CFI Brief: Latitude and Longitude

This week’s focus on the blog is aeronautical charts, specifically charts designed for VFR pilots. An overview of the Terminal, Sectional, and World Aeronautical charts was given in Mondays post and can be found here. Each one of these charts provides a wealth of aeronautical information on airports, airways, airspace, special use airspace, and even terrain. However what I would like to focus on today is how to identify a geographic coordinate using one of these aforementioned VFR charts. To do this we first need to understand the lines of longitude and latitude that are depicted on the chart.

To identify a point on the surface of the earth, a geographic coordinate, or “grid” system was devised. By reference to meridians of longitude and parallels of latitude, any position may be accurately located when using the grid system.

Equidistant from the poles is an imaginary circle called the equator. The lines running east and west, parallel to the equator are called parallels of latitude, and are used to measure angular distance north or south of the equator. From the equator to either pole is 90°, with 0° being at the equator; while 90° north latitude describes the location of the North Pole.

Meridians of longitude and parallels of latitude.

Meridians of longitude and parallels of latitude.

Lines called meridians of longitude are drawn from pole to pole at right angles to the equator. The prime meridian, used as the zero degree line, passes through Greenwich, England. From this line, measurements are made in degrees both easterly and westerly up to 180°.

Any specific geographical point can be located by reference to its longitude and latitude. For example, Washington, DC is approximately 39° north of the equator and 77° west of the prime meridian and would be stated as 39°N 77°W. Note that latitude is stated first.

In order to describe a location more precisely, each degree (°) is subdivided into 60 minutes (‘) and each minute further divided into 60 seconds (“), although seconds are not shown. Thus, the location of the airport at Elk City, Oklahoma is described as being at 35°25’55″N 99°23’15″W (35 degrees, 25 minutes, 55 seconds north latitude; 99 degrees, 23 minutes, 15 seconds west longitude). Degrees of west longitude increase from east to west. Degrees of north latitude increase from south to north.

In the figure below you will see Elk City airport, notice in the bottom right corner the numbers 35 and 99 which depict the latitude and longitude. Beginning with the latitude of 35° North count the tick marks up until you reach Elk City airport at about 26. Remember each tick mark represents 1 minute, so our latitude is 35° (degrees) 26’ (minutes)  North. You will do the same for longitude; note that as you move right to left your lines of longitude will be increasing. By the time you get to Elk City airport you will have counted 23 tick marks representing 23 minutes. Therefor the longitude is 99° (degrees) 23’ (minutes) W. Remember the VFR charts do not depict seconds so it’s best to round off to the closest minute mark.

Elk City airport -- Click image to enlarge!

Elk City airport — Click image to enlarge!

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Navigation: Aeronautical Charts

This introduction to aeronautical charts comes from the Pilot’s Handbook of Aeronautical Knowledge, a foundational text for any student pilot.

An aeronautical chart is the road map for a pilot flying under VFR. The chart provides information which allows pilots to track their position and provides available information which enhances safety. The three aeronautical charts used by VFR pilots are sectional charts, VFR terminal area charts, and world aeronautical charts.

Sectional Charts
Sectional charts are the most common charts used by pilots today. The charts have a scale of 1:500,000 (1 inch = 6.86 nautical miles (NM) or approximately 8 statute miles (SM)) which allows for more detailed information to be included on the chart.

The charts provide an abundance of information, including airport data, navigational aids, airspace, and topography. The figure below is an excerpt from the legend of a sectional chart. By referring to the chart legend, a pilot can interpret most of the information on the chart. A pilot should also check the chart for other legend information, which includes air traffic control (ATC) frequencies and information on airspace. These charts are revised semiannually except for some areas outside the conterminous United States where they are revised annually.

Sectional chart and legend.

Sectional chart and legend.

VFR Terminal Area Charts
VFR terminal area charts are helpful when flying in or near Class B airspace. They have a scale of 1:250,000 (1 inch = 3.43 NM or approximately 4 SM). These charts provide a more detailed display of topographical information and are revised semiannually, except for several Alaskan and Caribbean charts.
VFR terminal area chart and legend.

VFR terminal area chart and legend.

World Aeronautical Charts
World aeronautical charts are designed to provide a standard series of aeronautical charts, covering land areas of the world, at a size and scale convenient for navigation by moderate speed aircraft. They are produced at a scale of 1:1,000,000 (1 inch = 13.7 NM or approximately 16 SM). These charts are similar to sectional charts and the symbols are the same except there is less detail due to the smaller scale. These charts are revised annually except for several Alaskan charts and the Mexican/Caribbean charts which are revised every two years.
World aeronautical chart.

World aeronautical chart.

A detailed introduction to using aeronautical charts, as well as how they are used in conjunction with navigation can be found in the Pilot’s Handbook of Aeronautical Knowledge, available from ASA.

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CFI Brief: What causes weather?

The theory of weather is a complex yet intriguing topic to discuss. It’s often joked that by the time you complete training you’re an amateur meteorologist. Joke or not, that statement is fairly accurate. Weather can be one of the key factors in determining a go/no-go decision and to make an accurate assessment it is important for the pilot in command to understand the full spectrum of what causes weather.

Let’s start with the most basic and determine the overall source of where weather comes from. Below is an excerpt from ASA’s 2015 Private Pilot Test Prep.

The major source of all weather is the sun. Changes or variations of weather patterns are caused by the unequal heating of the Earth’s surface. Every physical process of weather is accompanied by or is a result of unequal heating of the Earth’s surface.

The heating of the Earth (and therefore the heating of the air surrounding the Earth) is unequal around the entire planet. Both north or south of the equator, one square foot of sunrays is not concentrated over one square foot of the surface, but over a larger area. This lower concentration of sunrays produces less radiation of heat over a given surface area; therefore, less atmospheric heating takes place in that area.

The unequal heating of the Earth’s atmosphere creates a large air-cell circulation pattern (wind) because the warmer air has a tendency to rise (low pressure) and the colder air has a tendency to settle or descend (high pressure) and replace the rising warmer air. This unequal heating, which causes pressure variations, will also cause variations in altimeter settings between weather reporting points.

Because the Earth rotates, this large, simple air-cell circulation pattern is greatly distorted by a phenomenon known as the Coriolis force. When the wind (which is created by high pressure trying to flow into low pressure) first begins to move at higher altitudes, the Coriolis force deflects it to the right (in the Northern Hemisphere) causing it to flow parallel to the isobars (lines of equal pressure). These deflections of the large-cell circulation pattern create general wind patterns as depicted in the figure below.

Prevailing wind systems.

Prevailing wind systems.

Let’s take a look at a few questions you might encounter on your FAA Private Pilot Knowledge Test. I will post the answers Monday morning in the comments section.

1. Every physical process of weather is accompanied by, or is the result of, a
A—movement of air.
B—pressure differential.
C—heat exchange.

2. What causes variations in altimeter settings between weather reporting points?
A—Unequal heating of the Earth’s surface.
B—Variation of terrain elevation.
C—Coriolis force.

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Weather: Americas Weather Regions, California

The United States of America has some diverse weather patterns. Thomas A. Horne‘s book Flying America’s Weather gives you a view of different weather regions around the U.S. from a pilots view. Here is an excerpt from the book discussing weather in the region of California:

For pilots or any other student of meteorology, the state of California represents one of the most interesting weather regions in the United States. It is a state with an abundance of different climatological areas in close proximity to each other, a condition made possible by a unique combination of widely disparate geographic features. This is especially true of southern California, where the pacific Ocean, coastal lowlands, mountain ranges, valleys, and a desert adjoin each other in a strip of land hardly more than 100 miles wide.

As might be expected of a state with 1,340 miles of coastline, California owes a great deal of its weather to the Pacific Ocean, and the air circulating above it. This oceanic circulation has some seasonal aspects central to the nature of California’s summers and winters–especially in southern California. Like the Atlantic Ocean, the Pacific is the site of a large, semipermanent high pressure system. And just as the Atlantic’s Bermuda high affects so much of the eastern United States’ weather, so the Pacific high influences the western coastal areas.

But the differences are great. The clockwise circulation around the “back side” of the Bermuda high sends warm, moist air from the Caribbean and Gulf of Mexico inland. In California, it’s the high’s “front side” that’s at work. Here, the clockwise flow sends air of more moderate temperature from the central pacific to Californian shores.

In the summer months, the Pacific high is situated more or less due west of central California, There, it exercises a blocking function, preventing low pressure areas from traveling to the southern regions of the state. The flow of air is nearly always from the west, both at the surface and aloft, and wind speeds are moderate–seldom exceeding 40 knots even at altitudes as high as 10,000 feet. In the fall and winter, the Pacific high drops to the south, and this permits low pressure and/or cold fronts to strike California as they are pushed through by the northernmost segment of the high’s flows.

In his book,Thomas A. Horne breaks the U.S. into 17 geographical weather regions and discusses weather aspects unique to that particular region. Want to know whats happening in your neck of the woods? Check out theFlying America’s Weather!

You can purchase Flying America’s Weather on our website at, where you can find more resources for student pilots.


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CFI Brief: Newton

It’s been a few days since I last posted; I believe we left off discussing Bernoulli’s principal as it relates to lift. Today, I want to discuss another important mathematician/physicist from around the same time, Sir Isaac Newton.

Sir Newton came up with what is known today as Newton’s Three Laws of Motion. The law in which we will focus on today is the third law: for every action there is an equal and opposite reaction. Along with Bernoulli, Newton’s Third Law is also a direct contributor to lift. Bob Gardner describes this in The Complete Private Pilot:

A second contributor to total lift is Newton’s Third Law: for every action there is an equal and opposite reaction. As the airfoil moves through the air it pushes the air downward and, in accordance with Newton’s Law, the air exerts an equal upward force. Because of differences in wing design and operating conditions, it is impossible to say what percentage of total lift can be attributed to Bernoulli or to Newton at any time.

Imagine as the wing passes through space the air strikes the underside of the wing and is deflected downward. Based on Newton’s Third Law the opposite reaction would be a force created in an upwards direction, better known to a pilot as lift. Remember when you were a kid and stuck your hand out the window like a wing? I’m sure you could feel the wind wanting to push your hand back and up, this is the same exact concept. Pretty cool stuff!

Can you think of any other areas where Newton’s Third Law might come into play? I’ll give you a clue, think about the four forces on the aircraft that we have already discussed.

How about thrust? An aircraft propeller’s job is to create thrust—it does this by pushing air backyards, the resultant force is the air pushing the propeller in the opposite direction (forwards). The same can be said for a jet engine.

Here’s another example, imagine yourself sitting in the cockpit of a Cessna 172 with the engine running. Looking out the window you will notice that the propeller is turning to your right. Obviously we all know that the prop is connected to the engine which in turn is bolted to the airframe (I hope you knew that). The opposing force from the propeller is felt on the airframe around the longitudinal axis, so the airframe wants to roll left as the prop turns right (see the figure below). This is known as torque reaction and manufactures take this into effect when designing aircraft. This is an area you will get more into when discussing P-Factor and torque.

Torque reaction.

Torque reaction.

Here are two questions that you are likely to see on your FAA Knowledge test that cover the information we have discussed. I will post the answers in the comments section of this post on Monday. Now enough of this Aerodynamics talk, let’s get into weather next week!

1. In what flight condition is torque effect the greatest in a single-engine airplane?
A—Low airspeed, high power, high angle of attack.
B—Low airspeed, low power, low angle of attack.
C—High airspeed, high power, high angle of attack.

2. Which statement relates to Bernoulli’s principle?
A—For every action there is an equal and opposite reaction.
B—An additional upward force is generated as the lower surface of the wing deflects air downward.
C—Air traveling faster over the curved upper surface of an airfoil causes lower pressure on the top surface.

Know the answer? Have a further question for the CFI? Leave a comment below, or send an email to, and be sure to check the comments on this post next week for the answers!

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