CFI Brief: Pitot-Static Systems and Flight Instruments, Part II

I am sure you have been waiting all week for Part II of the CFI Brief on the Pitot-Static system. So here it is: today we will get into some of the principals of operation of each of the three pitot-static instruments found in the cockpit: altimeter, vertical speed indicator, and airspeed indicator.

The altimeter measures the height of an aircraft above sea level or a given pressure level and works in conjunction with pressure entering through the static port. As the pressure enters through the static port it is able to freely flow through small lines connected to the back of the altimeter box as seen in figure 1 below. The main component of the altimeter is a stack of sealed aneroid wafers that has been set to an internal pressure of 29.92 Hg. These wafers are able to expand and contract as pressure within the instrument box changes. Remember as you go up in altitude pressure decrease allowing the wafers to expand and vice versa, as you decrease in altitude pressure increase contracting the wafers. Next time you drive over a mountain pass take along with you a sealed bag of chips and watch the bag expand as you drive up the pass. Once you get back down the other side the bag will be back to normal. This is essentially the same thing happening inside the altimeter. The aneroid wafers are connected through mechanical linkage to pointers on the face of the instrument that register the pressure presenting it as an altitude indication given in feet.

Figure 1. The altimeter.

Figure 1. The altimeter.

Next up, the vertical speed indicator, as you know this instrument indicates the rate of climb or descent of the aircraft. The VSI is considered to be what’s called a differential pressure instrument, meaning it uses the differences in pressure to indicate whether the aircraft is in a climb or descent. The internal components consist of a diaphragm, calibrated leak orifice, and mechanical linkage. Unrestricted air from the static line enters directly into the diaphragm while static air enters the air tight casing through the calibrated leak. If the aircraft were in level flight or on the ground this pressure would be equal. As the aircraft climbs or descends the pressure inside the diaphragm changes immediately. The case pressure however does not; because of the calibrated leak the pressure inside the instrument casing will remain higher or lower for a period of time. This difference in pressure between the two is what allows the diaphragm to expand and contract and through the mechanical linkage is shown as either a climb or descent on the instrument face.

Figure 2. The vertical speed indicator.

Figure 2. The vertical speed indicator.

Lastly, we have the airspeed indicator, the only instrument that uses both pitot and static pressure. The ASI measures the difference between pitot and static pressure (impact and dynamic) and registers it as an airspeed shown on the face of the instrument. When the two pressures are equal the airspeed is shown as zero. Ram air entering the pitot-tube is directed though pitot lines to a diaphragm contained within the instrument case (you can see this in figure 3 below). The greater the impact pressure from the pitot-tube the larger the diaphragm expands. Through the static line dynamic pressure enters into the instrument casing surround the diaphragm. As the diaphragm expands and contracts against the differences in pressure it indicates this through mechanical linkage to an indicating needle on the face of the instrument. The greater the pressure differences the higher the indicated airspeed.

Figure 3. The airspeed indicator.

Figure 3. The airspeed indicator.

This has been such a fun topic to discuss that I thought hey why not add a Part III! So next week, look for the conclusion of the CFI Brief on the pitot-static system, specifically focusing on errors and failures that can occur and how they will be reflected on the instruments. I might even through together a little quiz to test your knowledge so be prepared!

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Regulations: Pilot Ratings

Getting started with your flight training and curious about the differences between ratings? As per 14 CFR 61.5, there are seven pilot certificates: student, sport pilot, recreational, private, commercial, airline transport pilot, and flight instructor. This summary comes from Bob Gardner’s The Complete Private Pilot. The definitive compendium of all federal regulations pertaining to pilots in the United States is ASA’s FAR/AIM.

Student Pilot: Limited to solo or dual (instructional) flights only.

Sport Pilot: Sport pilots are limited to flying airplanes certificated as light sport aircraft: single engine, no more than two seats, 120 knots maximum cruise speed, 1,320 maximum gross weight, daytime only, with at least three miles visibility while maintaining visual contact with the ground. Maximum authorized altitude is 10,000 feet MSL or 2,000 feet AGL, whichever is higher. Sport Pilot certificates do not list category or type…all you need is an instructor’s endorsement that you have received ground and flight training in order to operate another category or class of light sport aircraft.

Recreational Pilot: Can carry only one passenger. Must receive additional instruction and endorsements to fly beyond 50 nm of the airport at which the pilot has received flight and ground instruction. Limited to a single engine of less than 180 hp and fixed landing gear. Cannot fly where radio communication is required. Cannot fly at night or internationally. Some of these restrictions can be removed with additional training and logbook endorsements.

Private Pilot: May carry passengers or cargo, day or night, as long as no charge is made. Is permitted to share expenses with passengers. May fly in conjunction with employment if flying is only incidental to the employment.

Commercial Pilot: May fly for compensation or hire. Must also meet requirements of Part 135 to fly as air taxi pilot.

Airline Transport Pilot: May fly as pilot-in-command on an airline flight or on a multiengine scheduled commuter flight.

A certificated flight instructor can give both flight and ground instruction under the conditions stated in 61.193 and 61.195. A flight instructor certificate must be renewed every 24 calendar months.

Your certificate will carry a category and class rating such as Airplane: Single Engine Land. You cannot carry passengers unless you hold the appropriate category and class ratings, and an instrument rating is required for instrument flight rules (IFR) whether you are carrying passengers or not. You can begin training for the instrument rating as soon as you receive your private pilot certificate; there is no minimum flight time requirement. The figure below shows the categories and the applicable class ratings.

Categories and class ratings.

Categories and class ratings.

Look for Part II of our CFI’s post on the three pitot-static instruments and their operation on Thursday!

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CFI Brief: Pitot-Static Systems and Flight Instruments, Part I

Today’s posts is the first part in a two part series on the pitot-static system and associated pitot-static instruments. We will begin by covering a quick general overview of the pitot-static system as seen in the picture below.

The pitot-static system is responsible for the operation of the airspeed indicator, altimeter, and vertical speed indicator—also known as the pitot-static flight instruments. This is a combined system providing information to the flight instruments through both static air pressure and dynamic pressure due to the motion of the aircraft through the air. Understanding how this system works and properly interrupting failures on the instruments is crucial to the safety of flight.

Pitot-Static System

Pito Static System

The pitot-tube is that odd shaped mechanism typically hanging below the left wing of the airplane, it is strategically positioned to hang in an area of undisturbed air. Pitot tubes have the unique ability to measure both the static air pressure and dynamic pressure ultimately providing information to the airspeed indicator. On the front end of the pitot-tube you have a small hole allowing ram air to enter the pressure chamber. On the back end you have another small hole; this is known as the drain hole and allows moisture to escape the pressure chamber. You can see how that might be important on a rainy day. During your preflight it is important to check that both of these holes are free and clear of any debris. The majority of all aircraft come with pitot-tube covers to protect from debris entering the pitot-tube while the aircraft sits on the ground. An important feature incorporated into the pitot-tube is pitot heat, this prevents any visible moisture entering the pressure chamber from freezing. The heater is controlled by a switch located on the cockpit panel and should be checked as part of your pre-flight duties. The pitot-tube should be hot to the touch when the pitot heater switch is turned on.

Static ports are located on the aircraft fuselage also in areas of free undisturbed air allowing static air to enter the instruments through small lines connecting the static ports to the instruments (seen in blue in the figure above). As the atmosphere and pressures change the static air is able to move freely in and out. Just like when checking the pitot-tube you should also check the static ports to verify they are free and clear of blockages. Often times when washing an airplane the static port is covered with tape to prevent moisture from entering. Most airplanes are equipped with an alternate static source typically located inside the cockpit. The alternate static source can provide static air pressure in the event your main static port becomes blocked. The airplane will be equipped with a switch or small pull tab to activate the alternate static source, however you should be aware that the pressure inside the cockpit will always be lower than that outside the cockpit. Because of this, when the alternate static is in use, you will observe the following indications:

  1. Altimeter will indicate a slightly higher than actual altitude.
  2. Airspeed indicator will show airspeed greater than actual.
  3. Your vertical speed indicator should momentarily show a climb when the alternate static is activated and then return to normal.

In any event, if all else fails, you can always break the glass on the face of the vertical speed indicator as a way of introducing static air into the system. It is typically chosen to break the glass on the VSI as this is the least important of the three static instruments and when the glass is broke that instrument will be rendered useless.

Next Thursday in Part II we will get into specifics on the three pitot-static instruments and the principal of operation of each.

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Flight Instruments: Airspeeds and the Airspeed Indicator (ASI)

Today, we’ll go over the airspeed indicator (ASI). This explanation comes from the FAA textbook Pilot’s Handbook of Aeronautical Knowledge.

The ASI is a sensitive, differential pressure gauge which measures and promptly indicates the difference between pitot (impact/dynamic pressure) and static pressure. These two pressures are equal when the aircraft is parked on the ground in calm air. When the aircraft moves through the air, the pressure on the pitot line becomes greater than the pressure in the static lines. This difference in pressure is registered by the airspeed pointer on the face of the instrument, which is calibrated in miles per hour, knots (nautical miles per hour), or both. (Figure 1)

Figure 1. The airspeed indicator.

Figure 1. The airspeed indicator.

The ASI is the one instrument that utilizes both the pitot, as well as the static system. The ASI introduces the static pressure into the airspeed case while the pitot pressure (dynamic) is introduced into the diaphragm. The dynamic pressure expands or contracts one side of the diaphragm,which is attached to an indicating system. The system drives the mechanical linkage and the airspeed needle.

Just as in altitudes, there are multiple types of airspeeds. Pilots need to be very familiar with each type.

  • Indicated airspeed (IAS)—the direct instrument reading obtained from the ASI, uncorrected for variations in atmospheric density, installation error, or instrument error. Manufacturers use this airspeed as the basis for determining aircraft performance. Takeoff, landing, and stall speeds listed in the AFM/POH are IAS and do not normally vary with altitude or temperature.
  • Calibrated airspeed (CAS)—IAS corrected for installation error and instrument error. Although manufacturers attempt to keep airspeed errors to a minimum, it is not possible to eliminate all errors throughout the airspeed operating range. At certain airspeeds and with certain flap settings, the installation and instrument errors may total several knots. This error is generally greatest at low airspeeds. In the cruising and higher airspeed ranges, IAS and CAS are approximately the same. Refer to the airspeed calibration chart to correct for possible airspeed errors.
  • True airspeed (TAS)—CAS corrected for altitude and nonstandard temperature. Because air density decreases with an increase in altitude, an aircraft has to be flown faster at higher altitudes to cause the same pressure difference between pitot impact pressure and static pressure. Therefore, for a given CAS, TAS increases as altitude increases; or for a given TAS, CAS decreases as altitude increases. A pilot can find TAS by two methods. The most accurate method is to use a flight computer. With this method, the CAS is corrected for temperature and pressure variation by using the airspeed correction scale on the computer. Extremely accurate electronic flight computers are also available. Just enter the CAS, pressure altitude, and temperature, and the computer calculates the TAS. A second method, which is a rule of thumb, provides the approximate TAS. Simply add 2 percent to the CAS for each 1,000 feet of altitude. The TAS is the speed which is used for flight planning and is used when filing a flight plan.
  • Groundspeed (GS)—the actual speed of the airplane over the ground. It is TAS adjusted for wind. GS decreases with a headwind, and increases with a tailwind.

Airspeed Indicator Markings
Aircraft weighing 12,500 pounds or less, manufactured after 1945, and certificated by the FAA, are required to have ASIs marked in accordance with a standard color-coded marking system. This system of color-coded markings enables a pilot to determine at a glance certain airspeed limitations that are important to the safe operation of the aircraft. For example, if during the execution of a maneuver, it is noted that the airspeed needle is in the yellow arc and rapidly approaching the red line, the immediate reaction should be to reduce airspeed.

Figure 2. ASI markings.

Figure 2. ASI markings.

As shown in Figure 2, ASIs on single-engine small aircraft include the following standard color-coded markings:

  • White arc—commonly referred to as the flap operating range since its lower limit represents the full flap stall speed and its upper limit provides the maximum flap speed. Approaches and landings are usually flown at speeds within the white arc.
  • Lower limit of white arc (VS0)—the stalling speed or the minimum steady flight speed in the landing configuration. In small aircraft, this is the power-off stall speed at the maximum landing weight in the landing configuration (gear and flaps down).
  • Upper limit of the white arc (VFE)—the maximum speed with the flaps extended.
  • Green arc—the normal operating range of the aircraft. Most flying occurs within this range.
  • Lower limit of green arc (VS1)—the stalling speed or the minimum steady flight speed obtained in a specified configuration. For most aircraft, this is the power-off stall speed at the maximum takeoff weight in the clean configuration (gear up, if retractable, and flaps up).
  • Upper limit of green arc (VNO)—the maximum structural cruising speed. Do not exceed this speed except in smooth air.
  • Yellow arc—caution range. Fly within this range only in smooth air, and then, only with caution.
  • Red line (VNE)—never exceed speed. Operating above this speed is prohibited since it may result in damage or structural failure.

As always, be sure to check back Thursday for a post from our CFI.

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CFI Brief: Steep Turns

Steep turns are a fun and exciting maneuver and right in line with this week’s discussion on load factors. As a student pilot part of your training will include performing steep turns to established standards as outlined in the Private Pilot Practical Test Standards and shown below. Key concepts to be learned are coordination, orientation, division of attention, and control techniques necessary for the execution of maximum performance turns. A steep turn is often performed at or near performance limits so caution must be taken and the pilot should have a complete understanding of aircraft limitations:


  1. Exhibits satisfactory knowledge of the elements related to steep turns.
  2. Establishes the manufacturer’s recommended airspeed or if one is not stated, a safe airspeed not to exceed VA.
  3. Rolls into a coordinated 360° turn; maintains a 45° bank. Performs the task in the opposite direction, as specified by the examiner.
  4. Divides attention between airplane control and orientation.
  5. Maintains the entry altitude ±100 feet; airspeed ±10 knots; bank ±5°; and rolls out on the entry heading ±10°.

To successfully complete steep turns you must first understand the theory and principals behind the maneuver. Take a look at this short excerpt from ASA Virtual Test Prep Flight maneuvers DVD.

Understanding how aerodynamic forces and load factors affect flight characteristics will allow you to successfully complete this maneuver to standards. For example, a common error students tend to make is a failure to maintain altitude +/- 100 feet. If you understand aerodynamic forces and load factors you know that changing bank will directly affect lift. In a steep turn you may need to make small corrections in control inputs to steepen or shallow the bank (remember you have +/- 5° to work with). If your nose drops through the horizon and you notice a descent on the altimeter, decreasing bank angle will allow the airplane to regain some lift. Vice versa, if you see your nose rising above the horizon and note a climb on the altimeter you can increase your bank, taking away from lift.

With the information given you should have no problem answering this sample knowledge test question.

 What force makes an airplane turn?

A. The horizontal component of lift

B. The vertical component of lift

C. Centrifugal force


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Aerodynamics: Turns and Load Factors

We’re devoting this week to aerodynamics, specifically the load factors experienced in turns. There’s more to turning your airplane than smoothly coordinating your ailerons and rudder pressure. Understanding the role of lift and gravity in a turn will help you fly efficiently and within the limitations of your airplane. The following is excerpted from William Kershner’s textbook The Student Pilot’s Flight Manual.

Lift is considered to act perpendicularly to the wingspan. Consider an airplane in straight and level flight where lift equals weight. Assume the airplane’s weight to be 2,000 pounds.

In Figure 1A everything’s great—lift equals weight. If the plane is banked is 60° as in Figure 1B, things are not so rosy. The weight’s value or direction does not change. It’s still 2,000 pounds downward. The lift, however, is acting at a different angle. The vertical component of lift is only 1,000 pounds, since the cosine of 60° is 0.500 (60° is used for convenience here; you certainly won’t be doing a bank that steep in the earlier part of your training). With such an unbalance, the plane loses altitude. The answer, Figure 1C, is to increase the lift vector to 4,000 pounds so that the vertical component is 2,000 pounds. This is done by increasing the angle of attack. Back pressure is applied to the elevators to keep the nose up.

Figure 1. The vertical component of lift must be equal to weight in a constant-altitude turn.

Figure 1. The vertical component of lift must be equal to weight in a constant-altitude turn.

If in our example of the 60° bank, you roll out level but don’t get rid of the extra 2,000 pounds of lift you have, obviously the airplane will accelerate upward (the “up” and “down” forces will no longer be in balance). Maybe your idea of coordination is that demonstrated by a ballroom dancer, but it’s necessary in flying too. Think of control pressures rather than movement. The smoother your pressures, the better your control of the airplane.

The turn introduces a new idea. It is possible to bank so steeply that the wings cannot support the airplane. The lift must be increased so drastically that the critical angle of attack is exceeded, and the plane stalls. In the previous example at 60° of bank, it was found that our effective wing area was halved; therefore, each square foot of wing area had to support twice its normal load. This is called a load factor of 2. A plane in normal, straight and level flight has a load factor of 1, or 1 “g.” You have this same 1 g load on your body at the time. Mathematically speaking, the load factor in the turn is a function of the secant of the angle of bank. The secant varies from 1 at 0° to infinity at 90°; so maintain altitude indefinitely in a constant 90° bank, an infinite amount of lift is required—and this is not available.

Figure 2. The effects of bank angle on the amount of lift that is directly opposing weight.

Figure 2. The effects of bank angle on the amount of lift that is directly opposing weight.

Putting it simply: The stall speed goes up in the constant altitude turn; and the steeper the bank, the faster the small speed jumps up, as can be seen in Figures 3 and 4. The load factors just discussed are “positive” load factors and are attained by pulling the wheel back, causing you to be pressed down in the seat. A negative load factor is applied if the control wheel is pushed forward abruptly, and in this case you feel “light” and tend to leave the seat. Lightplanes are generally stressed to take a maximum positive load factor varying from 3.8 to 6, and a negative load factor of between 1.52 and 3, depending on the make and model. Both you and the plane are able to stand more positive g’s than negative. Positive or negative load factors can be imposed on the plane by sharp up or down gusts as well as by the pilot’s handling of the elevators.

Figure 3. The relationship of stall speed to angle of bank

Figure 3. The relationship of stall speed to angle of bank.


Figure 4. Stall speed increases with bank.

Figure 4. Stall speed increases with bank.

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CFI Brief: Magnetos

So I’ve been told my airplane engine has two magnetos, but what the heck is a magneto? Well in a reciprocating airplane engine like that of Lycoming IO-360 found in many Cessna 172 aircraft the magnetos are a source of high-voltage electrical energy. This electrical energy is used to produce the spark to ignite the fuel-air mixture inside the cylinders of a reciprocating engine. They are called magnetos because they use a permanent magnet to generate the electrical current sent to the spark plugs.

Airplane Magneto

Airplane Magneto–About the size of a Coke can

Once the starter is engaged and the crank shaft begins turning, the magnetos will activate and start producing the electrical energy needed to create a spark in the cylinders. It is important to understand that the magnetos operate completely independent of the aircraft’s electrical system. This is done for safety; in the event of a complete electrical failure, the engine will not shut down.

Key point: as the crankshaft turns so do the magnets within the magnetos creating the aforementioned energy. So for the engine to initially start, some source of outside energy needs turn the crankshaft. This is most commonly done by engaging the starter within the engine which does require an initial amount of electrical energy that comes from the batteries. However, you may fly an older aircraft that does not contain a starter, as one of the aircraft engine components, in a case like this an individual would physical turn the crankshaft by hand propping the airplane (caution: hand propping is extremely dangerous, always consult the aircraft’s operating handbook and follow proper hand propping procedures).

You learned in Monday’s post that each magneto operates independently of one another and contains a 5-position ignition switch: OFF, R, L, BOTH, and START. When OFF is selected you have in turn grounded both magnetos preventing them from creating the necessary spark for engine ignition. If selecting R or L (Right or Left magneto) you are grounding only one magneto, the one which is not selected. For example, if the L is selected the right magneto is grounded. The system will operate on both magnetos when BOTH is selected. By moving the ignition switch to the START indication you will engage the aircraft engine starter and un-ground both magnetos. As in most cases, you will have to hold the switch in this position while engaging the starter, releasing the switch it will snap back into the BOTH position, as it is designed to do allowing the engine to run on the both magnetos.

5 Position Ignition Indicator Switch

5-Position Ignition Indicator Switch

So what happens if you accidentally turn the magnetos to the OFF position in-flight? Well, the engine will stop as no spark will be provided to the cylinders to create combustion. Even though the engine is stopped the propeller will likely still be windmilling due to aerodynamic forces. Because that prop is still spinning so is the crankshaft, so simply turning the ignition switch back to BOTH should allow your engine to restart without problem. Always consult the pilot operating handbook for all in-flight restart procedures as these can and will vary between aircraft. And please try not to accidentally turn your magnetos off.

Questions about the magnetos or ignition systems? Let us know in the comments section and we will do our best to answer your questions.

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Aircraft Systems: Ignition

You don’t have to be a mechanic to be a safe pilot, but a knowledge of how your engine works and what the engine instruments are telling you will make it easier to give your engine tender loving care and get long, reliable service from it. Today we’ll cover your airplane’s ignition system, with a post taken from The Complete Private Pilot by Bob Gardner.

There are many similarities between an automobile engine and an airplane engine. Both are internal combustion engines, both use spark plugs, and both use some type of fuel metering system related to throttle position. An aircraft is a four-cycle engine: Figure 1 illustrates the four cycles. The fuelair mixture is drawn into the cylinder as the piston moves downward on the intake stroke; as the piston moves upward with the valves closed, the mixture is compressed during the compression stroke. The burning of the fuel-air mixture after ignition drives the piston downward during the power stroke, and as the piston rises again with the exhaust valve open the exhaust stroke ends the four stroke cycle. Because your aircraft engine has four or more cylinders, each igniting at a different time, there is always one piston on a power stroke, and the process is continuous.

Figure 1. Four strokes of an aircraft engine.

Figure 1. Four strokes of an aircraft engine.

Your gas-powered airplane engine uses a magneto as the source of ignition. Magneto may not be a familiar term to you, but your gas lawnmower, chain saw, or outboard motor all use magnetos. A magneto is a self-contained source of electrical impulses, using the physical motion of a coil and a fixed magnetic field to develop ignition voltage. To start the engine, you provide that physical motion by pulling a cord on your lawnmower, chain saw, or outboard. The starter motor does the job in the airplane, rotating the engine until the magneto-developed spark ignites the mixture. You have probably seen older airplanes without electrical systems (and newer airplanes with starter problems) being started manually—rotating the propeller by hand (“propping”) causes the magneto to generate a voltage which goes to the spark plug to ignite the fuel/air mixture. Hand-propping an airplane is a hazardous undertaking which requires an experienced and knowledgeable person both in the cockpit and at the propeller. Once an airplane engine is started, the magnetos provide continuous ignition on their own—the airplane’s electrical system and the starter motor have done their jobs. The master switch plays no further role in engine operation.

Each cylinder in your airplane engine has two spark plugs, each fired by a different magneto (see Figure 2). This has two advantages: better combustion efficiency, and safety. The engine will run on either magneto if one should develop a problem. Magnetos are totally independent of the aircraft electrical system.

Figure 2. Spark plugs and magnetos.

Figure 2. Spark plugs and magnetos.

When you turn the ignition off, with a key or with switches, you are connecting the electrical output of the magneto to the metal block of the engine where it is shorted to electrical ground and cannot fire the spark plugs. This “shorting out” is done through a wire called a P-lead, and if a P-lead is broken its associated magneto can fire the spark plugs even with the ignition in the OFF position. For this reason, you should treat all propellers with respect—moving the propeller might cause a magneto to start the engine unexpectedly if a P-lead has broken. During the preflight check of the airplane and its systems you will run the engine on each magneto separately. The ignition switch is marked OFF-LEFT-RIGHT-BOTH, if there is a start button, and OFF-L-R-BOTH-START if there is not (the START position is spring-loaded to return to the BOTH position when finger pressure is removed). In the OFF position, the P-leads of both magnetos are grounded; in the LEFT position, the right magneto is grounded and you are checking the operation of the left magneto. In the RIGHT position, then, the P-lead of the left magneto is grounded, and in the BOTH position, both magnetos are capable of delivering a spark.

As you cut the ignition sources in half you will lose some power, reflected as a drop in revolutions per minute (rpm). If no drop occurs when one magneto is shut off, that magneto probably has a broken P-lead, and the flight should be delayed until a mechanic checks it. Some authorities recommend checking for a broken P-lead just before shutting the engine down after a flight, by turning the ignition switch to its “OFF” position momentarily while at idle power; if the engine continues to run, there is probably a broken P-lead.

You should check your engine’s magnetos each time you are in the runup area preparing for takeoff. Magnetos can develop faults that are not readily detectable in cruising flight but which might rob the engine of the power required for takeoff.

We’ll have more on aircraft engines from our CFI on Thursday.

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CFI Brief: Effective Communication

According to FAA research and safety reports there are three distinct types of communication errors:

An absence of a pilot readback. The pilot merely acknowledges the clearance that he/she in actuality misunderstood.

A Readback/hearback error. When a pilot reads back a clearance incorrectly and the controller fails to catch the error.

Hearback Type II Errors. This is when the pilot correctly reads back a clearance but the controller fails to notice that the clearance issued was not the intended one.

I point these errors out to show that effective communication relies heavily upon two people. If you plan on becoming an instructor, one day you will learn that the process of communication is composed of three elements: source, symbols, and receiver. Think of the source as the person (pilot or controller) transmitting the information and the receiver (pilot or controller) as just that the person listening and receiving that information. Symbols are those words or even signs used to transmit the information between the two. When a symbol is misunderstood confusion can occur.

In Monday’s post we learned that there is established phraseology and accepted techniques to be used while communicating on the radio. This is in place to alleviate the confusion that can occur between the pilot and controller through the process of transmitting symbols.

Standard procedural words and phrases.

Standard procedural words and phrases.

These question below you may likely encounter on the FAA Private Pilot Knowledge Exam and will test your knowledge on correct phraseology and technique used on the radios.

1. The correct method of stating 10,500 feet MSL to ATC is

2. The correct method of stating 4,500 feet MSL to ATC is

3. If instructed by ground control to taxi to Runway 9, the pilot may proceed
A—via taxiways and across runways to, but not onto, Runway 9.
B—to the next intersecting runway where further clearance is required.
C—via taxiways and across runways to Runway 9, where an immediate takeoff may be made.

4. When flying HAWK N666CB, the proper phraseology for initial contact with McAlester AFSS is

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Communication Procedures: Phraseology, Techniques, and Procedures

Effective communication is absolutely critical to your safety and the safety of those in the air around you and on the ground. There’s a well established phraseology and accepted techniques in aviation, so mastering this will be key in your flight training. Take a look at the introduction to radio communications, excerpted from Bob Gardner’s communication textbook Say Again, Please, as well as our CFI’s post on how the FAA expects you to understand radio phraseology. Today’s post comes from Bob Gardner’s The Complete Private Pilot and from the 2015 FAR/AIM.

Always use the phonetic alphabet when identifying your aircraft and to spell out groups of letter or unusual words under difficult communications conditions. Do not make up your own phonetic equivalents; this alphabet was developed internationally to be understandable by non-English speaking pilots and ground personnel.

AIM Table 4-2-2. Phonetic Alphabet/Morse Code

AIM Table 4-2-2. Phonetic Alphabet/Morse Code

Misunderstandings about altitude assignments can be hazardous. Check the Aeronautical Information Manual for more officially accepted techniques. However, as you monitor aviation frequencies you will hear pilots use a decimal system: TWO POINT FIVE for 2,500. The FAA has never commented on this practice and it is commonly accepted—don’t try it in another country.

500 . . . . . . . FIVE HUNDRED
10,000 . . . . . TEN THOUSAND

Pilots flying above 18,000 feet use flight levels when referring to altitude:


Bearings, courses, and radials are always spoken in three digits:


Address ground controllers as “SEATTLE GROUND CONTROL,” control towers as “O’HARE TOWER,” radar facilities as “MIAMI APPROACH,” or “ATLANTA CENTER.” When calling a flight service station, use radio: “PORTLAND RADIO, MOONEY FOUR VICTOR WHISKEY.”

When making the initial contact with a controller, use your full callsign, without the initial november: “BOISE GROUND, PIPER THREE SIX NINER ECHO ROMEO AT THE RAMP WITH INFORMATION GOLF, TAXI FOR TAKEOFF.”

Many uncontrolled airports share UNICOM frequencies, and if you do not identify the airport at which you are operating, your transmissions may serve to confuse other pilots monitoring the frequency. Don’t say, “STINSON FOUR SIX WHISKEY DOWNWIND FOR RUNWAY SIX,” say, “ARLINGTON TRAFFIC, STINSON FOUR SIX WHISKEY DOWNWIND FOR RUNWAY SIX, ARLINGTON.” That way, pilots at other airports sharing Arlington’s UNICOM frequency will not be nervously looking over their shoulders.

The most valuable word in radio communication is “unable.” It should be used whenever you are asked to do something you don’t want to do or are prohibited from doing, like flying to close to a cloud. An air traffic controller who hears “unable” will come up with an alternative plan. You are the pilot-in-command and the only person in position to determine the safety of a proposed action. The second most important word is “immediately.” If a controller tells you to turn left immediately, or to climb immediately or to do anything else immediately, do not reach for the microphone—do it. The other side of the coin is when you need to cut corners to get on the ground in a hurry—a sick passenger, for example. When you make your initial call, tell the controller that you need to land immediately.

Online Resources

Note: None of these sites are official and they should be used only for planning and orientation. Aerial views are not current.

You can find the frequencies to be used at any airport at

An excellent resource for radio communication procedures is “Say it Right,” produced by the Air Safety Foundation. It can be found at

More on communication procedures from our CFI on Thursday.

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