence, extensive vertical clouds, and severe weather.

Question 3

How can you determine the stability of the atmosphere? (AC 00-6)

Answer 3

When temperature decreases uniformly and rapidly as you climb (approaching 3°C per 1,000 feet), you have an indication of unstable air. If the temperature remains unchanged or decreases only slightly with altitude, the air tends to be stable. When air near the surface is warm and moist, suspect instability.

Question 4

List the effects of stable and unstable air on clouds, turbulence, precipitation and visibility. (AC 00-6)

Answer 4

Question 5

Most of the Earth’s weather occurs in what region of the atmosphere? (AC 00-6)

Answer 5

Most of the Earth’s weather occurs in the troposphere, which begins at the Earth’s surface and extends up to approximately 36,000 feet. As the gases in this layer decrease with height, the air becomes thinner and the temperature decreases from about 15°C (59°F) to -56.5°C (-70°F).

Question 6

What are the standard temperature and pressure values for sea level? (FAA-H-8083-25)

Answer 6

15°C (59°F) and 29.92”Hg (1013.2 mb)

Question 7

What are “isobars”? (AC 00-6)

Answer 7

An isobar is a line on a weather chart that connects areas of equal or constant barometric pressure.

Question 8

If the isobars are relatively close together on a surface weather chart or a constant pressure chart, what information will this provide? (AC 00-6)

Answer 8

The spacing of isobars on these charts defines how steep or shallow a pressure gradient is. When isobars are spaced very close together, a steep pressure gradient exists, which indicates higher wind speeds. A shallow pressure gradient (isobars not close together) usually means wind speeds will be lower.

Question 9

What does “dew point” mean? (AC 00-6)

Answer 9

Dew point is the temperature to which a sample of air must be cooled to attain the state of saturation.

Question 10

When temperature and dew point are close together (within 5°F), what type of weather is likely? (AC 00-6)

Answer 10

Visible moisture in the form of clouds, dew, or fog. These are also ideal conditions for carburetor icing.

Question 11

State the general characteristics in regard to the flow of air around high-pressure and low-pressure systems in the Northern Hemisphere. (AC 00-6)

Answer 11

Low Pressure—inward, upward, and counterclockwise

High Pressure—outward, downward, and clockwise

Question 12

If your route of flight takes you toward a low-pressure system, in general what kind of weather can you expect? What if you were flying toward a high-pressure system? (AC 00-6)

Answer 12

A low-pressure system is characterized by rising air, which is conducive to cloudiness, precipitation and bad weather. A high-pressure system is an area of descending air, which tends to favor dissipation of cloudiness and good weather.

Question 13

Describe the different types of fronts. (AC 00-6)

Answer 13

Cold front—occurs when a mass of cold, dense, and stable air advances and replaces a body of warmer air.

Occluded front—A frontal occlusion occurs when a fast-moving cold front catches up with a slow-moving warm front. The two types are the cold front occlusion and warm front occlusion.

Warm front—The boundary area formed when a warm air mass contacts and flows over a colder air mass.

Stationary front—When the forces of two air masses are relatively equal, the boundary or front that separates them remains stationary and influences the local weather for days. The weather is typically a mixture of both warm and cold fronts.

Question 14

What are the general characteristics of the weather a pilot would encounter when operating near a cold front? A warm front? (FAA-H-8083-25)

Answer 14

Cold Front—As the front passes, expected weather can include towering cumulus or cumulonimbus, heavy rain accompanied by lightning, thunder and/or hail; tornadoes possible; during passage, poor visibility, winds variable and gusting; temperature/dew point and barometric pressure drop rapidly.

Warm Front—As the front passes, expected weather can include stratiform clouds, drizzle, low ceilings and poor visibility; variable winds; rise in temperature.

Note: The weather associated with a front depends on the amount of moisture available, the degree of stability of the air that is forced upward, the slope of the front, the speed of frontal movement, and the upper wind flow.

Question 15

What is a “trough”? (AC 00-6)

Answer 15

A trough (also called a trough line) is an elongated area of relatively low atmospheric pressure. At the surface, when air converges into a low, it cannot go outward against the pressure gradient, and it cannot go downward into the ground; it must go upward. Therefore, a low or trough is an area of rising air. Rising air is conducive to cloudiness and precipitation; hence the general association of low pressure and bad weather.

Question 16

What is a “ridge”? (AC 00-6)

Answer 16

A ridge (also called a ridge line) is an elongated area of relatively high atmospheric pressure. Air moving out of a high or ridge depletes the quantity of air; therefore, these are areas of descending air. Descending air favors dissipation of cloudiness; hence the association of high pressure and good weather.

Question 17

What is the primary means of obtaining a weather briefing? (AIM 7-1-2, 7-1-4)

Answer 17

The primary source of preflight weather briefings is an individual briefing obtained from a briefer at the FSS. These briefings, which are tailored to your specific flight, are available 24 hours a day through the use of the toll-free number (1-800-WX BRIEF).

Question 18

What are some examples of other sources of weather information? (AIM 7-1-2, 7-1-7, 7-1-8)

Answer 18

a. Telephone Information Briefing Service (TIBS) (FSS)

b. Weather and aeronautical information from numerous private industry sources.

c. The Direct User Access Terminal System (DUATS) and Lockheed Martin Flight Services (DUATSII).

d. In Alaska, Transcribed Weather Broadcast (TWEB) locations and telephone access to the TWEB (TEL-TWEB).

Question 19

Does the weather data provided by commercial and/or third-party vendors satisfy the preflight action required by 14 CFR §91.103? (AIM 7-1-3)

Answer 19

Pilots and operators should be aware that weather services provided by entities other than the FAA, NWS or their contractors (such as the DUATS and Lockheed Martin Flight Services DUATS II) might not meet FAA/NWS quality control standards. All operators and pilots contemplating using such services should request and/or review an appropriate description of services and provider disclosure. When in doubt, consult with an FAA Flight Service Specialist.

Question 20

What type of weather briefings are available from an FSS briefer? (AIM 7-1-4)

Answer 20

Standard Briefing—Request anytime you are planning a flight and you have not received a previous briefing or have not received preliminary information through mass-dissemination media; e.g., TIBS, TWEB, etc.

Abbreviated Briefing—Request when you need information to supplement mass-disseminated data, update a previous briefing, or when you need only one or two items.

Outlook Briefing—Request whenever your proposed time of departure is six or more hours from the time of the briefing. This is for planning purposes only.

Inflight Briefing—Request when needed to update a preflight briefing.

Question 21

What pertinent information should a weather briefing include? (AIM 7-1-4)

Answer 21

a. Adverse Conditions

b. VFR Flight Not Recommended

c. Synopsis

d. Current Conditions

e. Enroute Forecast

f. Destination Forecast

g. Winds Aloft

h. Notices to Airmen

i. ATC Delay

j. Pilots may obtain the following from FSS briefers upon request: information on special use airspace (SUA) and SUA-related airspace, including alert areas, MOAs, MTRs (IFR, VFR, VR, and SR training routes), warning areas, and ATC assigned airspace (ATCAA); a review of the printed NOTAM publication; approximate density altitude data; information on air traffic services and rules; customs/immigration procedures; ADIZ rules; search and rescue; GPS RAIM availability for 1 hour before to 1 hour after ETA or a time specified by the pilot; and other assistance as required.

Question 22

What is a “flight information service” (FIS)? (FAA-H-8083-25)

Answer 22

Flight Information Services–Broadcast (FIS-B) is a ground broadcast service provided through the Automatic Dependent Surveillance–Broadcast (ADS-B) services network over the 978 MHz UAT data link. The FAA FIS-B system provides pilots and flight crews of properly equipped aircraft with a flight-deck display of aviation weather and aeronautical information.

Question 23

Can onboard datalink weather (FIS-B) be useful in navigating an aircraft safely around an area of thunderstorms? (AC 00-24; AIM 7-1-10)

Answer 23

Weather data linked from a ground weather surveillance radar system is not real-time information; it displays recent rather than current conditions. This data is typically updated every 5 minutes, but can be as much as 15 minutes old by the time it displays in the cockpit. Therefore, FIS aviation weather products are not appropriate for tactical avoidance of severe weather such as negotiating a path through a weather hazard area.

Question 24

What is HIWAS? (AIM 7-1-9)

Answer 24

Hazardous In-flight Weather Advisory Service is a continuous broadcast of inflight weather advisories including summarized Aviation Weather Warnings, SIGMETs, Convective SIGMETs, Center Weather Advisories, AIRMETs, and urgent PIREPs. HIWAS is an additional source of hazardous weather information which makes this data available on a continuous basis. NAVAIDs with HIWAS capability are depicted on sectionals by an “H” in the upper right corner of the identification box.

Question 25

What is ATIS? (AIM 4-1-13)

Answer 25

Automatic Terminal Information Service— the continuous broadcast of recorded noncontrol information in selected high activity terminal areas. Its purpose is to improve controller effectiveness and to relieve frequency congestion by automating the repetitive transmission of essential but routine information. The information is continuously broadcast over a discrete VHF radio frequency or the voice portion of a local NAVAID, and updated upon the receipt of any official hourly and special weather.

Question 26

What type of information is provided in an ATIS broadcast? (AIM 4-1-13)

Answer 26

Information includes the time of the latest weather sequence, ceiling, visibility, obstructions to visibility, temperature, dew point (if available), wind direction (magnetic), and velocity, altimeter, other pertinent remarks, instrument approach and runway in use.

Question 27

While en route, how can a pilot obtain updated weather information? (FAA-H-8083-25)

Answer 27

a. FSS on 122.2 and appropriate RCO (remote communication outlet) frequencies

b. ATIS broadcasts along the route of flight

c. HIWAS (Hazardous Inflight Weather Advisory Service)

d. Datalink weather—cockpit display of FIS-B information

e. ATC (workload permitting)

Question 28

What is a METAR? (AC 00-45)

Answer 28

The aviation routine weather report (METAR) is the weather observer’s interpretation of the weather conditions at a given site and time. There are two types of METAR reports: a routine METAR report that is transmitted every hour and an aviation selected special weather report (SPECI). This is a special report that can be given at any time to update the METAR for rapidly changing weather conditions, aircraft mishaps, or other critical information

Example:

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

Question 29

Describe the various types of weather observing programs now in use. (AIM 7-1-11)

Answer 29

Manual observations—Reports made from airport locations staffed by FAA or NWS personnel.

AWOS—Automated Weather Observing System; consists of various sensors, a processor, a computer-generated voice subsystem, and a transmitter to broadcast local, minute-by-minute weather data directly to the pilot. Observations will include the prefix AUTO in data.

AWOS broadcasts—In addition to the AWOS computer-generated voice, some systems are configured to permit station personnel to append the automated report with an operator-generated message.

ASOS/AWSS—Automated Surface Observing System (ASOS) /Automated Weather Sensor System (AWSS), the primary surface weather observing system of the U.S. Provides the continuous minute-by-minute observations necessary to generate METARs and other aviation weather information. The information may be transmitted over a discrete VHF radio frequency or the voice portion of a local NAVAID.

Question 30

What are PIREPs and where are they usually found? (AC 00-45)

Answer 30

A pilot report (PIREP) provides valuable information regarding the conditions as they actually exist in the air—information which cannot be gathered from any other source. Pilots can confirm the height of bases and tops of clouds, locations of wind shear and turbulence, and the location of inflight icing. There are two types of PIREPs: routine or “UA,” and urgent or “UUA.” PIREPs should be given to the ground facility with which communications are established (i.e., FSS, ARTCC, or terminal ATC). Altitudes are MSL, visibilities SM, and distances in NM. PIREPs are available from ATC, FSS, and on the internet at: https://aviationweather.gov/airep

Question 31

What are Terminal Aerodrome Forecasts (TAFs)? (AC 00‑45)

Answer 31

A TAF is a concise statement of the expected meteorological conditions significant to aviation for a specified time period within five statute miles (SM) of the center of the airport’s runway complex (terminal). The TAFs use the same weather codes found in METAR weather reports, in the following format:

a. Type of reports—a routine forecast (TAF); an amended forecast (TAF AMD), or a corrected forecast (TAF COR).

b. ICAO station identifier—4-letter station identifier.

c. Date and time of origin—the date/time of the forecast follows the terminal’s location identifier and shows the day of the month in two digits, and the time in which the forecast is completed and ready for transmission in four digits, appended with a Z to denote UTC. Example: 061737Z—the TAF was issued on the 6th day of the month at 1737 UTC.

d. Valid period date and time—The first two digits are the day of the month for the start of the TAF, followed by two digits that indicate the starting hour (UTC). The next two digits indicate the day of the month for the end of the TAF, and the last two digits are the ending hour (UTC) of the valid period. Scheduled 24- and 30-hour TAFs are issued four (4) times per day, at 0000, 0600, 1200, and 1800Z. Example: A 00Z TAF issued on the 9th of the month and valid for 24 hours would have a valid period of 0900/0924.

e. Forecasts—wind, visibility, significant and vicinity weather, cloud and vertical obscuration, non-convective low-level wind shear, and forecast change indicators (FM, TEMPO and PROB)

Question 32

What is an Aviation Area Forecast (FA)? (AC 00-45)

Answer 32

Abbreviated “FA,” this is a forecast of specified weather phenomena covering a flight information region or other area designated by the meteorological authority. Pilots should use the area forecast (in conjunction with AIRMETs, SIGMETs, convective SIGMETs, CWAs, etc.) to determine forecast enroute weather and to interpolate conditions at airports that do not have a terminal aerodrome forecast (TAF). FAs are issued 3 times daily for each of the 6 areas in the contiguous 48 states. FAs are also issued for the Gulf of Mexico, the Caribbean, Hawaii, and Alaska.

Note: Plans are to discontinue the six FAs covering the continental United States (CONUS) and the one FA covering Hawaii, and subsequently replace them with digital and graphical products (GFA) produced by the NWS. No near-term changes are planned for the FAs for Alaska, the Caribbean, or the Gulf of Mexico.

Question 33

What is a Graphical Forecast for Aviation (GFA)? (AWC)

Answer 33

The Graphical Forecast for Aviation (GFA) is intended to provide the necessary aviation weather information as a complete picture of the weather that may impact flight in the continental United States. The webpage includes observational data, forecasts, and warnings that can be viewed from 14 hours in the past to 15 hours in the future, including thunderstorms, clouds, flight category, precipitation, icing, turbulence and wind.

Question 34

What are the four types of Inflight Aviation Weather Advisories? (AIM 7-1-5)

Answer 34

Inflight Aviation Weather Advisories are forecasts to advise enroute aircraft of the development of potentially hazardous weather. The four types are the SIGMET (WS), the convective SIGMET (WST), the AIRMET (WA; text or graphical product), and the center weather advisory (CWA). All heights are referenced MSL, except in the case of ceilings (CIG) which indicate AGL.

Question 35

What is a convective SIGMET? (AC 00-45)

Answer 35

Convective SIGMETs (WST) imply severe or greater turbulence, severe icing and low-level wind shear. They may be issued for any convective situation which the forecaster feels is hazardous to all categories of aircraft. Bulletins are issued hourly at H+55, and special bulletins are issued at any time as required and updated at H+55. The text of the bulletin consists of either an observation and a forecast, or just a forecast (valid for up to 2 hours):

a. Severe thunderstorms due to:

• Surface winds greater than or equal to 50 knots.

• Hail at the surface greater than or equal to 3⁄4 inches in diameter.

• Tornadoes.

b. Embedded thunderstorms.

c. A line of thunderstorms.

d. Thunderstorms that produce precipitation levels greater than or equal to heavy-intensity precipitation, affecting 40% or more of an area at least 3,000 square miles.

Question 36

What is a SIGMET (WS)? (AIM 7-1-5)

Answer 36

A SIGMET (WS) advises of weather that is potentially hazardous to all aircraft. SIGMETs are unscheduled products that are valid for 4 hours. However, SIGMETs associated with tropical cyclones and volcanic ash clouds are valid for 6 hours. Unscheduled updates and corrections are issued as necessary. In the conterminous United States, SIGMETs are issued when the following phenomena occur or are expected to occur:

a. Severe icing not associated with thunderstorms.

b. Severe or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms.

c. Widespread dust storms or sandstorms lowering surface visibilities to below 3 miles.

d. Volcanic ash.

Question 37

What is an AIRMET (WA)? (AIM 7-1-5)

Answer 37

An AIRMET is an advisory of significant weather phenomena that describes conditions at intensities lower than those which require the issuance of SIGMETs. They are issued every 6 hours beginning at 0245 UTC. Pilots should use AIRMETs in the preflight and enroute phase of flight to enhance safety. AIRMET information is available in two formats: text bulletins (WA) and graphics (G-AIRMET). Unscheduled updates and corrections are issued as necessary. AIRMETs contain details about IFR, extensive mountain obscuration, turbulence, strong surface winds, icing, and freezing levels.

Question 38

What are the different types of AIRMETs? (AIM 7-1-5)

Answer 38

There are three types of AIRMETs, Sierra, Tango, and Zulu:

a. AIRMET Sierra describes IFR conditions and/or extensive mountain obscurations.

b. AIRMET Tango describes moderate turbulence, sustained surface winds of 30 knots or greater, and/or nonconvective low-level wind shear.

c. AIRMET Zulu describes moderate icing and provides freezing level heights.

Question 39

What is a winds and temperatures aloft forecast (FB)? (AC 00-45)

Answer 39

Winds and temperatures aloft are forecast for specific locations in the contiguous U.S. and also for a network of locations in Alaska and Hawaii. These forecasts, called FBs, are issued 4 times daily. In an FB, a 4-digit code group shows wind direction, in reference to true north, and wind speed in knots, with an additional 2-digit code group showing forecast temperatures in degrees Celsius. Wind forecasts are not issued for altitudes within 1,500 feet of a location’s elevation.

Question 40

What valuable information can be determined from an FB? (AC 00-45)

Answer 40

Most favorable altitude—based on winds and direction of flight.

Areas of possible icing—by noting air temperatures of +2°C to -20°C.

Temperature inversions—a temperature increase with altitude can mean a stable layer aloft reducing the chance for convective activity.

Turbulence—by observing abrupt changes in wind direction and speed at different altitudes.

Question 41

What is a Center Weather Advisory (CWA)? (AC 00-45)

Answer 41

Issued by a CWSU (Center Weather Service Unit), this is an aviation warning for use by aircrews to anticipate and avoid adverse weather conditions in the enroute and terminal environments. The CWA is a short-term “nowcast,” pinpointing hazardous weather already causing an impact or expected to cause an impact within a 2-hour period; therefore it is an inflight advisory rather than a flight planning tool. CWAs are valid for a maximum of 2 hours; if conditions are expected to continue beyond the 2-hour valid period, a statement will be included in the CWA.

Question 42

What is a Convective Outlook (AC)? (AC 00-45)

Answer 42

The convective outlook (AC) is a narrative and graphical outlook of the potential for severe (tornado, wind gusts 50 knots or greater, or hail 1 inch or greater in diameter) and non-severe (general) convection and specific severe weather threats during the following 8 days. It defines areas of marginal risk (MRGL), slight risk (SLGT), enhanced risk (ENH), moderate risk (MDT), or high risk (HIGH) of severe weather based on a percentage probability.

Question 43

What is a surface analysis chart? (AC 00-45)

Answer 43

A surface analysis chart is an analyzed chart of surface weather observations. It depicts the distribution of multiple items, including sea level pressure; the positions of highs, lows, ridges, and troughs; the location and character of fronts; and the various boundaries such as drylines, outflow boundaries, sea-breeze fronts, and convergence lines. The chart is produced eight times daily.

Question 44

Describe a Ceiling and Visibility Analysis (CVA). (AC 00-45)

Answer 44

The CVA product provides a real-time analysis of current observed and estimated ceiling and visibility conditions across the continental United States (CONUS). The product is primarily intended to help the general aviation pilot (particularly the visual flight rules [VFR]-only pilot) avoid instrument flight rules (IFR) conditions. However, CVA’s overview of ceiling and visibility conditions can be useful to others involved in flight planning or weather briefing. See http://aviationweather.gov/cva

Question 45

What information does a weather depiction chart provide? (AC 00-45)

Answer 45

A Weather Depiction Chart contains a plot of weather conditions at selected METAR stations and an analysis of weather flying categories (IFR, MVFR,VFR). It is primarily a briefing tool to alert pilots to the location of critical or near-critical operational minimums at terminals in the conterminous U.S. and surrounding land areas. The chart is issued eight times daily starting at 0100 UTC.

Note: The Weather Depiction Chart is being phased out by the NWS in favor of newer ceiling and visibility products, such as the CVA product.

Question 46

What information do short-range surface prognostic charts provide? (AC 00-45)

Answer 46

Short-range surface prognostic (prog) charts provide a forecast of surface pressure systems, fronts and precipitation for a 2½ day period. They cover a forecast area of the 48 contiguous states and coastal waters. Predicted conditions are divided into five forecast periods: 12, 18, 24, 48 and 60 hours. Each chart depicts a snapshot of weather elements expected at the specified valid time. Charts are issued four times a day and can be used to obtain an overview of the progression of surface weather features during the included periods.

Question 47

Describe a low-level significant weather chart. (AC 00-45)

Answer 47

The low-level significant weather (SIGWX) charts provide a forecast of aviation weather hazards and are primarily intended to be used as guidance products for pre-flight briefings. The forecast domain covers the CONUS and the coastal waters for altitudes Flight Level 240 and below. The chart depicts weather flying categories, turbulence, and freezing levels and provides a “snapshot” of weather expected at the specified valid time. The charts are issued four times per day by the NWS AWC. Two charts are issued: a 12-hour and a 24-hour prog. Both are available at: http://www.aviationweather.gov

Exam Tip: Be prepared to interpret and discuss current and forecast weather along your planned route of flight. The evaluator will expect you to demonstrate your ability to interpret the various aviation weather reports, forecasts, and charts/graphics and make an assessment of how the weather will affect your planned flight.

Question 48

What are NOTAMs? (AIM 5-1-3)

Answer 48

Notices To Airmen (NOTAM)—Time critical aeronautical information which is of either a temporary nature or not sufficiently known in advance to permit publication on aeronautical charts or in other operational publications receives immediate dissemination via the National NOTAM System. It includes such information as airport or primary runway closures, changes in the status of navigational aids, ILS’s, radar service availability, and other information essential to planned enroute, terminal, or landing operations.

Question 49

Explain the following types of NOTAMs: (D) NOTAMS, FDC NOTAMs, Pointer NOTAMs, Military NOTAMs, SAA NOTAMs, and FICON NOTAMs. (AIM 5-1-3)

Answer 49

a. (D) NOTAMs — Information that requires wide dissemination via telecommunication and pertains to en route navigational aids, civil public-use airports listed in the AFD, facilities, services, and procedures.

b. FDC NOTAMs — Flight information that is regulatory in nature including, but not limited to, changes to IFR charts, procedures, and airspace usage.

c. POINTER NOTAMs — Issued by a flight service station to highlight or point out another NOTAM; such as an FDC NOTAM. These NOTAMs assist users in cross-referencing important information that may not be found under an airport or NAVAID identifier.

d. MILITARY NOTAMs — Pertain to U.S. Air Force, Army, Marine, and Navy navigational aids/airports that are part of the NAS.

e. SAA NOTAMs — Issued when Special Activity Airspace will be active outside the published schedule times and when required by the published schedule. Pilots are still responsible for checking published schedule times for Special Activity Airspace as well as any NOTAMs for that airspace.

f. FICON NOTAMs — field condition NOTAM; provide contaminant measurements for paved runways.

Question 50

All (D) NOTAMs will have keywords contained within the first part of the text. What are several examples of these keywords? (AIM 5-1-3)

Answer 50

RWY TWY RAMP APRON AD

OBST NAV COM SVC AIRSPACE

U (unverified aeronautical information)

O (other aeronautical information)

Question 51

Where can NOTAM information be obtained? (AIM 5-1-1; 5-1-3)

Answer 51

a. FSS

b. DUATS vendors—CSC DUATS and Lockheed Martin Flight Services DUATS II.

c. Notices to Airmen Publication (NTAP)—published every 28 days; data of a permanent nature can be published in the NTAP as an interim step between publication cycles of the Chart Supplement U.S. and aeronautical charts.

d. NOTAMs are available at the FAA website:https://pilotweb.nas.faa.gov/PilotWeb (case-sensitive)

Question 52

What are the three principal types of thunderstorms? (AC 00-6)

Answer 52

Single cell—also called ordinary cell thunderstorms, this type consists of only one cell; they are easily circumnavigated except at night or when embedded in other clouds. Single cell thunderstorms are rare, as almost all thunderstorms are multi-celled.

Multicell (cluster and line)—consists of a cluster of cells at different stages of their life cycles. As the first cell matures, it is carried downwind, and a new cell forms upwind to take its place. A multicell may have a lifetime of several hours (or more), which makes it tougher to circumnavigate than a single-cell thunderstorm. May have supercells embedded within them.

Supercell—consists primarily of a single, quasi-steady rotating updraft that persists for an extended period of time. Updraft speeds may reach 9,000 fpm (100 knots). They may persist for many hours (or longer) and their size and persistence make them tough to circumnavigate.

Question 53

When attempting to avoid turbulence around thunderstorms, explain several operational procedures a pilot should never attempt. (AIM 7-1-28)

Answer 53

a. Never land or take off in the face of an approaching thunderstorm. A sudden gust front of low-level turbulence could cause loss of control.

b. Never attempt to fly under a thunderstorm even if you can see through to the other side. Turbulence and wind shear under the storm could be hazardous.

c. Never attempt to fly under the anvil of a thunderstorm. There is a potential for severe and extreme clear air turbulence.

d. Never fly without airborne radar into a cloud mass containing scattered embedded thunderstorms. Scattered thunderstorms not embedded usually can be visually circumnavigated.

e. Never trust the visual appearance to be a reliable indicator of the turbulence inside a thunderstorm.

f. Never assume that ATC will offer radar navigation guidance or deviations around thunderstorms.

g. Never use data-linked next generation weather radar (NEXRAD) mosaic imagery as the sole means for negotiating a path through a thunderstorm area (tactical maneuvering).

Question 54

When flying an airplane without onboard thunderstorm detection equipment, describe procedures a pilot can take to avoid thunderstorms and/or the turbulence associated with them. (AIM 7-1-28)

Answer 54

a. Remember that the data-linked NEXRAD mosaic imagery shows where the weather was, not where the weather is. The weather conditions may be 15 to 20 minutes older than the age indicated on the display.

b. Listen to chatter on the ATC frequency for PIREPs and other aircraft requesting to deviate or divert.

c. Ask ATC for radar navigation guidance or to approve deviations around thunderstorms, if needed.

d. Use data-linked weather NEXRAD mosaic imagery (i.e., FIS-B) for route selection to avoid thunderstorms entirely (strategic maneuvering).

e. Advise ATC, when switched to another controller, that you are deviating for thunderstorms before accepting to rejoin the original route.

f. Always ensure that after an authorized weather deviation, before accepting to rejoin the original route, that the route of flight is clear of thunderstorms.

g. Avoid by at least 20 miles any thunderstorm identified as severe or giving an intense radar echo. This is especially true under the anvil of a large cumulonimbus.

h. Circumnavigate the entire area if the area has 6/10 thunderstorm coverage.

i. Remember that vivid and frequent lightning indicates the probability of a severe thunderstorm.

Question 55

Can ATC provide inflight assistance in avoiding thunderstorms and severe weather? (AIM 7-1-13)

Answer 55

Yes, to the extent possible, controllers will issue pertinent information on weather or chaff areas and assist pilots in avoiding such areas when requested. Pilots should respond to a weather advisory by either acknowledging the advisory or by requesting an alternate course of action as appropriate.

However, the controller’s primary responsibility is to provide safe separation between aircraft. Additional services such as weather avoidance assistance can only be provided to the extent that it doesn’t interfere with their primary function. ATC radar limitations and frequency congestion may also limit the controller’s capability to assist.

Question 56

Give some examples of charts and reports useful in determining the potential for and location of thunderstorms along your route. (AC 00-45)

Answer 56

a. Convective Outlook (AC)—a narrative and graphical outlook of areas of slight, moderate, or high risk of severe thunderstorms for a 24-hour period.

b. Significant Weather Chart (SIGWX)—provides a forecast of aviation weather hazards; depicts a snapshot of weather expected at the specified valid time.

c. Weather Radar Observations—(and their resultant images) are graphical displays of precipitation and non-precipitation targets detected by weather radars (NEXRAD). Regional and national radar mosaics can be found on the websites of the NWS, AWC, all NWS weather forecast offices (WFOs), as well as commercial aviation weather providers.

d. Convective SIGMETs (WST)—issued for any convective situation involving severe, embedded, and lines of thunderstorms.

e. Pilot Reports (PIREPs)—help determine actual conditions along your planned route of flight.

f. Supplementary weather products—can be used for enhanced situational awareness; supplementary weather products must only be used in conjunction with one or more NWS primary weather products.

Question 57

What are microbursts? (AIM 7-1-25)

Answer 57

Microbursts are small-scale intense downdrafts which, on reaching the surface, spread outward in all directions from the downdraft center. This causes the presence of both vertical and horizontal wind shears that can be extremely hazardous to all types and categories of aircraft, especially at low altitudes. Due to their small size, short life span, and the fact that they can occur over areas without surface precipitation, microbursts are not easily detectable using conventional weather radar or wind shear alert systems.

Question 58

Where are microbursts most likely to occur? (AIM 7-1-25)

Answer 58

Microbursts can be found almost anywhere there is convective activity. They may be embedded in heavy rain associated with a thunderstorm or in light rain in benign-appearing virga. When there is little or no precipitation at the surface accompanying the microburst, a ring of blowing dust may be the only visual clue of its existence.

Question 59

What are some basic characteristics of a microburst? (AIM 7-1-25)

Answer 59

Size: less than 1 mile in diameter as it descends from the cloud base; can extend 21⁄2 miles in diameter near ground level.

Intensity: downdrafts as strong as 6,000 feet per minute; horizontal winds near the surface can be as strong as 45 knots resulting in a 90-knot wind shear (headwind to tailwind change for traversing aircraft).

Duration: an individual microburst will seldom last longer than 15 minutes from the time it strikes the ground until dissipation. Sometimes microbursts are concentrated into a line structure, and under these conditions activity may continue for as long as an hour.

Question 60

What types of weather information will you examine to determine if microburst/windshear conditions might affect your flight? (AC 00-54)

Answer 60

The following should be examined for clues of potential microburst/windshear conditions affecting the flight:

TAFs—examine the terminal forecast for convective activity.

METARs—inspect for windshear clues (thunderstorms, rainshowers, blowing dust).

Severe weather watch reports—check for issuance since severe convective weather is a prime source for microbursts and windshear.

LLWAS reports—Low Level Windshear Alert System, designed to detect wind shifts between outlying stations and a reference station.

TDWR—Terminal Doppler Weather Radar, deployed at 45 airports across the United States; detects microbursts, gust fronts, wind shifts and precipitation intensities and provides severe weather alerts and warnings to ATC and pilots.

SIGMETs and convective SIGMETs—may provide essential clues.

Visual clues from the cockpit—heavy rain (in a dry or moist environment) which can be accompanied by curling outflow, a ring of blowing dust or localized dust in general, flying debris, virga, a rain core with rain diverging away horizontally from the rain core, or tornadic features (funnel clouds, tornadoes). At night, lightning may be the only visual clue.

PIREPs—reports of sudden airspeed changes in the airport approach or landing corridors provide indication of the presence of windshear.

Airborne weather radar—to detect convective cells.

Question 61

Define wind shear and state the areas in which it is likely to occur. (AC 00-54)

Answer 61

Wind shear is the rate of change of wind velocity (direction and/or speed) per unit distance; conventionally expressed as vertical or horizontal wind shear. It may occur at any level in the atmosphere but three areas are of special concern:

a. Wind shear with a low-level temperature inversion;

b. Wind shear in a frontal zone or thunderstorm; and

c. Clear air turbulence (CAT) at high levels associated with a jet stream or strong circulation.

Question 62

Why is wind shear an operational concern to pilots? (AC 00-6)

Answer 62

Wind shear is an operational concern because unexpected changes in wind speed and direction can be potentially very hazardous to aircraft operations at low altitudes on approach to and departing from airports.

Question 63

What airplane characteristics will be observed in the following wind shear situations?

—a sudden increase in headwind.

—a sudden decrease in headwind.

Answer 63

Increased headwind—As a tailwind shears to a constant headwind, an increase in airspeed and altitude occurs along with a nose-up pitching tendency. The usual reaction is to reduce both power and pitch. This reaction can be dangerous if the aircraft suddenly encounters a downdraft and tailwind. Now the situation demands the exact opposite of the pilot’s initial reaction: a need for more performance from the airplane instead of less (more power/increased pitch attitude).

Decreased headwind—As a headwind shears to a calm or tailwind, pitch attitude decreases, airspeed decreases, and a loss of altitude occurs. The required action is more power and higher pitch attitude to continue a climb or remain on the glide slope.

Question 64

Concerning wind shear detection, what does the abbreviation LLWAS indicate? (AIM 4-3-7)

Answer 64

Low-Level Wind Shear Alert System (LLWAS) is a computerized system that detects the presence of a possible hazardous low-level wind shear by continuously comparing the winds measured by sensors installed around the periphery of an airport with the wind measured at the center of the airport. If the difference between the center field wind sensor and a peripheral wind sensor becomes excessive, a thunderstorm or thunderstorm gust front wind shear is possible.