Content:

• Pitot-Static Instruments?

• Gyroscopic Instruments

• Magnetic Compass

• Digital Flight Instruments

Effects of Atmospheric Conditions

• Air exerts 14.7 pounds per square inch at sea level

• Changes in temperature affect atmospheric pressure

• Warm air rises resulting in lower pressure?

• Cold air sinks resulting in higher pressure

• The standard atmosphere at sea level consists of:

• Barometric pressure of 29.92 inches of mercury

• Temperature of 59 degrees Fahrenheit

• Temperature and pressure normally decrease with an increase in altitude

• Standard pressure lapse rate is approximately 1 in. Hg for each 1,000 feet of altitude

• Standard temperature lapse rate is approximately 2°C for each 1,000 feet of altitude change

1. Pitot-Static Instruments?

• Used to determine an aircraft’s speed, altitude, and altitude trend

• The system generally consists of:

• Pitot Tube

• Pitot pressure (impact or ram air pressure) is supplied by the forward facing pitot port

• Higher ram air pressure means higher airspeed

• Exposed to relative wind also relates to the pitot system

• Static Port

• Static or atmospheric pressure enters the pitot-static system through a static port in an area of relatively undisturbed air

• Static air pressure is used to operate:

• Airspeed indicator

• Vertical speed indicator

• Altimeter

• The airspeed indicator is the only instrument to operate using both pitot and static pressure

i. Airspeed Indicator?

• Operates using both pitot and static pressure

• The airspeed indicator compares ram air pressure with static air pressure to determine the airspeed in knots

• V-speed:?describe the performance limits and characteristics of airplanes

• Divided into three color-coded arcs and a red line:

• White arc indicates the flap operating range:

• The upper end indicates the maximum airspeed you can fly with flaps fully extended (V_FE)

• The lower end indicates the speed the airplane stalls with the flaps fully extended (V_SO)

• Green arc indicates the normal operating range:

• The upper end indicates the maximum structural cruising speed (V_NO)

• The lower end indicates the airplane's stall speed when the airplane is at the maximum takeoff weight, the flaps are up, and, if applicable, the landing gear retracted (V_S1)

• Yellow arc indicates the caution range:

• The range of speed above normal operating range that you should enter only in smooth air and only with caution

• Red line indicates the never exceed speed:

• Never operate above this speed because structural damage to the aircraft could occur (V_NE)

• Other V-speeds:

• V_A (V_O): Design maneuvering speed (listed in the POH; might be greater when the aircraft is heavily loaded and lower when the load is light)

• V_LO: Maximum landing gear operating airspeed

• V_LE: Maximum landing gear extended airspeed

Types of Aircraft Speeds:

• Indicated airspeed (IAS): The reading on the airspeed indicator

• Does not reflect variations in air density

• Important performance airspeeds are always the same indicated airspeed, regardless of altitude

• Calibrated airspeed (CAS): Indicated airspeed corrected for installation error and instrument error

• Manufactures try to keep airspeed errors to a minimum

• Listed in the POH

• True airspeed (TAS): Actual speed through the air

• Groundspeed: Actual speed over the surface (equal to TAS in a no wind situation)

• A headwind decreases groundspeed

• A tailwind increases groundspeed

ii. Altimeter

• Measures the aircraft's altitude

• Based on mean sea level (MSL)

• Three pointers to indicate the altitude:

• The longer of the two needles on the altimeter indicates multiples of 100 feet

• The shorter of the two needles on the altimeter indicates multiples of 1,000 feet

• The pointer indicates multiples of 10,000 feet

• The altimeter setting window is sometimes referred to as the Kollsman window

• 1 inch?of change in the altimeter setting equals 1,00 feet of indicated altitude change
  

• The knob on the altimeter adjusts the setting in the Kollsman window to compensate for changes in local barometric pressure

• Altimeter settings are accurate only in the vicinity of the reporting station on which they are based

Types of Altitude:

• Indicated altitude: The altitude measured by the altimeter, and the altitude used most often during the flight

• Pressure altitude: The height above the standard datum plane (SDP), which is a theoretical level where the weight of the atmosphere is 29.92 in. Hg as measured by a barometer

• Density altitude: Pressure altitude corrected for temperature

• True altitude: The vertical distance above mean sea level (MSL)

• Absolute altitude: the actual height of the aircraft above the earth's surface, commonly referred to as height AGL

• Calibrated altitude: Indicated altitude corrected to compensate for any instrument error

Altimeter Errors:

• Failing to keep the altimeter set (most common)?

• Flying from high pressure to low pressure?

• When you fly into an area of higher pressure, the true altitude will be higher than the indicated altitude

• When you fly into an area of lower pressure, the true altitude will be lower than the indicated altitude

• "When flying from high to low, look out below"

• Not monitoring the temperature

• When atmospheric temperature is higher than standard, true altitude is higher than indicated altitude

• When atmospheric temperature is lower?than standard, true altitude is lower?than indicated altitude

• If the temperature is 10°C higher/lower than standard, the true altitude is 4% higher/lower than indicated altitude

iii. Vertical Speed Indicator (VSI):

• Measures the rate at which an aircraft gains and loses altitude

• The VSI dial is calibrated in 100-foot increments between 0 and 10, and then in increments of 500 feet

• The VIS displays two types of information:

• Trend information: Shows an immediate indication of an increase or decrease in the aircraft's rate of climb or descent

• Rate information: Shows a stablized rate of change in altitude

Blockage of the Pitot-Static System:

• Incorrect readings on the pitot-static instruments usually indicate a blockage of:

• Blocked pitot tube

• When the pitot tube slowly becomes blocked, the indicated airspeed gradually decreases

• When the blockage seals the tube completely, the airspeed srops to the lowest value on your airspeed indicator

• The blockage traps pressurized air inside the airspeed indicator, so the indicator displays the airspeed at the time of the blockage, regardless of actual airspeed

• If the pitot system becomes completely clogged and the static system remains clear, the airspeed indicator acts more like an altimeter

• Blocked static ports

• If the static system becomes blocked, but the pitot tube remains clear, the following instruments are affected:

• Airspeed Indicator: Continues to operate, but the indications are inaccurate

• When the aircraft is above the altitude where the blockage occured, the instrument indications are slower than the actual airspeed

• When the aircraft is below?the altitude where the blockage occured, the instrument indications are faster?than the actual airspeed

• Altimeter: Air pressure in the system remains unchanged and so does the indicated altitude

• VSI: Displays a continuous zero reading

• Both Blocked

• A clogged pitot tude affects the accuracy of only the airspeed indicator

• Blockage of the static system affects all three?Pitot-Static Instruments

• Turn on the pitot heat to prevent pitot tube icing?when flying in a visible moisture

2. Gyroscopic System Components

• The Most common instruments containing gyroscopes are:

• Turn coordinator

• Heading indicator

• Attitude indicator

• All mechanical gyroscopic instruments enclose a spinning gyro mounted into brackets called gimbals

• The spinning gyro:

• Senses the aircraft's movement

• Displays aircraft movement on the instrument face

• Gyroscopic operation rests on two fundamental principles:

• Rigidity in space

• Fixed position in space

• Tends to remain rigid

• REsists external forces

• Precession

• Reaction in the direction of the rotation

• Slow drifting and minor error indications

i. Turn Coordinator:

• Two components of the turn coordinator:

• Turn indicator (roll movement)

• Inclinometer (yall movement)

• Indicates:

• Rate

• Coordination

• Standard rate turn is a turn of three degrees per second; to perform a standard rate turn, align the wing of the indicator with the turn index in the direction of the turn. During a coordinated turn, the ball remains centered between the reference lines.?

• Slip: The rate of turn is too slow for the angle of bank, and the ball moves to the inside of the turn?

• Skid:?The rate of turn is too great?for the angle of bank,?and the ball moves to the outside?of the turn?

• To correct a slip or skid, center the ball by varying the angle of bank or applying rudder pressure in the direction of the deflected ball, or a combination of both actions

ii. Attitude Indicator:

• An artifical reference for pitch and roll attitude with respect to the earth's surface

• Displays the angle of bank by:

• The relationship of the airplane indicator to the deflected horizon bar

• The alignment of the pointer with the bank scale

• Displays pitch by the position of the nose with respect to the horizon bar

iii. Heading Indicator:

• Displays heading information based on a 360-degree compass; the final zero is omitted

• The primary source of heading information

• It must be set before each flight and periodically adjusted throughout the flight to align it with the magnetic compass

Flight Instrument Sources of Power:

• Gyroscopic instruments are powered by either of the following sources:

• Electrical Power

• Turn Coordinator

• Vacuum System

• Attitude Indicator

• Heading Indicator

3. Magnetic Compass

• A simple and reliable source of heading information

• Use the magnetic compass to:

• Indicate the magnetic heading of the aircraft

• Set the gyroscopic heading indicator to correct for precession

• Back up the heading indicator

• Requires no electrical or vacuum power

Variation:

• The angular difference between true north and magnetic north

• Isogonic lines: Lines on an aeronautical chart that connect points of equal magnetic variation

• Agonic line: The line that connects points where the magnetic variation is zero

• To convert a true course to magnetic course, subtract easterly variation and add westerly variation - "East is least, west is best"

Deviation:

• A compass error caused by magnetic disturbances from electrical and metal components in the aircraft

• Manufacturers can decrease deviation error by installing compensating magnets inside the compass housing

• Use the compass correction card to correct for deviation

Compass Errors:

• Freedom of movement makes the magnetic compass sensitive to in-flight turbulence

• Magnetic dip occurs while turning or changing speed, even in smooth air

• Turning

• The greater the dip, the greater the turning error

• Increases near the poles, where magnetic dip is more apparent

• No longer occurs when you fly near the equator

• In the northern hemisphere, when making a turn from a northerly heading, the compass gives an inital indication of a turn in the opposite direction. Then it begins to show the turn in the proper direction, but lags behind the actual heading

• When turning from an easterly or westerly heading to a northerly heading, no error occurs as the turn begins. However, as the hending approchaes north, the compass increasingly lags behind the aircraft's actual heading

• When making a turn from a southerly heading, the compass gives an indication of a turn in the correct direction, but leads the actual heading. Turning error disappears as the aircraft approaches an east or west heading

• Accelerating/Decelerating

• In the northern hemisphere, when your aircraft accelerates, the compass indicates a turn to the north

• In the northern hemisphere, when your aircraft decelerates, the compass indicates a turn to the south

• The compass returns to its correct indication when the acceleration/deceleration stops

• Are more pronounced as you fly east or west

• Do not occur when you fly on a north or south heading

• "ANDS: Accelerate North, Decelerate South"

• Is accurate only in straight-and-level, unaccelerated flight in smooth air

4. Introduction to Digital Displays

• Airspeed Indicator

• Altimeter

• Horizontal Situation Indicator

• Vertical Speed Indicator

• Turn Coordinator + Attitude Indicator