Introduction to Aircraft Instruments

This lesson will focus only on flight instruments and only "steam gauges" are covered here - "glass cockpit" gauges come later.  Navigation instruments will be covered in a separate lesson.

If you do not already have it installed you will need Adobe Reader (this may be an app within your web browswer so try that first by just clicking on the link) -  Adobe Reader  NOTE:   YOU MIGHT WANT TO UN-CHECK THE OPTIONAL OFFERS BEFORE DOWNLOADING

This publication from the FAA goes into a good bit of detail on aircraft instrument systems - Aircraft Instrument Systems - FAA   BUT - there is a lot of information in this publication and some things that will be covered in more detail in later lessons so focus only on the basic instruments - air speed indicator, altimeter, vertical speed indicator, turn coordinator and turn-and-bank indicator, artificial horizon, heading indicator ("gyro compass") and conventional magnetic compass ("whiskey compass").  You do NOT need to know all the details on how these instruments actually work, BUT - Since the basic instruments identified above (including more sophisticated instruments such as those used in large transport aircraft where flight management may be done through a computerized flight management system) rely on a pitot-static system and gyro systems for operation you should be familiar with the basics of those systems and how instruments that use these systems work (and what happens to the basic instruments' function when they fail).  A review of this is included in the Aircraft Instrument Systems - FAA materials but information specific to the pitot-static system and related instruments can be found here, courtesy of the Free Online Private Pilot Ground School - Flight Instruments   

.

You can search for websites that provide information on basic aircraft instruments but because it is never clear if providing specific sites violates copyright and other rules we will leave it to you and Google to find them on your own - and those in Canada might focus on sites in their part of the world like learntofly.ca.  But one site we will provide is:

Basic Flight Instruments - Grumman Cadet Sqdrn Civil Air Patrol  - and those interested in progressing to real-world flying or would just like to get involved in service to others consider contacting your local Civil Air Patrol squadron

Things you should know:

  • Interpretation of the information given by the airspeed indicator including what the colored arcs and lines represent

    • The green arc

    • The yellow arc

    • The red line

    • The white arc (note that some aircraft use the top of the arc as the maximum IAS for full-flaps while others use this as the maximum IAS for any degree of flap deployment so read the Operating Handbook)

 

 

 

 

 

 

 

Note that specific points on some arcs correspond to specific aircraft performance speeds known as V-speeds.  As we learned in the previous lessons aircraft performance is based on indicated airspeed so the V-speeds are fixed points on the airspeed indicator (since it gives indicated air speed).  Two different stall speeds VSO and VS1 which correspond to the stall speed with flaps and gear down ("SO" - think "stuff out") and in a clean flaps and gear up configuration ("S1" - think of the 'one' as an "I" so "stuff in").  Find the other V-speeds and their definitions - Google to the rescue!

  • Understanding how to properly set an altimeter and understand the information it provides

    • Setting the local barometric pressure using the Kollsmann window

    • How improperly set altimeters can cause errors (and potential disaster)

      • Near sea level one inch of mercury (inHg) change in barometric pressure represents about 1000 feet in altitude - so if your altimeter is incorrectly set by 1/2 inHg your actual altitude would be 500 feet different than what you think it is.  And ...

      • If your altimeter is set below the actual barometric pressure as you move to that higher pressure area your actual altitude will be higer than what the altimeter reads ("Low to high, you're up in the sky")

      • If your altimeter is set above the actual barometric pressure as you move to that lower pressure area your actual altitude will be lower than what the altimeter reads ("High  to low, look out below")

  • The attitude indicator ("gyro horizon")

    • The parts of the display and what they represent

      • The standard for the white lines at the top is that each thin - and sometimes shorter - white line represents 10 degrees of bank and the heavier white line indicates a 30 degree bank

      • The aircraft is sometimes represented by a fixed symbol that looks something like a straight pair of wings (and in some cases can be adjusted up and down) or may be represented by two thin triangle shaped "swept wings"

    • How to interpret the position of and changes of position of the display

  • The turn coordination and turn and slip indicator (see the example of a turn coordinator (on the left) and turn and slip indicator (on the right) shown at the bottom of the page

    • Understanding how to identify a standard (two-minute) turn - a turn that requires two minutes to go a full 360 degrees

    • Understanding the slip / skid indicator (the inclinometer or "ball") and how to correct slip or skid to maintain a coordinated turn

      • Slip occurs when there is rudder application in the opposite direction of the turn or if there is inadequate rudder application in the direction of the turn.  Note that sometimes applying opposite rudder to cause a significant slip is done intentionally to lose altitude with little airspeed gain

      • Skid occurs when there is excess rudder application in the same direction of the turn - correction is by reducing the amount of rudder being applied for the turn.  Keep in mind that a skid is potentially more dangerous than a slipping turn so a skidding turn should not be done intentionally.

      • The rule for correcting for slip or skid - "Step on the ball" - apply rudder that corresponds to the direction the ball is off center - ball to the right = add more right rudder (or, ease off the amount of left rudder being applied), ball to the left = add more left rudder (or, ease off the amount of right rudder being applied)

  • Heading indicator (Directional gyro) - how to set this and how to keep it set properly.

  • Understanding the standard layout of the vertical speed indicator and Interpretation of the information provided by it.

Note that you may see different styles of instruments - most resemble each other to a great degree but one that may not appear basically the same is the turn coordination guage.  There are two basic styles, one with an airplane in the middle, where the wing tilts to a straght white line that indicates the bank of a standard rate turn and the other where a vertical needle moves right or left and when the needle comes to rest under the pointed square (the "dog house") you are at the bank angle of a standard rate turn.  Both have a similar appearing inclinometer (the "ball") -