PT1 CHP4 Aircraft Instruments Flashcards
What is the weight of pressure a column of air 1 sq. in. by 1 sq. in. at sea level?
14.7 PSI
What is the pressure of a column of air 1 sq. in. by 1 sq. in. at 18,000 feet?
7.4 PSI
What is the concept to remember that relates to a column of air 1 sq. in. by 1 sq. in. at sea level versus at 18,000 feet?
At sea level, the column of air will have a weight of 14.7 PSI and 7.4 PSI (half) at 18,000 feet. As altitude increases (the aircraft climbs), pressure decreases
What is the temperature, pressure and altitude on a standard day?
Temperature: 15°C (59°F)
Pressure: 29.92” Hg
Altitude: sea level
29.92 is referred to as the Standard Datum Plane
Standard atmosphere pressure at sea level is know as what?
1 atmosphere (atm)
What is the equivalent of atm/psi/in Hg when not flying in the US?
hPa (hectoPascals)
mb (millibars)
mm Hg (millimeters of mercury)
What is the rate that pressure decreases?
1” Hg for per 1,000 feet (28.86” Hg at 1,000 feet)
Which flight instruments are Pitot-Static?
ASI (airspeed indicator)
Altimeter
VSI (vertical speed indicator)
What is the Pitot-Static System?
- Provides RAM air that enters the pitot tube from an opening at the front
- Pressure accumulates in the pressure chamber provided from the RAM air (faster the speed, the faster the pressure)
- The static port/hole will measure the outside pressure surrounded by the aircraft
- The drain hole will drain anything unnecessary (rain/condensation)
- The heater will melt any ice accumulation (turned by the heather switch)
Which flight instrument is the only instrument that solely relies on the pitot tube?
ASI (airspeed indicator)
Are the VSI (vertical speed indicator and altimeter connected to the pitot tube?
No
What does the static port measure?
The pressure from the outside and indicates that decrease/increase in pressure
Which instruments is the static port connected to?
- ASI (airspeed indicator)
- VSI (vertical speed indicator)
- Altimeter
If the static port becomes clogged, what can be used?
Alternate static port
If the static port becomes clogged and you use the alternate static port, what pressure does the static port use/measure?
The pressure inside the cabin
What does the altimeter measure?
Indicates height of the aircraft above a reference point (usually sea level)
What does each needle on the altimeter indicate?
- 100s (long, thick)
- 1,000s (short, thick)
- 10,000s (short, thin)
What does the long, thick needle on the altimeter measure?
100s of feet
What does the short, thick needle on the altimeter measure?
1,000s of feet
What does the short, thin needle on the altimeter measure?
10,000s of feet
What is the principle of operation of the altimeter?
- Inside, there is an aneroid wafer that is contains a specific pressure (29.92)
- The static port sends pressure to the aneroid wafer that causes it to expand or contract
- As altitude increases/decreases, the outside pressure decreases/increases, which the static port sends lower/higher pressure inside the altimeter
- The pressure inside the wafer remains the same (29.92)
- The wafer will expand/contracts as the outside pressure is lower (less)/ higher (more)
Describe what happens inside the altimeter as altitude increases.
- The outside pressure decreases
- The static port sends lower (less) pressure inside the altimeter
- The pressure inside the wafer remains the same (29.92)
- The wafer will expand as the outside pressure is lower (less)
- The instrument needles will indicate an increase in altitude
Describe what happens inside the altimeter as altitude decreases.
- The outside pressure increases
- The static port sends higher (more) pressure inside the altimeter
- The pressure inside the wafer remains the same (29.92)
- The wafer will contract as the outside pressure is higher (more)
- The instrument needles will indicate an decrease in altitude
In order for the altimeter to properly measure outside air pressure, what adjustment to the instrument must be made?
Turn the knob on the altimeter so the Kollsman window will indicate the correct outside pressure
Does the Kollsman window need to be updated through the flight? Why?
Yes, as pressure changes at different altitudes
How do you find the outside pressure?
METAR, ATIS, or ask ATC
On a low-pressure day, how is the standard datum plane affected?
It is lowered
Ex. outside pressure on a low-pressure day is 29.72, since the pressure is .2” Hg lower than normal, the aircraft will read at 200ft without any adjustment
On a high-pressure day, how is the standard datum plane affected?
It is raised
Ex. outside pressure on a high-pressure day is 30.12” Hg, since the pressure is .2” Hg higher than normal, the aircraft will read at 0 feet without any adjustment (really -200ft but the altimeter doesn’t read negative below 0)
What is the rule of thumb when travelling from an area of high pressure to low pressure?
High (pressure) to Low (pressure) look out below
When flying high pressure to low pressure without adjusting the Kollsman window, how will that affect the indicated altitude?
The actual altitude will be lower than indicated altitude
What is the rule of thumb when travelling from an area of high temperature to low temperature?
High (temperature) to Low (temperature) look out below
When from flying warm air to low air without adjusting the Kollsman window, how will that affect the indicated altitude?
The actual altitude will be lower than indicated altitude
What is the margin the altimeter should be within when set to the correct altimeter setting?
±75 feet of airport elevation
What are the types of altitude?
Indicated, True (MSL), Absolute (AGL), Pressure, Density
What is indicated altitude?
read directly from the altimeter
What is true altitude?
vertical distance of the aircraft above sea level (MSL)
What is absolute altitude?
vertical distance of the aircraft above the ground/obstacle (AGL)
What is pressure altitude?
altitude indicated on the altimeter when set to 29.92 pressure setting, corrected for non-standard pressure
What is density altitude?
pressure altitude corrected for non-standard temperature (how the airplane feels it’s flying at)
Describe what the Vertical Airspeed (VSI) is.
- Indicates whether the aircraft is climbing or descending
- Rate of climb/descent is indicated in feet per minute (fpm)
- Should indicate zero (or close) when on the ground
What is the principle of operation of the altimeter?
- Static port is connected to two tubes, one directs pressure into the aneroid wafer, the other (calibrated leak) directs the pressure into the empty space inside the instrument
- The static port sends pressure to the aneroid wafer that causes it to expand or contract
- As altitude increases (climb) or decreases (descend), the pressure outside the aircraft decreases/increases, which the static port sends lower/higher pressure inside the VSI t
- The static port also sends pressure through a tiny pinhole called the calibrated leak, which slowly releases static pressure inside the instrument around the wafer and slowly decreases pressure around the wafer
- this results in a high pressure outside the wafer and a lower pressure inside the wafer
- as the wafer contracts, this will indicate a positive vertical speed
- as wing level, the calibrated leak will equalize the pressure around the wafer to be equal inside the wafer, the needle will then go back down to zero (will lag)
What does the airspeed indicator measure and indicate?
The difference between pitot and static pressures
- As the aircraft moves through the air, the pitot pressure is more than the static pressure
What unit or metric is speed expressed?
Knots (most common) or MPH
What are the types of airspeed?
Indicated, Calibrated (CAS), True, Grounspeed
What is indicated airspeed?
Read directly on the instrument
What is calibrated airspeed?
Indicated airspeed (IAS) corrected for installation error
What is installation error?
Due to the distance between the pitot tube and static port, there will be a minor loss in pressure and a minor loss of indicated airspeed
How do you find the calibrated airspeed (CAS) for the aircraft?
Use the calibration chart in the aircraft manual
What is true airspeed?
calibrated airspeed corrected for altitude and non-standard temperatures
- because air density decreases as altitude increases, the difference between pitot and static also decreases
What is groundspeed?
The actual speed of aircraft over the ground
- without wind, GS = TAS
- decreases with a headwind (move slower)
- increases with a tailwind (move faster)
On the ASI, what does the white arc signify?
flap operating range (flaps extended or retracted)
Which arc represents the flap operating range?
white arc
What is Vso?
- Bottom of the white arc
- Stall speed in the landing configuration (gear down, flaps extended at a certain angle)
The bottom of the white arc, the stall speed in the landing gear configuration is which Vspeed?
Vso
What is Vfe?
- Top of the white arc
- Maximum flap extended speed
The top of the white arc, maximum flap extended speed is which Vspeed?
Vfe
On the ASI, what does the green arc signify?
Normal operating range
Which arc represents the normal operating range?
green arc
What is Vs1?
- Bottom of the green arc
- stall speed in specified configuration
The bottom of the green arc, stall speed in specified configuration is which Vspeed?
Vs1
What is Vno
- Top of the green arc
- Maximum structural cruising speed
The top of the green arc, maximum structural cruising speed is which Vspeed?
Vno
On the ASI, what does the yellow arc signify?
caution range
Which arc is the caution range?
yellow
On the ASI, what does the red arc signify?
Never exceed speed Vne
What is the never exceed Vspeed?
Vne
What is Va?
Maneuvering speed, the range that depends on aircraft weight
Maneuvering speed, the range that depends on aircraft weight is which Vspeed?
Va
What is Vlo?
- Landing gear operating speed
- Maximum speed for extending or retracting the landing gear
Landing gear operating speed, maximum speed for extending or retracting the landing gear is which Vspeed?
Vlo
What is Vle?
- Landing gear extended
- Maximum speed with gear extended
Landing gear extended, maximum speed with gear extended is which Vspeed?
Vle
What is Vmc?
- Minimum controllable speed in a twin-engine aircraft with on inoperative engine
Minimum controllable speed in a twin-engine aircraft with on inoperative engine is which Vspeed?
Vmc
What is Vx?
Best angle-of-climb airspeed (Vx) gives the greatest altitude gain in the shortest horizontal distance
The best angle-of-climb airspeed that gives the greatest altitude gain in the shortest horizontal distance is which Vspeed?
Vx
What is Vy?
Best rate-of-climb airspeed (Vy) gives the greatest altitude gain in the shortest time
The best rate-of-climb airspeed that gives the greatest altitude gain in the shortest time is which Vspeed?
Vy
What types of pitot-static system blockage scenarios are possible?
- Blocked pitot + open drain hole
- Blocked pitot + blocked drain hole (level flight)
- Blocked pitot + blocked drain hole (climb/descent)
What types of static system blockage scenarios are possible?
- Blocked static + open pitot
- Blocked static (altimeter + VSI)
What will be indicated on the ASI when the pitot tube is blocked but the drain hole is open?
- Pressure/RAM air will never enter
- Only will get static pressure
- the ASI will show zero (0)
- no differential pressure between RAM air and static pressure
What will be indicated on the ASI when the pitot tube is blocked but the drain hole is closed during level flight?
- The pressure inside will remain inside, will not change (increase or decrease)
- The ASI will show the same
- If the speed is 120 knots, it will remain 120 knots regardless if the airspeed increases or decreases
What will be indicated on the ASI when the pitot tube is blocked but the drain hole is closed during if the aircraft accelerates or decelerates?
- The pressure inside will remain inside, will not change (increase or decrease)
- The ASI will show the same
- If the speed is 120 knots, it will remain 120 knots regardless if the airspeed increases or decreases
What will be indicated on the ASI when the pitot tube and drain hole are open and static port is unclogged, but there is a blockage between the tube from the pitot to the ASI when climbing?
- The pressure from the pitot tube remains the same due to the blockage
- The pressure from the static port will decrease
- Will show an increase in airspeed
- Works as a reserve altimeter
What will be indicated on the ASI when the pitot tube and drain hole are open and static port is unclogged, but there is a blockage between the tube from the pitot to the ASI when descending?
- The pressure from the pitot tube remains the same due to the blockage
- The pressure from the static port will increase
- Will show a decrease in airspeed
- Works as a reserve altimeter
What will be indicated on the ASI when the pitot tube is open but the static port is clogged?
- The ASI will indicate an airspeed, but it will be inaccurate
- There is no proper reference from the static port
What will be indicated on the ASI when the pitot tube is open but the static port is clogged if the aircraft climbs?
- Indicated airspeed will decrease
- Pitot pressure will decrease but not the static pressure
What will be indicated on the VSI and altimeter when the pitot tube is open but the static port is clogged if the aircraft climbs?
- The altimeter will freeze at whatever altitude was indicate before the blockage because the pressure around the wafer will remain the same
- The VSI will indicate zero (0) because there is no differential pressure
Which flight instruments are Gyroscopic?
Turn Coordinator, Heading Indicator, Attitude Indicator
What types of systems power gyroscopic instruments?
Vacuum (air) system or Electrical system
What are the principles of gyroscopes?
- Any spinning object exhibits gyroscopic properties
- Two fundamental properties of gyroscopic action are: rigidity in space and precession
What is rigidity in space?
- As the wheel increases speed, it becomes more stable
- The gimbal remains in place while the airplane rotates around it
What is precession?
- The tilting or turning of a gyro in response to a deflective force
- A small force is applied whenever the aircraft changes direction
- Instead of gyro responding at the source of the force, the result will instead occur 90° ahead of that point in direction of rotation
- Sometimes the instruments may have some unwanted errors such as slow drifting and minor erroneous indications in the insrutments
Which instruments are powered by the vacuum system?
Heading indicator and attitude indicator
The heading and attitude indicators are powered by which system?
vacuum system
Which instrument is powered by the electrical system?
Turn coordinator
The turn coordinator is powered by which system?
Electrical system
Describe the vacuum system?
It sucks air via a vacuum pump to make the gyro spin
What is a typical vacuum system consisted of?
- Vacuum air filter
- Directly to the Heading indicator and suction gauge (indicates how much suction) then to the Attitude indicator
- Vacuum relief valve
- Engine-driven vacuum pump (sucks air in)
- Overboard vent line
What does the attitude indicator do?
indicates the aircraft attitude (climbing or turning)
- primary instrument for instant information
What principle does the attitude indicator use?
rigidity in space
How many degrees do each tick mark on the top of the attitude indicate?
1st tick: 10°
2nd tick: 20°
3rd tick: 30°
4th tick: 60°
5th tick/horizon: 90°
How many degrees do each vertical tick mark in the center of the attitude indicate?
Positive 2nd bar: +10°
Positive 1st bar +5°
Horizon: level
Negative 1st bar: -5°
Negative 2nd bar: -10°
What is the heading indicator?
A mechanical device designed to facilitate the use of the magnetic compass
- the compass has numerous errors that make it difficult to use in all phases of flight
What principle does the heading indicator use?
rigidity in space
What is the turn indicator?
- indicates a rate of turn (yaw) and rate of role
- contains an inclinometer (the ball)
- indicates standard-rate turn of 3° per second
What principle does the turn coordinator use?
precession
When the ball is centered on the inclinometer, what type of turn is this?
A coordinated turn
What is used to ensure a turn is coordinated?
use the rudder pedal to “kick the ball” and remain coordinated
When the ball is to the right on the inclinometer, what type of turn is this?
a slipping turn (slip in)
When the ball is to the left on the inclinometer, what type of turn is this?
a skidding turn (skid out)
What is the magnetic compass?
a magnet in a kerosene-type liquid that aligns with the Earth’s magnetic field
What flight conditions is the magnetic compass accurate?
straight and level, unaccelerated flight
What errors is the magnetic compass subject to?
- Variation
- Deviation
- Dip errors
- Turning errors
- Acceleration error
What is variation?
The difference between the true and magnetic north, measured in degrees
- the closer North, the less variation
- varies depending on your location on Earth and is identified as East or West
- East is least (subtract), west is best (add)
What is Deviation?
- magnets align with any magnetic fields, including the ones generated by the aircraft itself
What what the turning errors for the magnetic compass?
- a tendency that lags or leads when turning to northerly or southerly headings
- lag (slow) turning toward northerly headings
- lead (fast) turning toward southerly headings
- Remember UNOS*
What does UNOS mean?
U-undershoot
N-north
O-overshoot
S-south
What are the acceleration errors for the magnetic compass?
The compass is also affected when accelerating or decelerating while on easterly and westerly headings
* Remember ANDS*
What does ANDS mean?
Accelerate
North
Decelerate
South
What are the two main references to orientate ourselves?
True North and Magnetic North
What is True North?
the physical Earth’s North Pole, most maps are oriented in relation to the True North
What is Magnetic North?
the location of the Earth’s magnetic field’s northern position
What does the outside air temperature gauge measure?
Acts as a thermometer that measures the outside temperature
How can the outside air temperature gauge be helpful?
helpful to determine icing conditions or performance calculations
