Ch. 2 - C - Flight Instruments

Question 1

What are the basic categories of instruments grouped according to their method of operation?

Answer 1

Pitot-Static Instruments: speed, rate of climb or descent, and altitude.
The operate using air pressure differentials.
Gyroscopic: A pictorial view of the airplane’s attitude and rate of turn is provided by the attitude indicator and turn coordinator. The airplanes heading indicator also functions gyroscopically, but must be set using the compass.
Magnetic: The compass functions magnetically and is used to set the heading indicator.

Question 2

How do Pitot-Static instruments work?

Answer 2

They rely on air pressure differences to measure speed, altitude.

Question 3

How is static pressure defined, and which instruments use static air pressure to derive readings?

Answer 3

Static pressure is the surrounding air pressure. The airspeed indicator, altimeter, and vertical speed indicator all use static pressure.

Question 4

What is pitot pressure, and which instruments use it?

Answer 4

Pitot pressure is the static pressure, plus the pressure generated by the aircraft moving through the air (pitot pressure).
It is only used for the airspeed indicator.

Question 5

What is the typical amount of static pressure at sea level?

Answer 5

At sea level, air exerts about 14.7 pounds of pressure per square inch (lb./in^2).

Question 6

As altitude increases, what happens to static pressure?

Answer 6

As altitude increases, pressure decreases. At 18,000 ft. the pressure is roughly half of sea level (7.35 lb./in^2).

Question 7

How does air temperature effect air pressure?

Answer 7

Ceteris paribus, A cooler air temp will result in lower air pressure because the cold slows down air molecules and they are less active in their ability to exert force.
Warmer air increases air pressure.

Question 8

What is a visually memorable way of defining air pressure?

Answer 8

Atmospheric pressure may be defined as the weight of a single column of air. The weight measures the force, exerted by the air, called pressure.
The area of the column is 1 square inch, and at sea level that column exerts 14.7 lb./in^2). Moving up the column results in a decrease of pressure all the way to the top of the atmosphere.

Question 9

What is the ISA?

Answer 9

The International Standard Atmosphere.

Provides a common reference for temperature and pressure.

Question 10

Most flight instruments and airplane performance data is based on the ISA determined “standard conditions.” What are the standard atmospheric conditions at sea level?

Answer 10

Standard sea level atmospheric conditions are defined by the combo of barometric pressure and temperature.

Barometric Pressure = 29,92 in. Hg. (1013.2 millibars).

Temperature = 15 degrees Celsius (59 degrees Fahrenheit).
Under standard conditions, mercury in an inverted tube rises to 29.92 in. Hg. This translates to a weight of 14.7 lb./in^2.

Question 11

What is the purpose of standard lapse rates?

Answer 11

Both air pressure and temperature decrease with altitude, so standard lapse rates graph the typical changes as one moves upward through the atmosphere. It helps to calculate and anticipate the changes at various altitudes.

Question 12

What is the numerical value of the air temperature standard lapse rate?

Answer 12

In the lower atmosphere, standard air temp lapse rate = 3.5 degrees Fahrenheit (2 degrees Celsius) per every 1,000 ft. of elevation gained.

Question 13

What is the numerical value of the air pressure standard lapse rate?

Answer 13

Air pressure standard lapse rate = 1.00 in. Hg. per every 1,000 ft. climbed.

Question 14

What is the pitot tube’s function?

Answer 14

The pitot tube supplies impact/ram air pressure to the pitot-static system. The pitot tube is usually mounted on the nose or wing so it is out in front and not affected by the airplanes structure. The opening is exposed to relative wind. An increase in speed increases ram air pressure.

Question 15

What is a static port, and its function?

Answer 15

Static pressure enters the pitot-static system via the static port. It usually is flush mounted on the side of the fuselage in an area of relatively undisturbed air.

Question 16

What is the pitot heating switch?

Answer 16

Electrical heating elements that deice the pitot tube.

Question 17

Can there be two static ports or a system with a combined pitot tube and static port?

Answer 17

Yes and yes. There may be one or more static ports. If there are two they are typically on either side of the fuselage and provide an avg. static pressure reading.

Some designs combine static port with the pitot tube.

Question 18

What is the only instrument to operate using both static and pitot pressure readings?

Answer 18

The Airspeed indicator reading is derived by comparting the ram air pressure with the static air pressure - The greater the differential, the greater the airspeed.

Question 19

What are V-speeds?

Answer 19

V-speeds are the colored arcs corresponding to air speed limitations of the aircraft.

Question 20

What is Vne ?

Answer 20

Vne is the red line, and stands for never exceed. Operating above this speed may result in damage or structural failure.

Question 21

What is the yellow arc on airspeed indicator?

Answer 21

Indicates caution range. You may fly within this range only in smooth air and only with caution.

Question 22

What is Vno?

Answer 22

The upper limits of the green arc (or normal operating range). This is the limit of normal operations, or max structural cruising speed. You should not exceed unless in very smooth air.

Question 23

What is the green arc on airspeed indicator?

Answer 23

The normal operating range for the aircraft. Most flying occurs in this range.

Question 24

What is Vfe ?

Answer 24

Fe means flaps extended. The Vfe is the upper limit of the white arc which indicates the range in which it is safe to extend flaps.

Question 25

What is the white arc?

Answer 25

Referred to as the flap operating range since its lower limit represents the full flap stall speed, and upper limit provides the max speed in which flaps may be extended.
Approaches and landings are performed at speeds within the white arc.

Question 26

What is Vs1 ?

Answer 26

It is the lower limit of the green arc. It is defined as the stalling speed, or minimum steady flight speed.
For small airplanes, this is the power-off stall speed at the max allowable takeoff weight in clean configuration (gear up and flap up).

Question 27

What is Vs0 ?

Answer 27

The lower limit of the white arc. This is the stalling speed, or minimum steady flight speed when in the landing configuration (gear and flaps down) instead of the clean configuration (gear and flaps up).
The power off stall speed at the max landing weight.

Question 28

What important air speed limitations are not shown on the airspeed indicator ? Why is it not shown like other V-speeds?

Answer 28

The Va (maneuvering speed) is not shown on the airspeed indicator because it changed with weight.

For complex aircraft:
Vle is the speed which should not be exceeded after landing gear had been extended.
Vlo is the max speed at which it is safe to initially lower the landing gear.

All found in the POH or placards.

Question 29

What is Va airspeed limitation?

Answer 29

It is the max speed at which full and abrupt control movement may be applied without risking structural damage. It is also the max speed able to be used in turbulent conditions. It is listed in the POH and changes significantly with weight. It is not marked on the air speed indicator because it changes with weight.

Question 30

What are the 4 types of airspeed?

Answer 30

Indicated, calibrated, true airspeed, and groundspeed.

Question 31

What effect does altitude have on indicated airspeed? Will the performance airspeeds such as those for takeoff, landing and stall speeds change with altitude?

Answer 31

Indicated air speed remains the same regardless of changes in altitude. The indicated airspeed recommended for takeoff, landing, and stalling in a specific configuration remains the same regardless of altitude.

Question 32

What is IAS, how is it defined?

Answer 32

Indicated Air Speed (IAS): The reading you get from the airspeed indicator. It is the speed of the airplane through the air, but lacks any adjustments made for changes in air density as altitude increases. It also does not take into account the installation position and instrument errors.

Question 33

What is CAS, how is it defined?

Answer 33

Calibrated Air Speed (CAS): It is indicated air speed, but corrected for installation and instrument errors. Attempts are made to minimize errors which occur due to installation position and instrument error, but they cannot be entirely eliminated throughout the full range of operating speeds, weights, and flap settings.
To calculate CAS, read the IAS and use the chart in the POH to correct the IAS.

Question 34

What is TAS and how is it defined?

Answer 34

True Air Speed: The true airspeed of your plane through the air. It is the CAS, but with additional corrections for altitude and non standard temperature.
As altitude increases the air density decreases.
As Temperature increases, air density decreases.
For a given IAS, TAS increases with altitude.

Question 35

What is GS, how is it defined?

Answer 35

Ground Speed: Represents the actual speed of the airplane over the ground. It is the TAS, but has an additional correction for the wind. Groundspeed decreases with a headwind and increases with a tailwind.

Question 36

When flying a retractable gear plane, what are the two other types of airspeed which are not depicted on the airspeed indicator?

Answer 36

Vle = Speed not to exceed with landing gear extended. 
Vlo = Max speed at which you can raise or lower landing gear. Reference POH.

Question 37

Does the indicated airspeed at which a plane stalls in a specific configuration change with altitude?

Answer 37

No, regardless of altitude, the airspeed which will induce a stall remains the same for a given configuration.

Question 38

What does the longest pointer on the altimeter represent>?

Answer 38

The longest = hundreds of feet

Question 39

What does the middle-sized pointer on the altimeter represent?

Answer 39

The middle-sized = Thousands of feet.

Question 40

What does the smallest pointer on the altimeter represent?

Answer 40

Smallest = Tens of thousands.

Question 41

What is the altimeter adjustment setting knob indicate and what impact does adjusting it up or down have on the indicated altitude?

Answer 41

The barometric pressure can be changed about 1- ft. for each .01 in. Hg. to compensate for changed in atmospheric pressure.
Increasing the altimeter setting will cause the indicated altitude to increase, and decreasing the altimeter setting cause indicated altitude to decrease.

Question 42

What is indicated altitude?

Answer 42

Altitude as measures by your altimeter.

Question 43

What is pressure altitude?

Answer 43

If you set your altimeter to 29.92 in. Hg. (1013 Mb.) Your indicated altitude will equal pressure altitude. The vertical distance above the theoretical pressure line call the standard datum plane. The height above the standard datum plane when set to 29.92
Standard datum plane = sea level in a standard atmosphere. Pressure altitude has to do with elevation of the airport above sea level. Increasing elevation by 5,000 ft. results in a 5in. Hg. decrease in station pressure. So setting your altimeter to standard 29.92 in Denver would cause your altimeter to read 5,000 ft. above the standard datum plane.

Question 44

What is density altitude?

Answer 44

Density altitude is pressure altitude corrected for non standard temperatures. Density altitude increases as the ambient temp increases.
On a standard day density altitude is equal to pressure altitude. However, when ambient air temp is above standard, density altitude is higher than pressure altitude.
When density altitude is higher than pressure altitude aircraft performance is reduced.

Question 45

What is calibrated altitude?

Answer 45

Calibrated altitude is indicated altitude corrected for instrument standard error.

Question 46

What is true altitude?

Answer 46

It is the actual height of an object above mean sea level (MSL). On charts the height of obstacles like TV antennas are shown in true altitude.
When standard atmospheric conditions exist, the true altitude is equal to pressure altitude and indicated altitude. True altitude is equal to field elevation when the altimeter is set to the local pressure setting.

Question 47

What is absolute altitude ?

Answer 47

It is the height above ground level (AGL). The height of the aircraft above the surface over which it is flying. It changes based on the height of the airplane and the ground topography.

Question 48

What is the most common altimeter error?

Answer 48

When flying from an area of high pressure to an area of low pressure and failing to adjust the altimeter to the new pressure setting.
The altimeter will indicate an altitude that is higher than the true altitude and you will find yourself flying at a lower altitude than you intended.
The altimeter will show you that you are higher than you actually are because it runs based on atmospheric pressure which decreases with altitude. So if the atmospheric pressure gets lower just by changing location, it will display a higher reading. Leading you to think you are high, but you are actually lower than indicated.
“When flying from high to low, look out below”

Question 49

How can you compute altimeter error based on change in atmospheric pressure from one location to the next?

Answer 49

Atmospheric pressure decreases about 1 in. Hg. for every 1,000ft. increase in altitude. A 1 in. change in