CFI Brief: Deciphering the METAR

Today we are going to take a look at your most common type of weather report, the Aviation Routine Weather Report, abbreviated as METAR. A METAR is an observation of current surface weather reported in a standard international format. The purpose is to provide pilots with an accurate depiction of current weather conditions at an airport. METARs are issued on a regularly scheduled basis, usually somewhere close to the top of the hour, unless significant weather changes have occurred. If this is the case then a special METAR or ‘SPECI’ will be issued at any time between routine reports.

Here is an example of a routine METAR report for a station location.

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR

This METAR reports contains the following typical information in sequential order which is the standard formatted coding for all METAR reports.

1. Type of report. There are two types of METAR reports. The first is the routine METAR report that is transmitted on a regular time interval. The second is the aviation selected 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.

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR]

2. Station identifier. A four-letter code as established by the International Civil Aviation Organization (ICAO). In the 48 contiguous states, a unique three-letter identifier is preceded by the letter “K.” For example, Gregg County Airport in Longview, Texas, is identified by the letters “KGGG,” K being the country designation and GGG being the airport identifier. In other regions of the world, including Alaska and Hawaii, the first two letters of the four-letter ICAO identifier indicate the region, country, or state. Alaska identifiers always begin with the letters “PA” and Hawaii identifiers always begin with the letters “PH.” Station identifiers can be found by searching various websites such as DUATS and NOAA’s Aviation Weather Aviation Digital Data Services (ADDS).

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR

3. Date and time of report. Depicted in a six-digit group (161753Z). The first two digits are the date. The last four digits are the time of the METAR/SPECI, which is always given in coordinated universal time (UTC). A “Z” is appended to the end of the time to denote the time is given in Zulu time (UTC) as opposed to local time. This METAR was issued on the 16th at 1753 Zulu.

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR

4. Modifier. Denotes that the METAR/SPECI came from an automated source or that the report was corrected. If the notation “AUTO” is listed in the METAR/SPECI, the report came from an automated source. It also lists “AO1” (for no precipitation discriminator) or “AO2” (with precipitation discriminator) in the “Remarks” section to indicate the type of precipitation sensors employed at the automated station. When the modifier “COR” is used, it identifies a corrected report sent out to replace an earlier report that contained an error. If this was the case for this example the word AUTO would be replaced with COR.

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR

5. Wind. Reported with five digits (14021KT) unless the speed is greater than 99 knots, in which case the wind is reported with six digits. The first three digits indicate the direction the true wind is blowing from in tens of degrees. If the wind is variable, it is reported as “VRB.” The last two digits indicate the speed of the wind in knots unless the wind is greater than 99 knots, in which case it is indicated by three digits. If the winds are gusting, the letter “G” follows the wind speed (G26KT). After the letter “G,” the peak gust recorded is provided. If the wind direction varies more than 60° and the wind speed is greater than six knots, a separate group of numbers, separated by a “V,” will indicate the extremes of the wind directions.

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR

6. Visibility. The prevailing visibility (¾ SM) is reported in statute miles as denoted by the letters “SM.” It is reported in both miles and fractions of miles. At times, runway visual range (RVR) is reported following the prevailing visibility. RVR is the distance a pilot can see down the runway in a moving aircraft. When RVR is reported, it is shown with an R, then the runway number followed by a slant, then the visual range in feet. For example, when the RVR is reported as R17L/1400FT, it translates to a visual range of 1,400 feet on runway 17 left.

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR

7. Weather. Can be broken down into two different categories: qualifiers and weather phenomenon (+TSRA BR). First, the qualifiers of intensity, proximity, and the descriptor of the weather are given. The intensity may be light (–), moderate ( ), or heavy (+). Proximity only depicts weather phenomena that are in the airport vicinity. The notation “VC” indicates a specific weather phenomenon is in the vicinity of five to ten miles from the airport. Descriptors are used to describe certain types of precipitation and obscurations. Weather phenomena may be reported as being precipitation, obscurations, and other phenomena, such as squalls or funnel clouds. Descriptions of weather phenomena as they begin or end and hailstone size are also listed in the “Remarks” sections of the report. The coding for qualifier and weather phenomena are shown here in this chart. The weather groups are constructed by considering columns 1–5 in this table sequence: intensity, followed by descriptor, followed by weather phenomena. As an example “heavy rain showers” is coded as +SHRA.

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR


8. Sky condition. Always reported in the sequence of amount, height, and type or indefinite ceiling/height (vertical visibility) (BKN008 OVC012CB, VV003). The heights of the cloud bases are reported with a three-digit number in hundreds of feet AGL. Clouds above 12,000 feet are not detected or reported by an automated station. The types of clouds, specifically towering cumulus (TCU) or cumulonimbus (CB) clouds, are reported with their height. Contractions are used to describe the amount of cloud coverage and obscuring phenomena. The amount of sky coverage is reported in eighths of the sky from horizon to horizon as shown in this table. Less than 1/8 is abbreviated as Sky Clear, Clear, or Few. 1/8 – 2/8 Few. 3/8 – 4/8 Scattered. 5/8 – 7/8 Broken. 8/8 Overcast. For aviation purposes, the ceiling is the lowest broken or overcast layer, or vertical visibility into an obscuration.

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR


9. Temperature and dew point. The air temperature and dew point are always given in degrees Celsius (C) or (18/17). Temperatures below 0 °C are preceded by the letter “M” to indicate minus. 10.

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR

10. Altimeter setting. Reported as inches of mercury (“Hg) in a four-digit number group (A2970). It is always preceded by the letter “A.” Rising or falling pressure may also be denoted in the “Remarks” sections as “PRESRR” or “PRESFR,” respectively.

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR

11. Remarks—the remarks section always begins with the letters “RMK.” Comments may or may not appear in this section of the METAR. The information contained in this section may include wind data, variable visibility, beginning and ending times of particular phenomenon, pressure information, and various other information deemed necessary. An example of a remark regarding weather phenomenon that does not fit in any other category would be: OCNL LTGICCG. This translates as occasional lightning in the clouds and from cloud to ground. Automated stations also use the remarks section to indicate the equipment needs maintenance.

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR

Putting it all together you would read this sample METAR as follows:

Routine METAR for Gregg County Airport for the 16th day of the month at 1753 zulu automated source. Winds are 140 at 21 knots gusting to 26 knots. Visibility is ¾ statute mile. Thunderstorms with heavy rain and mist. Ceiling is broken at 800 feet, overcast at 1,200 feet with cumulonimbus clouds. Temperature 18 °C and dew point 17 °C. Barometric pressure is 29.70″Hg and falling rapidly.


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Regulations: Notices to Airmen

Today, we’ll take a look at NOTAM’s with an excerpt from Bob Gardner’s textbook The Complete Private Pilot (PPT-12). For all of the regulations pertaining to aviation, check out our annual FAR/AIM series.

Information that might affect the safety of a flight, such as a runway closure, Temporary Flight Restriction (TFR), NAVAID outage, lighting system change, etc., is available from your flight service station briefer.

Your briefer has access to NOTAMs. So do you, at PilotWeb. If you use one of the computer flight planning products such as DUATS or the AOPA flight planner, you will also receive current NOTAMS—but be aware that TFRs can pop up without warning. Always check for them with flight service before takeoff to avoid being intercepted by F-16s or Coast Guard helicopters and forced to land.

If you want to know about VOR outages, runway closures, men and equipment on the runway, etc., look for or ask for D NOTAMs. For long cross-countries it is always valuable to call one of the fixed-base operators at the destination airport for last-minute information, such as “the power is out and we can’t pump gas!”

To make it easier for pilots to scan through a list of NOTAMs for information specific to their flight, the FAA uses “key words” in the first line of text. See the figure below—although this FAA document does not include recent additions: ODP, SID, STAR, CHART, DATA, IAP, VFP, ROUTE, SPECIAL, or (O); also, the keyword RAMP will no longer be used. As a VFR pilot, you are definitely interested in Visual Flight Procedure (VFP) and Obstacle Departure Procedure (ODP) NOTAMs which, although intended for instrument pilots, might contain information useful to you.

Every 28 days the FAA releases the Notices to Airmen publication that contains all current NOTAM (D)s and FDC NOTAMs, except for Temporary Flight Restrictions. When a NOTAM is published here (or in the Chart Supplements U.S.) it no longer shows up on the briefer’s screen; if you don’t ask the briefer for any published NOTAMs that will affect your flight, you will never find out about them. You can get this publication online at


Example of FAA NOTAM “key words” (see AIM Table 5-1-1 for more keywords and definitions). (Click to expand)

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CFI Brief: New GFA Supplement Figures

In the latest Airman Knowledge Testing Supplement for Instrument Rating (CT-8080-3F), the FAA has added several Graphical Forecast for Aviation (GFA) figures. These figures are 260 through 271 in the supplement and although the FAA has not yet added questions to the Instrument knowledge test on GFA, this weather tool is still something to become familiar with.

The GFA at the Aviation Weather Center (AWC) website is an interactive display providing continuously updated observed and forecast weather information over the continental United States (CONUS). It is intended to give users a complete picture of weather critical to aviation safety. The GFA display shows user-selected weather categories, each containing multiple fields of interest at altitudes from the surface up to FL480. Depending on the field of interest chosen, weather information is available from -6 in the past (observed) to +15 hours in the future (forecast).

The GFA is not considered a weather product but an aggregate of several existing weather products. The information and data from the various weather products are overlaid on a high-resolution basemap of the United States: The user selects flight levels and current time period for either observed or forecast weather information. Mouse-clicking or hovering over the map provides additional information in textual format, such as current METAR or TAF for a selected airport. The GFA replaces the textual area forecast (FA) for the CONUS and Hawaii with a more modern digital solution for obtaining weather information. The Aviation Surface Forecast and Aviation Cloud Forecast graphics are snapshot images derived from a subset of the aviation weather forecasts.

The Aviation Surface Forecast displays surface visibility with overlays of wind and gusts, predominant precipitation type (i.e., rain, snow, mix, ice, or thunderstorm) coincident with any cloud and predominant weather type (i.e., haze, fog, smoke, blowing dust/sand). The graphical AIRMETs (Airmen’s Meteorological Information) for instrument flight rules (IFR) and strong surface wind are overlaid. See FAA Figure 260. Forecast surface visibility is contoured for Low IFR (0 – 1 statute miles), IFR (1 – 3 statute miles), and Marginal VFR (MVFR; 3 – 5 statute miles) conditions. Visibilities in excess of 5 statute miles are not shown. Winds are depicted with a standard wind barb, in red when indicating gusts (see the figure below).


Below are some sample questions for what you could expect to see on an FAA knowledge test in the near future using those aforementioned GFA figures.

1. (Refer to Figure 261.) The precipitation type forecast to occur over southern ND (area C) is
A—Freezing rain.
B—Freezing drizzle.
C—Moderate snow.instrument_261

2. (Refer to Figure 266.) Precipitation throughout Washington and Oregon is predominantly
A—Light rain and rain showers.
B—Heavy rain showers.
C—Freezing rain.instrument_266
3.(Refer to Figure 269.) The cloud coverage around area B on the Aviation Cloud Forecast is forecast to be
A—Bases at 6,000 feet, tops at 7,000.
B—BRKN tops at 7,000 feet.
C—OVC at 7,000 feet.instrument_269

Answers and explanations

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Human Factors: Optical Illusions

Of the senses, vision is the most important for safe flight. However, various terrain features and atmospheric conditions can create optical illusions. These illusions are primarily associated with landing. Since pilots must transition from reliance on instruments to visual cues outside the flight deck for landing at the end of an instrument approach, it is imperative that they be aware of the potential problems associated with these illusions and take appropriate corrective action. Today, we’ll take a look at the major illusions leading to landing errors with an excerpt from the Pilot’s Handbook of Aeronautical Knowledge.

Runway Width Illusion
A narrower-than-usual runway can create an illusion that the aircraft is at a higher altitude than it actually is, especially when runway length-to-width relationships are comparable. The pilot who does not recognize this illusion will fly a lower approach, with the risk of striking objects along the approach path or landing short. A wider-thanusual runway can have the opposite effect with the risk of the pilot leveling out the aircraft high and landing hard or overshooting the runway.

Runway and Terrain Slopes Illusion
An upsloping runway, upsloping terrain, or both can create an illusion that the aircraft is at a higher altitude than it actually is. The pilot who does not recognize this illusion will fly a lower approach. Downsloping runways and downsloping approach terrain can have the opposite effect.


(Click to expand)

Featureless Terrain Illusion
An absence of surrounding ground features, as in an overwater approach over darkened areas or terrain made featureless by snow, can create an illusion that the aircraft is at a higher altitude than it actually is. This illusion, sometimes referred to as the “black hole approach,” causes pilots to fly a lower approach than is desired.

Water Refraction
Rain on the windscreen can create an illusion of being at a higher altitude due to the horizon appearing lower than it is. This can result in the pilot flying a lower approach.

Atmospheric haze can create an illusion of being at a greater distance and height from the runway. As a result, the pilot has a tendency to be low on the approach. Conversely, extremely clear air (clear bright conditions of a high attitude airport) can give the pilot the illusion of being closer than he or she actually is, resulting in a high approach that may result in an overshoot or go around. The diffusion of light due to water particles on the windshield can adversely affect depth perception. The lights and terrain features normally used to gauge height during landing become less effective for the pilot.

Flying into fog can create an illusion of pitching up. Pilots who do not recognize this illusion often steepen the approach abruptly.

Ground Lighting Illusions
Lights along a straight path, such as a road or lights on moving trains, can be mistaken for runway and approach lights. Bright runway and approach lighting systems, especially where few lights illuminate the surrounding terrain, may create the illusion of less distance to the runway. The pilot who does not recognize this illusion will often fly a higher approach.

How To Prevent Landing Errors Due to Optical Illusions
To prevent these illusions and their potentially hazardous consequences, pilots can:

  1. Anticipate the possibility of visual illusions during approaches to unfamiliar airports, particularly at night or in adverse weather conditions. Consult airport diagrams and the Chart Supplement U.S. (formerly Airport/Facility Directory) for information on runway slope, terrain, and lighting.
  2. Make frequent reference to the altimeter, especially during all approaches, day and night.
  3. If possible, conduct an aerial visual inspection of unfamiliar airports before landing.
  4. Use Visual Approach Slope Indicator (VASI) or Precision Approach Path Indicator (PAPI) systems for a visual reference, or an electronic glideslope, whenever they are available.
  5. Utilize the visual descent point (VDP) found on many nonprecision instrument approach procedure charts.
  6. Recognize that the chances of being involved in an approach accident increase when an emergency or other activity distracts from usual procedures.
  7. Maintain optimum proficiency in landing procedures.

In addition to the sensory illusions due to misleading inputs to the vestibular system, a pilot may also encounter various visual illusions during flight. Illusions rank among the most common factors cited as contributing to fatal aviation accidents. Sloping cloud formations, an obscured horizon, a dark scene spread with ground lights and stars, and certain geometric patterns of ground light can create illusions of not being aligned correctly with the actual horizon. Various surface features and atmospheric conditions encountered in landing can create illusions of being on the wrong approach path. Landing errors due to these illusions can be prevented by anticipating them during approaches, inspecting unfamiliar airports before landing, using electronic glideslope or VASI systems when available, and maintaining proficiency in landing procedures.

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CFI Brief: Sunset Weather

What could be better than taking your significant other on a romantic sunset flight around your local airport? I’ll tell you what, taking your significant other on a romantic sunset flight during an absolutely epic sunset! Sounds awesome right, but just how are you suppose to know when an epic sunset is going to happen? Easy… check the forecast. has come up with an algorithm to forecast the sunrise and sunset quality throughout the United States and all over the world! Take a look below at the sample sunset forecast for the United States.

Sunset Forecast

Areas of better sunset quality are denoted by warmer colors like the yellows, oranges and reds. It appears that the highest quality sunset will be visible throughout Central California according to this forecast. So if you happen to live in say Sacramento, CA it would be an excellent evening for that sunset cruise.

For the latest forecast visits and follow them on twitter @sunset_wx .

Now remember, since you will potentialy be flying prior to civil twilight, it is important to make sure your aircraft has the minimum required equipment under 14 CFR 91.205 for night flight. This is in addition to required equipment for day flight.

14 CFR 91.205

…(c) Visual flight rules (night). For VFR flight at night, the following instruments and equipment are required:

(1) Instruments and equipment specified in paragraph (b) of this section.

(2) Approved position lights.

(3) An approved aviation red or aviation white anticollision light system on all U.S.-registered civil aircraft. Anticollision light systems initially installed after August 11, 1971, on aircraft for which a type certificate was issued or applied for before August 11, 1971, must at least meet the anticollision light standards of part 23, 25, 27, or 29 of this chapter, as applicable, that were in effect on August 10, 1971, except that the color may be either aviation red or aviation white. In the event of failure of any light of the anticollision light system, operations with the aircraft may be continued to a stop where repairs or replacement can be made.

(4) If the aircraft is operated for hire, one electric landing light.

(5) An adequate source of electrical energy for all installed electrical and radio equipment.

(6) One spare set of fuses, or three spare fuses of each kind required, that are accessible to the pilot in flight.


To help you remember you can use this simple mnemonic ‘FLAPS’.

F uses (spare) or circuit breakers

L anding light (if for hire)

A nticollision lights

P osition lights

S ource of electricity


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We’re here at EAA Airventure Oshkosh 2017!

We’re here! Come find us at our booth (2075-2079) in Hangar B, showcasing our current line of training products and pilot supplies along with some new products. Come say hello and get your flight training questions answered by ASA staff.


On Monday, July 24th (tonight!), ASA will be hosting the Collegiate Tailgate Party in Aviation Gateway Park from 5:00-6:30 PM. We had a great time hanging out last year and are looking forward to doing it again. There will be food, music, games, and prizes, so come on out and join us!


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CFI Brief: Part 107 sUAS Operating Limitations

If you plan on operating an sUAS under 14 CFR Part 107, make sure you fully understand your operating limitations.

Operating Limitations

The sUAS must be operated in accordance with the following limitations:

• Cannot be flown faster than a ground speed of 87 knots (100 miles per hour).

• Cannot be flown higher than 400 feet above ground level (AGL) unless flown within a 400-foot radius of a structure and not flown higher than 400 feet above the structure’s immediate uppermost limit. See Figure 1-1.


Figure 1-1. Flying near a tower

Crewmembers must operate within the following limitations:

• Minimum visibility, as observed from the location of the control station, must be no less than 3 statute miles.

• Minimum distance from clouds must be no less than 500 feet below a cloud and 2,000 feet horizontally from the cloud.

Note: These operating limitations are intended, among other things, to support the remote pilot’s ability to identify hazardous conditions relating to encroaching aircraft or persons on the ground, and to take the appropriate actions to maintain safety.

Below is the regulation outlined in 14 CFR Part 107.51

§107.51   Operating limitations for small unmanned aircraft.

A remote pilot in command and the person manipulating the flight controls of the small unmanned aircraft system must comply with all of the following operating limitations when operating a small unmanned aircraft system:

(a) The groundspeed of the small unmanned aircraft may not exceed 87 knots (100 miles per hour).

(b) The altitude of the small unmanned aircraft cannot be higher than 400 feet above ground level, unless the small unmanned aircraft:

(1) Is flown within a 400-foot radius of a structure; and

(2) Does not fly higher than 400 feet above the structure’s immediate uppermost limit.

(c) The minimum flight visibility, as observed from the location of the control station must be no less than 3 statute miles. For purposes of this section, flight visibility means the average slant distance from the control station at which prominent unlighted objects may be seen and identified by day and prominent lighted objects may be seen and identified by night.

(d) The minimum distance of the small unmanned aircraft from clouds must be no less than:

(1) 500 feet below the cloud; and

(2) 2,000 feet horizontally from the cloud.


You can find all the sUAS Part 107 regulations in this years 2018 FAR|AIM available NOW!

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Procedures and Airport Operations: Crosswind Takeoff

Since The Pilot’s Manual: Flight School (PM-1C) is now available in eBook format (from ASA and iTunes), this week we’ll feature another maneuver from the textbook. The fifth edition of Flight School covers everything you need to know in order to fly your airplane through the maneuvers required for certification.

Not all airports have a runway that faces upwind on a given day. For this reason, takeoffs and landings on runways where there is a crosswind component are frequent events. Every airplane type (from the smallest trainer up to the Airbus A340 and Boeing 747) has a maximum crosswind component specified in the flight manual and pilot’s operating handbook. If the actual crosswind component on the runway exceeds the limit for the airplane or what you feel is your own personal limit, then use a different runway (which may even mean proceeding to a different airport).

Takeoff Run
A crosswind blowing under the upwind wing will tend to lift it. Counteract this effect and keep the wings level with aileron; that is, move the control column upwind. While full deflection might be required early in the takeoff run, this can be reduced as the faster airflow increases control effectiveness. You do not have to consciously think of aileron movement; just concentrate on keeping the wings level.

A right crosswind, for example, requires right control column and left rudder (crossed controls). A glance at the wind sock before you open the throttle for the takeoff run will allow you to anticipate this and position the controls correctly.

As speed increases, the amount of aileron and rudder required will reduce until, at liftoff, there will probably be some rudder still applied, but little or no aileron. There is no need to consciously think about this; just:

  • keep straight with rudder; and
  • keep the wings level with the ailerons.

Allow the aircraft to accelerate. Use as much rudder as necessary but avoid braking. In a crosswind takeoff, hold the airplane on the ground during the ground run (with slight forward pressure on the control column) and then lift off cleanly and positively. It may be advisable to delay liftoff until 5 knots or so past the normal rotation speed to achieve a clean (no skip) liftoff.

Drift After Takeoff
As the airplane enters the air mass after liftoff, it will tend to move sideways with it. Any tendency to sink back onto the ground should be resisted to avoid the strong sideways forces that would occur on the landing gear.

Once well clear of the ground, the aircraft will naturally yaw upwind (weathervane) to counteract the drift. Keep the wings level. Any remaining crossed controls are removed once airborne by centralizing the balance ball and keeping the wings level. Climb out normally on the extended centerline of the runway.


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CFI Brief: Can you be a pilot with Diabetes?

Today we are featuring a guest editorial column by  

In this article we will explore whether or not you can become a pilot if you have diabetes. We will look at piloting for a commercial airline with diabetes and piloting for a private company with diabetes. We will also look at other jobs centered on aviation, such as being a flight instructor, or flying gliders and other small aircraft.

We will look at whether or not you can pilot an aircraft if you have Type 1Type 2, or pre-diabetes. We will look at whether or not it matters if you are taking insulin, other injections for diabetes, oral medications, or are diet and exercise controlled.

We have already been looking at some promising careers that we can have with diabetes that is well-controlled.

We have looked at being a long-distance truck driver, an EMS/Paramedic, a Firefighter, an air traffic controller, and a law enforcement officer. We have looked at whether or not you can be in the military with diabetes. Now we take on the most difficult career to date.

*Becoming a commercial airline pilot with diabetes requiring insulin is prohibited by a blanket ban in the United States. It is one of 15 conditions that can disqualify you when you go for your medical certificate with the FAA.

So what’s up? Let’s look…

You can read the article in it’s entirety by clicking on the image below.

Pilot Diabetes

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Aircraft Systems: Types of Electricity

Today, we’re featuring an excerpt from our new textbook Practical Electricity for Aviation Maintenance Technicians. As you can tell from the title, this book is geared for new AMT candidates, but it does feature a wealth of information on aircraft electrical systems useful to anyone flying or fixing airplanes.

There are two basic types of electricity: static and current. In static electricity, electrons accumulate on a surface and remain here until they build up a pressure high enough to force their way to another surface or device which has fewer electrons. Static electricity is generally a bother, and steps must be taken to prevent its formation and/or to get rid of it.

Current electricity, on the other hand, is the type most often used. There are two types of current electricity, Direct Current (DC), in which the electrons always flow in the same direction, and Alternating Current (AC), in which the electrons periodically reverse their direction of flow.

Static Electricity
When you slide across the plastic seat covers of an automobile, the friction between your clothing and the seat covers causes your clothes to pick up an excess of electrons from the seat. This is exactly the same thing described earlier when a piece of amber was rubbed with sheep’s wool.

If there is no conductor between your body and the car to make a path for these electrons to leak off, your body holds the extra electrons and is said to be charged because there is an electrically unbalanced condition between it and the car. But as soon as you touch or even come close to a bare metal part of the car, the extra electrons leave and jump to the metal in the form of a spark. This accumulation and holding of electrical charges is called static electricity.

Lightning is just a big spark. Friction of the air moving up and down inside the clouds causes water droplets in the clouds to become charged, and when enough electrons have concentrated in a cloud, the electrical pressure they produce forces them to move through the air. These electrons jump between clouds having different charges or from a cloud to the ground. This is the gigantic spark we call lightning.

As mentioned earlier, an object with an excess of electrons is negatively charged, and an object which has lost its electrons and wants to get them back is positively charged. Two positively charged or two negatively charged objects repel each other, while objects having opposite charges attract. When oppositely charged objects touch, the extra electrons travel from the negative object to the one with the positive charge and they become discharged, or electrically neutral. While static electricity has some uses, it is most often thought of as a nuisance. So a path must be provided to allow the electrons to pass harmlessly from one charged object to another before the charges can build up enough pressure to cause a spark to jump.

In addition to producing a mild shock when you touch the metal part of your car, static electricity can cause radio interference and can damage sensitive electronic components. It is possible, on a dry day, that just taking a few steps on a nylon carpet can build up more than 10,000 volts of static electricity on your body. When you have accumulated this much charge and touch some electronic components, they can be destroyed. When working with sensitive electronic equipment, always wear a grounded wrist strap to bleed off any charge on your body before handling the equipment.

Many airplanes have static discharge points or wicks installed on the trailing edges of the control surfaces. These devices allow the static charges that build up on the control surfaces as air flows over them to discharge harmlessly into the air and not cause static interference in the radio equipment.

Static discharge points are installed on the trailing edge of control surfaces to bleed off the static charges that build up as air flows over the surfaces.

Static discharge points are installed on the trailing edge of control surfaces to bleed off the static charges that build up as air flows over the surfaces.

Static electricity causes a serious fire hazard when aircraft are being fueled or defueled. The flow of gasoline or turbine fuel in the hose produces enough static electricity to cause a spark to jump and ignite explosive fumes.

Current Electricity
Current electricity is the form of electricity that has the most practical applications. A source of electrical energy such as a battery or alternator acts as a pump that forces electrons to flow through conductors. In this study of practical electricity, this flow is called current and because we are considering it to flow from positive to negative, it is positive current.

Aircraft must be electrically grounded before they are fueled. Bonding wires connect the aircraft and the fueling truck or pit together, and both of them are connected to the earth ground so that static charges that build up during fueling can pass harmlessly to ground.

Aircraft must be electrically grounded before they are fueled. Bonding wires connect the aircraft and the fueling truck or pit together, and both of them are connected to the earth ground so that static charges that build up during fueling can pass harmlessly to ground.

For current to flow, there must be a complete path from one terminal of the source back to the other terminal. The figure below shows a complete electrical circuit. The battery is the component in which chemical energy is changed into electrical energy, and current is forced out of the positive terminal, through the switch, the control device, to the lamp. The lamp acts as the load, which changes electrical energy into heat and light. The current then returns to the negative terminal of the battery. Current flows as long as the switch is closed, forming a complete path.

The electrical pressure that forces current through the circuit is measured in volts, with the basic unit of electrical pressure being one volt. Electrical current is measured in amperes or, as we more commonly call it, in amps. One amp is the flow of one coulomb per second, and one coulomb is 6.28 billion billion (6.28 x 1018) electrons. All conductors have some resistance which opposes the flow of electrons in much the same way that friction opposes mechanical movement. The basic unit of electrical resistance is the ohm. One volt of electrical pressure will force 1 amp of current to flow through 1 ohm of resistance.

This is a complete electrical circuit. When the switch is closed, current flows from the positive terminal of the battery through the lamp, where there is enough opposition that the filament gets white hot. After all of the pressure from the battery is dissipated by the lamp, the current returns to the negative terminal of the battery.

This is a complete electrical circuit. When the switch is closed, current flows from the positive terminal of the battery through the lamp, where there is enough opposition that the filament gets white hot. After all of the pressure from the battery is dissipated by the lamp, the current returns to the negative terminal of the battery.

When current flows through a resistor, power is dissipated and voltage is dropped. The voltage across a resistor can be measured with a voltmeter in the same way as the voltage produced by a battery. This voltage is caused by current (I) flowing through the resistor (R), and it is called an IR drop, or a voltage drop. The end of the resistor where the positive current enters is the positive end, and the end where it leaves is the negative end.

A battery is a source of electrical pressure that is also called an EMF, electromotive force, potential, or potential difference. All are measured in volts, and all mean essentially the same thing.

A battery is a source of electrical pressure that is also called an EMF, electromotive force, potential, or potential difference. All are measured in volts, and all mean essentially the same thing.

When current flows through a resistance, power is used, or dissipated, and voltage is dropped. The voltage dropped across a resistor can be measured with a voltmeter in the same way as the voltage produced across the terminals of a battery.

Electrical pressure caused by changing some other form of energy into electrical energy may be called an electromotive force (EMF) a potential difference, or just a potential. Electrical pressure caused by current flowing through a resistance is not a source of electrical energy; it is a drop in the electrical pressure. This voltage is usually called a voltage drop or an IR drop because the amount of drop may be found by multiplying the current (I) by the resistance (R) through which it flows. These terms for voltage are often used interchangeably, and all of them use the volt as the basic unit of measurement.

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