Flight Instruments

Question 1

Which instruments utilize pitot static sources?

Answer 1

• Air Speed Indicator
• Vertical Speed Indicator
• Altimeter

PHAK 8-2

Question 1

Which instrument is the only instrument to utilize the pitot tube?

Answer 1

Air Speed Indicator (ASI)

PHAK 8-2

Question 2

What instrument indications are observed when an alternate static source pressure is used?

Answer 2

1. Altimeter indicates a slightly higher altitude than actual
2. ASI indicates an airspeed greater than the actual airspeed
3. VSI shows a momentary climb and then stabilizes if altitude remains constant

PHAK 8-3

Question 3

If an aircraft is not equipped with an alternate static pressure source, what can the pilot do to introduce static pressure to the system?

Answer 3

break the glass face of the VSI

PHAK 8-3

We break the VSI because this is the lease important static source instrument for flight, and will likely render the instrument inop

Question 4

How does an altimeter operate?

Answer 4

A stack of sealed aneroid wafers set to an internal pressure of 29.92 “Hg are free to expand and contract with changes to static (ambient) pressure. Higher static pressure (lower altitude) squeezes the wafers and causes them to collapse. Lower static pressure (higher altitude) allows the wafers to expand. A mechanical linkage connects the wafer movement to the needles on the indicator face.

PHAK 8-3

Question 5

How does nonstandard pressure effect the altimeter?

Answer 5

• If the aircraft is flown from a high pressure area to a low pressure area, a constant altitude would be displayed but the actual height AGL would be lower than the indicated altitude. “FROM HIGH TO LOW, LOOK OUT BELOW”
• If flown from low pressure to high pressure, the true altitude of the aircraft is higher than the indicated altitude

PHAK 8-4

Question 6

How does nonstandard temperature effect the altimeter?

Answer 6

• When operating in temps that are colder than standard, the true altitude is lower than indicated. Differences due to colder temps are of primary concerns to the pilot. “FROM HOT TO COLD, LOOK OUT BELOW”

PHAK 8-4

Question 7

How is altimeter setting defined?

Answer 7

Station pressure reduced to sea level

PHAK 8-5

Question 8

How can a pilot determine the amount of altimeter error from original setting to a new reported setting?

Answer 8

Subtract the new setting from the original setting. Since 1 inch of pressure is approximately 1000 feet, multiply by 1000. Then subtract that number from the indicated altitude.

PHAK 8-6

Question 9

Define Indicated Altitude

Answer 9

read directly from the altimeter (uncorrected) when it is set to the current altimeter setting

PHAK 8-6

Question 10

Define True Altitude

Answer 10

the vertical distance of the aircraft above sea level–the actual altitude. Often expressed as ft MSL. Airport, terrain, and obstacle elevations on aeronautical chares are true altitudes

PHAK 8-6

Question 11

Define Pressure Altitude

Answer 11

the altitude indicated when the altimeter setting is adjusted to 29.92 “Hg. This is the altitude above the standard datum plane, which is a a theoretical plane where air pressure (corrected to 15 degrees C) equals 29.92 “Hg. Pressure altitude is used to compute density altitude, true altitude, true airspeed, and other performance data.

PHAK 8-7

Question 11

Define Density Altitude

Answer 11

Pressure altitude corrected for variations from standard temperature. When conditions are standard, pressure altitude and density altitude are the same. If temperature is above standard, the DA is higher than pressure altitude. If temp is below standard, the DA is lower than pressure altitude. This altitude is directly related to aircraft performance.

PHAK 8-7

Question 11

Define Absolute Altitude

Answer 11

The vertical distance between the aircraft and terrain, ft AGL

PHAK 8-7

Question 11

What is the allowable amount of error for the altimeter before it must be recalibrated?

Answer 11

75 feet from surveyed field elevation

PHAK 8-7

Question 12

Describe how the VSI operates

Answer 12

The VSI contains a diaphragm which is linked to the indicator inside an airtight case. The inside of the diaphragm is connected directly to the static link of the pitot-static system. The area outside the diaphragm is connected to the static line but through a restricted orifice (calibrated leak). Because the diaphragm receives unrestricted air and the case is restricted, changes in static pressure create a differential for a short time, indicating a climb or descent.

PHAK 8-7

Question 12

What types of information does the VSI indicate?

Answer 12

1. Trend information shows an immediate indication of an increase or decrease in rate of climb or descent
2. rate information show a stabilized rate of change in altitude

PHAK 8-8

Question 13

Describe how the ASI operates

Answer 13

The ASI contains a diaphragm which is linked to the indicating sytem. The ASI case is connected to the static system, while the pitot pressure is introduced into the diaphragm. The dynamic pressure from the pitot tube expands one side of the diaphragm as airspeed (and pressure) increases, and contracts when airspeed decreases.

PHAK 8-8

Question 14

Define Indicated Airspeed

Answer 14

The direct instrument reading obtained from the ASI, uncorrected for variations in atmospheric density, installation error, or instrument error. Used to determine aircraft performance. Takeoff, landing, and stall speeds listed in the AFM/POH are IAS and do not normally vary with altitude or temp.

PHAK 8-8

Question 15

Define Calibrated Airspeed

Answer 15

IAS corrected for installation error and instrument error. Generally greatest at low airspeeds. Refer to airspeed calibration chart to correct for possible airspeed errors.

PHAK 8-9

Question 16

Define True Airspeed

Answer 16

CAS corrected for altitude and nonstandard temp. TAS increases as altitude increases because air becomes less dense, therefore causing differential pressure to decrease between pitot and static pressures. This can be computed with a flight computer, or in a pinch, by adding 2% to CAS for each 1000’ of altitude. TAS is the speed used for flight planning and when filing a flight plan.

PHAK 8-9

Question 17

Define Groundspeed

Answer 17

The actual speed of the airplane over the ground. It’s TAS adjusted for wind.

PHAK 8-9

Question 18

Define Vbe

Answer 18

Best endurance, where the helicopter can maintain altitude the longest

Question 19

Define Vne

Answer 19

Never exceed speed, even in a dive

PHAK 8-9

Question 20

Define V*nea*

Answer 20

Never exceed speed for autorotations

Question 21

Define V*neao*

Answer 21

Never exceed speed with augmentation (SAS, SCAS or other) off

Question 22

Define V*bg*

Answer 22

Speed of best glide range, at which the helicopter can fly the maximum distance without power (autorotate)

Question 23

Define V*br*

Answer 23

Speed of best range, at which the helicopter can fly the longest distance given an amount of fuel

Question 24

Define V*c*

Answer 24

speed of cruise, convenient overall speed for fuel efficiency, transit time, maintenance and handling qualities

Question 24

Define V*g*

Answer 24

Speed of glide, at which the helicopter has the smallest descent rate (best endurance) without power (in autorotation)

Question 25

Define V*h*

Answer 25

Speed of max continuous power (MCP), at which the helicopter will consume the max power it can sustain level flight

Question 26

Define V*aft*

Answer 26

Never exceed speed in aft flight

Question 27

Define V*lat*

Answer 27

Never exceed speed in lateral flight

Question 28

Define V*taxi*

Answer 28

Never exceed speed in taxi operations

Question 29

Define V*x*

Answer 29

Speed at which the steepest climb angle is obtained (typically 0, giving a 90 degree vertical climb)

Question 30

Define V*y*

Answer 30

Speed at which the helicopter can climb fastest

Question 31

Define V*tocs*

Answer 31

recommended speed for takeoff and climb out

Question 32

Define the difference between endurance and range

Answer 32

Endurance is purely fuel-burn focused. Range takes into account speed. Eg. We have a helicopter that burns 200 pounds of fuel per hour (PPH) at 50 KIAS, and 300 PPH at 100 KIAS. Of course, the helicopter can fly for a longer time at 50 KIAS because less fuel is burned per second. However, it can fly further at 100 KIAS. The math follows. While any amount would work, let's just assume the helicopter has 300 pounds of fuel. It can fly at 50 KIAS for 300/200 or 1.5 hours, but it can only fly at 100 KIAS for 300/300 or 1.0 hours (i.e. it has better endurance at 50 KIAS). However, notice that it can only fly 50 KIAS times 1.5 hour or 75 nautical miles in the 1.5 hours at 50 KIAS, while it can fly 100 KIAS times 1 hour or 100 nautical miles at 100 KIAS (i.e. it has a better range at 100 KIAS)!

Question 33

Explain the required instrument check for the ASI

Answer 33

Prior to takeoff, ASI should read zero (unless there is a strong headwind). When beginning takeoff, ensure airspeed is increasing at an appropriate rate. | PHAK 8-10

Question 34

Describe what would be observed if the pitot tube becomes blocked and the pitot drain hole and static hole remain open

Answer 34

Ram air is no longer able to enter the system. Air already in the system vents via the drain hole, and remaining pressure drops to ambient pressure. The ASI reads 0 because it senses no difference between ram and static air pressure. | PHAK 8-10

Question 35

Describe what would be observed if the pitot tube opening and drain hole become blocked simultaneously

Answer 35

Pressure in the pitot tube would become trapped. No change would be observed on the ASI despite airspeed changes. If the static port is unblocked and the aircraft changes altitude, the ASI would indicate a change, basically behaving as an altimeter.

Question 36

Describe what would be observed if the static system becomes blocked but the pitot tube remains clear

Answer 36

**ASI** will continue to operate, but will be inaccurate. The airspeed indicates lower than actual airspeed when the aircraft is operated above the altitude at which the static ports became blocked because the trapped static pressure is higher than that of the ambient pressure at that altitude. The opposite is true when operated at a lower altitude. **Altimeter** will freeze at the altitude where the block occured. **VSI** will show a continuous zero indication.

Question 37

What are the primary gyroscopic instruments?

Answer 37

* Turn coordinator * heading indicator * attitude indicator | PHAK 8-15

Question 38

What are the two fundamental properties of gyroscopic instruments?

Answer 38

* Rigidity in Space - a gyroscope remains in a fixed position in the plane in which it is spinning * Precession - the tilting or turning of a gyro in response to a deflective force. The reaction to this force occurs 90 degrees later in the direction of rotations

Question 39

Describe the difference between a turn coordinator and a turn and slip indicator

Answer 39

Both of these instruments provide rate of turn information and slip/skid indications. The turn coordinator also provides banking indications and roll rate