3. Pitot-static system
Operates in response to air pressure
Two air pressures:
Static pressure
Taken from static vents, powers all three pitot-
static system instruments (ASI, VSI, Altimeter)
Impact pressure
Powers airspeed
indicator only
4. Static System & Altimetry
Static system powers altimeter
Altimeter operates as a barometer
Set altimeter on the ground to local settings
Air pressure decreases at a constant rate per
foot increased in lower atmosphere
(approximately 1000’ per 1” Hg)
Nonstandard temperature and pressure affect
altimeter
5. Altimeter
As static pressure decreases, indicated altitude increases
Altimeter setting is adjustable in “Kohlsman
Window”, aka Altimeter Setting Window
Local altimeter setting will
cause the instrument to read
the approximate field
elevation when located on
the ground at the airport
Reset altimeter to 29.92
when climbing through
18,000 feet.
6. Altitude Terminology
Indicated Altitude
Altitude read on the altimeter when it is set to the current
local altimeter setting
Absolute altitude
Height above the surface
True altitude
True height above Mean Sea Level (MSL)
Pressure altitude
Altitude indicated whenever the altimeter setting dial is set
to 29.92 (Standard Datum Plane)
Density altitude
Pressure altitude corrected for non-standard temperature
and/or pressure.
7. Altimetry
Standard day
29.92” Hg and +15 deg. C
On a standard day at sea level, pressure
altitude, true altitude, indicated
altitude, and density altitude are all
equal.
8. “High to low…look out below”
When flying from an area of low
pressure/low temperature to an area of
higher pressure/higher temperature
without adjusting the altimeter setting, the
altimeter will indicate lower than the true
altitude setting…and vice versa.
10. Vertical Speed Indicator (VSI)
Operates only on static
pressure, but is a
differential pressure
instrument
Operates on the
principle of a
calibrated leak…
Face of VSI outputs
change in pressure
over time displayed in
feet per minute.
11. Airspeeds and Airspeed Indicator
Airspeed Indicator
Displays difference
between pitot
(impact) pressure
and static pressure
Pressures are equal
when airplane is
parked on ground
in calm air.
12. Airspeeds
Indicated airspeed (IAS)
Uncorrected reading from the airspeed indicator
Calibrated airspeed (CAS)
Indicated airspeed corrected for installation and
instrument error.
True airspeed (TAS)
Calibrated airspeed corrected for temperature and
pressure variations.
Groundspeed (GS)
Actual speed of the airplane over the ground – this is
the TAS adjusted for wind.
13. Airspeeds – color coded
VSO – stall speed / minimum
steady flight in landing
configuration (lower limit of white
arc)
VFE – max. flap-extended speed
(upper limit of white arc)
VS1 – stall speed in specified
configuration (lower limit of green
arc)
VNO – max. structural cruising
speed (top of green arc, bottom
of yellow arc)
VNE – never exceed speed (upper
limit of yellow arc, marked in red)
14. Airspeeds, others
VLE – max. landing gear-extended speed.
VA – design maneuvering speed (flown in
rough air or turbulence to prevent
overstressing airframe)
VY – Best rate-of-climb airspeed (creates most
altitude in a given period of time)
VX – Best angle-of-climb speed (airspeed
resulting in most altitude in a given distance.)
15. Gyroscopic Principles
Rigidity in space Precession
Axis of rotation points in a Tilting or turning of a gyro in
constant direction regardless response to a deflective
of the position of its base. force.
16. The Attitude Indicator
Relies on rigidity in space
Direction of bank determined by relationship of
miniature airplane to the horizon bar.
Miniature airplane remains stationary –
horizon moves
17. Turn Coordinator
Relies on precession
As an airplane enters a
turn, the TC indicates
rate of roll. When bank
is held constant, TC
indicates rate of turn.
Most TCs display an
index on the “Standard-
rate turn”, wherein the
airplane takes 2 minutes
to turn 360 degreers.
The “ball” or inclinometer
indicates quality of turn
(skid/slip status).
18. Heading indicator
“Gyroscopic compass”
Magnetic compasses are difficult to read and suffer
from errors; the heading indicator (also known as a
directional gyro or DG)
DGs suffer from precession due to bearing friction –
the indicator must be realigned with the magnetic
compass during straight-and-level, unaccelerated
flight.
21. Dip errors
Magnetic dip:
When turning north from an easterly or westerly
heading, the compass lags behind the actual
aircraft heading. When a turn is initiated while
on a northerly heading, the compass first
indicates a turn in the opposite direction.
When turning south from an easterly or westerly
heading, the compass leads the actual heading.
When a turn is initiated on a southerly
heading, the compass immediately leads ahead.
Mnemonic: UNOS – undershoot
north, overshoot south
22. Dip errors continued
Accelerating or decelerating while heading
either east or west will also cause compass
errors.
When accelerating on an east or west
heading, the compass indicates a turn to the
north.
When decelerating on an east or west
heading, the compass indicates a turn to the
south.
Mnemonic: ANDS – accelerate
north, decelerate south.
Compass accurate only in S&L, unaccelerated
flight.
23. Variation Errors
Magnetic poles do not coincide with geographic
poles.
Most places on Earth, the
compass needle does not
point to True North. Angular
differences between
magnetic north and true
north are called variations
and are displayed on
aeronautical charts.
24. Deviation Errors
The metal, electrical systems, and
operating engine all create magnetic
fields from the aircraft.
Aircraft manufacturers install
compensatory magnets to prevent
most errors. Remaining errors are
called deviation.
A card in the aircraft will list the
deviation at various different compass
points.
25. Next Week…
- Regulations
- (FAR/AIM & Test Prep)
