Chapter 1


A. Certificates, Ratings and Currency Requirements

1. An applicant for an instrument rating must have at least how much and what type of flight time as pilot? (14 CFR §61.65)

An applicant must have:
a. 50 hours of cross-country flight time as PIC, of which at least 10 hours must be in airplanes;
b. 40 hours of actual or simulated instrument time (on the areas of operation specified);
c. 15 hours of instrument flight training from an authorized instructor in the aircraft category for which the instrument rating is sought;
d. 3 hours of instrument training appropriate to the instrument rating sought from an authorized instructor, in preparation for the practical test, within the 60 days preceding the date of test;
e. 250 NM cross-country, conducted under IFR, including 3 different kinds of approaches.

2. When is an instrument rating required? (14 CFR §61.3e, 91.157)

When operations are conducted:
a. Under instrument flight rules (IFR flight plan),
b. In weather conditions less than the minimum for VFR flight,
c. In Class A airspace,
d. Under Special VFR within Class B, Class C, Class D and Class E surface areas between sunset and sunrise.

3. What are the recency-of-experience requirements to be PIC of a flight under IFR? (14 CFR §61.57)

The recency-of-experience requirements are:
a. A biennial flight review;
b. To carry passengers, 3 takeoffs and landings within the preceding 90 days (full stop at night);
c. Within the preceding 6 calendar months, logged under actual or simulated instrument conditions, either in flight in the appropriate category of aircraft, or in a flight simulator or flight training device (representative of the category for the privileges sought) –
• At least six instrument approaches;
• Holding procedures; and
• Intercepting and tracking courses through the use of navigation systems.

4. If a pilot allows his / her instrument currency to expire, what can be done to become current again? (14 CFR §61.57)

A pilot is current for the first 6 months following his / her instrument check ride or proficiency check. If the pilot has not accomplished at least 6 approaches (including holding procedures, intercepting / tracking courses through the use of navigation systems) within this first 6 months, he / she is no longer legal to file and fly under IFR. To become legal again, the regulations allow a “grace period” (the second 6-month period), in which a pilot may get current by finding an “appropriately rated” safety pilot, and in simulated IFR conditions only, acquire the 6 approaches, etc. If the second 6-month period also passes without accomplishing the minimum, a pilot may reinstate his/her currency by accomplishing an instrument proficiency check given by an examiner, an authorized instructor, or an FAA-approved person to conduct instrument practical tests.

5. Define “appropriately rated safety pilot”. (14 CFR §§61.3, 91.109)

This person must hold at least a Private Pilot Certificate. They must also have a current medical certificate and be current in the category and class of aircraft being flown (i.e., airplane single-engine land). This person need not be instrument rated.

B. Preflight Action for Flight (IFR or Flight Not in the Vicinity of Airport)

1. What information must a pilot-in-command be familiar with before a flight? (14 CFR §91.103)

All available information including:
a. Weather reports and forecasts
b. Fuel requirements
c. Alternatives if the flight cannot be completed as planned
d. Known ATC delays
e. Runway lengths of intended use
f. Takeoff and landing distances

2. What are the fuel requirements for flight in IFR conditions? (14 CFR §91.167)

The aircraft must carry enough fuel to fly to the first airport of intended landing (including the approach), the alternate airport (if required), and thereafter, for 45 minutes at normal cruise speed. If an alternate airport is not required, enough fuel must be carried to fly to the destination airport and land with 45 minutes of fuel remaining.

C. Preflight Action for Aircraft

1. Who is responsible for determining if an aircraft is in an airworthy condition? (14 CFR §91.7)

The pilot-in-command is responsible.

2. What aircraft instruments / equipment are required for IFR operations? (14 CFR §91.205)

Those required for VFR day and night flight plus:
Generator or alternator of adequate capacity
Radios (appropriate for facilities used)
Altimeter (sensitive)
Ball (slip / skid indicator of turn coordinator)
Clock (sweep second hand or digital presentation)
Attitude indicator
Rate of turn (turn coordinator)
Directional gyro

3. What are the required tests and inspections of aircraft and equipment to be legal for IFR flight? (14 CFR §§91.171, 91.409, 91.411 and 91.413)

a. The aircraft must have an annual inspection. If operated for hire or rental, it must also have a 100-hour inspection. A record must be kept in the aircraft / engine logbooks.
b. The pilot / static system must have been checked within the preceding 24 calendar months. A record must be kept in the aircraft logbook.
c. The transponder must have been checked within the preceding 24 calendar months. A record must be kept in the aircraft logbook.
d. The altimeter must have been checked within the preceding 24 calendar months. A record must be kept in the aircraft logbook.
e. The VOR must have been checked within the preceding 30 days. A record must be kept in a bound log book.
f. ELT battery and inspection (12 calendar months).

4. May portable electronic devices be operated on board an aircraft? (14 CFR §91.21)

No person may operate nor may any PIC allow the operation of any portable electronic device:
a. On aircraft operated by an air carrier or commercial operator; or
b. On any other aircraft while it is operated under IFR.
Exceptions are: Portable voice recorders, hearing aids, heart pacemakers, electric shavers or any other portable electronic device that the operator of the aircraft has determined will not cause interference with the navigation or communication system of the aircraft.
5. What documents must be on board an aircraft to make it legal for IFR flight? (14 CFR §§91.9, 91.203)

Airworthiness Certificate
Registration Certificate
Radio station license (if conducting international operations)
Owner’s manual or operating limitations
Weight and balance data

6. When using GPS for navigation under IFR, how often must the database be updated? (AIM 1-1-19)

Every 28 days for IFR operations.

D. IFR Flight Plan

1. When must a pilot file an IFR flight plan? (AIM 5-1-7)

Prior to departure from within or prior to entering controlled airspace, a pilot must submit a complete flight plan and receive clearance from ATC if weather conditions are below VFR minimums. The pilot should file the flight plan at least 30 minutes prior to the estimated time of departure to preclude a possible delay in receiving a departure clearance from ATC.

2. When can you cancel your IFR flight plan? (AIM 5-1-14)

An IFR flight plan may be canceled at any time the flight is operating in VFR conditions outside of Class A airspace. Pilots must be aware that other procedures may be applicable to a flight that cancels an IFR flight plan within an area where a special program, such as a designated TRSA, Class C airspace, or Class B airspace, has been established.

3. What is a composite flight plan? (AIM 5-1-7)

It is a flight plan that specifies VFR operation for one portion of a flight, and IFR for another.

4. What type of aircraft equipment determine your “special equipment” suffix when filing an IFR flight plan? (AIM 5-1-8)

a. Radar beacon transponder
b. DME equipment
c. TACAN-only equipment
d. Area Navigation equipment (RNAV) – LORAN, INS
e. Advanced Area Navigation equipment – Global Positioning System (GPS) / Global Navigation Satellite System (GNSS)

5. The requested altitude on an FAA flight plan form (Block 7) represents which altitude for the route of flight – the initial, lowest, or highest? (AIM 5-1-8)

Enter only the initial requested altitude in this block. When more than one IFR altitude or flight level is desired along the route of flight. It is best to make a subsequent request direct to the controller.

6. What are the alternate airport requirements? (14 CFR §91.169c)

1-2-3 Rule – If from 1 hour before to 1 hour after your planned ETA at the destination airport, the weather is forecast to be at least 2,000-foot ceilings and 3-mile visibilities, no alternate is required. If less than 2,000 and 3 miles, an alternate must be filed using the following criteria:
a. If an IAP is published for that airport, the alternate airport minimums specified in that procedure or, if none are specified, the following minimums –
• Precision approach procedure: ceiling 600 feet and visibility 2 statute miles.
• Non-precision approaches: ceiling 800 feet and visibility 2 statute miles.
b. If no IAP has been published for that airport, the ceiling and visibility minimums are those allowing descent from the MEA, approach, and landing under basic VFR.

7. What is the definition of the term “ceiling”? (P/CG)

Ceiling is defined as the height above the Earth’s surface of the lowest layer of clouds or obscuring phenomena reported as “broken”, “overcast”, or “obscuration”, and not classified as “thin” or “partial”.

8. What minimum are to be used on arrival at the alternate? (14 CFR §91.169c)

If an instrument approach procedure has been published for that airport, the minimums specified in that procedure are used.

E. Route Planning

1. What are preferred routes and where can they be found? (P/CG)

Preferred routes are those established between busier airports to increase system efficiency and capacity. Preferred routes are listed in the Airport / Facility Directory.

2. What are En route Low-Altitude Charts? (AIM 9-1-4)

En route low-altitude charts provide aeronautical information for navigation under IFR conditions below 18,000 feet MSL. These charts are revised every 56 days.

3. What are En route High-Altitude Charts? (AIM 9-1-4)

En route high-altitude charts are designed for navigation at or above 18,000 feet MSL. This four-color chart series includes the jet route structure; VHF NAVAIDs with frequency, identification, channel, geographic coordinates; selected airports; reporting points. Revised every 56 days.

4. What are “area charts”? (AIM 9-1-4)

Area charts show congested terminal areas such as Dallas / Ft. Worth or Atlanta at a large scale. They are included with subscriptions o any conterminous U.S. set Low (Full set, East or West sets). Revised every 56 days.

5. Where can information on possible navigational aid limitations be found? (FAA-H-8083-15)

NOTAMs as well as A/FDs will contain current limitations to NAVAIDs.

6. What other useful information can be found in the Airport / Facility Directory which might be helpful in route planning? (A/FD)

The A/FD contains additional information for each of the seven regions covered, such as:

a. En route Flight Advisory Services – locations and communications outlets.
b. ARTCC – locations and sector frequencies.
c. Aeronautical Chart Bulletins – recent changes after publication.
d. Preferred IFR routes – high and low altitude.
e. Special notices – flight service station, GADO, Weather Service office phone numbers.
f. VOR receiver checkpoints – locations and frequencies.

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

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

8. What are the three categories of NOTAMs? (AIM 5-1-3)

There are three types of NOTAMs generated by the FAA:
a. NOTAM (D) – A NOTAM given (in addition to local) distant dissemination beyond the area of responsibility of the Flight Service Station. These NOTAMs will be stored and available until canceled. NOTAM (D)s contain information on all civil public use airports and navigational facilities that are part of the National Airspace System. NOTAM (D) items are serious enough to affect the usability of an airport or a certain facility.
b. NOTAM (L) – A NOTAM given local dissemination by voice and other means to satisfy local user requirements. NOTAM(L) information may cover items such as taxiway closures, persons and/or equipment near or crossing runways, and airport rotating beacon outages, and other information that would have little impact on non-local operations..
c. FDC NOTAM – The National Flight Data Center will issue these NOTAMs when it becomes necessary to disseminate information that is regulatory in nature. FDC NOTAMs contain items such as amendments to published IAPs and other current aeronautical charts. They are also used to advertise temporary flight restrictions caused by natural disasters or large scale public events that may generate congestion of air traffic over a site.

9. Which type of NOTAMs will be omitted from a pilot briefing, if not specifically requested by the pilot? (AIM 5-1-3 and 7-1-4)

NOTAM (D) information and FDC NOTAMs that have been published in the Notices to Airmen Publication (NTAP) are not included in pilot briefings unless a review of NTAP is specifically requested by the pilot. Also, NOTAM (L) information is distributed locally only and is not attached to the hourly weather reports. A separate file of local NOTAMs is maintained at each FSS for facilities in their area only. NOTAM (L) information for other FSS areas must be specifically requested, and the request made directly to the FSS with responsibility for the airport concerned.

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

a. Nearest FSs
b. DUATS vendors
c. NTAP printed NOTAMs; not normally a briefing. Pilots must make a specific request for them during briefing. The NTAP is also available online from the FAA’s website.
11. Will an FSS briefer provide GPS NOTAMs as part of a standard briefing? (AIM 1-1-19)

No. A pilot must request GPS NOTAMs during a preflight briefing from an AFSS briefer.

F. Flight Instruments
Pilot / Static System

1. What instruments operate from the pilot / static system? (FAA-H-8083-15)

The pilot / static system operates the altimeter, vertical-speed indicator, and airspeed indicator.

2. How does an altimeter work? (FAA-H-8083-15)

In an altimeter, aneroid wafers expand and contract as atmospheric pressure changes, and through a shaft and gear linkage, rotate pointers on the dial of the instrument.

3. What are limitations that a pressure altimeter is subject to? (FAA-H-8083-15)

Nonstandard pressure and temperature:

a. Temperature variations expand or contract the atmosphere and raise or lower pressure levels that the altimeter senses.
On a warm day – The pressure level is higher than on a standard day. The altimeter indicates lower than actual altitude.
On a cold day – The pressure level is lower than on a standard day. The altimeter indicates higher than actual altitude.

b. Changes in surface pressure also affect pressure levels at altitude.
Higher than standard pressure –The pressure level is higher than on a standard day. The altimeter indicates lower than actual altitude.
Lower than standard pressure – The pressure level is lower than on a standard day. The altimeter indicates higher than actual altitude.
Remember: High to low or hot to cold look out below!

4. For IFR flight, what is the maximum allowable error for an altimeter? (FAA-H-8083-15)

If the altimeter is off field elevation by more than 75 feet, with the correct pressure set in the Kollsman window, it is considered to be unreliable.

5. Define and state how to determine the following altitudes :

Indicated Altitude Density Altitude Pressure Altitude
Absolute Altitude True Altitude

Indicated altitude – Read off the face of the altimeter
Pressure altitude – Indicated altitude with 29.92” Hg set in the Kollsman window.
True altitude – Height above sea level. Use the flight computer.
Density altitude – Pressure altitude corrected for nonstandard temperature. Use the flight computer.
Absolute altitude – Height above ground. Subtract the terrain elevation from true altitude.

6. How does the airspeed indicator operate? (FAA-H-8083-15)

The airspeed indicator measures the difference between ram pressure from the pilot head and atmospheric pressure from the static source.

7. What are the limitations the airspeed indicator is subject to? (FAA-H-8083-15)

It must have proper flow of air in the pitot/static system.

8. What are the errors that the airspeed indicator is subject to? ( FAA-H-8083-15)

Position error- Caused by the static ports sensing erroneous static pressure; slipstream flow causes disturbances at the static port preventing actual atmospheric pressure measurement. It varies with airspeed, altitude, configuration and may be a plus or minus value.

Density error – Changes in altitude and temperature are not compensated for by the instrument.

Compressibility error – Caused by the packing of air into the pitot tube at high airspeeds, resulting in higher than normal indications. It usually occurs above 180 KIAS.

9. What are the different types of aircraft speeds? (FAA-H-8083-15)

Indicated airspeed – Read off the instrument; uncorrected for instrument or system errors.
Calibrated airspeed – IAS corrected for instrument and position errors; obtained from the POH / AFM for various flap and landing gear configuration
Equivalent airspeed – CAS corrected for adiabatic compressible flow at altitude
True airspeed – CAS corrected for non-standard temperature and pressure; obtained from a flight computer, AFM, or the A/S indicator slide computer.
Ground speed – TAS corrected for wind; speed across the ground; use the flight computer.

10. What airspeeds are indicated by the various color codes found on the dial of an airspeed indicator? (FAA-H-8083-25)

White arc Flap operating range
Bottom of white arc Flaps down stall speed
Top of white arc Maximum airspeed for flaps-down flight
Green arc Normal operating range
Bottom of green arc Flaps up stall speed
Top of green arc Maximum airspeed for rough air
Yellow arc Structural warning area
Bottom of yellow arc Maximum airspeed for rough air
Top of yellow arc Never-exceed airspeed
Red radial line Never-exceed airspeed

11. How does the vertical-speed indicator work? (FAA-H-8083-15)

In the VSI, changing pressures expand or contract a diaphragm connected to the indicating needle through gears and levers. The VSI is connected to the static pressure line through a calibrated leak; it measures differential pressure.

12. What are the limitations of the vertical-speed indicator? (FAA-H-8083-15)

It is not accurate until the aircraft is stabilized. Sudden or abrupt changes in the aircraft attitude will cause erroneous instrument readings as airflow fluctuates over the static port. These changes are not reflected immediately by the VSI due to the calibrated leak.

13. What instruments are affected when the pitot tube ram air inlet and drain hole freeze? (FAA-H-8083-25)

Only the airspeed indicator will be affected. It acts like an altimeter – it will read higher as the aircraft climbs and lower as the aircraft descends. It reads lower than actual speed in level flight.

14. What instruments are affected when the static port freezes? (FAA-H-8083-25)

Airspeed indicator- Accurate at the altitude frozen as long as static pressure in the indicator and the system equals outside pressure. If the aircraft descends, the airspeed indicator would read high (outside static pressure would be greater than that trapped). If the aircraft climbs, the airspeed indicator would read low.
Altimeter – Indicates the altitude at which the system is blocked.
Vertical speed – Will indicate level flight.

15. If the air temperature is +6°C at an airport elevation of 1,200 feet and a standard (average) temperature lapse rate exists, what will be the approximate freezing level?

4,200 MSL; 6° at the surface divided by the average temperature lapse rate of 2°C results in a 3,000-foot freezing level, converted to sea level by adding the 1,200-foot airport elevation.

16. What corrective action is needed if the pilot tube freezes? If the static port freezes? (FAA-H-8083-15)

For pitot tube – Turn pitot heat on
For static system – Use alternate air if available or break the face of a static instrument (either the VSI or A/S indicator).

17. What indications should you except while using alternate air? (FAA-H-8083-25)

In many unpressurized aircraft equipped with a pitot-static tube, an alternate source of the static pressure is provided for emergency use. If the alternate source is vented inside the airplane where static pressure is usually lower than outside, selection of the alternate static source may result in the following indications:

Altimeter will indicate higher than the actual altitude
Airspeed will indicate greater than the actual airspeed
Vertical speed will indicate a climb while in level flight
Note :Always consult the AFM/POH to determine the amount of error.

Gyroscopic System

1. What instruments contain gyroscopes? (FAA-H-8083-15)

Attitude indicator, heading indicator and turn coordinator / indicator.

2. Name several types of power sources commonly used to power the gyroscopic instruments in an aircraft. (FAA-H-8083-15)

Various power sources used are: electrical, pneumatic, venture tube, wet-type vacuum pump, and dry-air pump systems. Aircraft and instrument manufacturers have designed redundancy into the flight instruments so that any single failure will not deprive the pilot of his/her ability to safely conclude the flight. Gyroscopic instruments are crucial for instrument flight; therefore, they are powered by separate electrical or pneumatic sources. Typically, the heading indicator and attitude indicator will be vacuum-driven and the turn coordinator electrically-driven.
Note: It is extremely important that pilots consult the POH/AFM to determine the power source of all instruments to know what action to take in the event of an instrument failure.

3. How does the vacuum system operate? (FAA-H-8083-25)

The vacuum or pressure system spins the gyro by drawing a stream of air against the rotor vanes to spin the rotor at high speeds, essentially the same as a water wheel or turbine operates. The amount of vacuum or pressure required for instrument operation varies by manufacturer and is usually between 4.5 to 5.5 in. Hg. One source of vacuum for the gyros installed in light aircraft is the vane-type engine-driven pump, mounted on the accessory case of the engine.

4. What are two important characteristics of gyroscopes? (FAA-H-8083-15)

Rigidity – the characteristic of a gyro that prevents its axis of rotation tilting as the Earth rotates; attitude and heading instruments operate on this principle.
Precession – the characteristic of a gyro that causes an applied force to be felt, not at the point of application, but 90 degrees from that point in the direction of rotation. Rate instruments such as the turn coordinator use this principle.

5. How does the turn coordinator operate? (FAA-H-8083-15)

The turn part of the instrument uses precession to indicate direction and approximate rate of turn. A gyro reacts by trying to move in reaction to the force applied, thus moving the miniature aircraft in proportion to the rate of turn. The inclinometer in the instrument is a black glass ball scaled inside a curved glass tube that is partially filled with a liquid. The ball measures the relative strength of the force of gravity and the force of inertia caused by a turn.

6. What information does the turn coordinator provide? (FAA-H-8083-15)

The miniature aircraft in the turn coordinator displays the rate of turn, rate of roll and direction of turn. The ball in the tube indicates the quality of turn (slip or skid).
Slip – ball on the inside of the turn; not enough rate of turn for the amount of bank.
Skid – ball to the outside of the turn; too much rate of turn for the amount of bank.

7. What is the source of power for turn coordinator? (FAA-H-8083-15)

Turn coordinator gyros can be driven by wither air or electricity; some are dual-powered. Typically the turn coordinator is electrically powered, but always refer to the AFM for specifics.
8. How does the heading indicator work? (FAA-H-8083-25)

The operation of the heading indicator works on the principle of rigidity in space. The rotor turns in a vertical plane, and fixed to the rotor is a compass card. Since the rotor remains rigid in space, the points on the card hold the same position in space relative to the vertical plane. As the instrument case and the airplane revolve around the vertical axis, the card provides clear and accurate heading information.

9. What are the limitation of the heading indicator? (FAA-H-8083-25)

They vary with the particular design and make of instrument: on some heading indicators in light airplanes, the limits are approximately 55 degrees of pitch and 55 degrees of bank. When either of these attitude limits are exceeded, the instrument “tumbles” or “spills” and no longer gives the correct indication until it is reset with the caging knob. Many modern instruments used are designed in such a manner that they will not tumble.

10. What type of error is the heading indicator subject to? (FAA-H-8083-25, FAA-P-8740-16)

Because of precession, caused chiefly by friction, the heading indicator will creep or drift from the heading it is set to. The amount of drift depends largely upon the condition of the instrument (worn and dirty bearings and / or improperly lubricated bearings). Non-slaved heading indicators must periodically be compensated for drift. Three degrees in 15 minutes is normal. Significantly greater drift rates may signal impending gyro failure.

11. How does the attitude indicator work? (FAA-H-8083-25)

They gyro in the attitude indicator is mounted on a horizontal plane and depends upon rigidity in space for its operation. The horizon bar represents the true horizon and is fixed to the gyro; it remains in a horizontal plane as the airplane is pitched or banked about its lateral or longitudinal axis, indicating the attitude of the airplane relative to the true horizon.

12. What are the limitations of an attitude indicator? (FAA-H-8083-25)

Limits depend upon he make and model of the instrument; bank limits are usually from 100° to 110°, and pitch limits are usually from 60° to 70°. If wither limit is exceeded, the instrument will tumble or spill and will give incorrect indications until restabilized. Some modern attitude indicators are designed so they will not tumble.

13. Is the attitude indicator subject to errors? (FAA-H-8083-15)

Attitude indicators are free from most errors, but depending upon the speed with which the erection system functions, there may be a slight nose-up indication during a rapid acceleration and a nose-down indication during a rapid deceleration. There is also a possibility of a small bank angle and pitch error after a 180° turn. On rollout from a 180° turn, the AI will indicate a slight climb and turn in the opposite direction of rollout. These inherent errors are small and correct themselves within a minute or so after returning to straight-and-level flight.

Magnetic Compass

1. How does the magnetic compass work? (FAA-H-8083-15)

Magnets mounted on the compass card align themselves parallel to the Earth’s lines of magnetic force.

2. What limitations does the magnetic compass have? (FAA-H-8083-15)

The jewel-and-pivot type mounting gives the float freedom to rotate and tilt up to approximately 18° angle of bank. At steeper bank angles, the compass indications are erratic and unpredictable.

3. What are the various compass errors? (FAA-H-8083-15)

Oscillation error – Erratic movement of the compass card caused by turbulence or rough control technique.

Deviation error – Due to electrical and magnetic disturbances in the aircraft.

Variation error – Angular difference between true and magnetic north; reference isogonic lines of variation.

Dip errors :

a. Acceleration error – On east or west headings, while accelerating the magnetic compass shows a turn to the north, and when decelerating, it shows a turn to the south.

Remember : ANDS

b. Northerly turning error – The compass leads in the south half of a turn, and lags in the north of the turn.

Remember : UNOS

G. Fundamentals of Weather

1. At what rate does atmospheric pressure decrease with an increase in altitude? (AC 00-6A)

Atmospheric pressure decreases approximately 1” HG per 1,000 feet.

2. What are the standard temperature and pressure values for sea level? (AC 00-6A)

15°C and 29.92” Hg are standard at sea level.

3. State the general characteristics in regard to the flow of air around high and low pressure systems in the northern hemisphere. (AC 00-6A)

Low Pressure – Air flows inward, upward, and counterclockwise
High Pressure – Air flows outward, downward, and clockwise

4. What causes the winds aloft to flow parallel to the isobars? (AC 00-6A)

The Coriolis force causes winds aloft to flow parallel to the isobars.

5. Why do surface winds generally flow across the isobars at an angle? (AC 00-6A)

Surface friction causes winds to flow across isobars at an angle.

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

Visible moisture is likely, in the form of clouds, dew or fog.

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

The stability of the atmosphere determines type and vertical extent of clouds.
8. What is the difference between a stable and an unstable atmosphere? (AC 00-6A)

An unstable atmosphere is one in which, if air is displaced vertically, it will continue to move vertically; a stable atmosphere is one which tends to resist any vertical movement of air.

9. How do you determine the stability of the atmosphere? (AC 00-6A)

When temperature decreases uniformly and rapidly as you climb (approaching 3°C per 1,000 feet), you have an indication to unstable air. If the temperature remains unchanged or decreases only slightly with altitude, the air tends to be stable. The “K” index of a stability chart is also a means of determining stability prior to flight.

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

Stable Unstable

Clouds Stratiform Cumuliform
Turbulence Smooth Rough
Precipitation Steady Showery
Visibility Fair to Poor Good

11. What are the two main types of icing? (AC 00-6A)

Structural and Induction.

12. Name four types of structural ice. (AC 00-6A)

Clear ice – forms when large drops strike the aircraft surface and slowly freeze.
Rime ice – small drops strike the aircraft and freeze rapidly.
Mixed ice – combination of above; super cooled water drops varying in size.
Frost – ice crystal deposits formed by sublimation when temperature and dew point are below freezing.

13. What conditions are necessary for structural icing to occur? (AC 00-6A)

Visible moisture and below-freezing temperatures at the point moisture strikes the aircraft are necessary.

14. Which type of structural icing is more dangerous, rime or clear? (AC 00-6A)

Clear ice is typically the most hazardous ice encountered. It is hard, heavy and tenacious. Clear ice forms when, after initial impact, the remaining liquid portion of the drop flows out over the aircraft surface, gradually freezing as a smooth sheet of solid ice. This happens when drops are large, such as in rain or in cumuliform clouds. Its removal by deicing equipment is especially difficult due to the fact that it forms as it flows away from the deicing equipment.

15. What factors must be present for a thunderstorm to form? (AC 00-6A)

To form a thunderstorm there must be:

a. A source of lift (heating, fast-moving front)
b. Unstable air (nonstandard lapse rate)
c. High moisture content (temperature / dew point close)

16. What are “squall line” thunderstorms? (AC 00-6A)

A squall line is a non-frontal, narrow band of active thunderstorms. Often it develops ahead of a cold front in moist, unstable air, but it may also develop in unstable air far removed from any front. The line may be too long to easily detour and too wide and severe to penetrate. It often contains severe steady-state thunderstorms and presents the single most intense weather hazard to aircraft. It usually forms rapidly, reaching a maximum intensity during the late afternoon and the first few hours of darkness.

17. State two basic ways that fog may form. (AC 00-6A)

Fog forms:
a. By cooling air to the dew point
b. By adding moisture to the air

18. Name several types of fog. (AC 00-6A)

a. Radiation fog
b. Advection fog
c. Upslope fog
d. Precipitation –induced fog
e. Ice fog

19. What causes radiation fog to form? (AC 00-6A)

Conditions favorable for radiation are a clear sky, little or no wind, and small temperature-dew point spread (high relative humidity). The fog forms almost exclusively at night or near day break.

20. What is advection fog, and where is it most likely to form? (AC 00-6A)

Advection fog forms when moist air moves over colder ground of water. It is most common along coastal areas but often develops deep in continental areas. Unlike radiation fog, it may occur with winds, cloudy skies, over a wide geographic area, and at any time of the day or night. It deepens as wind speed increases up to about 15 knots; wind much stronger than 15 knots lifts the fog into a layer of lower stratus or stratocumulus.

21. Define upslope fog. (AC 00-6A)

Upslope fog forms as a result of moist, stable air being cooled adiabatically as it moves up sloping terrain. Once the upslope wind ceases, the fog dissipates. Unlike radiation fog, it can form under cloudy skies. It is common along the eastern slopes of the Rockies and somewhat less frequent east of the Appalachians; can often be quite dense and extend to high altitudes.

22. Define Ice fog. (AC 00-6A)

Ice fog occurs in cold weather when the temperature is much below freezing and water vapor sublimates directly as ice crystals. Conditions favorable for its formation are the same as for radiation fog except for cold temperature, usually -25°F or cooler. It occurs mostly in the Arctic regions, but is not unknown in middle latitudes during the cold season. Ice fog can be quite blinding to someone flying into the sun.

23. What is precipitation-induced fog? (AC 00-6A)

When relatively warm rain or drizzle falls through cool air, evaporation from the precipitation saturates the cool air and forms fog. Precipitation-induced fog can become quite dense and continue for an extended period of time. This fog may extend over large areas, completely suspending air operations. It is most commonly associated with warm fronts, but can occur with slow-moving cold fronts and with stationary fronts.

24. Other than fog, what rare several other examples of IFR weather producers? (AIM 00-6A)

Other examples of common IFR producers are low clouds (stratus), haze, smoke, blowing obstruction to vision, and precipitation. Fog and low stratus restrict navigation by visual reference more often than all other weather phenomena.

H. Obtaining Weather Information

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

The primary source of preflight weather briefing is an individual briefing obtained from a briefer at the AFSS/FSS.

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

a. Telephone Information Briefing Service (TIBS) (AFSS)
b. Transcribed Weather Broadcasts (TWEB)
c. Telephone Access to TWEB (TEL-TWEB)
d. Weather and aeronautical information from numerous private industry sources
e. The Direct User Access System (DUATS)

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

a. Adverse Conditions
b. VFR Flight Not Recommended
c. Synopsis
d. Current Conditions
e. En route Forecast
f. Destination Forecast
g. Winds Aloft
h. Notices to Airmen (NOTAMs)
i. ATC Delay

In addition, upon request pilots may obtain the following from AFSS/FSS briefers: Information on Special Use Airspace (SUA), SUA related airspace and MTR activity within the flight plan are and a 100 NM extension around the flight plan area, a review of printed NOTAM publications, approximate density altitude data, information on air traffic services and rules, customs / immigration procedures, ADIZ rules, search and rescue, LORAN-C NOTAMs available military NOTAMs, and runway friction measurement value NOTAMs,, GPS RAIM availability, and other assistance as required.

4. What is EFAS (AIM 7-1-5)

En route Flight Advisory Service (EFAS) is a service specifically designed to provide en route aircraft with timely and meaningful weather advisories pertinent to the type of flight intended, route of flight, and altitude. EFAS is also a central collection and distribution point for pilot reported weather information (PIREPs). EFAS provides for communications capabilities for aircraft flying at 5,000 feet above ground level to 17,5000 feet MSL on a common frequency of 122.0 MHz. It is also known as “Flight Watch.” Discrete EFAS frequencies have been established to ensure communications coverage from 18,000 through 45,000 feet MSL, serving in each specific ARTCC area. These discrete frequencies may be used below 18,000 feet when coverage permits reliable communication.

5. What is HIWAS? (AIM 7-1-10)

Hazardous In-flight Weather Advisory Service (HIWAS) is a continuous broadcast of in-flight 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.

I. Aviation Weather Reports and Observations

1. What is a METAR? (AC 00-45E)

The aviation routine weather report (METAR) is the weather observer’s interpretation of the weather conditions at a given site and time. It is used by the aviation community and the National Weather Service (NWS) to determine the flying category (VFR, MVFR, or IFR) of the airport, as well as produce the Terminal Aerodrome Forecast (TAF).

2. Describe the basic elements of a METAR. (AC 00-45E)

A METAR report contains the following elements in order presented :

a. Type of reports – the METAR (routine), and the SPECI (special observation).
b. Station identifier –(ICAO) four-letter station identifier; in the conterminous United States, the three-letter identifier is prefixed with K.
c. Date and time of report – a six-digit date/time group appended with Z to denote Coordinated Universal Time (UTC). The first two digits are the date followed with two digits for the hour and the two for minutes.
d. Modifier (as required) – if used AUTO identifies a METAR / SPECI report as an automated weather report with no human intervention.
e. Wind – five-digit group (six-digits if speed is over 99 knots); first three digits, direction of the wind from in tens of degrees referenced to true north. Directions less than 100 degrees are preceded with a zero; next two digits are the average speed in knots, measured or estimated or, if over 99 knots, the next three digits.
f. Visibility: prevailing visibility in statue miles followed by a space, fractions of statue miles (as needed), and the letters SM.
g. Runway visual range (RVR), as required- follows the visibility elements.
h. Weather phenomena – broken into two categories: qualifiers, and weather phenomena.
i. Sky condition –reported in the following format: Amount/Height/Type (as required) or Indefinite Ceiling/Height (Vertical Visibility).
j. Temperature/dew point group – two-digit format in whole degrees Celsius, separated by a solidus (/). Temperature below zero are prefixed with M.
k. Altimeter – four-digit format representing tens, units, tenths, and hundredths of inches of mercury prefixed with an “ A”. The decimal point is not reported or stated.
l. Remarks (RMK), as required – operational significant weather phenomena, location of phenomena, beginning and ending times, direction of movement.
Example: METAR KLAX 140651Z AUTO 00000KT ISM R35L/4500V6000FT – RA BR BKN030 10/10 A2990 RMK AO2

The following is an example of the phraseology used to relay this report to a pilot. Optional words or phrases are shown in parentheses: Los Angeles (California) (zero six five one observation), wind calm, visibility one, runway three five left RVR, variable between four thousand five hundred and six thousand feet, light rain, mist, broken ceiling 3,000 feet, temperature ten, dew point ten, altimeter two niner niner zero.

3. Describe several types of Automated Surface Observations now available. (AIM 7-1-12)

ASOS- Automated Surface Observing System; the primary U.S. surface weather observing system; up to 993 systems installed throughout the U.S., providing minute-by-minute observations, METARs and other aviation weather information; transmitted over a discrete VHF radio frequency or the voice portion of a local NAVAID. An ASOS/AWOS report without human intervention will contain only that weather data capable of being reported automatically. The modifier for this METAR report is “AUTO”. When an observer augments or back-up an ASOS/AWOS site, the “AUTO” modifier disappears.

AWOS – Automated Weather Observation System, installed by the FAA at selected airports around the country. This system consists of automated reports of ceiling / sky conditions, visibility, temperature, dew point, wind direction / speeds / gusts, altimeter setting, and if certain conditions are met, automated remarks containing density altitude, variable visibility and variable wind direction. Automated observations are broadcast on ground-to-air radio and made available on a telephone answering device.

4. What are PIREPs (UA), and where are they usually found? (AC 00-45E)

An abbreviation for “pilot weather reports”. A report of meteorological phenomena encountered by aircraft in flight. Required elements for all PIREPs are type of report, location, time, flight level, aircraft type, and at least one weather element encountered. All altitude references are MSL unless otherwise noted. Distance for visibility is in SM; all other distances are in NM. Time is in UTC.

5. What are Radar Weather Reports (SDs)? (AC 00-45E)

General areas of precipitation, including rain, snow, and thunderstorms, can be observed by radar. The radar weather report (SD) includes the type, intensity, and location of the echo top of the precipitation. All heights are reported above MSL. Radar stations report each hour at H+35. SDs should be used along with METARs, satellite photos, and forecasts when planning a flight, to help in thunderstorm area avoidance. But once airborne, depend on Flight Watch, which has the capability to display current radar images, airborne radar, or visual sighting, to evade individual storms.

Note: Many meteorologists are now using Radar Observation Reports, or ROBs, in place of the SD. These provide the same information and are readily available from most weather stations.

J. Aviation Weather Forecasts

1. What are Terminal Aerodrome Forecasts (TAFs)? (AC 00-45E, AIM 7-1-31)

An Aerodrome Forecasts (TAF) is a concise statement of the expected meteorological conditions within a 5-SM radius from the center of an airport’s runway complex during a 24-hour time period. The TAFs use the same weather code found in METAR weather reports, in the following format:
a. Type of reports – a routine forecast (TAF); and an amended forecast, TAF AMD
b. ICAO station identifier – 4-letter station identifiers.
c. Date and time of origin – the date and UTC the forecast is actually prepared; 2-digit date, and 4-digit time, (no space) followed by the letter Z.
d. Valid period date and time – valid forecast period is a 2-sigit date followed by the 2-digit beginning and 2-digit ending hours in UTC. Routine TAFs are valid for 24 hours and are issued four times daily at 0000Z, 0600Z, 1200Z, and 1800Z.
e. Forecasts – wind, significant weather, sky condition, non-convective low-level wind shear, change indicators, probability.

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

A forecast of visual meteorological conditions (VMC), clouds, and general weather conditions over an area the size of several states. Must be used along with in flight weather advisories to determine forecast en route weather and to interpolate conditions at airports where no TAFs are issued. In order to understand the complete weather picture. FAs are issued 3 times a day by the Aviation Weather Center (AWC) for each of the 6 areas in the contiguous 48 states.

3. What information is provided by an Aviation Area Forecast (FA)? (AC 00-45E)

The FA is comprised of four sections:

a. Communications and product header section – identifies the office from which the FA is issued, the date and time of issue, the product name, the valid times and the states and/or areas covered by the FA.
b. Precautionary statement section – between the communications/products headers and the body of the forecast are three precautionary statements which are in all Area Forecasts:

Alerts user that IFR conditions and/or mountain obscurement may be occurring or may be forecast to occur in a portion of the FA area.

A reminder of the hazards existing in all thunderstorms.

Alerts user that heights, for the most part, are heights above sea level. All heights are in hundreds of feet. The tops of clouds, turbulence, icing and freezing level heights are always MSL. Heights above ground level are noted in either of two ways: ceilings by definition are above ground; therefore, the contraction “CIG” indicates above ground. The contraction “AGL” means above ground level; thus, if the contraction “AGL” or “CIG” is not denoted, height is automatically above MSL.
c. Synopsis section – a brief summary of the location and movements of fronts, pressure systems, and circulation patterns for an 18-hour period. References to low ceilings and/or visibilities, strong winds, or any other phenomena the forecaster considers useful, may also be included.
d. VFR Clouds and Weather section – contains a 12-hour specific forecast, followed by a six-hour (18-hour in Alaska) categorical outlook giving a total forecast period of 18 hours (30 hours in Alaska). The VFR CLDS/WX section is usually several paragraphs long. The breakdown may be by states or by well-known geographical areas. The specific forecast section gives a general description of clouds and weather which cover an area greater than 3,000 square miles and is significant to VFR flight operations.

4. What are In flight Aviation Weather Advisories (WST,WS,WA)? (AC 00-45E)

Forecasts that advise en route aircraft of development of potentially hazardous weather. All heights are referenced MSL, except in the case of ceilings (CIG) which indicate AGL. The advisories are of three types: convective SIGMET (WST), SIGMET (ES), and AIRMET (WA).

5. What is a Convective SIGMET? (AC 00-45E)

A Convective SIGMETs (WST) implies severe or greater turbulence, severe icing and low-level wind shear. It may be issued for any convective simulation which the forecaster feels is hazardous to all categories of aircraft. Convective SIGMET bulletins are issued for the Eastern (E), Central( C ) and Western (W) united States (Convective SIGMETs are not issued for Alaska or Hawaii). Bulletins are issued hourly at H+55. 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. The forecast is valid for up to 2 hours.

a. Severe thunderstorm due to:
• Surface winds greater than or equal to 50 knots.
• Hail at the surface greater than or equal to ¾ inches in diameter.
• Tornadoes
b. Embedded thunderstorms
c. A line of thunderstorms
d. Thunderstorms producing greater than or equal to heavy precipitation that affects 40% or more of an area at least 3,000 square miles.

6. What is a SIGMET (WS)? (AC 00-45E)

A SIGMET (WS) advises of non-convective weather that is potentially hazardous to all aircraft. SIGMETs are issued for the six areas corresponding to the FA areas. The maximum forecast period is four hours. In the conterminous United States, SIGMETs are issued when the following phenomena occur or are expected to occur:

a. Severe icing not associated with a thunderstorm;
b. Severe or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms;
c. Dust storms or sandstorms lowering surface or in flight visibilities to below 3 miles;
d. Volcanic ash.

7. What is an AIRMET (WA)? (AC 00-45E)

Advisories of significant weather phenomena that describe conditions at intensities lower than those which require the issuance of SIGMETs, intended for use by all pilots in the preflight and en route phase of flight to enhance safety. AIRMET Bulletins are issued every 6 hours beginning at 0145 UTC during Central Daylight Time and at 0245 UTC during Central Standard Time. Unscheduled updates and corrections are issued as necessary. Each AIRMET Bulletin includes an outlook for conditions expected after the AIRMET valid period. AIRMETs contain details about IFR, extensive mountain obscuration, turbulence, strong surface wins, icing, and freezing levels.

8. What is a TWEB? (AC 00-45E)

NWS offices prepare transcribed weather broadcast (TWEB) text products for the contiguous U.S., including synopsis and forecast for more than 200 routes and local vicinities. TWEB products are valid for 12 hours and are issued 4 times a day at 0200Z, 0800Z, 1400Z, and 2000Z in a variety of sources (TIBS, PATWAS, and more).
A TWEB route forecast or vicinity forecast will not be issued if the TAF for that airport has not been issued. A TWEB route forecast is for a 50-NM wide corridor along a line connecting the end points of the route. A TWEB local vicinity forecast covers an area with a radius of 50 NM. These forecasts describe sustained surface winds (25 knots or greater), visibility, weather and obscuration to vision, sky conditions (coverage and ceiling/cloud heights), mountain obscurement, and nonconvective low-level wind shear.

9. What is a Winds and Temperatures Aloft Forecast (FD)? (AC 00-45E)

Winds and temperature aloft are forecasted for specific locations in the contiguous U.S., and also prepared for a network of locations in Alaska and Hawaii. Forecasts are made twice daily based on the 00Z and 12Z data for use during specific time intervals. FDs contain the following:

a. The valid period the FD may be used, and annotation “TEMPS NEG ABV 24000”. Since temperatures above 24,000 feet are always negative, the minus sign is omitted.
b. “FT” indicates the levels of the wind and temperature data. Through 12,000, feet the levels are true altitude. From 18,000 feet and above, the levels are pressure altitude.
c. A 4-digit group shows wind direction in tens of degrees, and the second 2 digits are the wind speed in knots. A 6-digit group included forecast temperatures in degrees Celsius.
d. No winds are forecasted within 1,500 feet of station elevation.
e. No temperatures are forecasted for any level within 2,500 feet of station elevation.
f. If a wind direction is coded between 51 and 86, the wind speed is 100 knots or greater. For example, winds forecast for 39,000 feet indicate “731960”. To decode, subtract 50 from the wind direction and add 100 knots to the wind speed. Wind direction is from 230 degrees (73-50=23); speed is 119 knots (100+19=119) and temperature is -60°C.
g. If the wind speed is forecasted to be 200 knots or greater, the wind group is coded as 99 knots. For example, “7799” is decoded as 270 degrees at 199 knots or greater.
h. When the forecast speed is less than 5 knots, the coded group is “9900” which means, “Light and Variable”.

10. What valuable information can be determined form Winds and Temperatures Aloft Forecasts (FD)? (AC 00-45E)

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

11. What are Center Weather Advisories (CWA)? (AC 00-45E)

A Center Weather Advisory (CWA) is an aviation warning for use by aircrews to anticipate and avoid adverse weather conditions in the en route and terminal environments. The CWA is not a flight planning product; instead it reflects current conditions expected at the time of issuance and/or is a short-range forecast for conditions expected to begin within 2 hours of issuance. 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.

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

A Connective Outlook (AC) describes the prospects for general thunderstorm activity during the following 24 hours. Describes area in which there is high, moderate, or slight risk of severe thunderstorms, as well as areas of general (non-severe) thunderstorms. The times of issuance for Day 1 are 0600Z, 1300Z, 1630Z, 2000Z, and 0100Z. The initial Day 2 issuance is at 0830Z during standard time and 0730Z during daylight time, updated at 1730Z. The AC is a flight planning tool used to avoid thunderstorms.

K. Aviation Weather Charts

1. Give some examples of current weather charts, which are used in flight planning and available at the FSS or NWSO (AC 00-45E)

a. Surface Analysis Chart.
b. Weather Depiction Chart
c. Radar Summary Chart
d. Significant Weather Prognostic Chart
e. Winds and Temperatures Aloft Chart
f. Composite Moisture Stability Chart
g. Convective Outlook Chart
h. Constant Pressure Analysis Chart
i. Volcanic Ash Forecast Transport and Dispersion Chart

2. What is a Surface Analysis Chart? (AC 00-45E)

The Surface Analysis Chart is a computer-prepared chart that covers the contiguous 48 states and adjacent areas. The chart is transmitted every three hours. The surface analysis chart provides a ready means of locating pressure systems and fronts. It also gives an overview of winds, temperatures and dew point temperatures at chart time. When using the chart, keep in mind that weather moves and conditions change. Using the surface analysis chart in conjunction with other information gives a more complete weather picture.

3. What information dies a Weather Depiction Chart provide? (AC 00-45E)

This chart is computer-generated (with frontal analysis by an observer) from METAR reports, and gives a broad overview of the observed flying category conditions at the valid time of the chart. The chart begins at 01Z each day, is transmitted at 3-hour intervals, and is valid at the time of the plotted data. Observations reported by both manual and automated observation locations provide the following data: total sky cover, cloud height or ceiling, weather and obstructions to vision and visibilities. The weather depiction chart is an ideal place to begin preparing for a weather briefing and flight planning. From this chart one can get a “bird’s-eye” view of areas of favorable and adverse weather conditions at chart time.

4. Define the terms: IFR, MVFR and VFR. (AC 00-45E)

IFR: (Instrument Flight Rules) – Ceilings less than 1,000 and/or visibilities less than 3 miles

MVFR: (Marginal VFR) – Ceiling 1,000 to 3,000 feet inclusive and/or visibility 3 to 5 miles inclusive

VFR: (Visual Flight Rules) – No ceiling, or ceiling greater than 3,000 and visibility greater than 5 miles

5. What are Radar Summary Charts? (AC 00-45E)

This chart is a computer-generated graphical display of a collection of automated radar weather reports (SDs or ROBs), displaying areas of precipitation as well as information about type, intensity, configuration, coverage, echo top, and cell movement of precipitation. Severe weather watches are plotted if they are in effect when the chart is valid. The chart is available hourly with a valid time of 35 minutes past each hour.
This chart aids in preflight planning by identifying general areas and movement of precipitation and/or thunderstorms. It displays drops or ice particles of precipitation size only; it does not display clouds and fog. Therefore, since the absence of echoes does not guarantee clear weather, and cloud tops will most likely be higher than the tops of the precipitation echoes detected by radar, the radar summary chart must be used along with other charts, reports, and forecasts for best effectiveness.

6. What are Significant Weather Prognostic Charts? (AC 00-45E)

Called “Progs”, these charts portray forecasts of selected weather conditions at specified valid times (12,24,36 and 48 hour progs). Each valid time is the time at which the forecast conditions are expected to occur, made from a comprehensive set of observed weather conditions. The observed conditions are extended forward in time and become forecasts by considering atmospheric and environmental processes. Forecast information for the surface to 24,000 feet is provided by the low-level significant weather progchart. Forecast information from above 24,000 to 60,000 feet is provided by the high-level significant weather prog chart.

7. Describe a U.S. Low-Level Significant Weather Prog Chart. (AC 00-45E)

It is a “Day One” forecast of significant weather for the conterminous U.S., pertaining to the layer from surface to FL240 (400mb). With two forecast periods, 12 hours and 24 hours, the chart is composed of four panels. The two lower panels depict the 12- and 24-hour surface progs, and the two upper panels depict the 12- and 24-hour significant weather progs. Issued four times a day at 00Z, 06Z, 12Z, and 18Z. Covered are forecast positions and characteristics of pressure systems, fronts, and precipitation. Much insight can be gained by evaluating the individual fields of pressure patterns, fronts, precipitation, weather flying categories, freezing levels, and turbulence displayed on the chart.

8. Describe a U.S. High-Level Significant Weather Prog Chart. (AC 00-45E)

The U.S. High-Level Significant Weather Prog is also a “Day One” forecast of significant weather. Information provided pertains to the layer from above 24,000 to 60,000 feet (FL250 – FL600) and covers a large portion of the Northern Hemisphere and a limited portion of the Southern Hemisphere. The area covered by the prog is divide into sections with each section covering a part of the forecast area. Each prog chart is issued four times a day (00Z, 06Z, 12Z, and 18Z).

9. What information may be obtained from the U.S. High-Level Significant Weather Prog Charts? (AC 00-45E)

The high-level significant weather prog is used to get an overview of selected flying weather conditions above 24,000 feet. Conditions routinely appearing on the chart are:
a. Jet streams
b. Cumulonimbus clouds
c. Turbulence
d. Tropopause heights
e. Surface fronts
f. Significant tropical storm complexes including tropical cyclones
g. Squall lines
h. Volcanic eruption sites
i. Sandstorms and dust storms

10. What is a Forecast Winds and Temperatures Aloft Chart (FD)? (AC 00-45E)

This is a computer-generated chart depicting both observed and forecast winds and temperatures aloft, prepared for eight levels on eight separate panels. The levels are 6,000, 9,000, 12,000, 18,000, 24,000, 30,000, 34,000 and 39,000 feet MSL. They are available daily as 12-hour progs valid at 1200Z and 0000Z. These charts are typically used to determine winds at a proposed altitude or to select the best altitude for a proposed flight. Temperatures also can be determined from the forecast charts. Interpolation must be used to determine winds and temperatures at a level between charts and data when the time period is other than the valid time of the chart.

11. What is a Composite Moisture Stability Chart? (AC 00-45E)

This is a computer-generated chart composed of four panels including stability, freezing level, precipitable water and, average relative humidity conditions, with information obtained from analysis of upper-air observation data. It is available twice daily with valid times of 12Z and 00Z.The chart is used to identify the distribution of stability, moisture, and freezing level properties of the atmosphere. These properties and their association with weather systems provide important insights into existing and forecast weather conditions as well as possible aviation weather hazards.

12. What is a Convective Outlook Chart? (AC 00-45E)

This chart depicts areas forecast to have thunderstorms, and is presented in two panels. The left-hand panel is the Day 1 Convective Outlook, and the tight-hand panel is the Day 2 Convective Outlook. “Day 1” outlines areas in the continental U.S. where thunderstorms are forecasted during that period. It is issued five times daily (0600Z, 1300Z, 1630Z, 2000Z, and 0100Z) and all issuances are valid till 12Z the following day. The outlook issued qualifies the level of risk (i.e., SLGT, MDT, HIGH) as well as the areas of general thunderstorms.
The Day 2 Convective Outlook contains the same information as the Day 1 chart, and is issued twice a day (0830Z and 1730Z) in a period from 12Z the following day to 12Z the next day.

13. What are Constant Pressure Analysis Charts? (AC 00-45E)

Any surface of equal pressure in the atmosphere is constant pressure surface. A constant pressure analysis chart is an upper air weather map where all information depicted is at the specified pressure of the chart. From these charts, a pilot can approximate the observed air temperature, wind, and temperature/dew point spread along the proposed route. They also depict highs, lows, troughs, and ridges aloft by the height contour patterns resembling isobars on a surface map. Twice daily, six computer-prepared constant pressure charts are transmitted by facsimile for six pressure levels:

850 mb …………………5,000 ft
700mb………………..10,000 ft
500 mb……………….18,000 ft
300 mb……………….30,000 ft
250 mb……………….34,000 ft
200 mb……………….39,000 ft

14. What significance do height contour lines have on a Constant Pressure chart? (AC 00-45E)

Heights of the specified pressure for each station are analyzed through the use of solid line called contours to give a height pattern. The contours depict highs, lows, troughs, and ridges aloft in the same manner as isobars on the surface chart. Also, closely spaced contours mean strong winds, as do closely-spaced isobars.

15. What significance do isotherms have on a Constant Pressure Chart? (AC 00-45E)

Isotherms (dashed lines) drawn at 5°C-intervals show horizontal temperature variations at chart altitude. By inspecting isotherm, you can determine if your flight will be toward colder or warmer air. Subfreezing temperatures and a temperature / dew point spread of 5°C or less suggest possible icing.

16. What is the significance of the isotach lines on a Constant Pressure Chart? (AC 00-45E)

Isotach are lines of constant wind speed analyzed on the 300,250, and 200 mb charts; they separate higher wind speeds from lower wind speeds and are used to map wind speed variations over a surface. Isotach are drawn at 20-knot intervals and begin at 10 knots. Isotach gradients identify the magnitude of wind speed variations. Strong gradients are closely spaced isotachs and identify large wind speed variations. Weak gradients are loosely spaced isotachs and identify small wind speed variations. Zones of very strong winds are highlighted by hatches.

17. What is a Volcanic Ash Forecast Transport and Dispersion chart? (AC 00-45E)

The VAFTAD chart presents the relative concentrations of ash following a volcanic eruption for three layers of the atmosphere in addition to a composite of ash concentration through the atmosphere. Atmospheric layers depicted are : surface to flight level (FL) 200, surface to FL550 (composite), FL200 to FL350, and FL350 to FL550. The chart focuses on hazards to aircraft flight operations caused by a volcanic eruption with an emphasis on the ash cloud location in time and space. It uses forecast data to determine the location of ash concentrations over 6-hour and 12-hour intervals, with valid times beginning 6,12,24, and 36 hours following a volcanic eruption.