PHAK 8: Flight Instruments Flashcards
Pitot-Static System
Which three instruments rely on the pitot-static system?
Airspeed Indicator (ASI)
Altimeter
Vertical Speed Indicator (VSI)
Pitot-Static System
What does the pitot-static system measure?
Static air pressure and dynamic pressure due to aircraft motion.
Pitot-Static Flight Instruments: Pitot Tube
What does the pitot tube measure?
Total pressure (dynamic + static pressure).
Pitot-Static Flight Instruments: Pitot Tube
What should be checked before flight regarding the pitot tube?
Ensure the openings are not blocked by debris, bugs, or moisture.
Pitot-Static Flight Instruments: Pitot Tube
What happens if the pitot tube’s openings are blocked?
The ASI will not function properly, potentially leading to incorrect airspeed readings
Pitot-Static Flight Instruments: Static Pressure
Where is static pressure vented from?
Through small holes on the side(s) of the aircraft into the static chamber.
Pitot-Static Flight Instruments: Static Pressure
What instruments utilize static pressure?
- Altimeter
- VSI (and as part of the ASI for dynamic pressure calculation)
Pitot-Static Flight Instruments: Alternate Static Source
Why is an alternate static source used?
To provide static pressure if the primary static source is blocked.
Pitot-Static Flight Instruments: Alternate Static Source
Where is the alternate static source located?
Inside the flight deck.
Pitot-Static Flight Instruments: Alternate Static Source
What errors can occur when using the alternate static source?
- Altimeter: Indicates higher altitude than actual.
- ASI: Indicates higher airspeed than actual.
- VSI: Momentary climb, then stabilizes.
Pitot-Static Flight Instruments: Alternate Static Source
What action can be taken if no alternate static source is available, and the primary source is blocked?
Break the glass face of the VSI, as it is the least critical static instrument.
Pitot-Static Flight Instruments: Dynamic Pressure
How is dynamic pressure generated?
By the aircraft’s motion through the air or wind relative to the aircraft.
Pitot-Static Flight Instruments: Dynamic Pressure
What role does dynamic pressure play in the ASI?
It is the remaining pressure after static pressure is canceled out, indicating airspeed.
Pitot-Static Flight Instruments: Maintenance Tip
Why are pitot tube covers used?
To prevent bugs, debris, or moisture from entering when the aircraft is not in use.
Pitot-Static Flight Instruments: Altimeter
What does the altimeter measure?
The height of an aircraft above a given pressure level.
Pitot-Static Flight Instruments: Altimeter
Why is the altimeter considered vital?
It is the only instrument capable of indicating altitude.
Pitot-Static Flight Instruments: Altimeter
What is the primary component of the altimeter?
A stack of sealed aneroid wafers.
Pitot-Static Flight Instruments: Altimeter
What pressure are the aneroid wafers evacuated to?
29.92 “Hg
Pitot-Static Flight Instruments: Altimeter
What happens to the aneroid wafers when static pressure increases?
They compress, indicating a decrease in altitude.
Pitot-Static Flight Instruments: Altimeter
What happens to the aneroid wafers when static pressure decreases?
They expand, indicating an increase in altitude.
Pitot-Static Flight Instruments: Altimeter
How is the movement of the wafers translated into altitude readings?
A mechanical linkage connects the wafers to the needles on the altimeter face.
Pitot-Static Flight Instruments: Altimeter
Where is static pressure introduced in the altimeter?
Into the rear of the sealed altimeter case.
Pitot-Static Flight Instruments: Altimeter
What is the role of the sealed outer chamber of the altimeter?
It allows the static pressure to surround the aneroid wafers for accurate readings.
Pitot-Static Flight Instruments: Altimeter
What happens if static pressure equals the pressure inside the wafers?
The wafers remain stable, and there is no change in altitude reading.
Pitot-Static Flight Instruments: Altimeter
How does the altimeter respond to higher-than-standard atmospheric pressure?
The wafers compress, and the altimeter shows a lower altitude.
Pitot-Static Flight Instruments: Altimeter
How does the altimeter respond to lower-than-standard atmospheric pressure?
The wafers expand, and the altimeter shows a higher altitude.
Pitot-Static Flight Instruments: Altimeter
What type of device is a pressure altimeter?
An aneroid barometer.
Pitot-Static Flight Instruments: Altimeter
What does the pressure altimeter measure?
The atmospheric pressure at the level where the altimeter is located, presenting the measurement as altitude in feet.
Pitot-Static Flight Instruments: Altimeter
What is the relationship between atmospheric pressure and altitude?
Atmospheric pressure decreases as altitude increases.
Pitot-Static Flight Instruments: Altimeter
How are altitudes indicated on a multipointer altimeter?
- Tens of thousands of feet: Long, thin needle with an inverted triangle.
- Thousands of feet: Short, wide needle.
- Hundreds of feet: Long needle.
Pitot-Static Flight Instruments: Altimeter
What does the arrangement of numbers on the altimeter dial look like?
Numerals arranged clockwise from zero to nine.
Pitot-Static Flight Instruments: Altimeter
Under what conditions does the altimeter provide correct readings?
- Standard sea level barometric pressure of 29.92 inches of mercury (“Hg).
- Standard sea level free air temperature of 15°C (59°F).
- Standard pressure and temperature decrease with altitude.
Pitot-Static Flight Instruments: Altimeter
What happens when atmospheric conditions are nonstandard?
The altimeter must be adjusted using the barometric pressure setting.
Pitot-Static Flight Instruments: Altimeter
What is the barometric scale on the altimeter also called?
The Kollsman window.
Pitot-Static Flight Instruments: Altimeter
How does the barometric scale affect the altimeter reading?
Adjusting the barometric pressure setting corrects the indicated altitude to account for nonstandard pressure conditions.
Pitot-Static Flight Instruments: Altimeter
What is the “indicated altitude”?
The altitude read directly from the altimeter after the barometric pressure is set in the Kollsman window.
Altimeter, Effect of Nonstandard Pressure and Temperature
What happens to the altimeter reading when flying from high to low pressure without adjustment?
- The actual altitude is lower than the indicated altitude.
- Memory aid: “From high to low, look out below.”
Altimeter, Effect of Nonstandard Pressure and Temperature
What happens when flying from low to high pressure without adjustment?
The actual altitude is higher than the indicated altitude.
Altimeter, Effect of Nonstandard Pressure and Temperature
What is the danger of altimeters unable to set pressures above 31.00 “Hg?
The aircraft’s actual altitude is higher than the altimeter indicates.
Altimeter, Effect of Nonstandard Pressure and Temperature
What is the recommendation when barometric pressure falls below 28.00 “Hg?
Flight operations are not recommended for aircraft unable to set the actual altimeter setting.
Altimeter, Effect of Nonstandard Pressure and Temperature
How does colder-than-standard temperature affect true altitude?
True altitude is lower than the indicated altitude.
Memory aid: “From hot to cold, look out below.”
Altimeter, Effect of Nonstandard Pressure and Temperature
How does warmer-than-standard temperature affect true altitude?
True altitude is higher than the indicated altitude.
Altimeter, Effect of Nonstandard Pressure and Temperature
Why is colder-than-standard temperature a concern in mountainous terrain?
It places the aircraft lower than the altimeter indicates, increasing the risk of terrain collision.
Altimeter, Effect of Nonstandard Pressure and Temperature
What should a pilot do when flying in cold temperatures for terrain clearance?
Fly at a higher indicated altitude than usual.
Altimeter, Effect of Nonstandard Pressure and Temperature
What tool can be used to compute altitude corrections for temperature?
A navigation computer.
Altimeter, Effect of Nonstandard Pressure and Temperature
What are the memory aids for pressure and temperature effects?
- Pressure: “From high to low, look out below.”
- Temperature: “From hot to cold, look out below.”
Pitot-Static Flight Instruments: Setting the Altimeter
What is the purpose of the altimeter setting window (Kollsman window)?
It adjusts the altimeter for variations in atmospheric pressure.
Pitot-Static Flight Instruments: Setting the Altimeter
How is the altimeter setting obtained?
From ATC, AWOS/ASOS, or ATIS broadcasts.
Pitot-Static Flight Instruments: Setting the Altimeter
What is the definition of “altimeter setting”?
Station pressure reduced to sea level.
Pitot-Static Flight Instruments: Setting the Altimeter
Why must the altimeter setting be updated en route?
To account for changes in pressure and ensure accurate altitude readings.
Pitot-Static Flight Instruments: Setting the Altimeter
What happens when the actual pressure is lower than the set altimeter pressure?
The actual altitude is lower than the indicated altitude.
Pitot-Static Flight Instruments: Setting the Altimeter
What happens when the actual pressure is higher than the set altimeter pressure?
The actual altitude is higher than the indicated altitude.
Pitot-Static Flight Instruments: Setting the Altimeter
What does “GOING FROM HIGH TO LOW, LOOK OUT BELOW” mean?
Flying from a high-pressure to a low-pressure area without adjustment results in flying lower than indicated.
Pitot-Static Flight Instruments: Setting the Altimeter
What is the altimeter error when transitioning from 29.94 “Hg to 29.69 “Hg?
- 250 feet lower than indicated.
- Calculation: 29.94 − 29.69 = 0.25 × 1000 = 250
Pitot-Static Flight Instruments: Setting the Altimeter
How do you compute the corrected altitude when pressure settings change?
- Subtract the calculated difference from the indicated altitude.
- Calculation: 29.94 − 29.69 = 0.25 × 1000 = 250
- Example: 2,600 − 250 = 2,350
Pitot-Static Flight Instruments: Setting the Altimeter
What happens when transitioning from 29.94 “Hg to 30.56 “Hg?
- 620 feet higher than indicated.
- Calculation: 29.94 − 30.56 = −0.62 × 1000 = −620
- Subtraction of a negative number results in addition:
2,600 − (−620) = 3,220
Pitot-Static Flight Instruments: Setting the Altimeter
Why is maintaining the correct altimeter setting critical for safety?
Prevents altitude deviations that can lead to terrain or obstacle collisions.
Pitot-Static Flight Instruments: Setting the Altimeter
What is the relationship between 1 inch of pressure and altitude?
1 inch of pressure = approximately 1,000 feet of altitude.
Pitot-Static Flight Instruments: Setting the Altimeter
Why should pilots allow extra altitude over mountainous terrain?
To account for possible altimeter errors and downdrafts.
Pitot-Static Flight Instruments: Setting the Altimeter
What should you always do when computing altitude deviations?
Use the original setting as the top number for subtraction.
Pitot-Static Flight Instruments: Setting the Altimeter
How do you interpret a negative difference in pressure settings?
Subtracting a negative difference is equivalent to adding it to the indicated altitude.
Pitot-Static Flight Instruments: Altimeter Operation
What are the two means by which the altimeter pointers can be moved?
- A change in air pressure
- An adjustment to the barometric scale
Pitot-Static Flight Instruments: Altimeter Operation
How does the altimeter respond to a decrease in pressure?
It indicates an increase in altitude.
Pitot-Static Flight Instruments: Altimeter Operation
How does the altimeter respond to an increase in pressure?
It indicates a decrease in altitude.
Pitot-Static Flight Instruments: Altimeter Operation
Why is the altimeter important for pilots?
It ensures the aircraft is flying high enough to clear terrain and obstacles, especially in restricted visibility.
Pitot-Static Flight Instruments: Altimeter Operation
What happens if the pressure changes from 29.98 “Hg to 29.68 “Hg on the ground?
The altimeter shows an increase of 300 feet in altitude.
Pitot-Static Flight Instruments: Altimeter Operation
How can the altimeter be reset to display the correct altitude on the ground?
Adjust the barometric scale to the current pressure (e.g., 29.68 “Hg).
Pitot-Static Flight Instruments: Altimeter Operation
Why might the altimeter show a higher altitude after an overnight pressure drop?
The altimeter interprets the pressure drop as a climb.
Pitot-Static Flight Instruments: Altimeter Operation
What happens to true altitude if the altimeter setting remains constant while flying into lower pressure?
The true altitude decreases.
Pitot-Static Flight Instruments: Altimeter Operation
Why must pilots be especially vigilant about altitude in low visibility conditions?
To ensure clearance of terrain and obstacles.
Pitot-Static Flight Instruments: Altimeter Operation
How does maintaining the correct altitude reduce the risk of midair collisions?
It ensures compliance with air traffic rules and proper altitude separation.
Pitot-Static Flight Instruments: Altimeter Operation
What is the relationship between barometric pressure and altitude?
It ensures compliance with air traffic rules and proper altitude separation.
Pitot-Static Flight Instruments: Altimeter Operation
Why is it important to adjust the barometric scale regularly during flight?
To maintain accurate altitude indications relative to changing atmospheric pressure.
Pitot-Static Flight Instruments: Types of Altitude
Indicated Altitude:
Directly read from the altimeter (uncorrected) when set to the current altimeter setting.
Pitot-Static Flight Instruments: Types of Altitude
True Altitude:
- Vertical distance above mean sea level (MSL)—the actual altitude.
- Used for airport elevations, obstacles, and terrain as depicted on aeronautical charts.
Pitot-Static Flight Instruments: Types of Altitude
Absolute Altitude:
Vertical distance above ground level (AGL).
Pitot-Static Flight Instruments: Types of Altitude
Pressure Altitude:
- Altitude shown when the altimeter is set to 29.92 “Hg.
- Used for performance calculations (e.g., density altitude, true airspeed).
Pitot-Static Flight Instruments: Types of Altitude
Density Altitude:
- Pressure altitude corrected for nonstandard temperature.
- Directly affects aircraft performance:
Higher density altitude → Reduced engine and airfoil efficiency.
Lower density altitude → Improved performance.
Pitot-Static Flight Instruments: Types of Altitude
Higher Density Altitude:
- Fewer air molecules (low pressure + high temperature).
- Requires longer takeoff roll, reduced climb rate, and overall decreased performance.
Pitot-Static Flight Instruments: Types of Altitude
Lower Density Altitude:
- Denser air (low temperature).
- Shorter takeoff roll, better climb rate, and enhanced performance.
Pitot-Static Flight Instruments: Altimeter Instrument Check
What should a pilot check on the altimeter before each flight?
Proper indications by setting the barometric scale to the current altimeter setting.
Pitot-Static Flight Instruments: Altimeter Instrument Check
Where can the current altimeter setting be obtained?
From ATC, FSS, ATIS, AWOS, or ASOS.
Pitot-Static Flight Instruments: Altimeter Instrument Check
What should the altimeter indicate when set to the correct barometric pressure in a pre-flight check?
The surveyed field elevation of the airport.
Pitot-Static Flight Instruments: Altimeter Instrument Check
What is the acceptable deviation for the altimeter indication?
No more than 75 feet from the surveyed field elevation.
Pitot-Static Flight Instruments: Altimeter Instrument Check
What should be done if the altimeter deviates more than 75 feet?
Refer the instrument to a certificated repair station for recalibration.
Pitot-Static Flight Instruments: Vertical Speed Indicator (VSI)
What does the VSI indicate?
Whether the aircraft is climbing, descending, or in level flight, with the rate shown in feet per minute (fpm).
Pitot-Static Flight Instruments: Vertical Speed Indicator (VSI)
What are the two types of information displayed by the VSI?
- Trend Information: Immediate indication of an increase or decrease in climb/descent rate.
- Rate Information: Stabilized rate of altitude change in fpm.
Pitot-Static Flight Instruments: Vertical Speed Indicator (VSI)
How does the VSI operate?
It uses static pressure as a differential pressure instrument with a diaphragm connected to the static line and a case connected through a restricted orifice.
Pitot-Static Flight Instruments: Vertical Speed Indicator (VSI)
What causes the VSI needle to move?
A pressure differential between the diaphragm (immediate pressure changes) and the case (delayed pressure changes).
Pitot-Static Flight Instruments: Vertical Speed Indicator (VSI)
What is the time delay in VSI readings called?
Lag—the time it takes for the needle to stabilize and show an accurate rate of climb or descent (6–9 seconds).
Pitot-Static Flight Instruments: Vertical Speed Indicator (VSI)
What instrument reduces the lag of a typical VSI?
Instantaneous Vertical Speed Indicator (IVSI), which uses accelerometers.
Pitot-Static Flight Instruments: Vertical Speed Indicator (VSI)
What can extend the lag period in VSI readings?
Rough control inputs and turbulence.
Pitot-Static Flight Instruments: VSI Instrument Check
What should the VSI indicate during a preflight check?
It should indicate a near-zero reading.
Pitot-Static Flight Instruments: VSI Instrument Check
What should you do if the VSI shows a value other than zero before takeoff?
Treat that value as the zero mark for reference during flight.
Pitot-Static Flight Instruments: VSI Instrument Check
What should the VSI indicate immediately after takeoff?
The VSI should trend upward, showing a positive rate of climb.
Pitot-Static Flight Instruments: VSI Instrument Check
What should the VSI indicate during a stabilized climb?
A steady rate of climb appropriate to the aircraft’s performance.
Pitot-Static Flight Instruments: ASI
What does the Airspeed Indicator (ASI) measure?
The difference between pitot (dynamic) pressure and static pressure.
Pitot-Static Flight Instruments: ASI
Which two systems does the ASI utilize?
The pitot system and the static system.
Pitot-Static Flight Instruments: ASI
What is Indicated Airspeed (IAS)?
The direct reading from the ASI, uncorrected for density, installation, or instrument errors.
Pitot-Static Flight Instruments: ASI
What is Calibrated Airspeed (CAS)?
IAS corrected for installation and instrument errors.
Pitot-Static Flight Instruments: ASI
When are IAS and CAS approximately the same?
At cruising and higher airspeeds.
Pitot-Static Flight Instruments: ASI
What is True Airspeed (TAS)?
CAS corrected for altitude and nonstandard temperature.
Pitot-Static Flight Instruments: ASI
How does TAS change with altitude?
TAS increases as altitude increases for the same CAS.
Pitot-Static Flight Instruments: ASI
How can you approximate TAS using a rule of thumb?
Add 2% to CAS for every 1,000 feet of altitude.
Pitot-Static Flight Instruments: ASI
What is Groundspeed (GS)?
- TAS adjusted for wind;
- increases with a tailwind, decreases with a headwind.
Pitot-Static Flight Instruments: Airspeed Indicator Markings
What is the purpose of the color-coded markings on an ASI?
To quickly indicate airspeed limitations for safe aircraft operation.
Pitot-Static Flight Instruments: Airspeed Indicator Markings
What does the White Arc represent?
Flap operating range:
* Lower limit (VS0): Stalling speed in the landing configuration.
* Upper limit (VFE): Maximum speed with flaps extended
Pitot-Static Flight Instruments: Airspeed Indicator Markings
What does the Green Arc represent?
The normal operating range:
* Lower limit (VS1): Stalling speed in a specified configuration (e.g., gear up, flaps up).
* Upper limit (VN0): Maximum structural cruising speed (do not exceed except in smooth air).
Pitot-Static Flight Instruments: Airspeed Indicator Markings
What does the Yellow Arc represent?
Caution range—fly only in smooth air and with caution.
Pitot-Static Flight Instruments: Airspeed Indicator Markings
What does the Red Line (VNE) indicate?
Never exceed speed—operating above this speed is prohibited due to risk of structural damage or failure.
Pitot-Static Flight Instruments: ASI, Instrument Check
What should the ASI read prior to takeoff?
Zero, unless strong wind is blowing directly into the pitot tube, which may cause a slightly higher reading.
Pitot-Static Flight Instruments: ASI, Instrument Check
What should be checked on the ASI during takeoff?
Ensure the airspeed is increasing at an appropriate rate.
Pitot-Static Flight Instruments: Blockage of the Pitot-Static System
What can cause blockage in the pitot-static system?
Moisture (including ice), dirt, or insects.
Pitot-Static Flight Instruments: Blockage of the Pitot-Static System
What happens if the pitot tube is blocked but the drain hole remains open?
The ASI reading decreases to zero as the system vents to ambient pressure.
Pitot-Static Flight Instruments: Blockage of the Pitot-Static System
What occurs if both the pitot tube opening and drain hole are blocked?
The ASI freezes at the airspeed where the blockage occurred, unaffected by changes in actual airspeed.
Pitot-Static Flight Instruments: Blockage of the Pitot-Static System
How does a blocked static port affect the ASI, altimeter, and VSI?
It causes errors in all three instruments.
Pitot-Static Flight Instruments: Blockage of the Pitot-Static System
What does the ASI rely on to function?
Both dynamic pressure (from the pitot tube) and static pressure (from the static port).
Pitot-Static Flight Instruments: Blockage of the Pitot-Static System
How does the ASI behave if the static port is clear but the pitot tube is blocked?
ASI shows inaccurate changes based on altitude changes rather than airspeed.
Pitot-Static Flight Instruments: Blockage of the Pitot-Static System
What is the result of a climb with a blocked pitot tube and clear static port?
The ASI falsely indicates an increase in airspeed.
Pitot-Static Flight Instruments: Blockage of the Pitot-Static System
What is the result of a descent with a blocked pitot tube and clear static port?
The ASI falsely indicates a decrease in airspeed.
Pitot-Static Flight Instruments: Blockage of the Pitot-Static System
How can a pilot prevent pitot tube blockage due to visible moisture?
Use pitot heat as specified in the AFM/POH.
Pitot-Static Flight Instruments: Blockage of the Pitot-Static System
What happens to the ASI if the static system is blocked but the pitot tube remains clear?
The ASI continues to operate but gives inaccurate readings:
- Above the blocked altitude: Indicates lower than actual airspeed.
- Below the blocked altitude: Indicates higher than actual airspeed.