Flight Instruments Flashcards
Explain the different in pressure between static air and air in motion
Air in motion exerts dynamic pressure. Static air exerts static pressure all around
What is the purpose of the pitot tube?
To measure ram air pressure (dynamic pressure due to forward motion)
What is the purpose of the static port?
To measure static or ambient air pressure through ports placed parallel to the relative airflow
How does the static port affect air pressure?
It allows air pressure inside the instruments to become equal with the air pressure outside the cases
What should be done in an emergency for an aircraft not equipped with an alternate static source?
Break the face glass of the VSI to provide static pressure from the cabin
Describe the set up of the pilot static system
Describe the VSI, ASI, and ALT readings when a pitot or static blockage occurs
When is pitot heat used?
Anytime ice is suspected in the pitot tube. The ice could create erroneous or no readings on the ASI
An aircraft is not in motion. What is the ASI reading?
0
In what unit does the ASI display airspeed?
knots or miles per hour
How does the ASI measure airspeed?
By measuring the difference between dynamic and static pressure. The larger the difference, the higher the reading
Describe the different ASI markings
Red line: VNE (never exceed)
Yellow arc: VNO - VNE (caution range)
Green arc: VS1 - VNO (normal operating range)
White arc: VSO - VFE (flap operating range)
List the causes of ASI errors
Position error (angle of attack)
Compressibility error (250kts+)
Density error (temperature, pressure)
What kind of instrument is the VSI? What does it display?
A trend instrument that displays the rate of climb or descent
Describe the set up of an aneroid barometer
List three things to do doing a VSI serviceability check
Check if VSI reads 0 on the ground
Check static port clean
Check alternate static source (VSI should jump)
What is the standard international atmosphere?
- Perfectly dry gas
- 15°C
- Surface pressure of 29.92” Hg
- Lapse rate of 2°C/1000’ within troposphere
- Weight of column of air is 14.7lbs
Describe the purpose of the altimeter. When does it work properly?
Indicates correct altitude above sea level when conditions of temperature and pressure are those of the ISA
Describe what happens to the altimeter readins when pressure varies along the route
What happens to the altimeter reading if temperature is standard? Why is this dangerous?
Error in reading. This is dangerous because extreme variations in temperature may cause a 2500’ difference in indicated altitude
Describe the affect of nonstandard temperature and pressure on actual and indicated altitude
Where does a mountain wave form?
Where wind faster than 50 knots blows within 30 degrees of the perpendicular to the main axis of the mountain range
How far can the effect of a mountain wave extend?
As far as 100 miles downward of the moutains to altitudes many times higher than the mountain elevation
Describe the pre flight altimeter serviceability check
Must read within +/- 50’ of the field elevation
Static source checked clean and clear
Alternative static source checked (ALT should jump)
How often should the pilot static system and altimeter be calibrated for IFR flight?
Every 24 months
What should you do if you have no altimeter setting available at the aerodrome?
Adjust the altimeter setting knob to the known field elevation until the altimeter indicates that same elevation
What is an advantage of the encoding altimeter?
Aircraft can be 3D identified by ATC
Define the magnetic meridian and magnetic variation
Magnetic meridian - magnetic line in which in the compass needle lies in
Magnetic variation - angle between the true meridian and magnetic meridian
List sources of compass error
Magnetic dip, deviation, turning error, acceleration error
What is a cause of compass deviation? How can deviation from the magnetic meridian be determined?
The compass can be influenced by the aircraft’s metal frame, the engine, or electrical devices. Deviation can be determined by swinging the compass
Describe what a compass correction card looks like
Describe when an acceleration error occurs. What happens to the compass readings?
Describe what happens during turning errors
On turns from north, northerly turning error causes the compass to lag
On turns from south, northerly turning error causes compass to lead
Describe how a gyroscope is powered using the vacuum system
What speed do gyros spin at?
12-20 thousand RPM
Describe the principle of operation of the Heading Indicator
Gyro is gimbaled with one degree of freedom (yaw)
The spin axis is horizontal
The plane of rotation is vertical
Gyro remain fixed in space while the a/c rotates around it
A compass card is fixed to the gyro
List some limits of the heading indicator
55 degrees pitch and bank in older types
85 degrees pitch and bank in newer types
If limits are exceeded, gyro may topple (spins, spirals, unusual attitudes)
List some errors of the heading indicator
Precession due to friction
Apparent drift due to the earth’s rotation.
How can you fix apparent drift due to earth’s rotation on the HI?
set the HI to the magnetic compass every 10-15 minutes
List the serviceability checks for the HI
Check the HI indicates properly doing left and right turns while taxiing
Allow the gyro to reach normal operating speed ( 5 minutes for vacuum, and 3 min for electric)
Check suction during the run-up
Set the HI prior to taxi and take-off.
What is the purpose of the attitude indication?
Provides pilot with articial horizon as means of reference when natural horizon cannot be seen
Describe the principle of operation of the AI
Works on principle of rigidity in space
Aircraft moves about the fixed gyro
Horizon bar is connected to the gyro
Miniature aircraft is connected to the instrument case, which is attached to the aircraft
List the limit of the AI. What happens when limits are exceeded?
Older types - 55 degrees pitch and bank
Newer types - 85 degrees pitch and bank
Aerobatic types - 360 degrees pitch and bank
If limits are exceeded, gyro may topple.
List the serviceability checks for the AI
Allow the gyro 5 minutes to spool up if vacuum, or 3 minutes if electric
Check the suction gauge within limits during run-up
What does the turn coordinator indicate?
The aircraft yaw rate (TBI) or both yaw and roll rate (TC)
What is the ball in a turn coordinator used for?
The ball shows the quality of the turn and is used for yaw control
How does the turn coordinator use the principle of gyroscopic precesion?
When the aircraft turns (yaws) precession causes the gyro to tilt slightly. The amount of needle deflection is proportional to yaw rate
What is the difference between a slip and skid?
In a slip there is not enough rate of turn for the amount of bank
In a skid, the rate of turn is too high for the amount of bank
Describe what the turn coordinator would show during a slip and skip
What is a limit of the turn coordinator?
Not accurate beyong a Rate 1 turn
Describe two errors turn coordinators are prone to. How is one of these errors fixed?
Needle oscillates from side to side in turbulent air
Fix: Average out the oscillations when interpreting the indication
Does not indicate bank attitude when the ball is not centered.
Describe the serviceability checks for turn coordinators
Check deflections in left and right turns while taxiing
Allow gyro to attain normal operating speed (3 minutes if electric)
Can calibrate in flight by comparing indication with actual rate of turn
Describe the direct and indirect information provided by different aircraft instruments
Describe the relationship between control and performance instruments
Describe the relationship between instruments during a straight and level flight
Describe the relationship between instruments during a straight climb
Describe the relationship between instruments when approaching desired altitude
Describe the relationship between instruments when level and approaching desired altitude
Describe the opposite turning illusion
Fluid in the ear slowly catches up with the rotating canal whereby the hairs stand straight up again and indicate no movement. If the rotation / turn now slows, you will register a movement in the opposite direction
Describe the coriolis illusion
Associated with a sudden tilting (forward or backwards) of the pilot’s head while the aircraft is turning. This can produce an overpowering sensation that the aircraft is rolling, pitching, and yawing all at the same time. This illusion can make the pilot quickly become disoriented and lose control of the aircraft
Describe the leans illusion
A pilot may not notice a slow turn or a bank maintained long enough. After the pilot levels the wings, there is an illusion that the plane is banking too much. Thus, the pilot leans in the direction of the original turn in an attempt to allow straight and level flight
Describe somatogravic illusions
An optical illusion that can result in spatial disorientation. A rapid acceleration during takeoff can create an illusion of being in a nose-up attitude. The disoriented pilot will push the aircraft into a nose-low, or dive, attitude. A rapid deceleration by quick reduction of the throttles can have the opposite effect, with the pilot pulling the aircraft into a nose-up, or stall, attitude
Describe how raising your during flight head can affect acceleration
