Attitude Instrument Flying
Basic T Arrangement
Since about 1953 aircraft instrumentation was standardized into a basic T arrangement
This allows pilots to transition from one plane to another
It also allows for an efficient scan of the instruments for information
Pitot Static Instruments
Airspeed
Altimeter
Vertical Speed Indicator
Altimeter
Corrugate bronze aneroid wafers
Expand as altitude is increased
Compress as altitude is decreased
The Sensitive Altimeter has a Kollesman window
The scale goes from 28.00″ to 31.00″
Altimeter
How to read it
Flagged area disappears at 15,000
Altimeter Errors
2 types:
Mechanical
A properly set altimeter should be within 75 feet of elevation
Inherent
Temperature
Pressure
Altimeter Errors
Cold weather errors
As temp drops below standard the airmass shrinks
We can calculate how much by figuring True Altitude using the E6b or the ICAO table
This is one reason for the MEA 2,000 in mountainous and 1,000 non mountainous clearance
Altimeter Errors
To use the table, find the reported temperature in the left column, and then read across the top row to the height above the airport/reporting station.
Subtract the airport elevation from the altitude of the final approach fix (FAF).
The intersection of the column and row is the amount of possible error.
Altimeter Errors
Knowing the reporting station elevation is needed to find an accurate True Altitude
This generally isn’t a problem if the reporting station is at the airport your doing approaches to
The station temperature will probably be different than the temperature at your altitude
Altimeter Errors
Nonstandard pressure has a similar effect on altitude
As pressure decreases, so does True Altitude
As pressure goes down, altitude goes up
This looks like a climb on the altimeter, so the pilot adjusts by descending
As a rule of thumb a new pressure should be obtained every 100 miles
During IFR x-country operations, this happens when you’re handed off to another sector
It’s important to be on the correct setting for the sector you’re operating in to maintain separation
Also so that your mode C matches what is read on the altimeter and ATC mode C data
Altimeter
When flying from high to low look out below
When flying from low to high your high in the sky
Altitudes
There are 5 different types of altitudes
Indicated Altitude
Pressure Altitude
Density Altitude
Absolute Altitude
True Altitude
Vertical Speed Indicator
Aka Vertical Velocity Indicator VVI
Hooked directly into the static line
Is a pressure differential instrument
Small adjustment screw, use a nonmagnetic screw driver
Lag times vary but generally 6-9 seconds
Instantaneous Vertical Speed Indicator IVSI
Uses two accelerometer actuated air pumps to take out the lag
VSI
Both the case and the aneroid are vented to the static source
The case pressure enters and leaves through a pinhole size calibrated leak
This cause the pressure to change more slowly than in the aneroid
As a climb is entered pressure decreases instantaneously in the aneroid but not in the case
This causes the aneroid to be compressed and a climb is indicated on the needle
In a descent the reverse happens
Airspeed Indicator
The airspeed indicator is also a differential pressure instrument
Static pressure is directed into the case
Ram pressure is directed into the aneroid
As velocity increases, so does Ram pressure causing the aneroid to expand
ram-static=dynamic
Airspeed Indicator
Types of Airspeed
Indicated
Calibrated
Equivalent
True
Some indicators include a true airspeed window
Some are combo Mach/Airspeed
Blockage in the Pitot Tube
If the ram air intake is blocked and the drain hole remains open, airspeed drops to 0
If the ram air and drain are blocked, the airspeed will act as an altimeter
This means a climb will indicate more airspeed
This may cause the pilot to think more pitch is necessary
A descent will indicate less
If an alternate static source is used, all 3 will indicate higher
Blockage in the Static Ports
Airspeed will operate but be inaccurate
When operated below the altitude of blockage A/S is lower than actual
When operated above, higher
The altimeter will indicate the altitude of blockage
The VSI will remain at 0
If an alternate static source is used, all 3 will indicate higher
If you break the VSI to vent a blocked static system, the VSI needle may read backwards
Magnetic Compass
Magnetic Compass
Two magnetic needles attached to a floating card inside a sealed case filled with acid free white kerosene.
The kerosene
supports the card
dampens oscillations
lubricates the pivot assembly that the card rotates around.
Lubber line inside the glass face.
There is a Deviation Card located on the compass to compensate for errors.
Magnetic Compass
Magnetic Compass Errors
Variation is the angular difference between true north and magnetic north
Deviation is the pull of the aircraft’s magnetic fields generated by radios and such on the compass card
Northerly and southerly turning errors
Acceleration/deceleration errors (ANDS)
Oscillation error
Magnetic Compass Errors
Magnetic Dip
Varies from none at the equator to large amounts the closer to the poles
The correction is roughly equal to 15 + ½ latitude
Magnetic Dip is the culprit behind the
Northerly & Southerly turning errors
Acceleration/deceleration errors
Magnetic Compass Errors
Heading north, the compass will momentarily indicate a turn in the correct direction then turn opposite.
Heading south, the compass will indicate direction correctly, but at a faster rate.
Magnetic Compass Errors
Northerly turning error
When the plane banks the card banks with the plane because of centrifugal force.
This bank causes the vertical component of the earth’s magnetic field to pull the compass off course.
This results in the need for the Lead and lag diagram (remember latitude rule).
Lead/Lag
Magnetic Compass Errors
Accelerate and it turns north
Decelerate and it turns south
This is due to the weights placed under the card on the north pole side of the magnet
Remember the south pole of the magnet is attracted to the earth’s magnetic north pole
The weights help counteract magnetic dip but provide inertia at a right angle to direction of travel when on an east or west heading
Flux Gate Compass
The Gyroscopic Instruments
Attitude Indicator
Heading Indicator
Turn Coordinator
The Gyroscopic Instruments
The attitude and heading indicators operate on the principle of “rigidity in space”
A spinning gyro resists the movement of the airplane by means of gimbals.
The gyro remains stationary while the airplane moves around it.
Because the gyro is mechanically linked to the plane, there is some friction felt by the gyro, which causes precession.
The turn coordinator functions by using precession
Vacuum System
Vacuum system diagram
Attitude indicator
Heading indicator
Instrument air gauge (inches of mercury)
Vacuum System
Backup vacuum systems
Venturi type vacuum systems
Pressure systems
Turn Coordinator/Turn And Slip Indicator
In our airplanes, this is an electric gyro instrument
However, some are vacuum
All indicate rate of turn in seconds
A standard rate turn is 3 degrees per second
A 360 degree turn takes 2 minutes
Turn Coordinator/Turn And Slip Indicator
Actually a combination of two instruments
Slip indicator curved glass tube filled with kerosene and a steel ball bearing or black agate
Centrifugal force or lack of it accounts for the ball’s movement
Turn Coordinator/Turn And Slip Indicator
Turn coordinator gyro is mounted on a 30 deg angle
The turn coordinator can sense both roll and yaw
Displays only rate of roll and rate of turn doesn’t directly display bank angle
Turn Coordinator/Turn And Slip Indicator
Turn and slip gyro is horizontal
The turn needle indicates the rate of turn about the vertical axis in degrees per second
Older models required 1 needle with deflection for standard rate turn
Some have dog houses on them and others are calibrated for a 4 minute turn
Attitude Indicator
Pitch and bank vacuum driven gyro; some are electric or pressure driven
Gyro is gimbled on 3 axis
Rotor spins horizontally,
Pivots about the lateral axis on a gimbal
Which turns about the longitudinal axis
Attitude Indicator
Attitude Indicator
Bank limits 100 to 110 degrees
Pitch limits 60 to 70 degrees
If limits are exceeded gyro precesses abruptly causing the gyro to tumble and become unreliable until it precesses back to horizontal at about 8 degrees per minute
Newer attitude indicators don’t have this problem
They are equipped with a self erection mechanism rather than a caging knob that older ones have
Attitude Indicator
Markings are at 10, 20, 30, 60 and 90 degrees bank
Pitch markings are usually on the 5s
Heading Indicator & HSI
Directional gyro instrument that is vacuum driven; some are electric; some are pressure driven
Ours are both electric and vacuum driven
10,000 to 18,000 rpm
Pitch and bank limits of about 55 degrees (older ones)
Heading Indicator
Precession error of no more than 3 degrees in 15 minutes
Gyro spins in the vertical axis and remains rigid in space as the azimuth card rotates around it
Attitude Instrument Flying
2 methods:
Control and Performance
Primary and Supporting
Control and Performance
This method controls the airplane by controlling attitude and power
The control instruments:
Attitude indicator
Power instruments, like Tachometer, Manifold pressure, fuel flow
The performance instruments:
Altimeter
Airspeed
VSI
Primary and Supporting
This method controls the plane by using each instrument associated with pitch, bank, yaw and power
So for each control task a set of instruments are used to determine what inputs to make
For example for straight and level
Primary pitch is altimeter
Supporting pitch is airspeed, VSI and attitude
Primary bank is heading indicator
Supporting bank is turn coordinator, mag compass
Primary power is airspeed
Supporting power is tach or manifold pressure
One of the biggest differences between control and performance and primary and supporting is the attitude indicator is only primary when transitioning to a climb, turn or descent
Scan Patterns
Radial scan
V/Inverted V
Rectangular
Attitude Instrument Flying
Which ever method is used there are some basic fundamental skills:
Instrument cross check
Instrument interpretation
Aircraft control
Common errors:
Omission
Fixation
Misinterpretation
Trim control is critical to being able to fly instruments well
Emergency Stuff
- Loss of electrical
- Which instruments are non-functional
- IMC at night
- Loss of vacuum
- No gyro vectors AIM 5-4-11
- Start turn, stop turn
- Half standard rate when on final approach course
- Pitot tube clogging