Stage 3 Lesson 13: Flight Instruments

Pitot-Static Instrument

combined system that utilizes the STATIC air pressure and the DYNAMIC pressure due to the motion of the aircraft

Impact Pressure

pressure caused by motion, also known as Dynamic pressure

Static Pressure

It is the barometric pressure in the local area. Also known as ambient pressure, it is always present whether the aircraft is moving or at rest.

Altimeter

Instrument that measures the height of an aircraft above a pressure level

How does an Altimeter work?

The expansion and contraction of the wafers moves the mechanical linkage which drives the needles on the face of altimeter

Effects of Nonstandard Pressure

"Going form a high to a low, look out below"

If you fly from a high-pressure area to a low pressure water without adjusting your altimeter, your altimeter will overestimate your latitude - meaning you are lower than you think.

Effects of Nonstandard Temperature

"From hot to cold, look out below."

If the air is colder than standard, your aircraft is lower than what the altimeter shows. This is especially dangerous during approach and landing in mountainous or cold areas.

Setting the Altimeter

Most altimers are equipped with a barometric pressure setting window providing a means to adjust the altimeter

Altimeter Setting

Station pressure (the barometric pressure at the location the reading is taken) which has been corrected for the height of the station above sea level.

Indicated Altitude

the altitude read directly from the altimeter (uncorrected) after it is set to the current altimeter setting

True altitude

The vertical distance of the aircraft above sea level. (MSL)

Absolute Altitude

the vertical distance of an a rat above terrain, or ABOVE GROUND LEVEL (AGL)

Pressuder Altitude

The altitude indicated when the altimeter setting widow (barometric scale) is adjusted to 29.92 "Hg. This is the altitude above the standard datum plane.

Density Altitude

Pressure altitude corrected for temperature (where your plane feels like it is flying at)

Vertical Speed Indicator (VSI)

Indicates whether the aircraft is climbing, descending, or in level flight. Operates solely from the static pressure. Uses a calibrated leak to measure the vertical climb.

Airspeed Indicator (ASI)

• Measures the difference between impact (ram) air pressure from the pitot tube and ambient pressure from the static port. The result pressure is called dynamic pressure and corresponds to airspeed.

• dynamic pressure (airspeed) = Impact pressure - static pressure

Indicated Airspeed (IAS)

Airspeed read directly from the airspeed indicator, uncorrected for variations

Calibrated Airspeed (CAS)

IAS corrected for instrument and position errors.

True Airspeed (TAS)

CAS Corrected for Altitude and nonstandard temperature.

Groundspeed (GS)

the actual speed of the airplane over the ground. It is TAS adjusted for wind. Decreases with a headwind and increases with a tailwind.

Pitot tube blockage

The only instrument affected is the airspeed indicator.

■ Ram air inlet clogged and drain hole open? Airspeed drops to zero.

■ Both air inlet and drain hole are clogged? The airspeed indicator will act as an altimeter, and will no longer be reliable.

■ When suspecting a pitot blockage, consider the use of pitot heat to melt ice that may have formed in or on the pitot tube.

Air Data Computer (ADC)

An aircraft computer that receives and processes pitot pressure, static pressure, and temperature to calculate very precise altitude, indicated airspeed, true airspeed, and air temperature.

Most common Gyroscopic Instruments

Turn coordinator, heading indicator, and the attitude indicator.

Gyroscopic Principles

Rigidity in space and precession

Rigidity in Space

a spinning gyroscope (like a bicycle wheel) maintains it orientation in the plane it was spinning, resisting external movement.

Heading indicator stabilizes along the Y axis

Attitude indicator stabilizes along the X axis

Precession

the titling or turning of a gyroscope in response to an applied force, with the reaction occurring 90° later in the direction of rotation.

Turn coordinated uses this type of Gyroscopic principle

Sources of Power

Vacuum/pressure systems spin the gyro using airflow, similar to how a water wheel works; normal suction is usually 4.5-5.5 inches of mercury (Hg)

Redundant power sources ensure at least one instant proves reliable bank infonaut if another fails.

Turn Indicators

Operates on the principle of precession.

▷ Turn coordinators show rate-of-turn and rate of roll.

Turn and Slip Indicator

Gyro spins in the vertical plane along the aircraft's longitudinal axis, with a single gimbal and spring keeping it centered. Precession causes the gyro to tilt left or right in response to yaw, moving a turn needle to indicate direction and rate of turn.

Turn Coordinator

Uses a canted gyro to sense both roll and turn rate; the miniature airplane banks in the direction of roll, and the instrument shows rate and direction of turn, not angle of bank. Standard-rate turns (3°/sec) are indicated by aligning the miniature wings with the marked index.

Inclinometer

An instrument consisting of a curved glass tube, housing a glass ball, and damped with a fluid similar to kerosene. It may be used to indicate inclination, as a level, or, as used in the turn indicators, to show the relationship between gravity and centrifugal force in a turn.

Attitude Indicator

Miniture airplane and horizon bar. Indicates attitude of airplane relative to the true horizon.

Heading Indicator

mechanical instrument that provides stable heading information, unlike the magnetic compass, which is prone to errors—especially in turbulence.

AHRS (Attitude and heading reference system.)

Old School computer to figure out attitude and heading.

Uses gyroscopic system with magnets to tell you the change in attitude and heading.

Magnetic Compass

Half a ball that floats, plane turns around the compass as it stays pointed towards north and south

Lubber line- where you are at on the compass

Northerly Turning Error:

Compass leads the turn when turning north

Rule: Stop turn 15° + ½ latitude before desired heading.

Southerly Turning Error:

Compass lags the turn when turning south.

Rule: Stop turn 15° + ½ latitude after passing the desired heading.

Deviation

Caused by magnetic interference inside the aircraft. Depends on aircraft heading not location.

Compass Errors

Magnetic Deviation and Variation

UNOS

Under-read when turning North

Over-read when turning South

ANDS

Accelerate North Decelerate South

Magnetic Dip Error

A vertical attraction between a compass needle and the magnetic poles. The closer the aircraft is to a pole, the more severe the effect. Leads to turning errors.

Wants to find the pole closer to it. gets faster as you get closer

Instrument check: Altimeter

Checked every 24 calendar months

If air is outside more than 75 ft needs to be recalibrated and or fixed

Instrument check: Attitude indicator

Wait at least 5 minutes

Wait till run up area, after rmp mag check and everything

No more than 5 degree turns while taxing

Instrument check: Heading Indicator

Compare to compass, within 10-15 degrees

Instrument check: Turn Slip Coordinates

Ball is moving while your taxi, and wings are dipping as you turn

Instrument check: Magnetic Compass

Moving freely, doing known heading (runway; taxiways along runway)

Instrument check: Vertical Speed Indicator

24 calendar months

Instrument check: Airspeed Indicator

24 months 91.41

Check pitot heat

"Temps and pressures are good, airspeed is coming alive"

Instrument check: Pitot Heat

Turn on and Touch it

Variation

Difference between true north and magnetic north

Outside Air Temperatures (OAT) Gauge

Helps to figure out air density, for takeoff, ground roll, and climb rate