Flight Instruments Flashcards
Pitot Static System has 3 instruments =
1) Airspeed indicator
2) Altimeter
3) Vertical Speed indicator
What does the pitot tube measure?
Dynamic Pressure (the speed that air enters the tube)
*ONLY talks to the airspeed indicator
Static Port in the pitot static system does what?
allows pressure in the pitot static system to equalize with outside atmosphere.
–Measures static outside air
Airspeed Indicator
uses both pitot & static sources.
–determines pressure outside and then takes speed at which it is moving through the pitot to determine airspeeding
IAS =
Indicated Airspeed
–uncorrected airspeed read from the indicator.
–This is what we actually reference when we fly.
CAS =
Calibrated Airspeed
–IAS when corrected for instrument & install error in pitot static pressure system
TAS =
True Airspeed
–Calibrated airspeed then corrected with density & temperature.
EAS
Equivalent Airspeed
–Calibrated airspeed corrected for compressibility factor 250knots & above
Pitot blockage =
ASI will “act like altimeter”
increase in a climb & decrease in a descent.
–will not affect vertical airspeed or altimeter
Static blockage =
ASI will “act opposite of altimeter”
decrease in a climb & increase in a descent.
*Altimeter will freeze & airspeed will read zero.
Fixing a blockage
1) focus on flying
2) determine cause
a) pitot blocked = try the pitot heat
OR switch to alternate pitot
b) static blockage = switch altnerate static source.
Emergency –> can break face ops VSI which will allow to read the static pressure in the plane.
Airspeed indicator errors
1) Position errors
Higher angles of attack = relative air is not head on = seems slower than it is.
Use airspeed correction chart in POH to compensate.
Airspeed indicator errors
2) Density error
ASI is calibrated to standard atmospheric conditions @ sea level.
To correct = add 2% of your airspeed / 1,000ft altitude.
Vertical speed indicator
measures rate of climb/descend.
100s ft/min
Altimeter errors
–blocks of pitot tube
–changes in temp
–changes in pressure
1) If static port were partially blocked = under read.
2) Statis port completely blocked = freeze.
3) Flying from warm to cold = being bold (it will over-read)
4) High pressure to relatively low pressure = over-read
high to low –> look out below!
Altimeter errors
–Mechanical
–Hysterisis
–Reversal
–Mountain Effect
1) Mechanical - misalignment or slip in gears/links
2) Hysterisis = Lag in instruments due to elastic properties of materials used in aneroids
3) Reversal = during abrupt or rapid attitude changes.
4) Mountain effect = decrease pressure due to air flowing through mountains. Due to downdrafts.
Altimeter encoding
relays altitude info to the transponder through altitude encoder. = ATC can see your position and altitude via the transponder.
Only works when switched to ALT - done prior to take off on every flight.
Indicated Altitude
The altitude read off of the altimeter
Pressure Altitude
altitude displayed on the altimeter when subscale is set to standard atmospheric conditions (29.92”hg)
Density Altitude
Pressure altitude corrected for temperature “the altitude the plane thinks it is”
True Altitude
Exact height above mean sea level (MSL)
Absolute Altitude
Exact height over the surface of the earth
Magnetic Variation
Angle between the true meridian & magnetic meridian
Magnetic Dip
Tendency of the compass to align itself with the earth magnetic lines
Magnetic compass error with turning (north & south)
Turn North = Lags.
–turns in the opposite direction
Turn South = Leads.
–turns extra
**North lags & South leads
ONLY trust magnetic compass in straight & level, unaccelerated flight
Magnetic compass error with acceleration/deceleration
When heading East/West
-Accelerating = compass reads more north.
-Deceleration = compass reads more south.
**ANDS = acceleration north, deceleration south
ONLY trust magnetic compass in straight & level, unaccelerated flight
What instruments use Gyroscopes
Attitude indicator
Heading indicator
Turn coordinator
which Gyroscopes are powered by an aircraft vacuum system verse electronically?
Airplanes vacuum system =
Attitude & heading indicators
Electronically = Turn coordinator
Heading Indicator
must be re-adjusted every 15mins.
unusual attitude may result in the gyro tumbling = erratic indications - just wait for it to settle.
Attitude indicator
artificial horizon
provides indication of pitch & bank.
Attitude indicator ERRORS
1) Acceleration = can falsely indicate nose up
2) Deceleration = falsely indicate nose down
Turn Coordinator
electrically powered gyro.
info on roll, yaw & rate of turn
–rate of turn NOT amount of bank
Ball = if turn is coordinated or not.
Skid =
Too much rudder or not enough aileron.
No practical value & can lead to spins.
Slip =
Not enough rudder or too much aileron.
Slips are performed for crosswind landing & to shed excess altitude without gaining airspeed.
Turn bank indicator
also electronically powered
–gives turn & yaw info - where as the turn coordinator also detects roll.
Flight instruments
1) Control
2) Performance
Control =
Attitude Indicator
Tachometer/Manifold Pressure
Performance =
ASI
VSI
Altimeter
Heading indicator
Turn coordinator
Selective Radial Scan
The attitude indicator is always the center of your scan.
from there radiate to other instruments depending on the task.
Scanning - what 3 questions should you always ask yourself?
1) What info do I need?
2) Which instruments give me that info?
3) Is the info reliable?
