Flight Instruments Flashcards
PHAK 8
Which instruments utilize pitot static sources?
- Air Speed Indicator
- Vertical Speed Indicator
- Altimeter
PHAK 8-2
Which instrument is the only instrument to utilize the pitot tube?
Air Speed Indicator (ASI)
PHAK 8-2
What instrument indications are observed when an alternate static source pressure is used?
- Altimeter indicates a slightly higher altitude than actual
- ASI indicates an airspeed greater than the actual airspeed
- VSI shows a momentary climb and then stabilizes if altitude remains constant
PHAK 8-3
If an aircraft is not equipped with an alternate static pressure source, what can the pilot do to introduce static pressure to the system?
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
How does an altimeter operate?
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
How does nonstandard pressure effect the altimeter?
- 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
How does nonstandard temperature effect the altimeter?
- 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
How is altimeter setting defined?
Station pressure reduced to sea level
PHAK 8-5
How can a pilot determine the amount of altimeter error from original setting to a new reported setting?
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
Define Indicated Altitude
read directly from the altimeter (uncorrected) when it is set to the current altimeter setting
PHAK 8-6
Define True Altitude
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
Define Pressure Altitude
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
Define Density Altitude
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
Define Absolute Altitude
The vertical distance between the aircraft and terrain, ft AGL
PHAK 8-7
What is the allowable amount of error for the altimeter before it must be recalibrated?
75 feet from surveyed field elevation
PHAK 8-7
Describe how the VSI operates
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
What types of information does the VSI indicate?
- Trend information shows an immediate indication of an increase or decrease in rate of climb or descent
- rate information show a stabilized rate of change in altitude
PHAK 8-8
Describe how the ASI operates
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
Define Indicated Airspeed
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
Define Calibrated Airspeed
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
Define True Airspeed
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
Define Groundspeed
The actual speed of the airplane over the ground. It’s TAS adjusted for wind.
PHAK 8-9
Define Vbe
Best endurance, where the helicopter can maintain altitude the longest
Define Vne
Never exceed speed, even in a dive
PHAK 8-9
Define Vnea
Never exceed speed for autorotations
Define Vneao
Never exceed speed with augmentation (SAS, SCAS or other) off
Define Vbg
Speed of best glide range, at which the helicopter can fly the maximum distance without power (autorotate)
Define Vbr
Speed of best range, at which the helicopter can fly the longest distance given an amount of fuel
Define Vc
speed of cruise, convenient overall speed for fuel efficiency, transit time, maintenance and handling qualities
Define Vg
Speed of glide, at which the helicopter has the smallest descent rate (best endurance) without power (in autorotation)
Define Vh
Speed of max continuous power (MCP), at which the helicopter will consume the max power it can sustain level flight
Define Vaft
Never exceed speed in aft flight
Define Vlat
Never exceed speed in lateral flight
Define Vtaxi
Never exceed speed in taxi operations
Define Vx
Speed at which the steepest climb angle is obtained (typically 0, giving a 90 degree vertical climb)
Define Vy
Speed at which the helicopter can climb fastest
Define Vtocs
recommended speed for takeoff and climb out
Define the difference between endurance and range
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)!
Explain the required instrument check for the ASI
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
Describe what would be observed if the pitot tube becomes blocked and the pitot drain hole and static hole remain open
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
Describe what would be observed if the pitot tube opening and drain hole become blocked simultaneously
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.
Describe what would be observed if the static system becomes blocked but the pitot tube remains clear
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.
What are the primary gyroscopic instruments?
- Turn coordinator
- heading indicator
- attitude indicator
PHAK 8-15
What are the two fundamental properties of gyroscopic instruments?
- 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
Describe the difference between a turn coordinator and a turn and slip indicator
Both of these instruments provide rate of turn information and slip/skid indications. The turn coordinator also provides banking indications and roll rate
