Standard Flight Instruments

Flight Instruments #

Static pressure system #

One of the main systems measures three things from the Static Vent:

  • Altimeter
  • Airspeed Indicator (ASI)
  • Vertical Speed Indicator (VSI)

This is sometimes prone to show false readings when the line is clogged (winter, helicopters, etc.) which causes issues on takeoff.

Altimeter #

Usage:

  • Ex. Will read “622ft” if you are at CYQG / your altimeter is set correctly.
  • Every airport will set it to MSL (mean sea level)
  • Understand that you will have to know the mean sea level altitude / elevation of the airport you are flying to.
  • Altitude is ALWAYS Above MSL. Height is AGL.

Definitions:

  • Indicated altitude: reading on altimeter when it is set to current barometric pressure
  • Pressure altitude: reading on altimeter when set to standard barometric pressure (29.992hg)
  • Density altitude: pressure altitude corrected for temperature
  • True altitude (mean sea level) MSL: exact height above mean sea level
  • Absolute altitude (above ground level) AGL: actual height above earth’s surface

General:

  • Special form of eneroid barometer (barometer without liquid) measures the pressure of the atmosphere.
  • Calibrated to +-20ft
  • Altimeters are fitted with barometric scale to account for the indicated height above sea level. The altimeter setting is given in inches of mercury which is given from towers and flight service stations
  • Very important on long cross country flight for a pilot to get up-to-date altimeter settings and reguarly reset the altimeter
  • Each .10" Hg added is approx 100ft
  • Most standard altimeters do not go higher than 31".
  • Going from HIGH to LOW pressure, your altimeter is going to read high because air is thinner.

Abnormally high pressure: If there is abnormally high pressure, you would not be able to set the setting higher than 31". So aerodomes will set the altimeter as 31.00 and you are advised to add extra caution (increase ceiling required by 100ft for each .10" over 31.00" Hg).

  • Altimeter Setting Region: When taking off or going to land, you should always set your altimeter to the one set by the aerodome.

  • If setting is not available, you can set the altimeter to read the elevation of the field above sea level.

  • An altitude which an airplane flies when using indicated height above sea level (MSL) is known as cruising altitude

  • Standard Pressure Region: Trans-oceanic and certain continental areas, altimeter settings are not available. These areas are flown at pressure altitude.

  • Radio reporting: You omit the last 2 digits when reporting your flight level. For example, you would say “Flight Level 150” (FL150) for an altitude of 15,000ft.

  • Field level pressure is the actual barometric pressure (not corrected to sea level) at any particular airport. If a pilot obtains the field level pressure by radio from an airport they are approaching and sets on their barometric scale, their altimeter will register 0 feet when they land.

  • When flying at temperatures below or near freezing, you must correct for the temperature.

  • Density altitude. Baromettric pressure and temp both affect density. It’s an important factor of takeoff performance in modern airplanes. Low density reduce thurst and aerodynamic lift.

Density Altitude = pressure altitude + [100 x (actual temp - standard temp)]

Three facts to remember:

  1. The temp of standard air is 15c at sea level
  2. Temp of standard air decreases 2c per 1,000ft of altitude
  3. For every 1c increase from standard air, there is a 100ft increase (or decrease if actual temp is less than standard air) in the pressure altitude

For example: To find the density altitude:

  • Pressure alt at airport: 2,000ft
  • Actual temp: 25c

The temp of standard air at 2,000ft should be: (15c less 2 per 1,000ft) = 11c Therefore, the density altitude is: 2,000 + [100 x (25c - 11c)] = 3,400ft

  • Another thing to note is there is altimeter mountain effect errors when flying near a mountain as the mountain ranges tend to increase speed which results in local decrease in pressure (Bernoulli’s Principle).

Air Speed Indicator (ASI) #

Definitions:

  • Indicated Airspeed (IAS): uncorrected speed read from the airspeed dial

  • Calibrated Airspeed (CAS): indicated airspeed corrected for instrument error and installation error in the pitot-static pressure system.

  • Equivalent Airspeed (EAS): calibrated airspeed corrected for compressibility factor, very significant to pilots of high speed aircraft, less so for smaller ones.

  • Red: Never Exceed Speed (Vne)

  • Yellow: “Caution speed” the lowest limit of the arc is the Maximum Structural Cruising Speed (Vno).

  • Green: Normal operating range. The lower limit of the green arc is the Power Off Stalling Speed with flaps and gear up (Vsl). The upper limis of the green arc is Vno( max cruising speed)

  • White: Speed range where fully extnded flaps may be used. Lower limit of the white arc is the Power Off Stalling Speed with flaps and gear down (Vso) the upper limit of the white arc is Maximum Flaps Extended Speed (Vfe).

General:

  • Bottom of white arch is sometimes called “dirty” stall with flaps
  • Bottom of green arc is sometimes called “clean” stall with no flaps

Errors:

  • Density Error: density of the air depends on atmospheric pressure and temp. Standard of calibrating airspeed indicators is normal sea level pressure, 29.92 inches of mercury at a temperature of 15c. A rough calculation is made by adding 2% to the indicated airspeed for every 1,000ft of pressure altitude.

For example:

  1. Indicated airspeed at 10,000ft is 130 knots
  2. Correction is 10 x 2% = 20%
  3. Therefore, 20% of 130kts = 26kts
  4. Therefore true airspeed = 130 + 26 = 156kts

Some airspeed indicators such as the one in the figure automatically incorporate that.

  • Position error: Error in the position of the angle of the pitot pressure source meeting the airflow caused by eddies.

  • Lag error: Mechanical error due to the friction fot he working parts of the instrument

  • Icing error: Ice formation of the pitot tube

  • Water error: Water in the system may cause very erratic airspeed indications. Errors may be high or low depending on whether the water is inthe dynamic or stattic pressure systems.

Vertical Speed Indicator (VSI) #

  • Shows the rate of climb in ft per minute.
  • Operates on the change in barometric pressure occurs with any change of height
  • Lag from 6 to 9 seconds before it will indicate the correct rate of climb or descent

Radar altimeter #

  • Sends signal down to earth that bounces back and gives the exact reading:w

  • Rotate the knob to select the desired decision height on the altitude scale. The lamp lights when the decision height has been reached. The flag then drops into view indicates that invalid altitude information is being displayed.

Heading indicator (HI) #

  • Must be set periodically by reference to magnetic compass
  • Provides a stable reference, but must be set

Attitude Indicator (AI) #

  • Also known as artification horizon or gyro horizon)
  • Pointer at the top indicates the degree of horizon from 0 to 90degrees right or left
  • Numbers indicate the angle of nose up and nose down

May be thought of and used in two different ways:

  • Some pilots like to consider it as a “window” through the instrument panel through fogs or clouds, the “natural” horizon
  • Fly the miniature airplane with respect to the horizon bar

Turn and Slip indicator #

  • Or turn and bank
  • Also known as the “needle and ball”
  • Indicates the amount of bank in the turn and whether there is any slipping or skidding in the turn
  • Indicates the rate of the turn, not the amount of the turn. Thus a standard rate or rate one, turn will give a rate of turn of 3degrees per second, or 360 degrees in two minutes.

Turn Co-Ordinator #

  • Same as the turn and slip indicator but instead uses a little “mini plane”.
  • Biggest advantage fo the turn co-ordinator is that it can be used to keep the wings level in straight flight if the attitude indicator has failed.

EFIS (Electronic Flight Instrument System) #

  • Replaces the “steam gauge” with an all-in-one electronic solution

Oil Pressure Gauge #

  • Should be checked immedietely after engine has been started
  • If does not register within 10 seconds, shut down engine and check
  • If starting with cold oil in the engine, it will invariably read high due to difficulty of forcing sluggish oil through small aperture. As oil warms up, regulator will improve. May require up to 15 minutes.

Oil Temperature Gauge #

  • Always remember that oil, in addition as lubrication, acts as a coolant

Tachometer #

  • Shows safe engine RPM range

Manifold Pressure Gauge #

  • Shows the pressure between the carb and the cylinders